1. Nominal diameter: (nominal diameter), also known as mean outside diameter, represents the symbol DN, which is the general diameter of various pipes and pipe accessories. Pipes with the same nominal diameter and pipe accessories can be connected with each other and are 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 unify the connection size of pipes and pipe fittings, the nominal diameter (also called nominal diameter and nominal diameter) is used. 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 not the outer diameter or the inner diameter, but a nominal size approximate to the inner diameter of ordinary steel pipes. Each nominal diameter corresponds to an outer diameter, and its inner diameter value varies with the thickness. The nominal diameter can be expressed in metric mm or English in. The pipe accessories are also represented by the nominal diameter, which is the same as the 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 for applications below 200 ℃; For cast iron valve body, it refers to the maximum allowable working pressure for applications below 120 ℃; For the control valve with stainless steel body, it refers to the maximum allowable working pressure for applications below 250 ℃. When the working temperature increases, the pressure resistance of the valve body will decrease. For example, the carbon steel control valve with a nominal pressure of 6.4 MPa (PN64) has a pressure resistance of 5.2 MPa at 300 ℃, 4.1 MPa at 400 ℃ and 2.9 MPa at 450 ℃. Therefore, the determination of the nominal pressure of the control valve should not only be based on the maximum working pressure, but also on the maximum working temperature and material characteristics, not only to meet the requirement that the nominal pressure is greater than the working pressure

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