Calgary, Alberta, Canada dzyanis@engineer.com

Fluid Power Pro

Pilot Operated Check Valves or Counterbalance Valves?

Summary:

  • When use Pilot Operated Check valves?
  • When use Counterbalance valves?
  • Design advises for topic valves.

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First of all, Pilot Operated check valves are NOT a cheap solution of Counterbalance valves.

Yes, both of them have next the same benefits:

  • Prevent a load from dropping in case of hose or tube failure.
  • Prevent a load from drifting caused by directional control valve spool leakage.
  • Leak-free load holding.

But each of them has the specific applications.

Pilot Operated check valves, or pilot-to-open check valves, are non-modulating valves and in operation they work as ON/OFF devices (fully open or fully closed). They are not capable of metering the oil flow through them.

Pilot Operated check valves should only be used in load holding or position holding applications where they work very well because of their typically near-zero leakage. Typical applications include: stopping a cylinder in place when the directional valve is centered, holding a clamp in position, or maintaining a tool position:

cv_vs_cbv_03

cv_vs_cbv_04

When trying to lower a load being acted on by gravity, the Pilot Operated check may cause severe “ratcheting” of the actuator and resultant shock in the hydraulic system. In this case a load must be controlled while in motion and 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.

Typical applications include: mobile applications, winch load lowering control, “over-center” load control and other applications where 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.

cv_vs_cbv_01

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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.

And couple design advises for both Pilot Operated Check Valves and Counterbalances Valves:

  • Locate valves at or near the actuator to provide maximum load holding protection in the event of hydraulic line failure.
  • Do not use these valves with closed-center directional control valves. Pressure trapped between the directional control valve and the actuator can pilot the counterbalance valve open and result in undesired load motion:

cv_vs_cbv_05

Sources:

  1. http://www.comatrol.com/application-notes
  2. http://www.sunhydraulics.com/sites/default/files/media_library/tech_resources/TT_US_Ctrbal_POCk.pdf
  3. http://www.qualityhydraulics.com/blog/load-holding-po-checks-or-counterbalance-valves/
  4. http://apps.boschrexroth.com/products/compact-hydraulics/pib-catalogs/pdf/counterbalance.pdf

 

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