Torque Over Central Valve

One type of valve used in hydraulic systems to regulate hydraulic fluid flow is the Torque over-center valve. It's a free flow check relief valve that operates with assistance from a pilot.

Whether the actuator is a rotary (from a hydraulic motor) or linear (from a cylinder), Torque over-center valves work best when installed within the motor. 
An Target over-center valve main function is to reduce the speed at which motors or cylinders connected to the first port move. 
Actuator motion and stop in a single direction are managed by single over-center valves. The two directions' motion and stop are managed by two over-center valves.
A reverse flow check valve is included in certain hydraulic over-center valve versions. This valve prevents the actuator from overrunning and is utilized as a power saver.