- By design
- By function
Design:This classification is based on the motion of the valve stem.
The available designs are:
1) On/Off or Isolation
2) Control or Modulating.
Gate valves:They get their name from Gate like closure member. The varieties available in Gate valves are Wedge Gate valve (Solid & Flexible wedge), Split wedge gate valves, Parallel slide gate valve, Knife edge etc.
Globe valves:In this type the seating is parallel to the line of flow. These valves are normally used for modulating applications. Possible variations in this type are valve with parabolic plug, Double seated globe valve, Angle type globe valve etc.
Diaphragm valves:Normally recommended for Corrosive, Abrasive, Sticky, Viscous & Aseptic services. The two designs of Diaphragm valves that are available are Weir type & Straight through type.
Ball valves:The variation available in the design & construction of ball valves makes it the most popular valve.
- Design: Floating & Trunnion mounted.
- Construction: Full bore & Regular bore.
Few of the critical applications in modern industry where valves are required to perform are
- Valve for Cryogenic application for temperature as low as – 196 deg cel.
- Valve for hot reformer gas for temperature over 1100 deg cel.
- Valve for vacuum system to 0.02 torr.
- Valve for high pressure Synthesis gas at 400 bar.
- Valve for piggable line.
- Cavity free construction food grade valve
- Valve for high-pressure drop with anti-cavitation trim.
- Process fluid
- Permissible pressure drop
- End connections
- Safety regulations
- Frequency of operation.
Automation is commonly used for:
- Inaccessibility (Remote operation)
- Continuous valve operation
- Sequence control
- Ease of operation
- Operation in Hazardous environment
- Reduction in operating costs
- Fail safe requirement, etc.
1) Electro - Pneumatic
3) Electro Hydraulic
4) Self actuated
The key factors involved in selection of actuators are:
- Energy source available
- Hazardous area classification
- Control requirement
- Process response
- Valve characteristics including torque
- Operating cycle
- Valve orientation in pipe line