300X piston type slow closing check valve, using the hydraulic control principle, through the pressure of the medium itself in the pipeline to achieve the up and down movement of the piston, so as to control the opening and closing of the main valve. Its main valve disc closes quickly. It is achieved by adjusting the opening of the outlet ball valve. The 300X piston type slow closing check valve produced by our company is limited to DN500mm or more, and DN500mm diameter below is diaphragm type.