Baofang seal: the nominal diameter of the valve, also known as the average outer diameter, is the size of all the pipeline accessories in the pipeline system represented by numbers. The nominal diameter is a convenient round integer for reference, and has only a loose relationship with the processing size. The nominal diameter is marked with the letter 'DN' followed by a number. For example, the nominal diameter of 200mm should be marked as DN200. The valve's nominal diameter DN will be marked on the valve body. In layman's terms, the nominal diameter of the valve directly determines the diameter of the valve and the diameter of the pipeline. The nominal diameter is just a sign, and the nominal size cannot represent the measured valve diameter value. The actual diameter value of the valve is specified by the relevant standards. Generally, the actual measured value (unit mm) shall not be less than 95% of the nominal size value. Nominal diameter is the general diameter of various pipes and pipeline accessories. Pipes and pipeline accessories of the same nominal diameter can be connected to each other and are interchangeable. It is not the actual outside diameter or inside diameter of the pipe, although its value is closer or equal to the inside diameter of the pipe. For example, there are several types of seamless steel pipes with a nominal diameter of 100mm, such as 102×5 and DN108×5. 108 is the outer diameter of the pipe, and 5 indicates the wall thickness of the pipe. Therefore, the inner diameter of the steel pipe is (108-5-5 )u003d98mm, but it is not exactly equal to the difference between the outer diameter of the steel pipe and twice the wall thickness. Under normal circumstances, the channel diameter of the valve is the same as the nominal diameter, but when the valve body adopts a welded structure or the pipe connected to it is connected with a standard steel pipe flange, the actual channel diameter of the valve is not equal to the nominal diameter. Dimensions of bore diameter DN. For example, when a seamless steel pipe of 54mm×3mm is used, the nominal diameter of the valve is DN50, but the actual inner diameter D is 48mm. Common nominal diameters are DN1, DN2, DN3, DN4, DN5, DN6, DN8, DN10, DN15, DN20, DN25, DN32, DN40, DN50, DN65, DN80, DN100, DN125, DN150, DN175, DN200, DN225, DN250, DN300, DN350, DN400, DN450, DN500, DN600, DN700, DN800, DN900, DN1000, DN1100, DN1200, DN1300, DN1400, DN1500, DN1600, DN18000, DN2000, DN2200, DN2400, 3000, DN3200 DN3400, DN3600, DN3800, DN4000, etc.