A check valve is the simplest type of directional control valve used in hydraulic systems. Check valves stop the flow of fluid in one direction and allow free flow in the opposite direction. They are also known as non-return valves.
Pilot operated check valves are used to block the cylinder in one direction. The flow is free in one direction and blocked in reverse direction until pilot pressure is applied.
These valves are used on double acting cylinder where only one side will be blocked.