Under normal circumstances, industrial valves are not subjected to a strength test during use, but the valve body and bonnet or the valve body and bonnet damaged by corrosion should be subjected to a strength test after repair. For safety valves, the constant pressure and return pressure and other tests shall comply with the specifications and relevant regulations. The valve strength test and valve sealing test should be done on the valve hydraulic test bench before the valve is installed. 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. The pressure testing methods for various industrial valves including pneumatic valves are as follows:
1. Pressure test method of stop valve
For the strength test of the shut-off valve, the assembled valve is usually placed in a pressure test frame, the valve disc is opened, the medium is injected to the specified value, and the valve body and valve cover are checked for sweat and leakage. The strength test can also be carried out in a single piece. The tightness test is only for shut-off valves. During the test, the valve stem of the shut-off valve is in a vertical state, the valve flap is opened, and the medium is introduced from the bottom end of the valve flap to the specified value, and the packing and gasket are checked; after passing the test, the valve flap is closed, and the other end is opened to check for leakage. If both the valve strength and tightness tests are to be done, the strength test can be done first, and then the pressure is reduced to the specified value of the tightness test, and the packing and gaskets are checked; then the valve flap is closed and the outlet end is opened to check whether the sealing surface is leaking.
2. Pressure test method of ball valve
The strength test of the pneumatic ball valve should be carried out with the ball half open.
① Floating ball valve tightness 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 packing and gasket at the same time The sealing performance of the place, there must be no leakage. Then introduce the test medium from the other end and repeat the above test.
②Fixed ball valve tightness test: before the test, rotate the sphere without load for several times, the fixed ball valve is in the closed state, and the test medium is introduced from one end to the specified value; use the pressure gauge to check the sealing performance of the lead-in end, use The accuracy of the pressure gauge is 0.5 to 1, and the range is 1.6 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.
③The three-way ball valve should be tested for tightness at each position.
3. Pressure test method of butterfly valve
The strength test of the pneumatic butterfly valve is the same as that of the globe valve. The sealing performance test of the butterfly valve should introduce the test medium from the end of the medium flow, the butterfly plate should be opened, the other end should be closed, and the pressure should be injected to the specified value; after checking the packing and other seals for no leakage, close the butterfly plate, open the other end, and check the butterfly No leakage at the plate seal is qualified. The butterfly valve used to adjust the flow can not be tested for sealing performance.
4. Pressure test method of diaphragm valve
In the diaphragm valve strength test, introduce the medium from either end, open the valve flap, and close the other end. After the test pressure rises to the specified value, it is qualified to see if the valve body and valve cover have no leakage. Then reduce the pressure to the tightness test pressure, close the valve flap, and open the other end for inspection. No leakage is considered qualified.
5. Pressure test method of check valve
Check valve test state: the lift check valve disc axis is in a position perpendicular to the horizontal; the swing check valve channel axis and the disc 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. It is qualified if there is no leakage in the valve body and bonnet.
Tightness test introduces the test medium from the outlet end, and checks the sealing surface at the inlet end. It is qualified if there is no leakage at the packing and gasket.