Hydraulic Lock

A hydraulic lock is a common solution used to keep a load or actuator — for example, a cylinder or hydraulic motor — stationary.

A hydraulic lock usually consists of two pilot-operated check valves or counterbalance valves with the pilot lines cross-connected.

For single-acting cylinders, a simpler hydraulic lock is used, consisting of only one pilot-operated valve.

Hydraulic Lock with Pilot-Operated Check Valve

A pilot-operated check valve is a check valve that is completely closed in one direction, blocking the flow and thereby holding the load. The valve is opened using pressure applied to its pilot port — in a hydraulic lock, this pilot pressure comes from the line on the opposite side of the actuator.

Drained Center Position on the Directional Valve

To ensure that the load remains stationary, the pilot lines should be drained in the center position of the directional valve.
If the actuator is a hydraulic motor, a hydraulic lock cannot be used, as the motor has internal leakage — instead, an external brake must be installed.

Hydraulic Lock with Counterbalance Valve

Counterbalance valves can also be used in these circuits, as they often utilize the same cavities.
This can be beneficial when you want to protect the actuator from external forces or thermal expansion, or when you require a smoother and more controlled lifting and lowering motion.

Hydraulic Locks and Backpressure Issues

Pilot-operated check valves are sensitive to backpressure.
If backpressure is present, vented valves should be used — either vent-to-air types or valves with separate drain ports.
A common misconception is that if a valve is drained, you can use a directional valve with a closed center position.
However, this is not the case — the drain does not relieve the pilot line.

Pilot Ratio and Opening Pressure

SUN’s pilot-operated check valves almost always have a 3:1 pilot ratio.
The higher the load-induced pressure acting on the valve, the higher the pilot pressure required to open it.
With counterbalance valves, however, the load itself helps open the valve, meaning they require a lower pilot pressure to operate.

Hydraulic Locks in Various Manifold Configurations

Hydraulic Locks in Various Block Configurations

• We offer ready-made block solutions for:
• Line-mounted hydraulic locks
• Sandwich-mounted hydraulic locks
• Motor-mounted hydraulic locks
• “Banjo”-mounted hydraulic locks, i.e., directly mounted on the cylinder
• This function can also be easily integrated into custom-designed special manifolds.

View line-mounted hydraulic locks
View sandwich-mounted blocks with hydraulic locks
View banjo blocks with hydraulic locks
View motor-mounted blocks with hydraulic locks