Control Valve designing presentation .ppt
- 2. 2 Introduction Types and components of Control Valves Control Valve Theory Accessories – Actuators, Positioners, Regulator Contents
- 3. 3 Control Valve ISA Definition - A power operated device forming the final element in a process control system. It consists of a body assembly containing internal means for changing the flow rate of the process system. The body is linked to an actuator which responds to a signal transmitted from a controlling element.
- 4. 4 Function of a Control Valve The control valve is involved with the disposition of energy in a process.
- 5. 5 Flow Through a Restriction Vena Contracta: Point downstream of the restriction where the process is at the Highest Velocity and Lowest Pressure
- 6. 6 Control Valve Applications Flow Control Pressure Control Level Control Temperature Control Pump Recycle / Compressor Kickback Split Range Control Depressure
- 7. 7 Control Valves Types of Control Valves: - Reciprocating - Rotary Application Types: - General Service valves - Severe Service Valves Accessories - Actuators, Positioners - I/P Transducers, E/P Transducers
- 8. 8 Packing Bonnet Body Stem Guide Bushing Retainer or Cage Plug Seat Ring Components of a Control Valve
- 9. 9 Control Valve Theory Incompressible, Non-Vaporizing Turbulent Flow Bernoulli’s Equation Continuity Equation Constant 2 2 gZ P g V C 2 2 2 1 1 1 V A V A
- 10. 10 Non-Vaporizing Liquid Without Reducer Correction 2 1 P P G q C f v f v G P P C q 2 1
- 11. 11 Control Valve Theory C CV - Valve Flow Coefficient V - Valve Flow Coefficient The number of U.S. gallons of water at The number of U.S. gallons of water at 60° F which will pass through a given 60° F which will pass through a given flow restriction with a pressure drop of 1 flow restriction with a pressure drop of 1 PSI in one minute. PSI in one minute.
- 12. 12 Control Valve Process Data To size a control valve we need – flow – pressure drop – line size – fluid properties
- 13. 13 Control Valve Characteristic Flow Characteristic of a control valve is the relationship between Percent of Rated Cv and Percent of Valve Travel. (This is accomplished by machining the internal trim components of the valve to give the correct Characterization.)
- 14. 14 Inherent Flow Characteristics 0 20 40 60 80 100 120 0 20 40 60 80 100 120 % TRAVEL % CV LINEAR EQUAL PERCENTAGE QUICK OPENING Linear Linear Equal % Equal % Quick Quick Opening Opening
- 15. 15 Components of a Control Valve Cv and Characterization In Post Guided and Rotary Control Valves the Plug, Disc, or Ball Characterizes the Flow.
- 16. 16 Reciprocating Control Valves Top Guided Cage Guided Double Port Three Way Angle
- 17. 17 Reciprocating Type Top Guided Top guided control valves use a contoured plug for controlling the flow of the process fluid. In this type of control valve the plug is guided by bushings around the stem or post.
- 18. 18 Reciprocating Type Top Guided Advantages Simple, Open Flow Path Rugged, Top Guiding Guide Area Removed from Flow Path. Threaded or Quick Change Trim. Class IV, V, VI Shut Off. Wide Selection of Trims – Full Area, Red., Anti-Cav
- 19. 19 Reciprocating Type Cage Guided Cage guided valves use an internal cage to provide alignment of the plug. The ports in the cage also characterize the flow instead of the plug as in a top guided valve. Seal Ring Plug Cage
- 20. 20 Reciprocating Type Three Way Three way valves are used to divert or combine process fluids. They have a double plug design that throttles between two seats. Skirts on the side of the plug serve to guide the plug. Plug Skirts Seat Ring
- 21. 21 Reciprocating Type Angle Angle valves have similar features of Top guided and Cage guided valves. They are distinguished by having a flow path that flows at a right angle.
- 22. 22 Rotary Control Valves Butterfly – Butterfly Valves are used for a variety applications with high flow rates and low delta P’s.
- 23. 23 The spherical plug of the ball valve lends itself not only to precise control of the flow through the valve body but also to tight shutoff. Thus the ball valve may assume the double role of control and block valve. Special materials used for valve seats help achieve these functions. The Ball Valves tight shutoff characteristics correspond to ANSI Class IV and VI. Rotary Control Valves Ball
- 25. Cavitation Cavitation: Downstream of the vena contracta the pressure rises. When vapor pressure is reached, the vapor bubbles implode, releasing microjets that will damage any metallic surface in the area.
- 26. 26 What is Flashing? Flashing occurs when the downstream pressure of a control valve is less than the upstream vapor pressure, part of the liquid changes to a vapor and remains in a vapor state. Flashing is defined by the liquid vapor pressure and downstream pressure and is not something that can be prevented.
- 27. Actuators 1. Spring and Diaphragm 2. Pneumatic Piston 3. Electric Motor 4. Electro-Hydraulic
- 28. 28 Pneumatic single spring diaphragm actuator Air Inlet Diaphragm Actuator Case Diaphragm Plate Stem Spring Spring Seat Yoke Travel Scale
- 29. 29 Pneumatic single spring diaphragm actuator
- 30. 30
- 31. 31 What is Positioner ? • A positioner is a valve mount device that proportionally and accurately positions a control valve over the control signal span. • Positioners must be valve mounted. • Valve Positioner will decrease the valve’s Hysteresis & Deadband, Repeatability and increases sensitivity to the control signal.
- 32. 32 Positioners • Input Signal is generally a pneumatic or electric impulse sent from a controller to the final control element. • Valve Positioners come in two basic types: - Pneumatic (air input, 3-15 psi) - Electro-Pneumatic (current input, 4-20 mA) *** Smart (HART Protocol, Fieldbus) ***
- 33. 33 Regulator
- 34. 34 Regulator Regulation of steam, gas, air, and liquids.
- 35. 35 Any Question ?
Editor's Notes
- #9: Control valve equation is derived from energy equation and the continuity equation also called as conservation of mass: For Liquid in steady state, Energy equation is Bernoulli's Equation is Continuity equation is When the fluid passes through the restriction, some static energy is converted to Kinetic energy. At the point of minimum cross sectional area (vena contracta), the fluid velocity is at a maximum. , No elevation change.
- #28: Spring range Definition components of actuator Adjustable spring
- #29: Spring range Definition components of actuator Adjustable spring
- #31: - A positioner is a high gain plain proportional controller which measures the valve stem position, compares that measurement to its setpoint (the controller output signal), and if there is a difference , corrects the error. - When the valve is under automatic (closed loop) control, the positioner will be helpful when the loop response is not very fast (analysis, temperature, liquid level, blending, slow flow, large volume gas flow), while the positioner will degrade loop response, contribute to proportional offsets, and limit cycling in fast loops (fast flow, liquid pressure, small volume gas pressures). - Actuators without springs always require positioners.
- #34: In this slide a typical pressure control loop is compared with a pressure regulator. Note that in the common feedback control loop, in addition to the control valve, a pressure transmitter and controller are required, as well as an external power source, either air or electrical. With the pressure regulator, the process pressure supplies the power and the regulator serves the purpose of the control valve, transmitter and controller in one device. A much simpler, cheaper alternative, when the process allows.