Rexroth Z2s10 Vertical Stacking Hydraulic Pilot Operated Check Control Valve 

The pilot port of the valve will not connect with external oil sources, but when the low pressure, the valve function like a regular one-way valve. Pilot operated check valve is also called bi-directional hydraulic lock, is connected by a pair of two chambers of the executing actuator, the pilot port connected to the other connected to the cylinder rod chamber's in the main hydraulic system, so that the system can achieve a sudden loss of pressure, the actuator position is locked at the moment and will remain the same position, in order to avoid security risks.