A suspended or overhauling load can drive a hydraulic cylinder faster than the pump supplies oil. A direction valve alone may not control this motion, and a closed valve may be too far from the actuator to protect against a damaged hose. A correctly selected counterbalance valve can hold the load and meter oil leaving the loaded chamber during lowering.
What the valve does
The valve is placed in the load-bearing flow path. Its spring-loaded element resists outflow until the load pressure and a pilot signal from the opposite line open it. If the load begins to run ahead and pilot pressure falls, the valve tends to restrict flow. Parker describes this as control of an overrunning load and notes that it can help avoid cavitation. Some products incorporate a check path for free flow into the cylinder in the opposite direction.
Counterbalance and pilot-operated check valves are different choices
A pilot-operated check valve is principally a locking device; it is not automatically a stable lowering controller. A counterbalance valve is selected for both load holding and modulated motion. Neither is a universal safety solution. Valve location, leakage, thermal expansion of trapped oil, emergency lowering and hose-failure behavior require a circuit-level review.
Information needed for selection
- Maximum load-induced pressure at the cylinder port, including machine geometry.
- Peak outflow from the loaded chamber, which can differ from pump flow.
- Desired lowering speed, expected load variation and backpressure.
- Available pilot pressure, required pilot ratio and valve response.
- Required behavior if power, a hose or the control signal is lost.
A valve that is undersized may create excessive loss or heating. One that is oversized or poorly matched to the pilot circuit can cause unstable motion. Parker’s technical notes also warn that trapped oil can expand as temperature rises; the protection strategy must account for this pressure. Commissioning should include the worst practical load and a controlled test of start, stop and lowering behavior by qualified personnel.
Use our mounting guide to review the load path and руководство по подбору размера порта to calculate the flow reaching the valve. The final circuit should follow the machine’s risk assessment and component ratings.
Ссылки: Parker Load and Motor Control Valves technical notes; Parker E2 counterbalance valve explanation. Обложка: оригинальная концептуальная схема.