Design points of triple eccentric butterfly valve and application of relevant standards
In general, industrial valves in use without strength tests, but after repairing the valve body and cover or corrosion damage to the valve body and cover should be strength tests.
Valve test pressure commonly used media are water, oil, air, steam, nitrogen, etc., various types of industrial valves including pneumatic valves test pressure methods are as follows.
1. Test pressure method of the globe valve and throttle valve
Globe valve and throttle valve strength test, usually the assembled valve in the pressure test frame, open the valve flap, inject the medium to the specified value, check whether the valve body and valve cover sweat and leakage. Strength test can also be done for a single piece. Sealing test is done only for shut-off valves. Test the stem of the globe valve into a vertical state, the valve flap open, the media from the bottom end of the valve flap introduced to the specified value, check the packing and gasket; to be qualified to close the valve flap, open the other end to check whether there is leakage.
If the valve strength and sealing test are to be done, the strength test can be done first, and then lower the pressure to the specified value of the sealing test, check the packing and gasket; then close the valve flap, open the export end to check whether the sealing surface leakage.
2. Gate valve pressure test method
Gate valve strength test is the same as the globe valve. Gate valve sealing test has two methods.
- ① Gate open, so that the pressure in the valve to the specified value; then close the gate, immediately remove the gate valve, check whether there is leakage on both sides of the gate seal or directly to the plug on the valve cover to inject test media to the specified value, check the seal on both sides of the gate. The above method is called the intermediate test pressure. This method is not suitable for sealing test in the gate valve below the nominal diameter DN32mm.
- ② Another method is to open the gate, so that the valve test pressure up to the specified value; then close the gate, open one end of the blind, check whether the sealing surface leakage. Then reverse the head, repeat the above test until qualified. Pneumatic gate valve packing and gasket at the sealing test should be carried out before the gate sealing test.
3. Ball valve pressure test method
The strength test of pneumatic ball valve should be carried out in the half-open state of the ball valve sphere.
- ① Floating ball valve sealability test: the valve in a half-open state, one end of the introduction of the test medium, the other end closed; the ball will be rotated several times, the valve is closed when the closed end of the open check, while checking the packing and gasket sealing performance, there shall be no leakage. Then introduce the test medium from the other end, repeat the above test.
- ② Fixed ball valve sealing test: Before the test, the ball will be idle rotate several times, fixed ball valve is in a closed state, from one end of the introduction of the test medium to the specified value; use a pressure gauge to check the sealing performance of the introduced end, the use of pressure gauge precision 0.5-1 level, the range of the test pressure 1.6 times. In the specified time, no pressure drop phenomenon is qualified; then introduce the test medium from the other end, repeat the above test. Then, the valve will be half open state, both ends closed, the cavity is full of media, check the packing and gasket at the test pressure, there shall be no leakage.
- ③ Three-way ball valve should be tested in each position for tightness.
4. Plug valve pressure test method
- ① Strength test of the plug valve, the medium from one end of the introduction, close the rest of the pathway, the plug will be rotated in turn to the full open working position for the test, the valve body is not found to be leaking for qualified.
- ② Sealing test, the straight-through plug should be kept in the cavity and the pressure of the pathway equal, the plug will be rotated to the closed position, from the other end to check, and then the plug will be rotated 180 ° to repeat the above test; three-way or four-way plug valve should be kept in the cavity and the pressure of one end of the pathway equal, the plug will be rotated to the closed position in turn, the pressure is introduced from the right-angle end, from the other end to check at the same time.
Plug valve test bench before allowing a layer of non-acidic thin lubricant on the sealing surface, no leakage and expanding water droplets found in the specified time for qualified. Plug valve test time can be shorter, generally according to the nominal diameter of the provisions of 1-3min.
Plug valve for gas should be 1.25 times the working pressure for air tightness test.
5. Butterfly valve pressure test method
The strength test of the pneumatic butterfly valve is the same as that of the globe valve. Butterfly valve sealing performance test should be introduced from the media inflow end of the test media, the butterfly plate should be opened, the other end closed, inject pressure to the specified value; check the packing and other sealing place no leakage, close the butterfly plate, open the other end, check the butterfly plate sealing place no leakage for qualified. The butterfly valve used for flow regulation may not do the sealing performance test.
6. Diaphragm valve pressure test method
Diaphragm valve strength test from either end of the introduction of the medium, open the valve flap, the other end closed, test pressure up to the specified value, see the valve body and valve cover no leakage for qualified. Then lower the pressure to the sealing test pressure, close the valve flap, open the other end for inspection, no leakage for qualified.
7. Check valve test pressure method
Check valve test state: lift check valve valve valve axis in the horizontal vertical position; swing check valve channel axis and valve axis in the position of the horizontal line is approximately parallel.
Strength test, the introduction of test media from the inlet end to the specified value, the other end closed, see the valve body and valve cover no leakage for qualified.
Sealing test from the export side of the introduction of the test medium, at the inlet end to check the sealing surface, packing and gasket at no leakage for qualified.
8. Pressure test method of safety valve
- ① The strength test of the safety valve is the same as other valves, it is tested with water. When testing the lower part of the valve body, the pressure is introduced from the inlet side, the sealing surface is closed; when testing the upper part of the valve body and valve cover, the pressure is introduced from the outlet side, the other end is closed. In the specified time valve body and valve cover no leakage phenomenon for qualified.
- ② Sealing test and pressure test, the general use of media are: steam safety valve with saturated steam as the test medium; ammonia or other gases with the valve with air as the test medium; water and other non-corrosive liquids with the valve with water as the test medium. For some important positions of the safety valve commonly used nitrogen as the test medium.
Seal test to the nominal pressure value for the test pressure, the number of times not less than two, no leakage in the specified time for qualified.
There are two methods of leak detection: one is to seal the connections of the safety valve, using butter to seal the thin paper on the export flange, thin paper bulging for leakage, not bulging for qualified; second, using butter to seal the thin plastic plate or other plates in the lower part of the export flange, water seal valve flap, test water does not bubble for qualified. Safety valve pressure setting and back to the seat pressure test not less than 3 times, in accordance with the provisions of the qualified.
9. Pressure reducing valve test method
① Strength test of pressure reducing valve is generally assembled after the test of single piece, or assembled after the test. Strength test duration: DN<50mm is more than 1min; DN65-150mm is more than 2min; DN>150mm is more than 3min.
After the bellows is welded with the assembly, 1.5 times of the highest pressure after applying the pressure reducing valve and strength test with air.
② Sealability test is conducted according to the actual working medium. When testing with air or water, 1.1 times the nominal pressure for the test; when testing with steam, the highest working pressure allowed under the working temperature. The difference between the inlet pressure and the outlet pressure requirement is not less than 0.2MPa.
Test method: After the inlet pressure is set, gradually adjust the adjusting screw of the valve so that the outlet pressure can change sensitively and continuously within the range of maximum and minimum values, without stagnation and jamming. For water and air pressure reducing valve, when the inlet pressure is adjusted, the outlet pressure is zero, close the pressure reducing valve for sealing test, no leakage within 2min is qualified.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.sfutube.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Stainless Steel Valves, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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