According to the outer diameter, it can be divided into 4 points and 6 points: 20mm is a 4-branch pipe and 25mm is a 6-branch pipe. In charge of several pipelines, the pipe diameter should be in millimeters.

Based on the four-point tap water supply plane diameter of11.5mm, the British pipeline standard has formulated the standard pipeline sizes of12.7mm,19.05mm, 25.4mm, 31.75mm and 50.8mm.

We can find the basis from the comparison of water supply planes: the standard wall thickness of a quarter copper pipe or lead pipe with a diameter of 12.7mm is 0.6mm, and the water supply plane after removing its wall thickness is 1 1.5mm, which is exactly the size of the water supply plane of a quarter faucet. Therefore, a pipe with a diameter of 12.7mm is used.

By analogy, a 25.4 mm pipe with four quarter taps can supply water at the same time, and the water supply pressure will not be weakened on the basis of scientific theory. But at the same time, the standard does not have any compatibility. If the pipeline system suddenly needs to add more faucets to use at the same time, the pipeline system under this standard system can only complete the task at the expense of partial pressure.

Extended data:

The expression of pipe diameter shall meet the following requirements:

1)? The pipe diameter of water gas transportation steel pipe (galvanized or non-galvanized), cast iron pipe and other pipes should be represented by nominal diameter DN;

2)? Seamless steel pipe, welded steel pipe (straight seam or spiral seam), copper pipe, stainless steel pipe and other pipes, the pipe diameter should be expressed by external diameter × wall thickness;

3)? For reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, cylindrical tile pipes and other pipes, the pipe diameter should be expressed as the inner diameter d;

4) The pipe diameter of plastic pipe should be expressed by product standard method;

References:

Baidu encyclopedia-sidangjia