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Pressure actuated by external fluid

Pressure actuated by external fluid

This type of valve is actuated by pressure acting on a piston or diaphragm. The fluid is usually neutral e.g. air, water, hydraulic oil. The pressure range varies and is specified accordingly in a data table.

"Normally Closed" (N/C) valves of this type remain closed under spring pressure, when de-activated.

"Normally Open" (N/O) valves of this type remain open under spring pressure, when de-activated.

When pressure is connected to port "Z" the valves open or close according to type.
A separate 3/2 pilot valve is used to supply pressure to port "Z", it is mounted either directly on the actuator or remotely.
In some cases a 4/2 or 5/2 pilot valve will be required. The main valve position can be N/C or N/O. The basic position is determined by connecting the pilot valve output lines accordingly. (The direction of flow is usually indicated by an arrow or shown schematically on the body).

Description of operation

Normally closed

In the basic position the depressurised chamber of the actuator is open to atmosphere via the exhaust port of the "pilot valve". When the solenoid of the "pilot valve" is energised the exhaust port closes and fluid passes through the pilot valve building pressure in the chamber.
The pressure builds up under the main piston/diaphragm and via the valve spindle lifts the valve seal off the valve seat and continues until the valve is fully open.

When the pilot valve is de-energised the supply pressure is shut off and the air pressure within the chamber vents to atmosphere. The piston/diaphragm now returns under spring pressure, the valve seal covers the valve seat and the valve closes and remains closed under spring pressure.
In some versions (closing with the flow) the fluid exerts a pressure on top of the valve seal that assists the closing process.