Pilot Operated Sequence Valve

Pilot Operated Sequence Valve

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Pilot Operated Sequence Valve

Pilot-operated sequence valves divert flow in a predetermined order, widely used in hydraulic systems, and are pressure control valves. A pilot-operated sequence valve is similar to a pressure relief valve and is used to control a set of operations in a pressure-related sequence.


Advantages of pilot operated sequence valve

• Direct fluid flow in sequence

• In some cases, it has a check valve for backflow

• Provides an ordered sequence of operations, such as in clamp and boost circuits

• Can be used as a safety valve with high or varying back pressure in the return line.

• Can be used as a compensator in a pressure compensated flow regulator circuit


Working principle of pilot-operated sequence valve

When the main system pressure exceeds the spring setting, the spool moves. Therefore, the outlet of the sequence valve will remain closed until the upstream pressure reaches a predetermined value, then the valve will open to allow air to transfer from the inlet to the outlet.

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The main functions of the pilot sequence valve are:

(1) Control the sequential actions of multiple components;

(2) Used in the pressure-holding circuit;

(3) It is used as a balance valve to prevent the cylinder piston from falling freely due to its own weight;

(4) Use the external control sequence valve as the unloading valve to unload the pump;

(5) Use the internal control sequence valve as the back pressure valve.


How do pilot operated valves work?

Pilot operated check valves work by allowing free flow from the inlet port through the outlet port. Supplying pilot pressure to the pilot port allows reverse flow. Air pressure at the top of the poppet assembly opens the seal, allowing air to flow freely.

What are the two types of sequence valves?

There are two different ways of classifying sequence valves. The first type is divided into direct acting type and pilot type according to its mechanism and structure. The second type of pressure control mode: internal control or external control.

How do sequence valves control pressure?

By using sequence valves, two or more actuators in a hydraulic circuit can be automatically sequenced. When the fluid flow is directed to the actuator portion of the circuit, the main actuator will move. The sequence valve will block flow to the auxiliary actuator until a predetermined pressure is reached, after which it will allow fluid flow to the actuator. The sequence valve is equipped with a check valve, which will allow fluid to flow freely around the valve when the direction of the actuator is reversed. A sequence valve is used when one pump powers both circuits and one circuit takes precedence over the other. Sequence valves are used in hydraulic circuits.

Selection rules

According to the different assembly structure, the sequence valve can realize different circuit functions, such as the functions of relief valve, sequence valve and balance valve.

If the opening and closing characteristics of the sequence valve are too poor, the primary pressure will be too high when the flow rate is large, and the loop efficiency will be reduced. The opening and closing characteristics have hysteresis, the opening pressure is lower than the closing pressure, and attention should be paid when the load flow changes. Open the valve with too low pressure, and when the re-pressure is lower than the set pressure, front leakage occurs, causing the actuator to malfunction. Vibration or other instability occurs when the flow through the valve is much less than the rated flow. At this time, measures should be taken on the circuit again.

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