Shut-off valve is closed parts （valve） moves along the centerline of the valve seat. According to this form of valve, valve seat and port change is proportional valve stroke. As such the valve stem to open or close the relatively short trip, but also has a very reliable cut-off function, and because changes in the valve seat and the valve port valve stroke proportional relationship is very suitable for the regulation of traffic. Therefore, this type of valve is suitable for cutting or adjustment, and throttling. Its selection principles are: 1, high-temperature, high-pressure pipeline medium or device shut-off valve should be selected. Fire power plants, nuclear power plants, petrochemical system temperature, high pressure pipeline. 2, convection resistance pipeline strict requirements of the pipeline. Namely, the pressure loss is not the place to consider. 3, a small needle valve can be used, instrumentation valves, sampling valves, pressure gauge valve. 4, a flow regulator or pressure regulator, but the regulator less precision, and pipe diameter and relatively small, such as ≤ 50mm nominal diameter of the pipeline, should use. 5, synthetic fertilizer industrial production of small and large fertilizer should use nominal PN160 PN320 PN nominal pressure 16MPa or 32MPa high-pressure or high-pressure angle type valve throttle angle. 6, Bayer alumina production desiliconizing workshop, easy coking pipeline, easy to use separate body type, can place the seat, carbide seal pair of DC-type throttle valve or DC. 7, urban construction, water supply, heating engineering, nominal pass through a smaller pipeline, the choice of cut-off, balancing valve or piston valve, such as the nominal diameter less than 150mm pipeline. The most obvious advantages are: the opening and closing process, because the valve sealing surface on the friction between the body than the gate is small, and therefore wear. Seat height is typically only open channel diameter of 1/4, so much smaller than the gate. Usually in the valve body and only one sealing surface, and thus the manufacturing process is better, ease of maintenance.