Two hand safety control of hydraulic cylinders - check valve blocks outlet flow from underside of cylinder and top side is exhausted when valve is released

摘要

A control circuit ensures that the power cylinder of a hydraulic press can only move when two manually operated valves are held open. The cylinder is supplied with fluid from a 4-way valve on two power lines. A pilot controlled check valve is located in the supply line to the underside of the piston and the controlling signal is generated from a control block. The top side of the piston is coupled to a controlled check valve and a pressure level valve, both of which are controlled by signals from the main control block. The control block has two valves each combining a 2-way function, with a three way function. Other than when both valves are actuated the power cylinder is held in a locked condition with low pressure on the top side and a closed column of fluid on the underside. If the cylinder is in motion and one valve is released, the piston motion is immediately arrested.