Pilot Operated Check Valves in Hydraulic Systems

A pilot operated check valve is a type of check valve that allows free flow in one direction and blocks flow in the opposite direction until a pilot pressure is applied. Pilot operated check valves are commonly used in hydraulic systems to lock a cylinder or other actuator in place, prevent load drifting, and protect the system from pressure surges.

Working Principle

A pilot operated check valve consists of two main components: a check poppet and a pilot piston. The check poppet is a spring-loaded valve that opens when the fluid pressure in the inlet port (P) exceeds the spring force and the back pressure in the outlet port (A). The fluid then flows freely from P to A. The check poppet closes when the pressure in P is lower than the pressure in A, blocking the reverse flow from A to P.

The pilot piston is a smaller valve that controls the opening of the check poppet. The pilot piston is connected to a pilot port (X) that senses the pressure in the opposite side of the actuator. When the pilot pressure in X is high enough to overcome the spring force and the pressure in A, the pilot piston pushes the check poppet off its seat, allowing the fluid to flow from A to P. The pilot pressure in X is usually proportional to the load on the actuator.

Advantages and Disadvantages

Pilot operated check valves have some advantages and disadvantages compared to direct acting check valves. Some of the advantages are:

  • They are rated for higher pressure systems and can handle larger flow rates.
  • They are smaller and lighter than direct acting check valves with the same flow rating.
  • They have lower pressure drop and lower cracking pressure than direct acting check valves.

Some of the disadvantages are:

  • They require an external pilot line and a pilot pressure to open the valve in the reverse direction.
  • They are more complex and expensive than direct acting check valves.
  • They are more prone to leakage and contamination than direct acting check valves.

Applications

Pilot operated check valves are widely used in hydraulic systems for various applications, such as:

  • Locking a cylinder or a motor in a desired position when the directional control valve is in the neutral position.
  • Preventing load drifting or creeping when the actuator is holding a load against gravity or external forces.
  • Protecting the system from pressure surges or shocks caused by sudden changes in flow direction or load.
  • Isolating a part of the system from the rest of the system for maintenance or safety reasons.

A pilot operated check valve is a check valve that allows free flow in one direction and blocks flow in the opposite direction until a pilot pressure is applied. It is composed of a check poppet and a pilot piston. It is used in hydraulic systems to lock, prevent, protect, and isolate actuators. It has some advantages and disadvantages compared to direct acting check valves.

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