In the pipeline, pipe fittings, valves and pumps, we often encounter DN, inches, Φ and other units, but can not distinguish between the model. Today we will summarize the specific analysis of the three units.

1.Valve Diameter -DN(Nominal Diameter)

DN is a common specification unit in China and the European system to identify the specifications of pipes, valves, flanges, fittings, pumps. Many of us mistakenly think it is the inner diameter. Indeed it refers to the nominal diameter of the pipe. Note: This is neither the outside diameter nor the inside diameter, which is the average of the outside diameter and inside diameter, called the average inside diameter.

DN 10 Ball Valve

DN 20 Ball Valve

2.Inch (”)

Inch (“) is a common unit of specification in the American system, widely used in steel pipes, valves, flanges, elbows, pumps, tees, etc. Inch (inch, abbreviated as in.) in the Dutch language originally means thumb, an inch is the length of a section of the thumb. Of course, the length of the human thumb is also the length of different. In the 14 century, King Edward II issued a “standard legal inches”. Its provisions are: from the middle of the barley ears to choose the three largest grain of wheat and in turn into a line of length is an inch.

General 1 “= 2.54cm = 25.4mm

 3. The Outer Diameter of the Pipe ( Φ)

The symbol of the outer diameter of the pipe diameter is “Φ”, which belongs to a Greek letter, pronounced “fai”. And it has a very close relationship with the previous two, because it can replace the above two identification units. And the pipeline or pipe using Φ identification is the most clear one, without the most direct conversion, such as Φ219, Φ508, Φ1020, etc. This identification method is also a more extensive one.

Below is the table to understand the conversion and relationship between DN, Inch and Φ.

DN	Inch	Φ
15	1/2	20
20	3/4	25
25	1	32
32	11/4	40
40	11/2	50
50	2	63
65	21/2	75
80	3	90
100	4	110
125	5	140
150	6	160

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