Under normal circumstances, industrial valves are not tested for strength during use, but the valve body and bonnet or corroded valve body and bonnet should be tested for strength after repair.
For safety valves, the set pressure and return pressure and other tests shall comply with the specifications and relevant regulations. The valve installation shall be tested for strength and tightness.
The low pressure valve is checked by 20%. If it is not qualified, it should be 100% inspection; the medium and high pressure valves should be checked 100%. Commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods for various industrial valves with pneumatic valves are as follows:
1. Ball pressure test method
The strength test of the pneumatic ball valve should be carried out with the ball half open.
1Floating ball valve tightness test: the valve is in a half-open state, one end is introduced into the test medium, and the other end is closed; the ball is rotated several times, the closed end is opened when the valve is closed, and the sealing performance at the packing and the gasket is checked. There must be no leakage. The test medium was then introduced from the other end and the above test was repeated.
2Fixed ball valve tightness test: Before the test, the ball is idling several times, the fixed ball valve is closed, the test medium is introduced from one end to the specified value; the pressure at the inlet is used to check the sealing performance of the lead end, and the accuracy of the pressure gauge is used. .5 to 1 level, the range is 1.5 times the test pressure. In the specified time, no depressurization is acceptable;
The test medium was introduced from the other end and the above test was repeated. Then, the valve is in a half-open state, the ends are closed, the inner cavity is filled with the medium, and the packing and the gasket are inspected under test pressure, and there is no leakage.we are gate valve china,you can know it.
3 Three-way ball valves should be tested for leaks at various locations.
2,check valve pressure test method
Check valve test state: the lift check valve disc axis is in a position perpendicular to the horizontal; the swing check valve passage axis and the flap axis are in a position approximately parallel to the horizontal line.
In the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed, and the valve body and the valve cover are not leaked.
The sealing test was introduced into the test medium from the outlet end. At the inlet end, the sealing surface was inspected, and no leakage at the packing and gasket was qualified.
3. Pressure test method for pressure reducing valve
1 The strength test of the pressure reducing valve is generally assembled after a single piece of test, and can also be tested after assembly. Duration of strength test: lmin of DN<50mm; more than 2min of DN65-150mm; more than 3min of DN>150mm. After the bellows and the assembly are welded, the maximum pressure of the pressure reducing valve is applied 1.5 times and the strength test is performed with air.
2The sealing test is carried out according to the actual working medium. When testing with air or water, the test is carried out at 1.1 times the nominal pressure; when using the steam test, the highest working pressure allowed at the operating temperature is carried out. The difference between the inlet pressure and the outlet pressure is not less than 0.2 MPa.
The test method is as follows: after the inlet pressure is set, the adjusting screw of the valve is gradually adjusted, so that the outlet pressure can be sensitively and continuously changed within the range of maximum and minimum values, and there is no stagnation or jamming phenomenon. For the steam pressure reducing valve, when the inlet pressure is adjusted, the valve is closed after the valve is closed, and the outlet pressure is the highest and lowest values. Within 2 minutes, the outlet pressure should be increased in accordance with Table 4.176-22, and the valve behind the valve The volume is qualified as specified in Table 4.18;
For the water and air pressure reducing valve, when the inlet pressure is set and the outlet pressure is zero, the pressure reducing valve is closed for the leak test, and no leakage is qualified within 2 minutes.
4,butterfly valve pressure test method
The strength test of the pneumatic butterfly valve is the same as that of the shut-off valve. The sealing performance test of the butterfly valve shall be introduced into the test medium from the end of the medium flow, the butterfly plate shall be opened, the other end closed, and the injection pressure shall be the specified value;
After checking the packing and other seals for no leakage, close the disc and open the other end to check that there is no leakage at the disc seal. As a butterfly valve for regulating the flow rate, the sealing performance test may not be performed.
5,the pressure test method of the plug valve
1 When the plug valve is tested for strength, the medium is introduced from one end, the remaining passages are closed, and the plugs are sequentially rotated to the fully open working positions for testing. No leakage is found in the valve body.
2In the sealing test, the straight-type cock should keep the pressure in the cavity equal to the passage pressure, rotate the plug to the closed position, check from the other end, and then rotate the plug 180° to repeat the above test; three-way or four-way plug valve The pressure inside the chamber should be kept equal to the end of the passage. The plug should be rotated to the closed position in turn, the pressure is introduced from the right angle end, and the inspection is performed simultaneously from the other end.
Before the plug valve test, a non-acid thin lubricating oil is allowed to be applied on the sealing surface, and no leaks and enlarged water droplets are found to be qualified within the specified time. The test time of the plug valve can be shorter, generally specified as 1 to 3 minutes according to the nominal diameter.
The plug valve for gas should be tested for air tightness at 1.25 times the working pressure.
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