Page 481 - Industrial Ancillaries 2020 Catalogue (Sterling)

Process Valves
12
Process Valves
Solenoid Valves with Differential Pressure
(servo assisted, pilot operated or indirect acting)
Pressure Actuated Valves – Principle of Operation
(pneumatically actuated isolating valves)
AP
Valve closed
These valves operate on the servo assistance principle, which requires a speci ed differential pressure for opening and closing. The solenoid opens the pilot seat. This relieves the pressure on the main closure device, which is raised into the open position by the increasing effective force on its underside.
Closure of the pilot seat builds up a closing force on the main closure device via bleed ori ces. Provided the inlet pressure is at least the required differential higher than the outlet pressure, the valve remains securely closed.
A
Valve closed
AP
Valve open
Valve open
NO NC
P
This type of valve is controlled by a pilot uid supplied to the actuator by means of a pilot valve.
A stem connects the closure device to the control element of the actuator. The spring acting on the control element forces the closure device down into the closed position on the valve seat.
The pilot supply overcomes the spring force to lift the control element into the open position.
These valves are mainly suitable for contaminated or extremely viscous process uids.
NO NC
P
A
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