Single Pilot Check valve is used to lock a cylinder or part of a circuit and to prevent reverse flow until the pilot pressure is applied. The purpose of the check valve is to permit flow in one direction and block it in the opposite direction. In a free flow direction through the inlet, the ball is unseated and the flow is out of the cylinder port. When the control valve is centered, the load is locked. With presssure applied at the pilot piston, the ball is held open thereby allowing return flow. The mechanism is internally piloted. The directional valve cylinder ports should be connected to the tank in the centre condition.