Pneumatic gate valve is a valve driven by compressed air. When the gate valve is closed, the sealing surface can be sealed only by medium pressure, that is, the sealing surface of the gate valve can be pressed to the valve seat on the other side by medium pressure to ensure the sealing of the sealing surface, which is self sealing. Most gate valves are forced sealed, that is, when the valve is closed, the gate shall be forced to the valve seat by external force to ensure the tightness of the sealing surface.

1. Nominal diameter: (nominal diameter), also known as mean outside diameter, represents the symbol DN, which is the general diameter of various pipes and pipeline accessories. Pipes and pipe accessories with the same nominal diameter can be connected with each other and are interchangeable. It is not the outer diameter or inner diameter of the pipe in the actual sense, although its value is close to or equal to the inner diameter of the pipe. In order to unify the connection dimensions of pipes and fittings, the nominal diameter is adopted (also known as nominal diameter and nominal diameter). For example, welded steel pipe can be divided into thin-walled steel pipe, ordinary steel pipe and thickened steel pipe according to thickness. Its nominal diameter is not outer diameter or inner diameter, but a nominal size similar to the inner diameter of ordinary steel pipe. Each nominal diameter corresponds to an outer diameter, and its inner diameter value varies with thickness. The nominal diameter can be expressed in metric mm or It is expressed in inch. Pipeline accessories are also expressed in nominal diameter, which has the same meaning as slotted pipe.

2. Nominal pressure: (nominal pressure) , indicating the symbol PN, the maximum allowable working pressure when applied at a certain temperature. For the control valve with carbon steel valve body, it refers to the maximum allowable working pressure when applied below 200 ℃; for the cast iron valve body, it refers to the maximum allowable working pressure when applied below 120 ℃; for the control valve with stainless steel valve body, it refers to the maximum allowable working pressure when applied below 250 ℃. When the working temperature increases, The pressure resistance of the valve body will be reduced. For example, the nominal pressure is 6.4Mpa (pn64) The pressure resistance of carbon steel control valve is 5.2mpa at 300 ℃, 4.1mpa at 400 ℃ and 2.9MPa at 450 ℃. Therefore, the nominal pressure of control valve shall be determined not only according to the maximum working pressure, but also according to the maximum working temperature and material characteristics, rather than only meeting that the nominal pressure is greater than the working pressure.