Basic information about workshop

Basic information about
Plumbing, Carpentry, Welding, Basic machining,
Centrifugal pump and Air conditioner
By:
Mr.B.Ramesh, M.E.,(Ph.D),
Research Scholar, CEG, Anna University, Chennai,
Associate Professor of Mechanical Engineering,
St. Joseph’s College of Engineering,
Jeppiaar Trust, Chennai-119
Plumbing:
* Vice : Bench vice, Pipe vice
* Taps : Taper tap, Intermediate tap(plug tap) and Bottoming tap
* Plumb bob : Used for checking vertical lines
* GI pipe : galvanized iron pipe ; SWGP : Stoneware glazed pipe
* Zinc is used for galvanizing. It protects ferrous metal from corrosion
* Flexible pipe : Alvin pipes are used for water supply in hilly areas and storey
areas. Armer pipe is a rubber pipe mainly used for temporary water supply of
large volume and it contains wiring over it.
* The entire supply pipe should be so installed that it should drain to one point.
* Cast iron pipes of larger size are joined with flanges while small size pipes are
joined by sockets.
* The water pressure does not become low by using bend.
* The other name of tap is cock.
* Nipple : It is a short piece of pipe (less than 300 mm in length). It consists of
three parts in that two parts will be screwed on to the two pipe ends and the
third one which is a nut, draws the pipes together tightly.
* Plug : For closing internal threaded openings temporarily.
Cap : For closing external threaded openings temporarily.
* Socket reducer : Used to connect a big pipe to a small pipe face to face.
* Piping diagram : single line and double line.
*
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* Pipe joints : Bell and spigot joints, flanged joints and threaded joints.
* Bell and spigot joints : where it is necessary to insert a fitting into an existing
pipe line.
* Water tight joints: Flanged joints – rubber gaskets are used for cold water pipe
and asbestos gaskets are used for hot water pipe.
* Threaded joints : eg. Coupling, nipple, close nipple.
* Plumbing is the art of design, installation and maintenance of pipe, pipe
fittings and other accessories in a building.
* The plumber is mentioned according to his experience by the following three
grades as apprentice, journeyman and master.
* An apprentice is a beginner and serves as a helper. The journey man performs
the task of plumbing installation and repair. The master being the skilled
person doing the business of plumbing, with knowledge of laws and
ordinances affecting plumbing.
* Laying pipe connection to the suction side of a pump – inlet :
* Should be short and direct
* Liquid velocities of 8 feet per second in the suction are usually
satisfactory.
* Flange should be used to connect the suction pipe to the pump. The
diameter of flange should not be same as that of the suction pipe.
Hence the eccentric reducer is used to connect the suction pipe and the
flange.
* Slope the suction pipe up to the pump. In order to avoid the air
bubbles inside the pipe, the suction pipe is laid at 20
downwards
towards the well.
* Do not use check valve in the suction pipe.
* Submerge the end of the suction line and the foot valve atleast three
feet below the lowest level of the liquid to be pumped.
* The suction lift( distance from the water surface to the pump centre
line including all losses) should not exceed 20 feet of water.
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* Avoid loops in the suction pipe which rise above the horizontal
centre line of the pump. Instead turn the loop downward. This prevents
the formation of air pockets in suction pipe.
* Suction pipe should be larger than the pump suction nozzle.
* Laying pipe connection to the delivery side of a pump – outlet :
* A check valve and a gate valve should be installed in the discharge
line. The check valve should be next to the pump. Use a nozzle
between the pump and the check valve.
* The size of the pipe on the discharge side of a pump should be
increased in order to reduce the friction losses.
* Close the gate valve in order to run the pump and to stop the pump.
Open the gate valve during the running of the pump.
* Metal pipes are used as a suction pipe for pump for the purpose of taking the
underground water and these pipes are used to supply water to the water tank.
* Plastic pipes are used for transferring water from the storage tank to the
various rooms of a house.
* Flexible pipes are used in house hold appliances like washing machine and
vacuum cleaner.
* In plastic pipes, thermoplastic material is used. Types of plastic pipes :
Polyethylene, Polypropylene, PVC and Cross linked polyethylene.
* The ends of cast iron water pipe are of three types and these are standard ends:
Bell and spigot, Flanged and Screwed.
* Bell and spigot ends are used mainly for underground work and in buildings
where there is too much space for the fittings and for caulking operations.
* Flanged ends are used in those buildings where space is limited. In this, the
pipes are held together by bolts having gaskets between the flanges to make it
leak proof.
* Threaded or screwed ends are used in small pipes in general practice, although
these are available in bigger diameter pipes also.
* Rubber is used in tubing and pipes either as hard or soft rubber to convey
liquids to which it is corrosion resistant.
* Soft rubber is used in hose for conveying water and other fluids such as steam
where flexibility is required.
* Separate set of pipe threading dies are required for each pipe size.
* Taps are used for cutting internal threads on a pipe or fitting. Three types of
tap are necessary to cut threads. Taper tap is used first and cuts light threads.
Then plug tap is used and finally bottoming tap is used which cut the threads
to the required depth.
* The various pipe fittings used in plumbing are Socket, Elbow, Bend, T, Four
way cross, Valves, Cock, Pipe union and Socket reducer.
* Joints used in pipe are : 1) Bell and spigot joints 2) Flanged joints and 3)
Threaded joints.
* Slope the suction pipe up to the pump. In order to avoid the air bubbles inside
the pipe, the suction pipe is laid at 20
downwards towards the well.
* Bell or Hub: That portion of a pipe which, for a short distance, is sufficiently
enlarged to receive the end of another pipe of the same diameter for the
purpose of making a joint.
* Plumber’s soil: A mixture of lampblack and glue used in lead work.
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Carpentry:
* Carpentry is the process of working with wood for applications such as floor
works, roofs and partitions in a building. Preparation of other wood works
such as windows, stairs, cupboards etc is called as joinery.
* Wood seasoning is the process of removing the excess moisture present in the
timber by evaporation. After seasoning of the wood the moisture content is
reduced to 9- 25 percentage.
* Advantages of seasoning : Strength and durability is increased, wood becomes
resilient and lighter, workability is increased, surface finish is improved and
distortion is minimized.
* Types of seasoning : water seasoning, natural seasoning, chemical seasoning
and kiln seasoning.
* Types of wood : Soft wood, Hard wood and Ply wood.
* Soft wood: It has straight fibers and is comparatively weaker. Easy to work.
Weight and durability are less. Compared to hard wood, soft wood catches fire
soon. Eg. Deodar, Kail and Chir.
* Hard wood: Hard wood has closed structure, heavy in weight, dark in colour,
more durable. Difficult to work. It has proper bonds inside. So it is very
strong. Eg. Teak, Shirham, Sal, Mango, Maple and Oak.
* Ply wood : It consists of three layers: 1) Top face plys layer 2) Core layer 3)
Bottom face plys layer. The face plys layers are bonded to the centre core,
which is thick and not of good quality.
* Annual rings are added to the timber every year.
* Try square is used for testing squareness(900
) and marking of joints. The blade
lengths available are 150, 225 and 300 mm.
* Mitre square is used for marking and measuring an angle of 450
. Length of
blade is between 200 to 300 mm. They are made up of steel blade with rose
wood stock.
* Bevel square is used for measuring the angle from 00
to 1800
. The shape of the
bevel square is like a try square.
* The type of gauges used in carpentry are: 1). Marking gauge 2) Mortise gauge
and 3). Cutting gauge.
* Gauges are used to mark lines parallel to the edge of a piece of wood. Marking
gauge has one marking point. Mortise gauge has two marking points. Divider
is used for dividing the centres.
* Front end of a blade along the teeth is called ‘point’. The back end is called
‘red’. The teeth of a saw are bent slightly to the left and right consecutively(a
small zig zag).
* Types of saw:
* Rip saw : Length of the blade is 650 – 710 mm. No. of teeth per 25
mm is either 4 or 5 .Suitable for sawing down the grain.
* Cross cut saw: Length of the blade is 600 – 650 mm. No. of teeth per
25 mm is 8 to 10. Suitable for cutting across the grain in thick wood.
* Back saw : Reinforced with a steel back. Length of the blade is 250 –
400 mm. No. of teeth per 25 mm is 13. Used for cross cutting when a
fine finish is required.
* Compass saw : Length of the blade is 250 – 400 mm. Used for sawing
small curves in confined spaces and has a narrow tapering blade.
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* Coping saw : Approximately 10 teeth per cm. Used for cutting quick or
sharp curves either internal or external.
* Key hole saw / Pad saw : Used for cutting thick internal curves where
it is impossible to use other saws.
* Bow saw : A saw with two handles. Used to produce curved surfaces
with quick turns.
* Chisels : Chisels are the tools produced from forged steel or tool steel
blades.
* Firmer chisel : Used for light and heavy work.
* Paring chisel : Has a thinner blade. Used for light work. Also
used for shaving or paring plane surfaces.
* Mortise chisel : Used to make mortises. Used for heavy cuts.
Blade thickness varies from 5 mm – 12 mm.
* Gauge chisel : Used to finish curved holes. Types : Inside and
outside gauge chisels.
* Planing tools :
* Wooden jack plane : Length varies from 355 – 380 mm.
Cutting iron width is between 50 – 62 mm. Cutting edge is very
slight curve. Also used in oblique planning. Used for rough
work.
* Iron jack plane : Used for better finish; costlier.
* Trying plane : A wooden jack plane in larger size. Length of
the plane is 550 to 650 mm. Blade width is 90 mm. Used for
planing large surfaces.
* Smoothing plane : Used for smoothing the surface of the wood
after the jack plane and trying plane are used. Length of the
plane is 200 to 250 mm.
* Rasp / Rasp file : It is a finishing tool. Used to make the wood
surface, remove sharp edge, finishing fillets and other interior
surface. Used in wood work only.
* Boring tools : Ratchet brace and wheel brace.
* Bradawl and Gimlet : Used for boring of small holes. The holes
obtained from this tool may be used to hold a nail.
* Striking tools :
* Cross-peen hammer: most used for positioning small nails.
* Claw hammer : used for removing and driving very large nails.
* Mallet: Used to give light blows.
* Holding tools : Bench vice
* C-clamp : Opening capacity varies from 50 to 350 mm. Used for
clamping small work and angled work.
* Pincer is used for pulling out nails.
* The operation of smoothing a wooden surface with the help of a
suitable plane is called planing/facing/edging. Planing should be done
the direction of wood grains.
* Mortising is the operation of producing a rectangular (or) square hole
and tenoning is the operation of making a corresponding projection so
that it fits into the mortise to form an assembly.
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* Grooving is the process of making grooves and tonguing is the process
of producing corresponding projection of wood to fit into grooves.
This operation is applied in wood partitions and drawing boards.
* Moulding : It is the process of producing convex, concave and other
complex types of curved surfaces on a piece of wood. It is done with
the use of moulding plane. Moulding work may be done for preparing
photo frames and for decorative purposes in doors and window frames.
* Rebating : It is the process of making a recess(rebate) taken out of the
edge of a piece of wood. It is done with rebating plane.
* Mortise → Rectangular hole. Tenon → Rectangular peg.
Width of the mortise is about 1/3 of the thickness of the material to be
mortised and length should not exceed six times the width.
* Dove tail joint : strongest of all corner joints. An angle of 1 : 6 ratio is
adopted.
* Bridle joint : Reverse of mortise and tenon joint. Used for square
section.
* Chisel is normally made up of forged steel.
* The other name of butt joint is rubbed joint.
* Setting of saw teeth: The teeth are bent alternately to the right and left
of the blade to enable it to pass through the cut being formed in the
timber with the minimum of friction.
* The cutting bevel angle in a chisel is 250
to 300
. Cutting angle for cross
cut saw is about 450
. Cutting angle for rip saw is about 600
.
* TPI stands for Teeth Per Inch. i.e. the no. of teeth is 5, 6, 7 and 8 per
inch.
* Mortise and tenon joint is generally used for framing work. Bridle joint
is often used where the members are of square section.
* Calipers are used for measuring diameters of curved surfaces.
* Centre punch : It will make a dent in wood or metal for starting a drill.
* Marking gauge : It is used for marking lines at a uniform distance from
the edge of a board or a piece of work.
* Marking knives: They are used mainly for accurately marking shoulder
lines before they are cut with a tenon saw.
* Mortise gauge : The gauge simplifies two parallel lines to be marked.
* Veeners: Veeners are thin sheet of wood that are peeled off and sliced
from a log of wood. Thickness of these sheets varies from 0.4 mm to 6
mm.
Welding :
* Welding is a metal joining process wherein localized coalescence is
produced by heating the metal to a suitable temperature, with or
without the use of filler metal and with or without the application of
pressure.
* Two types of welding are plastic welding(non-fusion) and fusion
welding.
* Plastic welding : Done under pressure without addition of filler
material. Eg. : forge welding and resistance welding.
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* Fusion welding : Done without application of pressure but with the
addition of filler material. Eg. : gas welding, electric arc welding and
thermit welding.
* Acetylene – oxygen → 3200 – 33000
C
* Thermit welding: Done by pouring super heated liquid thermit steel.
* Oxygen in black cylinder; acetylene in maroon cylinder.
* I C2H2 + O2 → 2Co + H2 + heat (small inner white cone flame
close to the tip)
II 2Co + O2 → 2Co2 ; 2H2 + O2 → 2H2O ( larger blue flame
surrounding the small white cone flame)
* Neutral flame → oxygen and acetylene in equal proportions.
Oxidising flame → excess of oxygen
Reducing flame (carburizing flame) → excess of acetylene
* Neutral flame : Temperature is 32600
C. Used for welding mild steel,
copper, aluminium, cast iron etc. oxygen : acetylene → 1.1 : 1
* Oxidising flame : Temperature is 34820
c. used for welding copper-
base metals and zinc-base metals. Will produce a hissing sound.
* Reducing flame (carburizing flame) Temperature is 30380
C. Much
brighter in colour. Used to weld high carbon steel, non-ferrous alloys
and zinc bearing alloys. Flame will burn quietly and have more length.
* Gas cutting or flame cutting : Special oxy-acetylene torch is used to cut
steel and iron. First the job will be pre-heated by producing a pre-
heating flame. Oxygen and acetylene mixed in the mixing chamber to
produce a pre-heating flame. The metal will be heated to its
kindling(combustion) temperature. At this high temperature, the metal
reacts with oxygen and iron oxides are formed. The metal will be
bright red. The iron oxides will be very weak, now, a jet of pure
oxygen will be supplied through the central hole of the torch by
pressing the oxygen lever in the torch. This oxygen will cut through
the pre-heated hot metal and the work piece will be cut.
* Gas cutting (flame cutting) : Only those metals whose
combustion/oxidizing/kindling temperature is below their melting
point can be cut. So iron and steel(upto 1000 mm) can be cut by flame
cutting. When combustion temperature is reached the metal reacts with
oxygen and iron oxides are formed.
* Gas welding techniques:
i) Leftward technique/ Forehand welding method: welding is done
from right to left direction. Suitable for upto 3 mm thick sheets.
ii) Rightward technique/ Backhand welding method : welding is done
from left to right direction. Suitable for large size jobs.
* No flux → low strength welds, poor quality.
* Flux prevents oxidation by preventing oxygen from contacting the
weld zone.
* No flux is used in the gas welding of steel.
* Flux materials → boric acid, soda ash and sodium chloride.
* The various types of gas welding are: i) Oxy-acetylene welding ii)
Oxy-hydrogen welding iii) Air-acetylene welding and iv) Pressure gas
welding.
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* The types of flame in oxy-acetylene welding are : oxidizing flame,
neutral flame and reducing flame.
* Copper piping in the presence of acetylene forms copper acetylide.
This is an unstable compound and disassociate violently at the slightest
shock. So a copper piping is never used for acetylene gas.
* LPG can be used in underwater cutting.
* Oxidising flame is used for welding brass material.
Arc welding:
* Welding may be carried out in air or in an inert atmosphere. Filler
material may or may not be used.
* Temperature of the arc is of the order of 36000
C.
* Job/working table → -ve
Electrode holder → +ve. D.C. supply.
* Electric motor generator (or) transformer sets are used.
* Transformer type welding machine produces A.C. Produces high
current and low voltage to the welding. Least expensive.
* Electric motor generator type welding machine produces D.C.
* A high current arc with a smaller arc length produces a very intense
heat.
*
Sl.No. AC arc welding machine
(Transformer )
DC arc welding machine
(Electric motor generator)
1 Ferrous metals Both ferrous and non ferrous
metals.
2 Only coated electrodes Both coated and bare electrodes
3 Less power 0.4 Consumes more power 0.7
4 Energy 4 Kwh/kg of metal
deposit
Energy 6 to 10 Kwh/kg of metal
deposit.
5 High efficiency 0.85 Low efficiency 0.6
6 Least expensive High expensive
7 50A – 400 A – AC 125 A – 600A - DC
8 Noiseless operation Gives noise
9 Suitable for welding thick
sections only
Suitable for welding thin
sections only
* Bare end for gripping in electrode holder is 20 mm.
*
Sl.No. Consumable electrodes Non-consumable electrodes
1 These electrodes are made up
of copper, steel, brass etc.
* Electrodes made up of carbon and
graphite varieties are used in DC arc
welding.
* Tungsten electrodes used for both AC
and DC welding.
* Chipping hammer is chisel-shaped one and it is used to remove the
slag from the weld bead.
* Hand screen → Fitter lens
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* Chipping goggle are used to protect the eyes while chipping the slag.
They are fitted with a plain glass to see the area to be cleaned.
* Hand gloves are used to protect the hands from electrical shock, arc
radiation and hot spatters.
* Set the welding current as per the diameter of the electrode to be used.
* Select the electrode as per true thickness of the metal to be welded.
* Hold the electrode at an angle of 700
– 800
with the weld line and 900
with the adjoining plate surface.
*
Plate thickness
in mm
Electrode current
Size
mm
Range
(Ampere)
1.6 1.6 40 – 60
2.5 2.5 50 -80
4 3.2 90 -130
6 4 120 -170
8 5 180 -270
25 6 300 - 400
* Arc producing methods : scratching method and tapping method
* Tapping method : In this method, the arc is produced by moving the
electrode slowly and holding it approximately 6 mm from the surface
for a few seconds and then lower it to approximately 4 mm from the
surface.
* Tack welded to maintain correct root gap during welding.
* Length of each electrode varies between 50 – 70 mm.
* Arc welding cannot be used to weld metal of thickness less than 1.6
mm.
* Three basic types of joints common to arc welding and gas welding are
Butt joint, Lap joint and T-fillet joint.
* Flux: During the welding, if the metal is heated in air, the oxygen in
the air reacts with the metal to form oxides which result in poor
quality, low strength welds (or) in some cases may even make welding
impossible. In order to avoid this problems, a flux is added during the
welding. This prevents oxidation.
* Filler material is the material added to the weld pool to assist in filling
the gap(or groove).
* Weaving implies giving a side-to-side motion to the welding arc during
transferring the material to weld joint. A slight weaving (or) oscillating
motion is preferred as this facilitates gas to escape from weld bead.
Weaving also produces a wider bead with better penetration.
* The materials used for coatings on electrodes are: copper, carbon,
graphite etc.
* Coating factor = [Diameter of the electrode/ Diameter of core wire]
* Types of electrodes: Bare electrode, lightly coated electrode, medium
coated electrode and heavily coated electrode.
* Welding defects: lack of fusion, undercut, cracking, oxidized weld,
incomplete penetration etc.
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* Alternating current(AC) : An electrical current that reverses its
direction at regular intervals, such as 60 cycles alternating current(AC)
or 60 hertz.
* Direct current (DC) : Flows in one direction and does not reverse its
direction of flow as does alternating current.
* Direct Current Electrode Positive (DCEP) : The specific direction of
current flow through a welding circuit when the electrode lead is
connected to a positive terminal and the work lead is connected to a
negative terminal of a DC welding machine. Also called direct current
reverse polarity(DCRP).
* Inverter: Power source which increases the frequency of the incoming
primary power. An inverter improves electrical characteristics of a
smaller size welding machine such as faster response time and more
control for pulse welding.
* Power efficiency : How well an electrical machine uses the incoming
electrical power.
* Weld transfer: Method by which metal is transferred from the wire to
the molten puddle. Eg. Short circuit transfer.
Basic machining :
* Machining is a process of converting the given work piece into the
required shape and size with the help of a machine tool.
* Types of head stock : belt driven head stock and geared head stock.
* H shaped part fitted on lathe bed → saddle
Cross slide is in the form of dove tail.
* Lead screw → ACME threads.
* The included angle in lathe centres is 600
.
* Face plate is used for mounting the type of jobs which cannot be held
by chucks. There are no. of holes and slots on the face of the face plate.
* Lathe carriers or dogs is used for transferring the motion from the
rotating driving plate(catch plate) to the work held between the centres.
* The types of dogs are : Bent tail, straight tail and clamp type.
* Steady rest supports cylindrically long jobs when machined between
the centres or by a chuck. Types : Fixed and traveling steady rest.
* Mandrel is a hardened piece of round bar for holding bored or reamed
jobs(i.e.hollow jobs). It has drill holes at both the ends. Work piece is
mounted over the mandrel and the mandrel is rotated between the
centres.
* Follower rest is used for supporting long slender work pieces, against
the cutting tool forces.
* Types of tool: Facing tool, Rough turning tool, Finishing tool and
Radius tool. The two types of radius tool are concave radius tool and
convex radius tool.
* Parting tool : Used for grooving and also to cut the job into two parts.
* Form turning tool : Used for jobs which require both convex and
concave turning.
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* Drawing slanting or square projecting lines on the surface of a job is
known as knurling.
* HSS → 18 : 4 : 1 → Tungsten : Chromium : Vanadium. 5 to 10 %
cobalt is also added to improve the heat resisting properties of the tool.
* Taper is defined as the uniform change in the diameter of a work piece
measured along its length. Taper = (D – d) /L where D = large
diameter, d = small diameter and L = length of taper.
* Knurling is a process of making serrations on the work piece.
Chamfering is a bevelling operation or turning a slope at the end of
work piece to remove burrs. Usually performed on bolts and nuts.
Tapping is a process of making internal threads in small jobs.
* Power feed is given to the carriage through lead screw and for one
rotation of the job, it covers the distance equal to the pitch.
* Right hand thread: View the screwed part of the thread in a direction
normal to its axis. If the threads found sloping downwards from top
from left to right then it is right hand thread.
* Left hand thread : If the threads found sloping downwards from top
from right to left, then it is called left hand thread.
* Calculation of change gears :
[Pitch of thread to be cut/Pitch of lead screw] = [Driver teeth / driven
teeth] = [speed of lead screw/speed of spindle]
* Generally, centre lathes are provided with a set of gears ranging from
20 to 120 teeth in steps of 5 teeth.
* Centre gauge : It is used for setting the thread cutting tool, square to
the spindle axis. It is also used for checking the thread cutting tool
angles, after grinding.
* Cutting speed = πDN m/min. It is the peripheral speed of the work
past the cutting tool. It is the speed at which metal is removed by the
tool from the work piece.
* Feed : It is the distance the tool advances for each revolution of the
work piece. Unit is mm / revolution.
* Depth of cut = [d1 – d2] / 2. d1 = diameter of the job before machining,
d2 = diameter of the job after machining.
* Different types of lathe machines are ; centre lathe, production lathe,
capstan lathe, turret lathe and auto lathe.
* Tail stock: It can be positioned anywhere in the bed. It is used for
supporting lengthy jobs and also carries tool to carry out operations
such as tapping, drilling and reaming.
* Mandrel: It is a hardened piece of round bar for holding bored or
reamed jobs. It has drill holes at both the ends. It is used for holding
hollow jobs.
* The cutting tools used in lathe are facing tool, rough turning tool,
parting tool, form turning tool, thread cutting tool, drill tool and
knurling tool.
* Various operations done in lathe are facing, turning, step turning, taper
turning, knurling, drilling and thread cutting.
* Knurling is a process of making a serration on the work piece. It is a
operation of creating a hand grip or roughened surface on a work
piece.
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* Cutting speed : It is the peripheral speed of the work past the cutting
tool. It is the speed at which metal is removed by the tool from the
work piece. It is expressed in meter/minute.
* Feed: It is defined as the rate of tool travel across a surface cutting it. It
is the distance the tool advances for each revolution of the work piece.
It is expressed in mm/revolution.
* Depth of cut: It is the perpendicular distance measured from the
machined surface to the uncut surface of work. It is expressed in mm.
Depth of cut = [d1 – d2]/2. In lathe if you rotate 10 divisions the tool
will advance by 0.5 mm ,thereby 1 mm in diameter can be reduced.
Machine assembly practice:
Centrifugal pump :
* The pump is a hydraulic machine which converts the mechanical
energy into hydraulic energy in the form of pressure energy. The
centrifugal pump is a hydraulic machine which converts the
mechanical energy into pressure energy by means of centrifugal force.
* The centrifugal pump works on the principle of forced vortex flow
which means that when a certain mass of liquid is rotated by an
external torque, the rise in pressure head of the rotating liquid takes
place. The rise in pressure head at any point of the rotating liquid is
proportional to the square of tangential velocity of the liquid at that
point. (i.e. Rise in pressure head = [V2
/2g] = [ω2
r2
/2g] ). Thus, at outlet
of the impeller where radius(r) is more, the rise in pressure head will
be more. Due to this pressure head, the liquid can be lifted to a high
level.
* The main parts of a centrifugal pump are : 1) Suction pipe 2) Impeller
3) Casing and 4) Delivery pipe.
* Some of the points to remember regarding installation of suction pipe :
1) Length of the suction pipe should be as small as possible.
2) Try to avoid bending in the suction pipe, If it is unavoidable make
the bend with maximum radius ( radius = five times of the diameter of
the suction pipe).
3) Use an eccentric reducer to join the suction pipe with inlet of the
pump.
4) Avoid the check valves in suction side of the pump.
5) Cross sectional area of the foot valve should be double the cross
sectional area of the suction pipe.
6) If the suction pipe is in horizontal position, the suction pipe must be
in 20
inclination with downwards.
* Impeller : The rotating part of a centrifugal pump is known as impeller.
It contains series of curved vanes. The impeller is mounted on a shaft
which is connected to the shaft of an electric motor which runs the
pump.
* Casing : Casing is an air-tight passage surrounding the impeller and is
designed such a way that the kinetic energy of the water discharged at
outlet of the impeller is converted into pressure energy before the
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water leaves the casing and enters into the delivery pipe. Three
common types of casing are :
1) Volute casing 2) Vortex casing and 3) Diffuser casing.
1) Volute casing : It is of spiral type in which area of flow increases
gradually. The increase in area of flow causes decrease in velocity of
the flow. The decrease in velocity, increase pressure of the water
flowing through the casing.
2) Vortex casing : In vortex casing a circular chamber is introduced in
between the casing and the impeller. The vortex casing reduces
formation of eddies and this results reduction in loss of energy. Thus
efficiency of the pump with vortex casing is more than the efficiency
with volute casing.
3) Diffuser casing: Here, the impeller is surrounded by a diffuser. Both
the diffuser and the outer casing are stationary parts. The diffuser has a
series of guide vanes. The guide vanes are designed in such a way that
the water from the impeller enters the guide vanes without stock.
Increasing area of guide vanes reduces the velocity of flow which
consequently increases the pressure. Also it reduces vibration of the
pump.
* Some of the points to consider regarding installation of the delivery
pipe :
1) Use a check valve and gate valve in the delivery side of the pipe.
Gate valve is used to regulate flow of the water. The check valve
allows water from pump to the delivery side. But it will not allow the
flow in the opposite direction.
2) The check valve must be placed in between the pump and the gate
valve.
* Multi stage centrifugal pump : If a centrifugal pump consists of two or
more impellers, the pump is called multi stage centrifugal pump. A
multi stage pump is used for two important purpose i.e. i) To produce
high head and ii) To produce large amount of discharge.
* Multi stage pump for high head : To get the high head, number of
impellers are connected in series i.e. on the same shaft. Water
discharged at the first impeller outlet with increased pressure enters
into the inlet of second impeller with the help of a connecting pipe.
Water from outlet of second impeller has more pressure than water
from the outlet of first impeller.
* Multi stage pump for high discharge: To get the high discharge, the
pumps should be connected in parallel. The parallel pumps are
connected to a common delivery pipe. Here, all the pumps are working
for a same head.
* Priming : Before starting the pump, air from suction pipe, casing and
portion of delivery pipe i.e. up to the valve is replaced by water. The
operation of replacing the air with water in the pump is called priming.
If the priming is not taken place, the pump will not deliver the water.
The head generated by the pump is independent of density of the fluid.
* Applications of centrifugal pump: 1) In houses it is used to fill the
overhead tank. 2). In agricultural sector centrifugal pump is used to
13

deliver the water from the well. 3). Centrifugal pumps are used to feed
the water to boilers in industries.
Air Conditioner :
* An air-conditioner is defined as an assembly of different parts of the
system used to produce a specified condition of air within a required
space or building below that of the atmosphere or surroundings.
* Minimum capacity of air-conditioner is 0.5 ton.
* An air-conditioning system works on vapour compression cycle. This
cycle works in following four phases: 1) Compression 2) Condensation
3) Expansion and 4) Evaporation.
* Boiling point of a refrigerant is very low.
* Generally Freon 12 is used as a refrigerant in the domestic air-
conditioner. It is observed that all the Chloro Fluoro Carbons (CFC)
including Freon affects the ozone layer causing global warming. Since
now-a-days the newly invented refrigerant Hydro-Fluoro-Carbon
(HFC) is used as refrigerant.
* Hermatic compressor is also called as sealed compressor.
* In hermatic compressor, the rotary compressor and motor are
assembled together and suspended inside a metal casing called
“Dome”.
* RSIR(Resistant Start Induction Run) or CSIR (Capacitor Start
Induction Run) type motor is used to operate the compressor.
* Function of the compressor is to provide the necessary pumping action
to the refrigerant thereby maintaining a continuous flow of the
refrigerant through the system.
* Normally the condenser and evaporator are made by copper aluminium
or iron pipe.
* The function of the expansion valve is to supply proper amount of
refrigerant to the evaporator after reducing its pressure considerably.
Due to the expansion the high pressure is reduced very much to allow
the vaporization of liquid at a very low temperature of about -100
C.
* If the selector switch is turned from any cool position to OFF position,
do not turn again to cool position before five minutes. If we do so the
compressor will not be able to start immediately after it is stopped.
_____________________________________________________________________
14

Basic information about workshop

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Basic information about workshop