Refrigeration and Air Conditioning

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Piri Reis University
Faculty of Maritime – Department of Marine Engineering
SM412-Refrigeration and Air Conditioning
1.Refrigeration System
1. Refrigeration System
Basic Refrigeration Cycle
 Liquids absorb heat when changed from
liquid to gas
 Gases give off heat when changed from
gas to liquid.
For an air conditioning system to operate with
economy, the refrigerant must be used
repeatedly. For this reason, all air conditioners
use the same cycle of compression,
condensation, expansion, and evaporation in a
closed circuit. The same refrigerant is used to move the heat from one area, to cool this area,
and to expel this heat in another area.
 The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then
moves out of the compressor as a high-pressure gas.
 The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its
heat to the outside air.
 The liquid then moves to the expansion valve under high pressure. This valve restricts the
flow of the fluid, and lowers its pressure as it leaves the expansion valve.
 The low-pressure liquid then moves to the evaporator, where heat from the inside air is
absorbed and changes it from a liquid to a gas.
 As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is
repeated.
Note that the four-part cycle is divided at the center into a high side and a low side This refers to
the pressures of the refrigerant in each side of the system

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Performance Testing
Compound Gauge (Low Side)
 The compound gauge derives its name from
its function. It will register both pressure or
vacuum.
 All air conditioning systems can, under certain
conditions, drop from a pressure into a
vacuum on the low side. It is necessary that a
gauge be used that will show either pressure (psi and kPa) or inches of mercury vacuum
(Hg.).
 The vacuum side of the gauge must be calibrated to show 0 to 30 inches (0 to 762 mm) Hg.
The pressure side of the gauge must be calibrated to register accurately from 0 pressure to a
minimum of 60 psi (414 kPa).
 The maximum reading of the pressure should not exceed 160 psi (1103 kPa). Practically all
readings of the low side of the system will be less than 60 psi (414 kPa) with the system in
operation.
High Pressure Gauge (High Side)
 The high pressure gauge is used to determine pressures in the high side of the system.
 The gauge is calibrated to register accurately from zero pressure to a minimum of 300 psi
(2070 kPa).
 A few systems operate under high head pressure during normal operation conditions. This is
why the high pressure gauge should have a reading of at least 600 psi (4140 kPa).
Gauge Manifold
 The gauge manifold mounts the high and low side gauges and connects the gauges into the
high and low sides of the system by means of test hoses.
 The gauges connect to the upper part of the manifold through holes drilled and tapped to a
1/8-inch pipe thread.
 Test hose connectors below the gauges on the lower side of the manifold direct the
refrigerant through the manifold to the gauges to obtain pressure readings.

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 A center test hose connector on the lower side of the manifold is connected to both pressure
gauges and the test hoses by a passage in the manifold.
 Refrigerant flow into the high and low side is controlled by a shutoff hand valve at each end
of the manifold.
Compressor
The purpose of the compressor is to circulate the refrigerant in the
system under pressure, this concentrates the heat it contains.
 At the compressor, the low pressure gas is changed to high
pressure gas
 This pressure buildup can only be accomplished by having a
restriction in the high pressure side of the system. This is a small
valve located in the expansion valve.
 The compressor has reed valves to control the entrance and exit
of refrigerant gas during the pumping operation. These must be
firmly seated.
 An improperly seated intake reed valve can result in gas leaking
back into the low side during the compression stroke, raising the low side pressure and
impairing the cooling effect.
 A badly seated discharge reed valve can allow condensing or head pressure to drop as it
leaks past the valve, lowering the efficiency of the compressor.
 Two service valves are located near the compressor as an aid in servicing the system.
 One services the high side, it is quickly identified by the smaller discharge hose routed to the
condenser.
 One is used for the low side, the low side comes from the evaporator, and is larger than the
discharge hose
 The compressor is normally belt-driven from the engine crankshaft. Most manufacturers use
a magnetic-type clutch which provides a means of stopping the pumping of the compressor
when refrigeration is not desired.

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Compressor Relief Valve
Some compressors have a relief valve for regulating pressure. If the system discharge pressure
exceeds rated pressure, the valve will open automatically and stay open until the pressure
drops. The valve will then close automatically.
Compressor Noise Complaints
Many noise complaints can be traced to the compressor mount and drive.
 If a unit is noisy at one speed and quiet at another, it is not compressor noise.
 Many times this kind of noise can be eliminated or greatly reduced by changing the belt
adjustment.
 Usually tightening mounts, adding idlers, or changing belt adjustment and length are more
successful in removing or reducing this type of noise, than replacing the compressor.
 Noises from the clutch are difficult to recognize because the clutch is so close to the
compressor. A loose bolt holding the clutch to the shaft will make a lot of noise.
 The difference, between suction pressure and discharge pressure, also plays an important
part on sound level.
 A compressor with low suction pressure will be more noisy than one with a higher pressure.
 Consider whether the system is properly charged, whether the expansion valve is feeding
properly to use the evaporator efficiently, and whether enough air is being fed over the
evaporator coil.
Condenser
 The purpose of the condenser is to receive the high-pressure gas from the compressor and
convert this gas to a liquid.
 It does it by heat transfer, or the principle that heat will always move from a warmer to a
cooler substance
 Air passing over the condenser coils carries off the heat and the gas condenses.
 The condenser often looks like an engine radiator.
Condensers used on R-12 and R-134a systems are not interchangeable. Refrigerant-134a has
a different molecular structure and requires a large capacity condenser.
As the compressor subjects the gas to increased pressure, the heat intensity of the refrigerant is
actually concentrated into a smaller area, thus raising the temperature of the refrigerant higher

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than the ambient temperature of the air passing over the condenser coils. Clogged condenser
fins will result in poor condensing action and decreased efficiency.
A factor often overlooked is flooding of the condenser coils with refrigerant oil. Flooding results
from adding too much oil to the system. Oil flooding is indicated by poor condensing action,
causing increased head pressure and high pressure on the low side. This will always cause poor
cooling from the evaporator.
Too-High Condenser Pressure
 Indicated by: Excessive head pressure on high side gauge.
 Caused by: Restriction of refrigerant flow in high side of system or lack of air flow over
condenser coils.
Too-Low Condenser Pressure
 Indicated by: Higher than normal pressure on low side gauge.
 Caused by: Failed compressor reed valve or piston. Heat exchange in the condenser will be
cut down, and the excessive heat will remain in the low side of the system.
Expansion Valve
The expansion valve removes pressure from the liquid refrigerant to allow expansion or change
of state from a liquid to a vapor in the evaporator.
The high-pressure liquid refrigerant entering the expansion valve is quite warm. This may be
verified by feeling the liquid line at its connection to the expansion valve. The liquid refrigerant
leaving the expansion valve is quite cold. The orifice within the valve does not remove heat, but
only reduces pressure. Heat molecules contained in the liquid refrigerant are thus allowed to
spread as the refrigerant moves out of the orifice. Under a greatly reduced pressure the liquid
refrigerant is at its coldest as it leaves the expansion valve and enters the evaporator.
Pressures at the inlet and outlet of the expansion valve will closely approximate gauge
pressures at the inlet and outlet of the compressor in most systems. The similarity of pressures
is caused by the closeness of the components to each other. The slight variation in pressure
readings of a very few pounds is due to resistance, causing a pressure drop in the lines and
coils of the evaporator and condenser.

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Two types of valves are used on machine air conditioning
systems:
 Internally-equalized valve - most common
 Externally-equalized valve special control
Internally-Equalized Expansion Valve
The refrigerant enters the inlet and screen as a high-pressure
liquid. The refrigerant flow is restricted by a metered orifice
through which it must pass.
As the refrigerant passes through this orifice, it changes from a
high-pressure liquid to a low-pressure liquid (or passes from the
high side to the low side of the system).
Let's review briefly what happens to the refrigerant as we change its pressure.
As a high-pressure liquid, the boiling point of the refrigerant has been raised in direct proportion
to its pressure. This has concentrated its heat content into a small area, raising the temperature
of the refrigerant higher than that of the air passing over the condenser. This heat will then
transfer from the warmer refrigerant to the cooler air, which condenses the refrigerant to a liquid.
The heat transferred into the air is called latent heat of condensation. Four pounds (1.8 kg) of
refrigerant flowing per minute through the orifice will result in 12,000 Btu (12.7 MJ) per hour
transferred, which is designated a one-ton unit. Six pounds (2.7 kg) of flow per minute will result
in 18,000 Btu (19.0 MJ) per hour, or a one and one-half ton unit.
Valve details
The refrigerant flow through the metered orifice is extremely important, anything restricting the
flow will affect the entire system.
 If the area cooled by the evaporator suddenly gets colder, the heat transfer requirements
change. If the expansion valve continued to feed the same amount of refrigerant to the
evaporator, the fins and coils would get colder until they eventually freeze over with ice and
the air flow is stopped.
 A thermal bulb has a small line filled with C02 is attached to the evaporator tailpipe. If the
temperature on the tail pipe raises, the gas will expand and cause pressure against the
diaphragm. This expansion will then move the seat away from the orifice, allowing an

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increased refrigerant flow. As the tail pipe temperature drops, the pressure in the thermal
bulb also drops, allowing the valve to restrict flow as required by the evaporator.
 The pressure of the refrigerant entering the evaporator is fed back to the underside of the
diaphragm through the internal equalizing passage. Expansion of the gas in the thermal bulb
must overcome the internal balancing pressure before the valve will open to increase
refrigerant flow.
 A spring is installed against the valve and adjusted to a predetermined setting at the time of
manufacture. This is the superheat spring which prevents slugging of the evaporator with
excessive liquid.
 Superheat is an increase in temperature of the gaseous refrigerant above the temperature at
which the refrigerant vaporizes. The expansion valve is designed so that the temperature of
the refrigerant at the evaporator outlet must have 8 to 12°F (4 to 7°C) of superheat before
more refrigerant is allowed to enter the evaporator.
 The adjusted tension of this spring is the determining factor in the opening and closing of the
expansion valve. During opening or closing, the spring tension retards or assists valve
operation as required.
 Normally, this spring is never adjusted in the field. Tension is adjusted from four to sixteen
degrees as required for the unit on which it is to be installed. This original setting is sufficient
for the life of the valve, and special equipment is required in most cases to accurately
calibrate this adjustment
Externally-Equalized Expansion Valve
Operation of the externally-equalized valve is the same as the internal type except that
evaporator pressure is fed against the underside of the diaphragm from the tail pipe of the
evaporator by an equalizer line. This balances the temperature of the tail pipe through the
expansion valve thermal bulb against the evaporator pressure taken from the tail pipe.
Evaporator
The evaporator works the opposite of the condenser, here
refrigerant liquid is converted to gas, absorbing heat from the air
in the compartment.
When the liquid refrigerant reaches the evaporator its pressure

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has been reduced, dissipating its heat content and making it much cooler than the fan air flowing
around it. This causes the refrigerant to absorb heat from the warm air and reach its low boiling
point rapidly. The refrigerant then vaporizes, absorbing the maximum amount of heat.
This heat is then carried by the refrigerant from the evaporator as a low-pressure gas through a
hose or line to the low side of the compressor, where the whole refrigeration cycle is repeated.
The evaporator removes heat from the area that is to be cooled. The desired temperature of
cooling of the area will determine if refrigeration or air conditioning is desired. For example, food
preservation generally requires low refrigeration temperatures, ranging from 40°F (4°C) to below
0°F (-18°C).
A higher temperature is required for human comfort. A larger area is cooled, which requires that
large volumes of air be passed through the evaporator coil for heat exchange. A blower
becomes a necessary part of the evaporator in the air conditioning system. The blower fans
must not only draw heat-laden air into the evaporator, but must also force this air over the
evaporator fins and coils where it surrenders its heat to the refrigerant and then forces the
cooled air out of the evaporator into the space being cooled.
Fan Speeds
Fan speed is essential to the evaporation process in the system. Heat exchange, as we
explained under condenser operation, depends upon a temperature differential of the air and the
refrigerant. The greater the differential, the greater the amount of heat exchanged between the
air and the refrigerant. A high heat load, as is generally encountered when the system is turned
on, will allow rapid heat transfer between the air and the cooler refrigerant.
A blower fan turned on to its highest speed will deliver the most air across the fins and coils for
rapid evaporation.
For the coldest air temperature from the evaporator, operate the blower fan at the lowest speed
so the heat will be absorbed by the refrigerant from the air
Problems of Flooded or Starved Evaporator Coils
Changing the state of the refrigerant in the evaporator coils is as important as the air flow over
the coils. Liquid refrigerant supplied to the coils by the expansion valve expands to a vapor as it
absorbs heat from the air. Some liquid refrigerant must be supplied throughout the total length of
the evaporator coils for full capacity.

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A starved evaporator coil is a condition in which not enough refrigerant has been supplied
through the total coil length. Therefore, expansion of the refrigerant has not occurred through the
whole coil length, resulting in poor coil operation and too-low heat exchange.
A flooded evaporator is the opposite of the starved coil. Too much refrigerant is passed through
the evaporator coils, resulting in unexpanded liquid passing onto the suction line and into the
compressor.
Magnetic Clutch
The clutches on machine air conditioning systems are of two types:
 Rotating coil
 Stationary coil
Rotating Coil
Clutches have the magnetic coil inside the pulley and rotating with it. The electric current is
carried to the coil by brushes mounted on the compressor frame and contacting a slip ring
mounted on the inside of the rotating pulley.
Stationary Coil
 Clutches have the magnetic coil mounted on the frame of the compressor and it does not
rotate. Since the coil is stationary, correct spacing is important to prevent the rotating pulley
from contacting the coil, while still bringing the hub and armature into position for the fullest
attraction of the magnetic force.
 When replacing either the clutch unit or the coil must note carefully that the voltage of the
replacement unit is correct for the vehicle on which it is to be installed.
 All clutches operate on the same principle whether the magnetic coil rotates or is stationary.
Each has a wound core located within a metal cup acting like a horseshoe magnet when the
coil is energized electrically (Fig. 35).
 The pulley rotates on a bearing mounted on the clutch hub (Fig. 34) except the Frigidaire
compressor, which mounts the bearing on the compressor front head assembly. The pulley
is free to rotate without turning the compressor crankshaft any time the clutch coil is not
energized. The free-rotating pulley and non-energized clutch coil stop compressor operation.
 An armature plate is mounted by a hub to the compressor crankshaft and is keyed into place
and locked securely with a lock nut, thus making connection to the crankshaft.

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 Energizing the clutch coil creates lines of magnetic force from the poles of the electromagnet
through the armature, drawing it towards the shoe plate or rotor that is a part of the pulley
assembly (Fig. 35). The solid mounting of the pulley prevents the pulley from moving in a
lateral direction; however, the armature can move until it contacts the rotor. Magnetic force
locks the rotor and the armature plate together. This solid connection then allows the pulley
to rotate the compressor crankshaft and operate the compressor. Compressor operation will
continue until the electrical circuit is broken to the clutch coil, when the magnetic force is
de-energized. The rotor and armature then separate, and the pulley rotates freely without
rotating the compressor crankshaft.
 Slots are machined into both the armature and the rotor to concentrate the magnetic field
and increase the attraction between the two when energized. Some scoring and wear is
permissible between these plates. However, it is important that full voltage be available to
the clutch coil as low voltage will prevent a full build-up of magnetic flux to the plates.
 The correct spacing between the pulley and the coil on stationary coil models must be
maintained to prevent the pulley from dragging against the coil. Correct spacing must also be
maintained between the rotor and the armature.
 Too close a clearance will allow the two plates to contact each other in the "OFF" position,
while too wide a space can prevent the rotor from contacting the armature solidly in the "ON"
position. Any of these variations can cause a serious clutch failure.
 Also be sure that the mating surfaces are not warped (from overheating)
Solenoid Bypass
Some automotive products use a solenoid bypass to control the evaporator pressure and
temperature. The thermal switch is attached to the suction pressure line at the evaporator outlet
manifold. The electrical contacts in the switch are connected in series with the temperature
control switch and the solenoid bypass valve winding. In the normal position, the contacts are
closed.
A decrease in the temperature of the refrigerant gas leaving the evaporator will cause a thermal
blade to bend and open the electrical circuit to the solenoid valve when the temperature reaches
approximately 25°F (-4°C). Opening the solenoid valve allows a charge of hot refrigerant gas to
flow into the evaporator. When the temperature increases

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Thermostat and Magnetic Clutch Systems
 During the earlier years of machine air conditioning, many systems did not provide a means
for stopping the pumping action of the compressor. A solid pulley was installed on the
compressor crankshaft, which resulted in compressor operation anytime the engine, was
operating. The only time the compressor could be stopped was when the belt was removed.
Even with the air conditioning controls in the "OFF" position during cold weather operation, a
slight amount of cold air would be given off by the evaporator
 Today, manufacturers are turning more and more to the thermostat-controlled system with a
magnetic clutch.
Thermostat Control
The opening and closing of electrical contacts in the
thermostat are controlled by a movement of a
temperature-sensitive diaphragm or bellows. The bellows
has a capillary tube connected to it which has been filled
with refrigerant. The capillary tube is positioned so that it
may have either the cold air from the evaporator pass
over it or may be connected to the tail pipe of the
evaporator
In either position, evaporator temperature will affect the
temperature-sensitive compound in the capillary tube by
causing it to contract as the evaporator becomes colder. The contraction of the gas will cause
the bellows to contract. This separates the electrical points and breaks the electrical circuit to the
compressor clutch, which stops compressor operation.
Now the evaporator begins to warm which, in turn, gas in the capillary tube to expand. The
bellows will also expand, moving the electrical circuit to the compressor clutch, energizing it and
bringing the compressor into operation again. THis cycle is repeated for as long as the air
conditioning is being used.
The thermostatic switch is made from a pivoting frame attached to the bellows. Movement of the
bellows during expansion and contraction cause the frame to pivot. Springs control and

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counteract the movement. Half of the electrical contacts are connected to the frame, the other
half are mounted to the switch, but insulated from the metal parts.
The distance the contacts must travel and the spring pressure must be overcome by the
expanding gas in the capillary tubes and bellows determine at what degree of evaporator the
contacts will close to complete the electrical circuit.
In all thermostats, the spring tension and point spacing may be varied by the operator to regulate
evaporator cooling for comfort. Temperature is controlled by rotating a cam (via a knob control)
which increases or decreases spring tension of a pivoting point.
Vapour-compression theoretical graphs
Figure: Absolute temperature –
Entropy
A-B : Isobaric Heat absorption in
the evaporator
B-C : Isentropic compression in
the compressor (frictionless
adiabatic compression in ideal
cycle)
C-D : Isobaric Heat removal in condenser
D-A : Constant enthalpy expansion in expansion valve
Heat energy equivalent of work done = Heat energy rejected- heat energy received
= Area ABCDA + Area under AD
heat energy received
Coefficient of performance = -----------------------------------------------------
Heat energy equivalent of work done
The coefficient of performance for Freon is about 4.7
It should be noted that undercooling increases the heat received by moving point A to the left
increasing the refrigerant effect.

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The critical point is the point above which:
a. The gas will not liquefy by the action of pressure alone. This is an important temperature for
refrigeration systems which rely on the change of state for heat transfer.
b. The gas will not liquefy by cooling alone.
Figure: p-h (Mollier) diagram
Figure: Typical system
The system shown above and described below is
typical of that fitted on may ships other than it is
more common to have two low temperature rooms
rather than one.
Cold rooms
Meat Room-Low temperature room typically working
at -17o
C
Veg/ handling room-typically working at +4o
C
Compressor
Generally, of the single stage, reciprocating type.
Larger systems have multple cylinders with an
unloader system using the suction pressure as its
signal. Refrigerant is compressed in the compressor
to a pressure dependent upon the temperature of
the cooling water to the condenser, and to a lesser extent the volume of gas in the system. As
the temperature of the cooling water rises so does the minimum temperature of the refrigerant
liquid rise, and with it the corresponding saturation pressure.

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Compressor safety devices
The compressor is protected by three safety switches; The OP switch or Oil Differential Pressure
switch compares the measured lubricating oil pressure to the Suction (crankcase) pressure.
Should the differential pressure fall below a pre-set minimum (about 1.2 bar) then the
compressor will trip and require a manual reset to restart. A time delay is built into the circuit to
allow sufficient time for the lubricating oil pressure to build up when starting before arming the
circuit.
The HP or High Pressure switch, is fitted to the outlet of the compressor before the isolating
valve. On over pressurization (dependent on the refrigerant, up to about 24bar bar for R22) the
switch will trip the compressor and a manual reset is required before restart.
The LP or Low Pressure switch when activated (at about 1 bar for R22) will trip the compressor
and require a manual reset before the compressor can be restarted.
Compressor control devices
This normally takes the form of an LP cut out pressure switch with
automatic reset on pressure rise. The cut out set point is just above
the LP trip point say at about 1.4bar. An adjustable differential is set
to about 1.4bar to give a cut in pressure of around 2.8 bar. The
electrical circuit is so arranged that even when the switch has reset,
if no room solenoid valves are open the compressor will not start.
This is to prevent the compressor cycling due to a leaky solenoid
valve.
In addition to this extra LP switches may be fitted which operate
between the extremes of the LP cut in and cut out to operate
compressor unloaders.
Compressor
Compressor bodies are normally of close grained castings of iron or
steel. Modern valves are of the reed or disc type mounted in the head and are of high grade
steel on stainless steel seats with a usual lift of about 2mm. Connecting rods are aluminum with
steel backed white metal big ends. The crankshaft is spheroidal graphite iron. The pistons are
made from cast iron in older units, and of aluminum alloy more recently. The piston is attached

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to the crankshaft by con rod in the normal manner. It should be noted that the crankcase is full of
refrigerant gas at suction pressure. Liners are made from high tensile cast iron. Lubrication is
generally splash only for smaller compressors with a crankshaft driven gear pump supplying
bearings on larger machines. It is important to understand that actual pumped lube oil pressure
is the indicated pressure less this crankcase pressure. The properties of the Lubricating oil used
in are compressors are critical and specific to the refrigerant gas used. The properties of this oil
will be dealt with in the tribology section.
By the nature of the system a possibility exists whereby liquid may be passed to the compressor
suction. To prevent serious damage, some form of unloading device is normally fitted. In this
case the suction valve assembly is held on the liner by a heavy gauge spring. In the event of
liquid passing to the compressor the suction valve will lift against this spring.
Should water enter the system, acids may be formed by the reaction with the refrigerant gas.
This is especially true for Freon systems. These acids attack the copper in the system- typically
the pipework- and allow it to be transported through the system. It is not uncommon to find this
deposited on the suction valve plate. More troublesome is when the deposit finds its way to the
crankcase seal destroying the running face. Thus the importance of maintaining filter dryers in
good condition can be seen. These should be changed at least on a schedule determined by the
ships planned maintenance system. In addition to this it is common to have liquid line flow
bullseye which incorporate a water detection element. Blockage of the filter dryer can be gauged
by feeling the filter. If it is cooler than the surrounding pipework, then the gas is being throttled
through it. Although not considered good practice in an emergency I have 'dried' the filter drier
element in the galley oven although this practice is not recommended.
Mechanical seal
It should be noted that for this design the carbon seal and flexible
bellows is fixed in way of the mounting plate and the hard running
surface is allowed to rotate. This is the opposite to the set up for
seals mounted on pumps.
The finish of the running surface of the seal is extremely fine.
However, in extenuating circumstances i.e. when the surface has
been damaged say by the deposit of copper, it is possible to lapm

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the face of the carbon. The method I would recommend is metal polish such as brasso, on a true
flat surface on which is laid chart paper. The chart paper absorbs the wear particles as they are
removed and a reasonable finish is possible.
Oil Separator
The purpose of the oil seperator, situated on the compressor
discharge line, is to return oil entrained in the gas, back to the
compressor sump.
The oil return may be float controlled as shown, electric solenoid
controlled on a timer, or uncontrolled with a small bore capillary
tube allowing continuous return.
With all of these methods a shut off valve is fitted between
separator and compressor to allow for maintenance.
The oil gas mix enters the separator where it is made to change
direction, the heavier oil droplets tend to fall to the bottom.
Condenser
Generally, a water cooled tube cooler. A safety valve and vent are fitted. The purpose of the vent
is to bleed off non-condensable such as air which can enter the system when the suction
pressure is allowed to fall below atmospheric or can be contained within the top up gas. The
presence of non-condensable is generally indicated by a compressor discharge pressure
considerably above the saturation pressure of the refrigerant.
The coolant flow to the condenser is sometimes temperature regulated to prevent too low a
temperature in the condenser which can effect plant efficiency due to the reduction in pressure.
Below the condenser, or sometimes as a separate unit, is the reservoir. Its purpose is to allow
accurate gauge of the level of refrigerant in the system. In addition to this it also allows a space
for the refrigerant liquid when the system is 'pumped down'. This refers to the evacuation of the
refrigerant gas to the condenser to allow maintenance on the fridge system without loss. For
systems not fitted with a reservoir, a sight glass is sometimes incorporated on the side of the
condenser. Care should be given to ensuring that the liquid level is not too high as this reduces
the surface area of the cooling pipes available for condensing the liquid and can lead to
increased discharge pressures.

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Sight Glass
Often of the Bulls eye form. This allows the operator to ensure that it is only liquid, and not a
liquid/gas mix going to the expansion valves. On some designs a water indicator is incorporated,
this is a colored ring in contact with the liquid, when water is detected it changes color, typically
from pink to blue.
Filter Drier
Can be either a compacted solid cartridge or bags of desiccant. The main purpose of this unit is
to remove the moisture from the refrigerant.
Moisture cause two main problems. Firstly, it can freeze to ice in the evaporator and cause
blockage. Secondly it can form acids by reaction with the freon refrigerants. This acid attacks the
copper in the lines and deposits it’s in other parts of the system. This can become particularly
troublesome when it is deposited on the compressor mechanical seal faces leading to damage
and leakage.
Fine particles which could possible block the expansion valve are removed.
Topping up the refrigerant
A filling connection is fitted in way off the filter dryer, either directly onto it or on the inlet line after
the inlet shut off valve. This allows additional refrigerant to be introduced into the system via the
dryer element.
The normal procedure is to shut or partially shut the inlet to the filter. The compressor is now
sucking from the system and delivering to the condenser where the gas liquifies. The filter dryer
is on the outlet from the condenser therefore with its inlet valve shut the liquid level begins to rise
in the reservoir. The inlet valve can be briefly opened to allow more refrigerant into the system.
Thermostat and Solenoid Valve
These two elements form the main temperature control of the cold rooms. The Thermostat is set
to the desired temperature and given a 3 to 4-degree differential to prevent cycling. When the
temperature in the room reaches the pre-set level the thermostat switch makes and the room
solenoid is energized allowing gas to the refrigerant liquid to the expansion valve.
A manual override switch is fitted as well as a relay operated isolating contact which shut the
solenoid when the defrost system is in use.

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System operation
Assume that the rooms are all warm and the compressor
is running with all the solenoid valves open supplying
refrigerant to the respective expansion valve and
evaporator.
Should one or two rooms be down to temperature the
solenoids close thus reducing the volume of gas
returning to the compressor. The suction pressure drops
and the compressor unloads. If more rooms shut down
then the suction pressure will drop to cut out point and
the compressor will stop. When the rooms warm the
solenoids open again, refrigerant passes back to the
compressor, the suction pressure rises and compressor
starts. With more rooms opening, the suction pressure
increases and the compressor load up more cylinders.
Thermostatic expansion valve
The purpose of this valve is to efficiently drop the
pressure of the refrigerant. It achieves this by passing the liquid through a variable orifice giving
a constant enthalpy pressure drop. The refrigerant at lower pressure has a corresponding lower
boiling point (saturation temperature). Undercooling in the condenser increases the efficiency of
the plant by allowing more heat to be absorbed during the vaporization process. In addition, it
also reduces the internal heat absorption process that occurs during the expansion stage which
is due to a small degree of flash off as latent heat (of vaporization) is absorbed from surrounding
liquid to reduce the temperature of the bulk liquid to the new corresponding saturation
temperature for the reduced pressure
By this process of boiling (vaporization) and latent heat absorption i.e. change of state, the
refrigerant removes heat from the cold rooms. The expansion process is controlled by the action
of the bellows and push pins acting on the orifice valve plate. The bellows is controlled by a bulb
which measures the temperature of the gas at outlet from the evaporator. To ensure no liquid
passes through to the compressor, the expansion valve is set so that the gas at outlet from the

19
evaporator has 2 to 3 degrees of superheat. For larger systems where a significant pressure
drop exists across the evaporator it is necessary to fit a 'Balance line'. This is a small bore tube
which feeds the outlet pressure back to the thermostatic valve 'motor' element. Therefore, the
measured temperature is directly related to the superheat temperature at outlet pressure. Some
systems are designed so 5% liquid is available through the evaporator to coat the internal
surfaces of the tubes increasing heat transfer efficiency.
Careful note should be taken that system temperatures are set by the room solenoid and not by
the expansion valve which are generally factory set and do not require adjustment. This may
seem an obvious fact but you would be amazed as to the number of broken valve plates
removed from compressors due to the mal adjustment of the superheat. Adjustment of the back
pressure valves- which if they have not been touched by ships staff should be unnecessary- can
allow better system balance especially when certain rooms are being starved of gas.
Back pressure regulator valve
This valve is fitted to the higher temperature rooms, vegetable and flour (+5o
C) only and not to
the Meat and Fish rooms (-20o
C). They serve two main purposes.
1. when all solenoid valves are opened they act as system balancing diverters, that is they
restrict the liquid flow to the rooms which can be kept at the higher temperature and deliver
the bulk to the colder rooms
2. they serve to limit the pressure drop across the expansion valve by giving a set minimum
pressure in the evaporator coil. This in turn limits the temperature of the refrigerant thereby
preventing delicate foodstuffs such as vegetables from being damaged by having air at very
low temperatures blown over them. Ultimately they
may also be set to provide a safety limit to the room
temperature by restricting the pressure to give a
corresponding minimum saturation temperature of
0o
C.
Oil rectifier
In some installations there is a tendency for oil to
collect in the evaporator under certain conditions such
as low load when the speed of movement and agitation

20
of the evaporating refrigerant are insufficient to keep the oil moving. To prevent loss of oil from
the sump to the system, an oil rectifier may be fitted. The oil is automatically bled from the
evaporator to a heat exchanger in which liquid refrigerant mixed with the oil is vaporized. The
heat for vaporizing the refrigerant is obtained by passing warm liquid Freon from the condenser,
through the heat exchanger. Vapour and oil are passed to the compressor where oil returns to
the sump while the Freon passes to the compressor suction. The regulator is thermostatically
controlled valve which operates in the same way as the expansion valve on the main system. It
automatically bleeds the oil from the evaporator so that the gas leaves the heat exchanger in a
superheated condition.
Defrost system
Moisture freezes onto the evaporator eventually causing a restriction and reducing the efficiency
of the plant. This must be periodically removed. For Veg and Flour rooms, were not restricted to
0o
C minimum by the back pressure valve, this is carried out once per day. For the Meat and Fish
rooms this has to be carried out two or more times. Due to the low temperature in the rooms it is
necessary to fit a drain heater. When on defrost the solenoid valve is shut and the fan is off. On
some systems at end of defrost the solenoid valve is opened momentarily before the fan is
started. This allows moisture to be snap frozen onto the surface of the element, creating a rough
increased surface area and thereby increasing the heat transfer rate.
Care should be taken after loading any great quantity of stores especially into the vegetable
rooms. The fresh stores tend to sweat and icing up of the evaporator can become rapid. The
only solution is constant monitoring and defrosting as soon as necessary.
Effects of under and over charge
The effects of overcharge are a full condenser/receiver gauge glass. System pressures are not
effected until highly overcharged when a possibility of excessive HP pressure exists.
Undercharge causes failure to maintain cold room temperatures and compressor cycling.
Compressor cycling is caused by there being insufficient gas to maintain the compressor loaded
even with all room solenoids open. In extreme the compressor will cut in and out. Undercharge
is detected by low levels in the condenser/receiver gauge glass/ bubbles in liquid sight glass,
compressor cycling and low suction pressures.

21
Troubleshoot
A ship had real problems with the control of room temperatures, one room in particular. attempts
to 'balance' the system using the back pressure valves usually resulted in rooms starved of gas
and/or the compressor tripping on Low Pressure trip. It turned out that sag on one or two of the
liquid line pipes allowed oil and debris to build up in this section and restrict flow.
On another ship the lagging around a penetration piece had been damaged and water had got
behind it into the insulation. This liquid had frozen and exerted a crushing force on the pipe
sufficient to severely restrict the flow. This was only found after some searching as before the
lagging was removed nothing wrong could be seen.
Ships Refrigeration System
Refrigeration (Provision Cooling) System is intended for creating and maintaining the set
temperature conditions for the storage of foods in cooling rooms (stores).
The following components are included in the system:
 Cooling rooms (Provision stores)
 Refrigeration compressor
 Gas a liquid lines with valves
 Cooling seawater pump
Temperatures maintained in the cooling rooms are:
 Butter – storage of butter at a temperature of -2 °С;
 Meat – storage of meat at a temperature of -15 °С;
 Fish – storage of fish at a temperature of -15 °С.
 Fruit – storage of fruit at a temperature of +2 °С;
 Vegetables – storage of vegetables at a temperature of +2 °С;
 Dry prov. – storage of dry provisions at a temperature of +8 °С.

22
Figure: Typical Refrigeration Compressor
Figure above represents a typical Refrigeration group of a commercial ship including;
 Control box
 Electric motor
 Compressor
 Receiver
 Condenser
 Dehydrator
 Filter
 Freon gas piping

23
Figure: Cooling cycle and Refrigeration system components

24
Expansion valve
Thermostatic expansion valve is a control device that meters the amount of refrigerant to the
evaporator to regulate cooling.

25
The refrigeration plants on merchant vessels play a vital part in carrying refrigerated cargo and
provisions for the crew on board. In reefer ships, the temperature of the perishable or
temperature sensitive cargo such as food, chemical, or liquefied gas, is controlled by the
refrigeration plant of the ship. The same plant or a smaller unit can be used for maintaining the
temperature of different provision rooms carrying food stuffs for crew members.
The main purpose of ship’s refrigeration plant is to avoid any damage to the cargo or perishable
material so that it is transported in good and healthy condition. Refrigeration prevents growth of
micro-organisms, oxidation, fermentation and drying out of cargo etc.

26
Main Components of Refrigeration plants
Any refrigeration unit works with different components inline to each other in series. The main
components are:
1. Compressor: Reciprocating single or two stage compressor is commonly used for
compressing and supplying the refrigerant to the system.
2. Condenser: Shell and tube type condenser is used to cool down the refrigerant in the system.
3. Receiver: The cooled refrigerant is supplied to the receiver, which is also used to drain out
the refrigerant from the system for maintenance purpose.
4. Drier: The drier connected in the system consists of silica gel to remove any moisture from
the refrigerant
5. Solenoids: Different solenoid valves are used to control the flow of refrigerant into the hold or
room. Master solenoid is provided in the main line and other solenoid is present in all individual
cargo hold or rooms.
6. Expansion valve: An Expansion valve regulates the refrigerants to maintain the correct hold
or room temperature.
7. Evaporator unit: The evaporator unit act as a heat exchanger to cool down the hold or room
area by transferring heat to the refrigerant.
8. Control unit: The control unit consist of different safety and operating circuits for safe
operation of the refer plant.

27
Working of Ship’s Refrigeration Plant
The compressor acting as a circulation pump for refrigerant has two safeties cut-out.
1. Low pressure (LP) and
2. High Pressure (HP) cut outs.
When the pressure on the suction side drops below the set valve, the control unit stops the
compressor and when the pressure on the discharge side shoots up, the compressor trips.
LP or low pressure cut out is controlled automatically i.e. when the suction pressure drops, the
compressor stops and when the suction pressure rises again, the control system starts the
compressor.
HP or high pressure cut out is provided with manual re-set.
The hot compressed liquid is passed to a receiver through a condenser to cool it down. The
receiver can be used to collect the refrigerant when any major repair work has to be performed.

28
The master solenoid is fitted after the receiver, which is controlled by the control unit. In case of
sudden stoppage of compressor, the master solenoid also closes, avoiding the flooding of
evaporator with refrigerant liquid.
The room or hold solenoid and thermostatic valve regulate the flow of the refrigerant in to
the room to maintain the temperature of the room. For this, the expansion valve is controlled by
a diaphragm movement due to the pressure variation which is operated by the bulb sensor filled
with expandable fluid fitted at the evaporator outlet.
The thermostatic expansion valve supplies the correct amount of refrigerants to evaporators
where the refrigerants takes up the heat from the room and boils off into vapors resulting in
temperature drop for that room. This is how temperature is maintained in the refrigeration plant
of the ship.
Fundamentals of refrigeration
Refrigeration is a general term. It describes the process of removing heat from spaces, objects,
or materials and maintaining them at a temperature below that of the surrounding atmosphere.
To produce a refrigeration effect, the material to be cooled needs only to be exposed to a colder
object or environment. The heat will flow in its NATURAL direction-that is, from the warmer
material to the colder material. Refrigeration, then, usually means an artificial way of lowering
the temperature. Mechanical refrigeration is a mechanical system or apparatus that transfers
heat from one substance to another. It is easy to understand refrigeration if you know the
relationships among temperature, pressure, and volume, and how pressure affects liquids and
gases.
The refrigeration Ton
The unit of measure for the amount of heat removed is known as the refrigeration ton. The
capacity of a refrigeration unit is usually stated in refrigeration tons. The refrigeration ton is
based on the cooling effect of 1 ton (2,000 pounds) of ice at 32°F melting in 24 hours. The latent
heat of fusion of ice (or water) is 144 BTU's. Therefore, the number of BTU's required to melt 1
ton of ice is 144 x 2,000= 288,000. The standard refrigeration ton is defined as the transfer of
288,000 BTU's in 24 hours. On an hourly basis, the refrigeration ton is 12,000 BTU's per hour
(288,000 divided by 24). The refrigeration ton is the standard unit of measure used to designate
the heat-removal capacity of a refrigeration unit. It is not a measure of the ice-making capacity of

29
a machine, since the amount of ice that can be made depends on the initial temperature of the
water and other factors.
Mechanical refrigeration systems
Various types of refrigerating systems are used for shipboard refrigeration and air conditioning.
The one usually used for refrigeration purposes is the vapor compression cycle with
reciprocating compressors.
The figure shows a general idea of this type of refrigeration cycle. As you study this system, try
to understand what happens to the refrigerant as it passes through each part of the cycle. In
particular, you need to understand (1) why the refrigerant changes from liquid to vapor, (2) why it
changes from vapor to liquid, and (3) what happens in terms of heat because of these changes
of state. In this section, the refrigerant is traced through its entire cycle, beginning with the
thermostatic expansion valve ( TXV ).
Liquid refrigerant enters the TXV that separates the high side of the system and the low side of
the system. This valve regulates the amount of refrigerant that enters the cooling coil. Because
of the pressure differential as the refrigerant passes through the TXV, some of the refrigerant

30
flashes to a vapor. From the TXV, the refrigerant passes into the cooling coil (or evaporator).
The boiling point of the refrigerant under the low pressure in the evaporator is about 20°F lower
than the temperature of the space in which the cooling coil is installed. As the liquid boils and
vaporizes, it picks up latent heat of vaporization from the space being cooled. The refrigerant
continues to absorb latent heat of vaporization until all the liquid has been vaporized. By the time
the refrigerant leaves the cooling coil, it has not only absorbed this latent heat of vaporization. It
has also picked up some additional heat; that is, the vapor has become superheated. As a rule,
the amount of superheat is 4° to 12°F.
The refrigerant leaves the evaporator as low-pressure superheated vapor. The remainder of the
cycle is used to dispose of this heat and convert the refrigerant back into a liquid state so that it
can again vaporize in the evaporator and absorb the heat again.
The low-pressure superheated vapor is drawn out of the evaporator by the compressor, which
also keeps the refrigerant circulating through the system. In the compressor cylinders, the
refrigerant is compressed from a low-pressure, low-temperature vapor to a high-pressure vapor,
and its temperature rises accordingly.
The high-pressure R-12 vapor is discharged from the compressor into the condenser. Here the
refrigerant condenses, giving up its superheat ( sensible heat ) and its latent heat of
condensation. The condenser may be air or water cooled. The refrigerant, still at high pressure,
is now a liquid again. From the condenser, the refrigerant flows into a receiver, which serves as
a storage place for the liquid refrigerant in the system. From the receiver, the refrigerant goes to
the TXV and the cycle begins again.
This type of refrigeration system has two pressure sides. The LOW-PRESSURE SIDE extends
from the TXV up to and including the intake side of the compressor cylinders. The
HIGH-PRESSURE SIDE extends from the discharge valve of the compressor to the TXV.
Main parts of a refrigeration
The main parts of a refrigeration system are shown diagrammatically in the figure below. The six
primary components of the system include the thermostatic expansion valve, evaporator,
capacity control system, compressor, condenser, and receiver. All refrigeration systems must
also be fitted with a relief valve. The system below shows a relief valve installed on the

31
discharge side of the compressor which relives pressure to the suction side when the
compressor discharge pressure exceeds the relief valve preset pressure.
Thermostatic Expansion Valve (TXV)
The TXV regulates the amount of refrigerant to the cooling coil. The amount of refrigerant
needed in the coil depends, of course, on the temperature of the space being cooled. The
thermal control bulb, which controls the opening and closing of the TXV, is clamped to the
cooling coil near the outlet (tail coil), and before the back pressure regulating valve if installed.
The substance in the thermal bulb varies, depending on the refrigerant used. The expansion and

32
contraction (because of temperature change) transmit a pressure to the diaphragm. This causes
the diaphragm to be moved downward, opening the valve and allowing more refrigerant to enter
the cooling coil. When the temperature at the control bulb falls, the pressure above the
diaphragm decreases and the valve tends to close. Thus, the temperature near the evaporator
outlet controls the operation of the TXV. Flash gas formed in the liquid line of a refrigeration
system due to low refrigerant may cause expansion valve pins and seats to erode. A leaking
expansion valve could result in excessively low temperature to the space regulated.
Evaporator
The evaporator consists of a coil of copper, aluminum, or aluminum alloy tubing installed in the
space to be refrigerated. Aluminum tubing with copper fins are used in ammonia systems. The
liquid R-12 enters the tubing at a reduced pressure and, therefore, with a lower boiling point. As
the refrigerant passes through the evaporator, the heat flowing to the coil from the surrounding
air causes the rest of the liquid refrigerant to boil and vaporize. Refrigerant temperature in an
evaporator is directly related to refrigerant pressure. After the refrigerant has absorbed its latent
heat of vaporization (that is, after it is entirely vaporized), the refrigerant continues to absorb
heat until it becomes superheated by approximately 10°F. The amount of superheat is
determined by the amount of liquid refrigerant admitted to the evaporator. This, in turn, is
controlled by the spring adjustment of the TXV. A temperature range of 4° to 12°F of superheat
is considered desirable. It increases the efficiency of the plant and evaporates all of the liquid.
This prevents liquid carry-over into the compressor (flooding back).
Excessive circulation of the lubricating oil will cause the evaporator temperature to increase. The
main cause of slugging is improperly adjusted thermal expansion valve.
Defrosting of evaporator coils of a multi-box, direct expansion type refrigeration systems, and ice
machines can be accomplished by passing hot vapors from the compression cycle through the
coils. A re-evaporator is one way to overcome the possibility of a large slug of liquid refrigerant
entering the compressor suction when hot gas defrosting a refrigeration system.
Compressor
The compressor in a refrigeration system is essentially a pump. It is used to pump heat uphill
from the cold side to the hot side of the system. The heat absorbed by the refrigerant in the
evaporator must be removed before the refrigerant can again absorb latent heat. The only way

33
the vaporized refrigerant can be made to give up the latent heat of vaporization that it absorbed
in the evaporator is by cooling and condensing it. Because of the relatively high temperature of
the available cooling medium, the only way to make the vapor condense is to compress it.
When we raise the pressure, we also raise the temperature. Therefore, we have raised its
condensing temperature, which allows us to use seawater as a cooling medium in the
condenser. In addition to this primary function, the compressor also keeps the refrigerant
circulating and maintains the required pressure difference between the high-pressure and
low-pressure sides of the system. Many different types of compressors are used in refrigeration
systems. The designs of compressors vary depending on the application of the refrigerants used
in the system. The figure below shows a motor-driven, single-acting, two-cylinder, reciprocating
compressor.
Compressors used in refrigeration systems may be lubricated either by splash lubrication or by
pressure lubrication. Refrigeration compressors require a lubricant with a low pour point, and low
wax content to keep any oil leaving the compressor from congealing in the evaporator. Splash
lubrication, which depends on maintaining a fairly high oil level in the compressor crankcase, is
usually satisfactory for smaller compressors. High-speed or large-capacity compressors use
pressure lubrications systems.
The sudden reduction of pressure occurring within the crankcase of a refrigeration compressor
during starting causes the release of refrigerant from the oil/refrigerant mixture. Foaming of the
oil in a refrigeration compressor crankcase is caused by refrigerant boiling out of the lube oil.
The oil in the sump of a secured refrigeration compressor is heated to reduce absorption of
refrigerant by the oil. Excessive oil foaming in the crankcase of a refrigeration compressor at
start up can cause compressor damage from improper lubrication. The oil level in a refrigeration
compressor, the most accurate reading is obtained immediately after shutdown following a
prolonged period of operation. The refrigerant has had time to separate from the oil.
Refrigerant entering the compressor should be superheated vapor. It’s possible to have liquid
refrigerant returned to the suction side of a compressor due to a faulty or improperly adjusted
expansion valve. A flapper valve, also known as a beam valve, is frequently used in
refrigeration compressor discharge valves, and is designed to pass liquid slugs. Some systems

34
have devices installed in the compressor suction line to boil off liquid refrigerant returning to the
compressor, such as liquid separators, liquid accumulators, economizers, and heat exchangers.
Capacity Control System
Most compressors are equipped with an oil-pressure-operated automatic capacity control
system. This system unloads or cuts cylinders out of operation following decreases in the
refrigerant load requirements of the plant. A cylinder is unloaded by a mechanism that holds the
suction valve open so that no gas can be compressed.
Since oil pressure is required to load or put cylinders into operation, the compressor will start
with all controlled cylinders unloaded. But as soon as the compressor comes up to speed and
full oil pressure is developed, all cylinders will become operative. After the temperature
pull-down period, the refrigeration load imposed on the compressor will decrease, and the
capacity control system will unload cylinders pressure accordingly. The unloading will result in
reduced power consumption. On those applications where numerous cooling coils are supplied
by one compressor, the capacity control system will prevent the suction pressure from dropping
to the low-pressure cutout setting. This will prevent stopping the compressor before all solenoid
valves are closed.

35

36
Several designs of capacity control systems are in use. One of the most common is shown in
figure above. The capacity control system consists of a power element and its link for each
controlled cylinder, a step control hydraulic relay, and a capacity control valve.

37
The system's components are all integrally attached to the compressor. The suction or
crankcase pressure of the refrigeration plant is sensed by the capacity control valve to control
the system. In other words, a change in the refrigeration load on the plant will cause a change in
suction pressure. This change in suction pressure will then cause the capacity control system to
react according to whether the suction pressure increased or decreased. The working fluid of the
system is compressor oil pump pressure. Compressor oil pump pressure is metered into the
system through an orifice. Once the oil passes the orifice, it becomes the system control oil and
does the work.
Another type of capacity control uses a solenoid valve, in conjunction with an unloader head.
The solenoid valve allows the refrigerant to pass from the suction chamber to the top of the
unloader piston, causing the piston to lift and unload the cylinder.
Locate the following components on figure 10-6, and refer to them as you read the next two
paragraphs.
A. Compressor oil pump pressure tap-off
B. Control oil strainer
C. Hydraulic relay
D. Hydraulic relay piston
E. Unloader power element
F. Unloader power element piston
G. Lifting fork
H. Unloader sleeve
İ. Suction valve
J. Capacity control valve
K. Crankcase (suction) pressure sensing point
The following functions take place when the compressor is started with a warm load on the
refrigeration system.
Compressor oil (A) is pumped through the control oil strainer (B) into the hydraulic relay (C).
There the oil flow to the unloader power elements is controlled in steps by the movement of the
hydraulic relay piston (D). As soon as pump oil pressure reaches a power element (E), the
piston (F) rises, the lifting fork (G) pivots, and the unloader sleeve (H) lowers, permitting the

38
suction valve (1) to seat. The system is governed by suction pressure, which actuates the
capacity control valve (J). This valve controls the movement of the hydraulic relay piston by
metering the oil bleed from the control oil side of the hydraulic relay back to the crankcase.
Suction pressure increases or decreases according to increases or decreases in the
refrigeration load requirements of the plant. After the temperature pull-down period with a
subsequent decrease in suction pressure, the capacity control valve moves to increase the
control oil bleed to the crankcase from the hydraulic relay. There is a resulting decrease in
control oil pressure within the hydraulic relay. This decrease allows the piston to be moved by
spring action. This action successively closes oil ports and prevents compressor oil pump
pressure from reaching the unloader power elements. As oil pressure leaves a power element,
the suction valve rises and that cylinder unloads. With an increase in suction pressure, this
process is reversed, and the controlled cylinders will load in succession. The loading process is
detailed in steps 1 through 7 in the figure above.
Shaft seals
Where the crankshaft extends through the
crankcase, a leak-proof seal must be
maintained to prevent the refrigerant and oil
from escaping and also to prevent air from
entering the crankcase when the pressure in
the crankcase is lower than the surrounding
atmospheric pressure. This is accomplished
by crankshaft seal assemblies. There are
several types of seals including the rotary
seal, and the diaphragm. The rotary seal
shown right consists of a stationary cover
plate and gasket, a rotating assembly which
includes a carbon ring, a neoprene seal, a
compression spring, and compression washers. The sealing points are located (1) be-tween the
crankshaft and the rotating carbon rings, and sealed by a neoprene ring; (2) between the
rotating carbon ring and the cover plate, and sealed by lapped surfaces; and (3) between the

39
cover plate and the crankcase, and sealed by a metallic gasket. The seal is adjusted by adding
or removing metal washers between the crankshaft shoulder and the shaft seal compression
spring.
A stationary bellows seal is illustrated left. It consists of a
bellows clamped to the compressor housing at one end to
form a seal against a rotating shaft seal collar on the other.
The sealing points are located (1) between the crankcase
and the bellows, and sealed by the cover plate gasket; (2)
between the crankshaft and the shaft seal collar, and
sealed by a neoprene gasket; and (3) between the surface
of the bellows nose and the surface of the seal collar, and
sealed by lapped surfaces. The stationary bellows seal is
factory set for proper tension and should not be altered.
The rotating bellows seals, figure right, consists of a
bellows clamped to the crankshaft at one end to form a
seal against a stationary, removable shaft seal shoulder on
the other end. The sealing points are located (1) between
the crankshaft and bellows, and sealed by a shaft seal
clamping nut; (2) between the removable shaft seal
shoulder and the crankcase and sealed by a neoprene
gasket; and (3) between the bellows nose piece and the
shaft seal collar, and sealed by lapped surfaces. This
type seal is also factory set
Condenser
The compressor discharges the high-pressure,
superheated refrigerant vapor to the condenser, where it
flows around the tubes through which water is being
pumped. As the vapor gives up its superheat (sensible
heat) to the seawater, the temperature of the vapor drops

40
to the condensing point. The refrigerant, now in liquid form, is sub-cooled slightly below its
condensing point. This is done at the existing pressure to ensure that it will not flash into vapor.
A water-cooled condenser is shown in figure left. Circulating water is obtained through a branch
connection from the fire main or by means of an individual pump taking suction from the sea.
Sea water condensers have zinc anodes in the end covers to protect against corrosion.
Newer ships use a closed fresh water system, consisting of circulating pump, and keel-cooler.
The purge connection (fig. left) is on the refrigerant side. It is used to remove air and other
non-condensable gases that are lighter than the refrigerant vapor.
If a large difference exists between the compressor discharge pressure and the pressure
corresponding to the existing condensing temperature the system, should be purged.
Most condensers used for shipboard refrigeration plants are of the water-cooled type. However,
some small units have air-cooled condensers. These consist
of tubing with external fins to increase the heat transfer
surface. Most air-cooled condensers have fans to ensure
positive circulation of air around the condenser tubes.
Receiver
The receiver (fig. below right) acts as a temporary storage
space and surge tank for the liquid refrigerant. The receiver
also serves as a vapor seal to keep vapor out of the liquid line
to the expansion valve. A pressure drop in the liquid line of a
refrigeration system may cause the liquid refrigerant to flash
to gas. Receivers are constructed for either horizontal or
vertical installation.
In addition to the five main components of a refrigeration
system, a number of controls and accessories are required.
The most important of these are described briefly in the
following paragraphs.
Dehydrator
Systems opened for repairs or service are vulnerable to
moisture contamination. The maximum level of moisture

41
permitted in an operating refrigeration system is 15 parts per million.
A dehydrator, or dryer, containing silica gel or activated alumina, is placed in the liquid
refrigerant line between the receiver and the TXV. In older installations, bypass valves allow the
dehydrator to be cut in or out of the system. In newer installations, the dehydrator is installed in
the liquid refrigerant line without any bypass arrangement. A dehydrator is shown in upper left
figure. A refrigeration system contaminated with moisture can be affected by, acid formation,
sludge formation, ice in the expansion valve, and corrosion.
If a liquid drying agent is used in a refrigeration system already equipped with a solid drying
agent, the liquid drying agent will release the moisture already trapped in the solid drying agent.
Moisture Indicator and Liquid Eye
A moisture indicator is located either in the liquid refrigerant line or built into the dehydrator. The
moisture indicator contains a chemically treated element that changes color when there is an
increase of moisture in the refrigerant. The color change is reversible and changes back to a
DRY reading when the moisture is removed from the refrigerant. Excessive moisture or water
will damage the moisture indicator element and turn it gray, which indicates it must be replaced.
In an operating refrigeration system low on refrigerant, a liquid line sight glass will show bubbles.
Solenoid Valve and Thermostatic Control Switch
A solenoid valve is installed in the liquid line leading to each evaporator. Figure right shows a
solenoid valve and the thermostatic control switch that
operates it. The thermostatic control switch is
connected by long flexible tubing to a thermal control
bulb located in the refrigerated space. When the
temperature in the refrigerated space drops to the
desired point, the thermal control bulb causes the
thermostatic control switch to open. This action closes
the solenoid valve and shuts off all flow of liquid
refrigerant to the TXV. When the temperature in the
refrigerated space rises above the desired point, the

42
thermostatic control switch closes, the solenoid valve opens, and liquid refrigerant once again
flows to the TXV. This is is an example of two position control.
The solenoid valve and its related thermostatic control switch maintain the proper temperature in
the refrigerated space. You may wonder why the solenoid valve is necessary if the TXV controls
the amount of refrigerant admitted to the evaporator. Actually, the solenoid valve is not
necessary on units that have only one evaporator. In systems that have more than one
evaporator and where there is wide variation in load, the solenoid valve provides additional
control to prevent the spaces from becoming too cold at light loads.
In addition to the solenoid valve installed in the line to each evaporator, a large refrigeration
plant usually has a main liquid line solenoid valve installed
just after the receiver. If the compressor stops for any reason
except normal suction pressure control, the main liquid
solenoid valve closes. This prevents liquid refrigerant from
flooding the evaporator and flowing to the compressor
suction. Extensive damage to the compressor can result if
liquid is allowed to enter the compressor suction.
Refrigeration Valve
Refrigeration valves are used to add and remove refrigerant
from the system. Most systems have refrigeration valves
installed in both, high and low pressure sides of the system.
Like most valves used in refrigeration they are double
seating. When the valve stem is rotated counter-clockwise to
the fully opened position the upper seat seals the valve from
leakage. Double seating valves should be used either fully
opened or closed. Double seating valves permit repacking under pressure. A cap is provided to
reduce the possibility of loss of refrigerant from the system. The valve shown has a gauge
connection.
Modulating Valves
Modulating valves are similar to solenoid valves, as they control the liquid refrigerant to the TXV.
A liquid line solenoid valve is either completely opened or closed, whereas a modulation valve is

43
positioned according to the strength of the applied electrical signal. The movement of the
armature within a modulating valve is controlled by the electromagnetic force of the coil and
opposed by spring pressure. This arrangement will cause the
valve to the open position due to the spring pressure acting
upon the armature if the coil fails.
Evaporator Pressure Regulating Valve
In some ships, several refrigerated spaces of varying
temperatures are maintained by one compressor. In these
cases, an evaporator pressure regulating valve is installed at
the outlet of each evaporator EXCEPT the evaporator in the
space in which the lowest temperature is to be maintained.
The evaporator pressure regulating valve is set to keep the
pressure in the coil from falling below the pressure
corresponding to the lowest evaporator temperature desired in
that space. The evaporator pressure regulating valve is used
on;
 water coolers
 units where high humidity is required (such as fruit and
vegetable stow spaces)
 installations where two or more rooms are maintained at
refrigeration unit. different temperatures by the use of the same
A cross section of a common evaporator pressure regulating valve (commonly called the EPR
valve) is shown in figure 10-11. The tension of the spring above the diaphragm is adjusted so
that when the evaporator coil pressure drops below the desired minimum, the spring will shut the
valve.
The EPR valve is not really a temperature control; that is, it does not regulate the temperature in
the space. It is only a device to prevent the temperature from becoming too low.

44
Back pressure regulating valve
Also known as an evaporator pressure regulating valve, is used to maintain a minimum
evaporator pressure. In a direct expansion type cargo refrigeration system, a box is normally
changed from chill to freeze by adjusting the back pressure regulating valve.
Low-Pressure Cutout Switch
The low-pressure cutout switch is also known as a suction pressure control switch. Pressure
acting on a bellows opens and closes contacts causing the compressor to go on or off as
required for normal operation of the refrigeration plant. It is located on the suction side of the
compressor and is actuated by pressure changes in the suction line.
When the solenoid valves in the lines to the various evaporators are closed, the flow of
refrigerant to the evaporators is stopped. This action causes the pressure of the vapor in the
compressor suction line to drop quickly. When the suction pressure has dropped to the desired
pressure, the low-pressure cutout switch stops the compressor motor. When the temperature in
the refrigerated spaces rises enough to operate one or more of the solenoid valves, refrigerant is
again admitted to the cooling coils. This causes the compressor suction pressure to build up
again. At the desired pressure, the low-pressure cutout switch closes, starting the compressor,
and the cycle is repeated again. The pressure range between the system cut in and cut out
pressures in a refrigeration unit is known as differential. The low pressure cutout switch used on
a refrigeration system compressor is set to cut in at approximately 5 Psig and cutout at .5 Psig.
High-Pressure Cutout Switch
A high-pressure cutout switch is connected to the compressor discharge line to protect the
high-pressure side of the system against excessive pressures. The design of this switch is
essentially the same as that of the low-pressure cutout switch. However, the low-pressure cutout
switch is made to CLOSE when the suction pressure reaches its upper normal limit, while the
high-pressure cutout switch is made to OPEN when the discharge pressure is too high. As you
already have learned, the low-pressure cutout switch is the compressor control for the normal
operation of the plant. On the other hand, the high-pressure cutout switch is a safety device only.
It does not have control of the compressor under normal conditions.

45
Oil separator
Oil separators or traps, if supplied are located between the compressor discharge and the
condenser. Oil separators serve to return oil entrained in refrigerant vapor back to the
compressor crankcase.
Water Failure Switch
A water failure switch stops the compressor if there is a circulating water supply failure. The
water failure switch is a pressure-actuated switch. Its operation is similar to the low and high
pressure cutout switches previously described. If the water failure cutout switch fails to function,
the refrigerant pressure in the condenser quickly builds up to the point that the high-pressure
switch stops the compressor.
Strainer
Because of the solvent action of refrigerant, any particles of grit, scale, dirt, or metal that the
system may contain are circulated through the refrigerant lines. To avoid damaging the
compressor from foreign matter, a strainer is installed in the compressor suction connection.
Water Regulating Valve
A water regulating valve controls the quantity of circulating water flowing through the refrigerant
condenser. The water regulating valve is actuated by the refrigerant pressure in the compressor
discharge line. This pressure acts upon a diaphragm (or, in some valves, a bellows
arrangement) that transmits motion to the valve stem.
The primary function of the water regulating valve is to maintain a constant refrigerant
condensing pressure. Basically, the following two variable conditions exist:
 The amount of refrigerant to be condensed
 Changing water temperatures
The valve maintains a constant refrigerant condensing pressure by controlling the water flow
through the condenser. By sensing the refrigerant pressure, the valve permits only enough water
through the condenser to condense the amount of refrigerant vapor coming from the
compressor. The quantity of water required to condense a given amount of refrigerant varies
with the water temperature. Thus, the flow of cooling water through the condenser is
automatically maintained at the rate actually required to condense the refrigerant under varying
conditions of load and temperature.

46
Heat Interchanger
The function of a heat interchanger is to lower the temperature of liquid refrigerant before
entering the expansion valve, reduce the possibility of liquid refrigerant from flooding back to the
compressor, and minimize sweating of the suction line.
Pressure Gauges and Thermometers
A number of pressure gauges and thermometers are
used in refrigeration systems. The figure left shows a
compound R-12 gauge. The temperature markings on
this gauge show the boiling point (or condensing point)
of the refrigerant at each pressure; the gauge cannot
measure temperature directly. The red pointer is a
stationary marker that can be set manually to indicate
the maximum working pressure.
A water pressure gauge is installed in the circulating
water line to the condenser to indicate failure of the
circulating water supply.
Standard thermometers of appropriate range are provided for the refrigerant system.
Detecting and correcting problems
A number of symptoms indicate faulty operation of refrigeration and air-conditioning plants. The
table below list some possible causes and corrective measures and includes recommended test
procedures that may be used to isolate the problems.
Trouble Possible Cause Corrective Measure
High condensing pressure.
Inlet water warm. Purge air from condenser
Air on non-condensable gas in
system.
Increase quantity of condensing
water.
Insufficient water flowing through
condenser.
Increase quantity of water.
Condenser tubes clogged or scaled. Clean condenser water tubes.
Too much liquid in receiver,
condenser tubes submerged in liquid
refrigerant.
Draw off liquid into service cylinder.
Low condensing pressure.
Too much water flowing through
condenser.
Reduce quantity of water.
Water too cold. Reduce quantity of water.
Liquid refrigerant flooding back from
evaporator.
Change expansion valve adjustment,
examine fastening of thermal bulb.
Leaky discharge valve. Remove head, examine valves.

47
Replace any found defective.
Frosting or sweating of a liquid line.
Refrigerant line restriction.
Check for partially closed stop valve,
or stuck solenoid valve.
System low on refrigerant. Check for leaks, add refrigerant.
High suction pressure.
Compressor crankcase sweating
Overfeeding of expansion valve.
Regulate expansion valve, check
bulb attachment.
Leaky suction valve.
Remove head, examine valve and
replace if worn.
Low suction pressure.
Restricted liquid line and expansion
valve or suction screens.
Rump down, remove, examine and
clean screens,
Insufficient refrigerant in system. Check for refrigerant storage.
Too much oil circulating in system.
Check for too much oil in circulation.
Remove oil.
Improper adjustment of expansion
valves
Adjust valve to give more flow.
Expansion valve power element
dead or weak
Replace expansion valve power
element.
Compressor short cycles on low-
pressure control.
Low refrigerant charge.
Locate and repair leaks. Charge
refrigerant.
Thermal expansion valve not feeding
properly.
1. Dirty strainers.
2. Moisture frozen in orifice or
orifice plugged with dirt.
3. Power element dead or weak
Adjust, repair or replace thermal
expansion valve.
1. Clean strainers.
2. Remove moisture or dirt (use
system dehydrator).
3. Replace power element.
Water flow through evaporators
restricted or stopped. Evaporator
coils plugged, dirty, or clogged with
frost.
Remove restriction. Check water
flow. Clean coils or tubes.
Defective low-pressure control
switch.
Repair or replace low-pressure
control switch.
Compressor runs continuously.
Shortage of refrigerant. Repair leak and recharge system.
Leaking discharge valves. Replace discharge valves.
Compressor short cycles on high-
pressure control switch.
Insufficient water flowing through
condenser, clogged condenser.
Determine if water has been turned
off. Check for scaled or fouled
condenser.
Defective high-pressure control
switch.
Repair or replace high-pressure
control switch.
Compressor will not run.
Seized compressor. Repair or replace compressor.
Cut-in point of low-pressure control
switch too high.
Set L. P. control switch to cut-in at
correct pressure.
High-pressure control switch does
not cut-in.
1. Defective switch.
2. Electric power cut off.
3. Service or disconnect switch
open.
4. Fuses blown.
5. Over-load relays tripped.
6. Low voltage.
7. Electrical motor in trouble.
8. Trouble in starting switch or
Check discharge pressure and reset
P. H. control switch.
1. Repair or replace switch.
2. Check power supply.
3. 3.Close switches.
4. Test fuses and renew if
necessary.
5. Re-set relays and find cause of
overload.
6. Check voltage (should be within
10 percent of nameplate rating).
7. Repair or replace motor.
8. Close switch manually to test

48
control circuit.
9. 9. Compressor motor stopped by
oil pressure differential switch.
power supply. If OK, check
control circuit including
temperature and pressure
controls.
9. Check oil level in crankcase.
Check oil pump pressure.
Decreased capacity of the
compressor.
High vapor superheat. Adjust or replace expansion valve.
Sudden loss of oil from crankcase.
Liquid refrigerant slugging back to
compressor crank case.
Adjust or replace expansion valve.
Capacity reduction system falls to
unload cylinders.
Hand operating stem of capacity
control valve not turned to automatic
position.
Set hand operating stem to automatic
position.
Compressor continues to operate at
full or partial load.
Pressure regulating valve not
opening.
Adjust or repair pressure regulating
valve.
Capacity reduction system fails to
load cylinders.
Broken or leaking oil tube between
pump and power element.
Repair leak.
Low discharge pressure with high
suction pressure.
Discharge relief valve leaking back to
the suction side.
Replace relief valve.
Compressor continues to operate
unloaded.
Pressure regulating valve not
closing.
Adjust or repair pressure regulating
valve.
Compressor oil brownish in color
Copper plating caused by moisture in
the system.
Change filter drier, or dehydrator.
Compressor oil gray or metallic.
Compressor bearing wear or piston
scoring.
Replace or overhaul compressor.
Compressor oil black
Carbonization resulting from air in
the system.
Remove air from system.
Charging the system
One of the test questions states, "Before charging a refrigeration unit, the refrigerant charging
lines should be purged with the refrigerant". New laws regarding refrigerants require all charging
lines or hoses to be equipped with valves which seal the lines when they are not connected.
The amount of refrigerant charge must be sufficient to maintain a liquid seal between the
condensing and the evaporating sides of the system. When the compressor stops, under normal
operating conditions, the receiver of a properly charged system is about 85% full of refrigerant.
The proper charge for a specific system or unit can be found in the manufacturer's technical
manual or on the ship's blueprints. A refrigeration system must have an adequate charge of
refrigerant at all times; otherwise its efficiency and capacity will be impaired.
Low side passive charging of a refrigeration system may be speeded up by warming the service
cylinder with hot water to help boil off the liquid. The safest and quickest method of adding
refrigerant to a refrigeration system is to add the refrigerant through the charging valve as a
liquid.

49
A refrigeration system should not be charged if there are leaks or if there is reason to believe
that there is a leak in the system. The leaks must be found and corrected. A system should be
checked for leaks immediately following, or during the process of charging.
Container Refrigeration
If an evaporator or condenser coil of a container refrigeration system becomes dirty and requires
cleaning, one of the suggested methods is to use the high pressure wash system.
When a thermostatic expansion valve is installed in a container refrigeration system, the sensing
bulb may not require insulation if the bulb is installed outside of the cooled air stream. If the
evaporator coil horizontal return line of a container refrigeration system is less than 0.874" (2.21
cm) in diameter, the thermostatic expansion valve sensing bulb should be placed on the upper
surface of the line.
Safety precautions
 Secure and tag the electrical circuit of the system before working any shipboard system, to
prevent damage to the equipment, and injury to personal.
 On all vessels equipped with refrigeration units of over 20 cubic foot capacity, a gas mask
suitable for protection against each refrigerant used, or a self-contained breathing apparatus
must be provided.
 Use chemical safety goggles or a full face shield and rubber gloves while handling
refrigerant.
 Ammonia vapors in a low concentration can cause death, will dissolve in perspiration and
cause caustic burns, and can burn or explode.
 Coast Guard Regulations (46 CFR) require a method for the relief of an over-pressurized
refrigeration system. A rupture disk may be fitted in series with the relief valve.
 Overfilling a refrigerant container is extremely dangerous due to the high pressures
generated by hydrostatic pressure of the expanding liquid.
 Low pressure refrigeration containers used for transportation are not refillable. They rupture
disc set for 15 Psig, and are not to be heated, or stored in temperatures over 125°F.
Containers are to be pumped down to 0 Psig or below, and disposed of with the valve
opened.

50
Refrigeration Compressors
Metro high speed reciprocating compressors are manufactured with latest technology and most
modern method. These compressors are available in capacities up-to 12 cylinders in V & W
arrangements.
Suitable for industrial applications, Metro Compressors have compact design, built in suction
and discharge manifold with large size suction filter for protection of vital parts. All welded steel
construction of crankcase unit with provision of unloaded starting system and the safeguard
against incidental liquid hammer. The crank case is fully leak & impact proof, the smooth internal
surfaces of the crank case provides better condition for lubricants. Every parts is precision made
and interchangeable. These compressors are suitable for V-belt and direct drive system. Our
heavy duty Compressors can work smoothly for 24 hours continuously for a long span of time.
Ammonia Compressor High Speed -
Single Cylinder
Ammonia Compressor High Speed
- 2 Cylinder
Ammonia Compressor High Speed
-3 Cylinder
Piston / Cylinder Liner:
Pistons are made from special aluminum alloy. Gudgeon pins are case hardened steel and
grounded. Cylinder liners are made from special close grain alloy casting, precision boring,
horning and pressed into cylinders blocks. These liners can be easily replaced. Hydraulically
operated valve lifting mechanism on each cylinder ensures absolute capacity control and fully
unloading start.

51
Connecting Rod:
The connecting rod is die forged. It has steel backed White Metal shells on its big end bronze
bearings, while the smaller end has a wear resistant metal.
Crankshaft & Bearings:
Has exceptionally good running metal properties and wear resistance. All bearing surfaces are
grounded and dynamically balanced. The main Bearings are white metal lined steel shells, the
intermediate bearings are provided with split type for 4, 6, 9 & 12 cylinder compressor.
Lubrication:
Forced feed system is provided by crankshaft driven gear type oil pump that delivers oil to all
bearings and capacity control system.
Ammonia Compressor High Speed - 6 Cylinder Ammonia Compressor High Speed - 7 Cylinder
Shaft Seal Assembly:
The rotary face type, sliding surfaces are grounded to an extreme finish and lapped. Frictional
heat is removed by the full flow of lubricating oil that is directly fed from oil pump with provision
of water cooled system too.
Standard Accessories:
Every Metro Compressor is dispatched to the customer with the following standard accessories:

52
Drive set:
 Consisting of V- belts, Motor Pulley & Flywheel
 Plain base plate with foundation bolts
 Suction & Discharge Service valves (Shut-off
valves)
 Pressure gauge, gauge board and mounting
stand.
 Ferrules and pipes
 Hour meter
 Indicator- Bulbs & Switches
 Manual Regulator Capacity Control
 Oil Filter Set
 Rubber Seal Sets
 Tools Kit Box
Ammonia Compressor High Speed - 9 Cylinder
Optional Items
Ammonia Compressor High Speed - 12 Cylinder
 Base Frame Unit for compressor & Motor with
foundation bolts
 Crank Case heater for 2 stage
 Inter-stage Cooling system for 2 stage
 Cut-off switches L-P-H-P. & O.P
 Electrically operated capacity control
 Oil Separator
 Equalizer connections for parallel running of
Compressor
 Flexible direct coupling with guard
 V-Belt guard for Motor & Compressor

53
Single Stage Refrigeration Compressors
Technical Data: Refrigeration (NH3) Compressors –Single Stage
S. No Model MC-10 MC-20 MC-30 MC-40 MC-60 MC-90 MC-120
1. Cylinder Arrangement 1 L 1 x V 1 x w 2 x v 2 x W 3 x W 3 x W
2. Nos. of Cylinder 1 2 3 4 6 9 12
3. Cylinder Bore (mm) 160 160 160 160 160 160 160
4. Piston Stoke (mm) 114 114 114 114 114 114 114
5. Suction Size (mm) Discharge Size(mm)
50 65 80 80 100 125 150
40 50 65 65 80 100 100
6. Swept Volume (Cu.m³/hr) 135 270 405 540 810 1215 1620
7. Permissible Speed
V-belt driven from 450 to 1000 R.P.M. In steps of 50 RPM
(Minimum - 450 / Normal - 750 / Maximum - 1000 RPM)
8. Oil Charge Capacity (Ltr.) 12 14 16 20 22 30 35
9. Gross Weight (Khs)
Gross Weight
(Khs)
860 970 1190 1400 1975 2850
Two Stage Refrigeration Compressors
Technical Data: Refrigeration (NH3) Compressors - Two Stage
S. No Compressor Model MC-21 MC-31 MC-42 MC-51 MC-63 MC-72 MC-84 MC-93 MC-102
1. Cylinder Arrangement 1 x V 2 x V 2 x W 2 x W 3 x W 3 x W 4 x W 4 x W 4 x W
2. Nos. Compressor L.P 2 3 4 5 6 7 8 9 10
3. Nos. Compressor H.P 1 1 2 1 3 2 4 3 2
4. Cylinder Bore (mm) 160 160 160 160 160 160 160 160 160
5. Piston Stroke (mm) 114 114 114 114 114 114 114 114 114
6. Suction Size (mm) 80 80 100 100 125 125 125 125 125
7. Discharge Size (mm) 65 65 50 50 50 50 50 50 50
8. Swept Volume (m³/hr) 275 412 548 687 823 960 1097 1234 1371
9. Permissible Speed
V- belt driven from 450 to 1000 R.P.M in steps of 50 RPM (Minimum -450/ Normal
-750 / maximum-1000 RPM)
10. Oil Charge Capacity 12 20 22 22 30 30 35 35 35
11.
Cooling flow for each cylinder
Jackit
12 - LPM Cylinder at water inlet temp. 35°C
12. Gross Weight (kgs) 970 1190 1400 1400 1975 1975 2850 2850 2850
These are only guide lines. All specifications are subject to change without notice.

54

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