Isolation Valve

Valves used for isolation are:

• Gate Valve
• Ball Valve
• Butterfly Valve
• Plug Valve
• Diaphragm Valve
• Globe Valve

ESD Valves

ESDVs isolate the process system from risers or pipelines.  They are usually ball or gate valves fitted with a fail closed actuator.  They can be soft seated but if sand or other abrasive materials are present, a hard metal seated valve may be more appropriate.  If soft seated valves are used, some sort of seat protection should be provided during installation/commissioning.

Check Valves

Check valves are not isolation valves and should never be used as such. 

Control Valves

Control valves are used to control the process by controlling flow or pressure.  Control valves have a leakage associated with them and should not be relied on for isolation.  Further, if the seats or the control element is worn due to high velocities, the valve may leak.