Under normal circumstances, industrial valves are not subjected to a shell test when it use, but the valve body and bonnet or the valve body and bonnet damaged by corrosion should be subjected to a shell test after repair. For safety valves, the set pressure and back seat pressure and other tests shall comply with the specifications and relevant regulations. The strength and tightness test of the valve installation should be done. Low-pressure valves should be spot-checked 20%, if they are unqualified, 100% should be checked; medium and high-pressure valves should be 100% checked. Commonly used media for valve pressure testing include water, oil, air, steam, nitrogen, etc.
1. The shell test of the pneumatic ball valve should be carried out with the ball half open.
① Floating ball valve Seal test: put the valve in a half-open state, introduce the test medium at one end, and close the other end; rotate the ball several times, open the closed end when the valve is in the closed state, and check the sealing performance at the packing and gasket at the same time. There must be no leakage. Then introduce the test medium from the other end and repeat the above test.
②Fixed ball valve seal test: before the test, rotate the ball several times without load, the fixed ball valve is in the closed state, and the test medium is introduced from one end to the specified value; the pressure gauge is used to check the sealing performance of the inlet end, and the accuracy of the pressure gauge is 0 ．Level 5 to 1, the range is 1.5 times the test pressure. Within the specified time, if there is no depressurization phenomenon, it is qualified; then introduce the test medium from the other end, and repeat the above test. Then, put the valve in a half-open state, with both ends closed, and the inner cavity filled with medium. Check the packing and gasket under the test pressure, and there should be no leakage.
③ The three-way ball valve should be tested for seal at various positions.
2. Pressure test of check valve
Check valve test state: Lift check valve disc axis is in a position perpendicular to the horizontal; swing check valve channel axis and disc axis are in a position approximately parallel to the horizontal line.
During the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed. It is qualified if there is no leakage in the valve body and bonnet.
In the sealing test, the test medium is introduced from the outlet end, and the sealing surface is checked at the inlet end. No leakage at the packing and gasket is qualified.
3. Pressure test of pressure reducing valve
① The shell test of the pressure reducing valve is generally assembled after a single piece test, and it can also be tested after assembly. Strength test duration: 1min for DN<50mm; more than 2min for dn65～150mm; more than 3min for dn>150mm. After the bellows and the components are welded, apply 1.5 times the maximum pressure after the pressure reducing valve, and conduct a strength test with air.
②The sealing test shall be carried out according to the actual working medium. When testing with air or water, perform the test at 1.1 times the nominal pressure; when testing with steam, perform the test at the highest allowable working pressure at the working temperature. The difference between the inlet pressure and the outlet pressure must not be less than 0.2MPa. The test method is: after the inlet pressure is adjusted, gradually adjust the adjusting screw of the valve so that the outlet pressure can be changed sensitively and continuously within the range of the maximum and minimum values without stagnation or jamming.