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Indirectly solenoid actuated

Indirectly solenoid actuated

These valves operate according to the differential pressure or pilot principle (servo principle) and make use of the pressure energy of the operating fluid to open and close the valve seat. The pilot system functions as a booster, so that even with a solenoid of lesser magnetic force (than that of directly actuated valves) fluids flowing at high rates under high pressures can be controlled.
(Both pistons and diaphragms are used as sealing elements for the main seat).

Description of Function

Valve closed / Solenoid de-energised

The solenoid is de-energised and its core (pilot valve piston) closes the vent (pilot seat). The upstream pressure in P (greater than the downstream pressure in A) builds up through the bleed orifice in the diaphragm (2 bleed orifices in the piston) on the top side of the diaphragm (or piston). This pressure, multiplied by the area of the top of the diaphragm (or piston) produces a closing force which is greater than the opening force exerted on the diaphragm (or piston). It is forced onto its seat.

Valve opens / Solenoid energised

The solenoid is energised. The magnetic force, greater than the closing force exerted on the core (spring and pressure force), raises it from the vent. This relieves the pressure in the space above the diaphragm (or piston) and a balance of pressure with the A-side of the valve is achieved. This pressure relief continues, as less fluid can flow through the bleed orifice than can escape through the vent.
Thus the opening force, resultant from the higher upstream pressure in P on the diaphragm (or piston), is greater. This is raised from the valve seat and the valve remains open as long as the prescribed pressure differential remains between P and A. Depending on the type of valve this is between 0.5 and 1 bar.

Valve closes
The solenoid is de-energised and the core closes the vent by means of the spring and pressure force. Above the diaphragm (or piston) the same pressure as on the P-side builds up again, and the resultant force pushes the diaphragm (or piston) onto the valve seat.

The flow direction of the fluid is fixed.