Control valves

basic understanding of control valves
working principle of control valves
flow characteristics of control valves

1. Control Valves 1 Presented by: Syed Waqas Haider Process Engineer

2. Definition Control Valves control conditions ( flow, pressure, temperature, and liquid level ) open or clos e in response to signals received from controllers Controller compare a " setpoint " to a " process variable " ( value provided by sensors ) 2

3. Types 3 Control Valves Rotary Motion Butterfly valves Ball vales Plug valves Linear Motion Globe Valves

4. Control Valves Parts T hree main parts Valve's actuator Valve's positioner Valve's body 4

5. Actuator The purpose of the valve actuator is to accurately locate the valve plug in a position dictated by the control signal 5

6. Types of Actuators Pneumatic Valve Actuators: Adjust the position of the valve by converting air pressure into rotary motion or linear motion . Piston and Diaphragm Actuators are examples of Pneumatic Actuators Electric Valve Actuators: An electric actuator is powered by motor that converts electrical energy to mechanical torque Hydraulic actuator: Consists of a cylinder or fluid motor that uses hydraulic power to facilitate mechanical operation . The mechanical motion gives an output in terms of linear, rotary or oscillatory motion 6 according to their supply

7. Types of Actuators Multi-turn actuator gives torque for at least one full revolution Part-turn actuator gives torque for less than one full revolution Linear actuator opens and closes valves that can be operated via linear force--sometimes called rising stem valves 7 according to their movement

8. Positioner Positioners are instruments that help improve control by accurately positioning a control valve actuator in response to a control signal Positioners receive an input signal either pneumatically or electronically and provide output power to an actuator 8

9. Positioner Working Some of the mechanisms Force Balance Positioners Motion balance Positioners Electronic Positioners 9

10. Force Balance Positioners 10

11. Motion balance Positioners 11

12. Electro nic Positioners 12 Sensor to detect valve position Micro-Processor E rror = Position - Signal

13. Valve Bodies 13

14. Flow characteristics of Control valves 14 Quick Opening: Quick open plugs are used for on-off applications designed to produce maximum flow quickly Linear: produces equal changes in flow per unit of valve stroke regardless of plug position, used where valve pressure drop is a major portion of the total system pressure drop Equal Percentage: change in flow per unit of valve stroke is directly proportional to the flow occurring just before the change is made, generally used for pressure control