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Iconic Diagrams\Hydraulics\Valves\Basic Valves

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Domains: Continuous. Size: 1-D. Kind: Iconic Diagrams (Hydraulics).

Description

A pilot operated check valve is a check valve that is normally closed but can be opened for reverse flow by a signal from an external pilot supply.

The figure above shows the standard design using a pilot piston with a stem to unseat the check valve poppet for reverse flow. The pilot piston has an area three to four times that of the poppet seat. This produces enough force to open the poppet against backpressure. Some pilot-operated check valves have area ratios up to 100:1, allowing a very low pilot pressure to open the valve against high backpressure.

The flow through a pilot operated check depends on the differential pressure dp between the inlet port pa and the outlet port pb and is equal to:

flow = Q_nom * sqrt( dp / p_nom) + (Q_leak/p_nom)*dp

The variable valve indicates the valve opening and varies between zero (closed) and 1 (open). The opening depends on a force balance which depends on the pressures of the inlet and outlet port, the spring force and the pressure of the pilot port px:

valve = limit( ( pa.p - pb.p - pclosed + px.p*kp )/(popen - pclosed) , 0 , 1 )

The pilot ratio kp is ratio of the pilot piston area and the check valve area. For a large pilot ratio a relatively small pilot pressure is sufficient to open the valve against a large outlet pressure.

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