Terminology
On-Off Service
When the valve is used to start / stop the flow by being cycled to the full open or to full closed position
Modulating Service
When the valve is being used to throttle or regulate the flow by varying the opening between open and closed positions
Maximum shut-off Pressure
The pressure of the fluid flowing into the valve against which the valve will have to close
Service Temperature
The maximum and minimum temperature of the media
Supply Pressure
The plant air supply pressure available to operate a pneumatic actuator
Stem Torque
The force required at the valve stem to open or close the valve against system pressure and service conditions
Capactiy
Rate of flow through the valve under stated conditions
Fail - close
The condition wherein the valve port remains closed should the actuating power fail
Fail - open
The condition wherein the valve port remains open should the actuating power fail
Fail - last
The condition wherein the valve port remains in the last position should the actuating power fail
Control valve - end connections
Threaded
- smaller size valves
- isolation valves
- common for all sizes
- most general & severe service
- leak tight applications
- gas lines
Valve Plug Guiding
Top and Bottom Guided
- Valve plug is aligned by guide bushings in the bonnet & bottom flange
- High stability and minimum deflection (high pressure drop applications)
Cage Guided
- Valve plug is guided by a cylindrical cage throughout the travel range
- Increased trim life & lower stem friction (high pressure drop applications)
- Steam, gas and clean liquid applications only
Stem Guided
- Valve plug is aligned with the seat ring by a guide bushing in the bonnet
- commonly used for throttling applications
Top and Port Guided
- Valve plug is aligned by a guide bushing in the bonnet or body and also the port
