What is the specification of 2, 4 and 6 points in the pipe valve fittings? Oxygen valve, pipe valve, valve combustion reasons analysis
How do you differentiate valve sizes? Is it “minutes,” “inches,” or “DN…” ? Do you know what it means?
First of all, let’s popularize the origin of “inch” :
inch (inch, abbreviated as in.), in Dutch, the original meaning is thumb, an inch is the length of a thumb, of course, the length of the thumb is also different.
The sun never set. The British Empire was great. The country was powerful and had a voice. In the 14th century, King Edward II promulgated the “standard legal inch”. According to the rule, the length of three large wheat grains in a row is one inch (about 25.4 mm).
We get to the point, usually go to a hardware store to purchase the valve or the pipe, joint, etc., do not understand friend’s take samples to buy directly, judges the general description of specifications, for a few minutes or a few inches, actually see water valve and pipe joint body or marked on the packaging specifications, such as 1/2 ‘, 3/4 ‘, 1 ‘, DN15 and so on.
As shown below: Hot and cold water right-angle valve for toilet washbasin, size DN15.
Dear friends, if you want to understand and learn the specification and size of these valves, it is important to keep in mind the following common conversion relations:
Basic formula conversion: 1 inch ≈25.4 mm =8 points (points for short)
So: 1 inch = 1/8 ‘(in) ≈3.175mm
2 inch = 1/4 ‘(inch)
4 inch = 1/2 ‘(inch)
6 inch = 3/4 ‘(in)
(For memorization purposes, a few fractions of an inch is usually multiplied by 8 to get a score.)
The following figure shows the relationship between “minutes” and “inches” :
In life, the most used valve is 1/2 ‘(4 valve), sometimes labeled as DN15, in fact, the specifications are the same, but the form of labeling is different.
So we usually call 4 points and 6 points and 1 inch water valve or water pipe, 4 points, 6 points, 1 inch refers to the water valve or water pipe diameter of the British system, the full name is British.
As shown below: 1/2 inch is a 4 point valve (DN15) nominal diameter of 15, thread diameter of about 19mm.
Unit: mm
The matching silk is shown as below:
Sometimes even if the valve body is not marked with specifications, we can use a ruler to roughly measure the specification of the valve, usually 4 valve for the internal thread usually diameter of about 18 ~ 20mm, if the external thread can be measured thread diameter, the same.
The following picture shows the faucets for washing machines commonly used in families:
The following figure is 3/4 ‘, also known as 6 valve (DN20), nominal diameter of 20, usually about 24mm inside diameter.
Unit: mm
The following figure shows the method of measuring method to roughly estimate the 4 and 6 point valve:
From the above, many small partners will be confused, valve specification DN means what, in fact, DN valve specification DN20 is nominal diameter symbol, nominal diameter (also known as mean outs>
So DN is neither the outside diameter nor the inside diameter, but it’s closer to the inside diameter. Low pressure class, small wall thickness, DN less than the inner diameter; For high pressure class, the wall thickness is large, and the DN is greater than the inner diameter. DN** Nominal diameter, which is in millimeters, but nominal diameter is the nominal size, not the actual size of .
For example, the designer of the pipe or valve calculates that the pipe with an inner diameter of 102mm and a wall thickness of 3mm is required, and the outer diameter of the pipe is 108mm. According to the design standard of the steel pipe, there is just such a pipe. In this case, the pipe with an inner diameter of 102mm should be classified as the nominal diameter of the nearest, that is, the valve design is DN100. Obviously the nominal size is going to be smaller than the inner diameter. In another case, the pipe with an outer diameter of 108mm is still used. Due to the high pressure, the wall thickness is required to be 6mm, so the inner diameter of the pipe is 96. At this time, the valve used is still DN100, and the nominal size is greater than the inner diameter of the closed pipe.
The following figure is 1 ‘(in)DN25 valve, usually not called 8 valve, nominal diameter is 25, thread diameter is about 30mm, and so on:
Figure below shows a 1.2 ‘(in.)DN32 valve with nominal diameter of 32 and threaded inner diameter of approximately 39mm.
The following figure shows the 1.5 ‘(in.)DN40 valve, nominal diameter is 40, paper diameter is about 46mm
Below is a 2 ‘(in.)DN50 valve with nominal diameter of 50 and internal thread diameter of approximately 56mm
The following figure shows the corresponding relationship between pipe inch and nominal size:
Through the above illustrated detailed analysis, in-depth study, small partners should understand the common life water valve specifications, “points” and “inches” of the meaning of it.
Oxygen valve, pipe valve, valve combustion reasons analysis
Oxygen valve, pipe valve, valve combustion reasons analysis
With the increase of oxygen consumption, large users of oxygen are using oxygen pipeline delivery. Due to the long pipeline, wide distribution, coupled with the rapid opening or closing valve, resulting in oxygen pipeline and valve combustion accidents occur from time to time, so, *** analysis of oxygen pipeline and cold door existing hidden dangers, dangers, and take corresponding measures is crucial.
First, several common oxygen pipeline, valve combustion cause analysis
1. The rust, dust and welding slag in the pipeline friction with the inner wall of the pipeline or valve port, resulting in high temperature combustion.
This situation is related to the type of impurities, particle size and airflow speed. Iron powder is easy to burn with oxygen, and the finer the particle size, the lower the ignition point; The faster the gas velocity, the more likely it is to burn.
2. There are grease, rubber and other substances with low ignition point in the pipeline or valve, which will ignite at local high temperature.
The ignition point of several combustibles in oxygen (at atmospheric pressure);
Name of fuel Ignition point (℃)
Lubricating oil 273 ~ 305
Vulcanized fiber mat 304
Rubber 130 ~ 170
Fluorine rubber 474
Cross-linked with 392 b
Teflon 507
3. The high temperature generated by adiabatic compression causes combustibles to burn
For example, before the valve is 15MPa, the temperature is 20℃, and the pressure behind the valve is 0.1MPa. If the valve is opened quickly, the oxygen temperature after the valve can reach 553℃ according to the adiabatic compression formula, which has reached or exceeded the ignition point of some substances.
4. The ignition point reduction of combustible material in high pressure pure oxygen is the inducement of oxygen pipeline valve combustion
Oxygen pipeline and valve in high pressure pure oxygen, the risk is very great, the test has proved that the fire of the can be inversely proportional to the square of pressure, which poses a great threat to the oxygen pipeline and valve.
Second, preventive measures
1. The design shall comply with relevant regulations and standards
The design should comply with the 1981 Ministry of Metallurgy issued by the Iron and Steel Enterprise oxygen pipe network of several regulations, as well as the oxygen and related gas safety technical regulations (GB16912-1997), “Oxygen station design code” (GB50030-91) and other regulations and standards.
(1) The large flow rate of oxygen in carbon steel pipe should conform to the following table.
Large flow rate of oxygen in carbon steel pipe:
Working pressure (MPa) 0.1 0.1 ~ 0.6 0.6 ~ 1.6 1.6 ~ 3.0
Flow rate (m/s) 20, 13, 10, 8
(2) In order to prevent fire, a section of copper base alloy or stainless steel pipe with a length not less than 5 times the pipe diameter and not less than 1.5m should be connected behind the oxygen valve.
(3) Elbow and bifurcation head should be set as few as possible in oxygen pipeline. Elbow of oxygen pipeline with working pressure higher than 0.1MPa should be made of stamped valve type flange. The airflow direction of the bifurcation head shall be 45 to 60 angles from the direction of the main airflow.
(4) In the butt welding of concave-convex flange, copper welding wire is used as O-ring, which is a reliable sealing form of oxygen flange with flammability.
(5) The oxygen pipeline should have a good conductive device, the grounding resistance should be less than 10, the resistance between flanges should be less than 0.03.
(6) The end of the main oxygen pipeline in the workshop should be added with a release pipe to facilitate the purging and replacement of the oxygen pipeline. Before the long oxygen pipeline enters the regulating valve in the workshop, a filter should be set.
2. Installation Precautions
(1) all parts in contact with oxygen should be strictly degreased, degreased with dry air or nitrogen without oil.
(2) Welding shall be argon arc welding or arc welding.
3. Precautions for Operation
(1) When switching on and off the oxygen valve, it should be carried out slowly. The operator should stand on the side of the valve and open it once in place.
(2) It is strictly prohibited to use oxygen to brush the pipeline or use oxygen to test leakage and pressure.
(3) The implementation of the operation ticket system, in advance of the operation of the purpose, method, conditions to make a more detailed description and provisions.
(4) Manual oxygen valves with a diameter greater than 70mm are allowed to operate only when the pressure difference between the front and back of the valve is reduced to less than 0.3MPa.
4. Precautions for maintenance
(1) Oxygen pipeline should be regularly checked and maintained, rust removed and painted, every 3 to 5 years.
(2) The safety valve and pressure gauge on the pipeline should be checked regularly, once a year.
(3) Improve the grounding device.
(4) Before hot work, replacement and purging should be carried out. When the oxygen content in the blown gas is 18% ~ 23%, it is qualified.
(5) Valve, flange, gasket and pipe, pipe fitting selection should comply with the “Oxygen and related gas safety technical regulations” (GB16912-1997) relevant provisions.
(6) Establish technical files, train operation, overhaul and maintenance personnel.
5. Other security measures
(1) Improve the importance of construction, maintenance and operation personnel to safety.
(2) improve the vigilance of management personnel.
(3) Raising the level of science and technology.
(4) Continuously improve the oxygen delivery plan.
Conclusion:
The reason why the gate valve is banned is actually because the sealing surface of the gate valve in the relative movement (that is, the valve switch) will cause abrasion damage due to friction, once damaged, there is iron powder from the sealing surface off, such fine particles of iron powder is easy to burn, this is the real danger.
In fact, the oxygen pipeline is forbidden to gate valve, other stop valves have accidents, the sealing surface of the stop valve will be damaged, as likely to be dangerous, the experience of many enterprises is that the oxygen pipeline all use copper alloy valve, not carbon steel, stainless steel valve.
Copper alloy valve has the advantages of high mechanical strength, wear resistance, good safety (does not produce static electricity), so the real reason is because the sealing surface of the gate valve is easy to wear and produce iron is the main culprit, as for the decline in sealing is not the key.
In fact many gate of oxygen pipeline is not used as an accident, usually appear on both sides of the valve pressure difference is bigger, the valve opens faster, many accidents also shows that the ignition source and fuel is the cause of the end, disable gate valve is only a means to control fuel, and regular the purpose of rust, degreasing, banned oil are all the same. As for the control of flow rate, do a good job of electrostatic grounding is to eliminate the source of fire. Personally think that the valve material is factors, on the hydrogen pipe also appear similar problems, the new specifications have words will disable gate removed, is a testament, the key to find the reason, many companies are simply regardless of operating pressure, are forced by the copper alloy valve, but as some accidents occur, so controlling the fire and fuel, careful maintenance, The key is to tighten the safety string. – Provided by Sanjing Valve Technology Department
Post time: Oct-28-2022
