These valves are used to control the actuator movements and block in one direction. In order to have the descent of a load under control and avoid the load’s weight being carried away the valve will prevent any cavitation of the actuator. These valves are ideal when normal overcentre valves doesn’t work properly as it’s not sensitive to back pressure. They also allow the system pressure to move multiple actuators in series. Type “A” is different due to the connection positions and the pilot ratio.