Various valve pressure test methods (one)

Under normal circumstances, industrial valves are not subjected to strength tests when they are used, but strength tests should be performed on repaired valve bodies and bonnets or corrosion-damaged valve bodies and bonnets. For the safety valve, its set pressure, reseating pressure and other tests shall comply with the specifications of its instructions and relevant regulations. The strength and tightness test should be done before the valve is installed. 20% of the low-pressure valves are spot-checked, and 100% of them should be checked if they are unqualified; 100% of the medium and high-pressure valves should be checked. The commonly used media for pressure testing of valves are water, oil, air, steam, nitrogen, etc. The pressure testing methods of various industrial valves including pneumatic valves are as follows:

1. Pressure test method of ball valve
The strength test of the pneumatic ball valve should be carried out in the half-open state of the ball.
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; rotate the ball several times, open the closed end to check when the valve is in the closed state, and check the sealing performance of 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.

②Sealing test of fixed ball valve: Before the test, rotate the ball several times without load, and the fixed ball valve is in the closed state, and introduce the test medium from one end to the specified value; check the sealing performance of the introduction end with a pressure gauge, and use a pressure gauge with an accuracy of 0 ．Class 5~1, the measuring range is 1.5 times of 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, the valve is in a half-open state, both ends are closed, and the inner cavity is filled with medium. Check the packing and gasket under the test pressure, and there must be no leakage.

③ Three-way ball valves are to be tested for tightness at each position.

2. Pressure test method of check valve
Test status of the check valve: the disc axis of the lift check valve is in a position perpendicular to the horizontal; the channel axis and disc axis 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, and it is qualified to see that there is no leakage from the valve body and bonnet. In the tightness test, the test medium is introduced from the outlet end, and the sealing surface is checked at the inlet end. If there is no leakage at the packing and gasket, it is qualified.

3. Pressure test method of pressure reducing valve

① The strength test of the pressure reducing valve is generally carried out after single-piece test and then assembled, and the test after assembly is also possible. Strength test duration: 1min for DN<50mm; more than 2min for DN65~150mm; more than 3min for DN>150mm. After the bellows and components are welded, the pressure after the pressure reducing valve is 1.5 times, and the strength test is carried out with air.

② Carry out the tightness test according to the actual working medium. When using air or water, test at 1.1 times the nominal pressure; when using steam, test at the allowable working pressure at the working temperature. The difference between inlet pressure and outlet pressure is 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 range of the minimum value, without stagnation or jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the shut-off valve after the valve is closed, the outlet pressure is the sum value, within 2 minutes, the rise of the outlet pressure shall meet the requirements in Table
4.176-22, and at the same time, the volume of the pipeline behind the valve shall meet the requirements of It is qualified as stipulated in Table 4.18; for water and air pressure reducing valves, when the inlet pressure is adjusted and the outlet pressure is zero, close the pressure reducing valve and carry out the sealing test. If there is no leakage within 2 minutes, it is qualified.

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