CONTROL VALVE & SIZING: Selection & maintenance
OBJECTIVE
- Understand what happens inside a control valve from basic fluid mechanics point of view
- Appreciate the difference between cavitation and flashing, and know what choked flow is
- Do simple calculations to determine CV values
- Recognise severe service applications and have an appreciation for the methods of tackling the problems associated with such applications
- Know about all the different types of control valves commonly in use and understand the relative advantages of each
- Choose between different characteristics on offer and specify seat leakage rates
- Size actuators for linear and rotary applications and know the relative advantages of pneumatic, hydraulic and electric types
- Have a basic understanding on how to select materials for bodies, trims, packing boxes, and gaskets
- Make use of a computer sizing program to assist with the selection of control valves
- Understand the failure modes for control valves and demonstrate new approaches to troubleshooting
OUTLINE
- INTRODUCTION TO CONTROL VALVE THEORY
- Introduction
- Definition of a control valve
- Energy types
- What is happening inside a control valve
- Cavitation
- Flashing
- Choked Flow
- Valve Coefficient Cv
- DIFFERENT TYPES OF CONTROL VALVES
- Globe Valves
- Butterfly
- Eccentric disk
- Ball
- Rotary Plug
- Diaphragm and Pinch
- CHARACTERISTICS
- Equal percent
- Linear
- Quick opening
- Selection method
- HIGH PRESSURE DROP APPLICATIONS
- Cavitation Control
- Cavitation Elimination
- Low Noise
- Diffuser Plates
- Chokes
- Disk Stack Technology
- Pressure Balanced Trim
- USE OF COMPUTER PROGRAM FOR VALVE SIZING
- EXAMPLES OF HIGH PRESSURE DROP APPLICATIONS
- Water – pump bypass
- Steam – turbine bypass
- Gas – pressure reducing
- Oil – choke valve
- ACTUATORS
- Pneumatic
- Hydraulic
- Electric
- Sizing on rotary valves
- Sizing on linear valves
- Mounting considerations
- Manual overrides
- Accessories
- POSITIONERS
- Basic principles
- Conventional pneumatic
- Conventional electro-pneumatic
- Smart Positioners
- Feedback options