Hydraulic Load Holding: When to use P.O. Checks vs. Counterbalance Valves

Counterbalance valve or pilot-operated (P.O.) check valve – which is best? They both do the same job – don’t they? Sometimes referred to as a “poor man’s counterbalance valve”, the P.O. check valve is often applied where a counterbalance valve should have been used because of the check’s lower price. Here are some guidelines for when it is most appropriate to use a P.O. check valve and when a counterbalance valve is a much better choice.

Pilot-operated check valves, or pilot-to-open check valves, are non-modulating valves and in operation should be considered either fully open or fully closed. They are not capable of metering the oil flow through them. Therefore, they should only be used in load holding or position holding applications where they work very well because of their typically near-zero leakage. When trying to lower a load being acted on by gravity, the P.O. check valve may cause severe “ratcheting” of the actuator and resultant shock in the hydraulic system. Typical pilot-operated check valve applications include: stopping a cylinder in place when the directional valve is centered, holding a clamp in position, or maintaining a tool position.

If a load must be controlled while in motion, a counterbalance valve should be used. For this reason, counterbalances are often referred to as “motion control valves”. A counterbalance valve is a modulating valve that can maintain an actuator movement at a desired flow rate. The load will not “run away” due to the effects of external forces, such as gravity. A counterbalance valve will only open enough to allow the load to move at the desired flow rate, thus preventing the load from over-speeding the pump. This is especially useful in mobile applications. In a mobile cylinder, often the load goes “over-center” and becomes a negative load trying to make the actuator over-speed the pump. The load tries to move more quickly than the desired flow would provide. In this type of situation, a pilot-operated check valve is an especially poor choice as it would cause the load to ratchet down as cylinder pressure is repeatedly built and released at the pilot “opening” pressure.

So, in summary, for simple load-holding applications, the pilot-operated check valve is suitable and more economical. For load-holding and motion control, a counterbalance valve is the answer and worth the extra cost.