19.3: Describe the Function of a Bypass Check Valve in a Sequence Valve Circuit
- Page ID
- 117088
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In the earlier example, we saw how a sequence valve can control the extension of actuators. But what happens when the actuators also need to retract —or when oil must flow in the opposite direction? This becomes a challenge because a typical sequence valve is a normally closed valve. It only allows flow in one direction —after pressure builds —so it blocks flow in reverse.
To solve this, we add a bypass check valve. This simple but effective addition allows reverse flow around the sequence valve without disrupting the sequencing function in the forward direction.
A common application that uses a bypass check valve is a clamp-and-press machine. In this type of circuit, a sequence valve ensures that the clamp cylinder extends first and holds the workpiece before the press cylinder activates. However, once the press operation is complete, both cylinders need to retract. Without a bypass path, the sequence valve would block flow from the retracting press cylinder, causing a bottleneck or pressure buildup.
Here’s how the circuit works:
- When the directional control valve (DCV) is shifted to extend the actuators, the clamp cylinder moves first at low pressure.
- Once the clamp is fully extended and pressure rises, the sequence valve opens and the press cylinder extends.
- At this stage, the bypass check valve is closed, allowing the sequence valve to maintain proper control over the timing.
When the DCV is shifted in the opposite direction to retract both cylinders:
- The oil being forced out of the press cylinder’s cap end flows through the check valve, bypassing the sequence valve entirely.
- This allows unrestricted return flow to the reservoir and ensures that the press cylinder can retract freely, without delay or back-pressure from the sequence valve.
This setup preserves proper sequencing during extension and prevents problems during retraction, making it a reliable and efficient solution for many two-actuator hydraulic circuits.