Generally, industrial valves are not subjected to strength tests when in use, but the valve body and valve cover after repair or the valve body and valve cover with corrosion damage should be subjected to strength tests. For safety valves, the set pressure and return seat pressure and other tests should comply with the provisions of their instructions and relevant regulations. The valve should be subjected to strength and sealing tests after installation. 20% of low-pressure valves are randomly inspected, and if they are unqualified, they should be inspected 100%; medium and high-pressure valves should be inspected 100%. The commonly used media for valve pressure testing are water, oil, air, steam, nitrogen, etc. The pressure testing methods for various industrial valves including pneumatic valves are as follows:

1. Pressure testing method for ball valves

The strength test of pneumatic ball valves should be carried out with the ball half-open.

① Floating ball valve sealing test: put the valve in a half-open state, introduce the test medium at one end, and close the other end; turn the ball several times, open the closed end when the valve is in a closed state, and check the sealing performance of the packing and gasket at the same time. There should be no leakage. Then introduce the test medium from the other end and repeat the above test.

②Fixed ball valve sealing 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; use a pressure gauge to check the sealing performance of the inlet end, and use a pressure gauge with an accuracy of 0.5 to 1 level and a range of 1.5 times the test pressure. Within the specified time, if there is no pressure drop, it is qualified; then introduce the test medium from the other end and repeat the above test. Then, the valve is in a half-open state, both ends are closed, the inner cavity is filled with medium, and the packing and gasket are checked under the test pressure. There must be no leakage.

③Three-way ball valves should be tested for sealing at various positions.

2. Pressure test method of check valve

Test state of check valve: The axis of the valve disc of the lifting check valve is in a position perpendicular to the horizontal; the axis of the channel and the axis of the valve disc of the swing check valve 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 to see that there is no leakage in the valve body and valve cover.

The sealing test introduces the test medium from the outlet end, and checks the sealing surface at the inlet end. The packing and gasket are qualified if there is no leakage.

3. Pressure test method of pressure reducing valve

① The strength test of the pressure reducing valve is generally assembled after a single test, and 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 assembly are welded, the strength test is carried out with air at 1.5 times the maximum pressure after the pressure reducing valve.

② The 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 testing with steam, the test is carried out at the maximum working pressure allowed at the working temperature. The difference between the inlet pressure and the outlet pressure is required to be not less than 0.2MPa. The test method is: 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 maximum and minimum value range, and there must be no stagnation or blocking. For steam pressure reducing valves, when the inlet pressure is adjusted away, the shut-off valve behind the valve is closed, and the outlet pressure is the highest and lowest value. Within 2 minutes, the rise of its outlet pressure should meet the requirements of Table 4.176-22. At the same time, the volume of the pipeline behind the valve meets the requirements of Table 4.18 for qualified; for water and air pressure reducing valves, when the inlet pressure is adjusted and the outlet pressure is zero, the pressure reducing valve is closed for sealing test, and no leakage within 2 minutes is qualified.

4. Pressure test method of butterfly valve

The strength test of pneumatic butterfly valve is the same as that of stop valve. The sealing performance test of butterfly valve should introduce the test medium from the medium flow end, the butterfly plate should be opened, the other end should be closed, and the pressure should be injected to the specified value; after checking that there is no leakage in the packing and other sealing parts, close the butterfly plate, open the other end, and check that there is no leakage in the butterfly plate sealing part for qualified. The butterfly valve used for regulating flow does not need to be tested for sealing performance.

5. Pressure test method of plug valve

① When the plug valve is tested for strength, the medium is introduced from one end, the rest of the passage is closed, and the plug is rotated to the fully open working positions in turn for testing. The valve body is qualified if no leakage is found.

② During the sealing test, the straight-through plug valve should keep the pressure in the cavity equal to that in the passage, rotate the plug to the closed position, check from the other end, and then rotate the plug 180° to repeat the above test; the three-way or four-way plug valve should keep the pressure in the cavity equal to that at one end of the passage, rotate the plug to the closed position in turn, introduce pressure from the right-angle end, and check from the other ends at the same time.

Before testing the plug valve, it is allowed to apply a layer of non-acidic thin lubricating oil on the sealing surface. If no leakage or enlarged water droplets are found within the specified time, it is qualified. 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.

6. Pressure test method of diaphragm valves The strength test of diaphragm valves is to introduce medium from either end, open the valve disc, and close the other end. After the test pressure rises to the specified value, check if there is no leakage in the valve body and valve cover. Then reduce the pressure to the sealing test pressure, close the valve disc, open the other end for inspection, and pass if there is no leakage.

7. Pressure test method of stop valves and throttle valves

For the strength test of stop valves and throttle valves, the assembled valves are usually placed in the pressure test rack, the valve disc is opened, the medium is injected to the specified value, and the valve body and valve cover are checked for sweating and leakage. The strength test can also be carried out on a single piece. The sealing test is only performed on stop valves. During the test, the valve stem of the stop valve is in a vertical state, the valve disc is opened, and the medium is introduced from the bottom end of the valve disc to the specified value, and the packing and gasket are checked; after passing the test, the valve disc is closed and the other end is opened to check for leakage. If both valve strength and sealing tests are to be performed, the strength test can be performed first, and then the pressure can be reduced to the specified value for the sealing test, and the packing and gasket can be checked; then the valve disc can be closed and the outlet end can be opened to check whether the sealing surface is leaking.