There are two kinds of straight and right angle. Straight-way valve with threaded connections installed in the pipeline. Right Angle check valves with threaded connections, flanged plate connections and three forms. Check valve, also known as closed valves or valve packing, it is the same with the one-way valve to prevent reverse flow of oil. But in the hydraulic circuit can be reverse flow of the oil flow needed by the control oil pressure to open the check valve, the oil flow can flow in both directions. Check valve using a conical valve, so good sealing performance. In closing the oil requirements, the availability of a one-way valve lock into the sky as the oil pressure holding role. Leak way check valve to control the oil has leaked internally drained and type two kinds. The vent type available in the reverse oil flow of oil in the export of non-backpressure; otherwise required outflow type, to reduce the control oil pressure.