Nominal Diameter and Nominal Pressure of Vacuum Valve

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Nominal diameter: (nominal diameter), also known as the mean outside diameter, represents the symbol DN, which is the general diameter of various pipes and pipeline accessories. The pipes and pipe accessories of the same nominal diameter can be connected to each other, which is interchangeable. It is not the actual pipe outer diameter or inner diameter, although its value is close to or equal to the pipe inner diameter, in order to make the pipe and pipe fittings uniform in size , Adopt the nominal diameter (also called nominal diameter, nominal diameter). For example, welded steel pipes can be divided into thin-walled steel pipes, ordinary steel pipes and thickened steel pipes according to their thickness. Its nominal diameter is neither the outer diameter nor the inner diameter, but a nominal size similar to the inner diameter of ordinary steel pipes. Each nominal diameter corresponds to an outer diameter, and the value of the inner diameter varies with the thickness. The nominal diameter can be expressed in metric system mm or in imperial system in. Pipeline accessories are also expressed by nominal diameter, which has the same meaning as a seamed pipe.

Nominal pressure: (Nominal pressure), which means the symbol PN, the maximum allowable working pressure when applied at a certain temperature. For control valves with carbon steel body, it refers to the maximum working pressure allowed for applications below 200°C; for cast iron valve bodies, it refers to the maximum working pressure allowed for applications below 120°C; for control valves with stainless steel bodies, it refers to 250°C below Maximum working pressure allowed during application. When the working temperature increases, the pressure resistance of the valve body will decrease. For example, a carbon steel control valve with a nominal pressure of 6.4MPa (PN64) has a withstand pressure of 5.2MPa at 300°C, a withstand pressure of 4.1MPa at 400°C, and a withstand pressure of 2.9MPa at 450°C. . Therefore, the nominal pressure of the control valve must be determined not only based on the maximum working pressure, but also based on the maximum working temperature and material characteristics, not just to satisfy the nominal pressure greater than the working pressure.

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