A hydraulic trailer jack needs to control the load as well as lift it. Dual counterbalance valves help hold a double-acting jack in position when the pump is stopped and control movement when the load would otherwise drive the cylinder. They are an important feature to consider when choosing a jack or connecting one to an existing hydraulic system.
Lifting a trailer and controlling its movement
When a jack foot contacts the ground and lifts the trailer, the cylinder supports the load applied at that mounting point. That load can also push the cylinder back if oil is allowed to leave the loaded side.
During a lowering movement, the trailer's weight may try to move the cylinder faster than the pump is supplying oil. This is called an overrunning load. A properly selected and configured counterbalance valve controls oil leaving the loaded side to help keep that movement controlled.
What a counterbalance valve does
A typical pilot-assisted counterbalance valve allows oil to flow into the cylinder through a check-valve path. Flow leaving the cylinder is controlled by a pressure-responsive valve. Pressure from the opposite work line assists that valve in opening during a commanded movement.
With the pump stopped and the circuit correctly configured, the valve resists oil escaping from the loaded chamber. During operation, it controls that outgoing flow rather than simply opening an unrestricted path to the reservoir.
Hold the jack extended and keep it retracted
A double-acting jack has hydraulic connections to both sides of its cylinder. A dual counterbalance arrangement provides load-control functions for both sides. When the jack supports the trailer, it helps resist unintended retraction. When the leg is stowed, it helps resist unintended extension.
Both positions matter. A jack should stay extended while it is supporting the trailer and stay retracted during travel. Preventing the leg from drifting downward protects the intended stowed position and helps maintain ground clearance. A valve protecting only one cylinder side does not automatically provide that protection in the opposite direction.
The Primary Mover 12K hydraulic trailer jack uses dual counterbalance valves. Its load-control arrangement is intended to help hold the leg in both extended and retracted positions.
Controlled movement when the load tries to drive the jack
As the trailer lowers, its weight can push oil out of the cylinder. A counterbalance valve meters the outgoing flow so the load is less able to drive the jack ahead of the commanded hydraulic movement. This helps reduce runaway movement and supports smoother lowering under changing loads.
The result depends on the complete system, including valve settings, pump flow, plumbing and load. Dual counterbalance valves are an important motion-control feature, rather than a guarantee that every installation will behave identically.
A check valve and a counterbalance valve have different jobs
A basic check valve permits flow in one direction and blocks it in the other. A pilot-operated check valve can be opened by pilot pressure, but it is primarily an on/off load-holding device. Pilot-operated checks can be installed on one or both cylinder sides; their number and arrangement determine which directions they hold.
A counterbalance valve also controls an overrunning load by modulating outgoing flow. Load holding and controlled movement are different functions. A product described only as having a “holding valve” does not tell you which design it uses. Ask whether it has counterbalance valves, pilot-operated check valves or another arrangement, whether both sides are protected and how load-driven movement is controlled.
Why this matters with an X-Block setup
The X-Block adapter gives a compatible single-acting power unit directional control for a double-acting jack. Its red valve selects which side receives pressure and which side returns oil to the reservoir. It does not replace the jack's counterbalance valves.
Without suitable load control, an open return path can allow loaded oil to escape and the jack to move unexpectedly. We strongly recommend pairing the X-Block with a compatible jack equipped with dual counterbalance valves.
Read how a single-acting power unit operates a double-acting jack with the X-Block.
Choose the complete installation, not just a capacity number
Counterbalance valves do not increase the jack's lifting capacity or the strength of its mounting structure. Match the jack, pressure limits, hydraulic circuit and mounting arrangement to the application. Do not disconnect loaded hydraulic lines or bypass load-control valves to make a jack move.
Review the Primary Mover 12K jack manual and contact us before changing valve settings or adapting an unfamiliar hydraulic system.
Find the right jack and hydraulic hookup
Browse hydraulic trailer jacks and kits or use our jack-kit selector. For an existing compatible single-acting power unit, purchase the jack separately and add the X-Block Poly or Steel Tank Kit.
For application help, call 985-888-6554 or email sales@primarymover.com with photos of your jack and hydraulic setup.
Technical reference
Sun Hydraulics: Counterbalance and Pilot-to-Open Check Cartridges explains the distinction between load holding and overrunning-load control.