Under normal circumstances, industrial valves are not subject to strength tests when they are in use, but strength tests should be performed on valve bodies and bonnets after repairs or corrosion-damaged valve bodies and bonnets. For the safety valve, its constant pressure, reseating pressure and other tests shall comply with the specifications of its instructions and relevant regulations. Before the valve is installed, the valve strength test and valve sealing test should be carried out on the valve hydraulic test bench. 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 globe valve and throttle valve

For the strength test of globe valve and throttle valve, usually put the assembled valve in the pressure test frame, open the valve disc, inject medium to the specified value, and check whether the valve body and valve cover are sweating and leaking. The strength test can also be carried out on a single piece. The tightness test is only for the stop valve. During the test, the valve stem of the stop valve is in a vertical state, the valve disc is opened, the medium is introduced from the lower 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 whether there is leakage. If the strength and sealing test of the valve is to be done, the strength test can be done first, and then the pressure is reduced to the specified value of the sealing test, and the packing and gasket are checked; then the valve disc is closed, and the outlet port is opened to check whether the sealing surface is leaking.

2. Pressure test method of gate valve

The strength test of the gate valve is the same as that of the globe valve. There are two methods for the sealing test of gate valves.

① Open the gate to raise the pressure in the valve to the specified value; then close the gate, take out the gate valve immediately, check whether there is leakage at the seals on both sides of the gate or directly inject the test medium into the plug on the valve cover to the specified value , check the seals on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for sealing tests on gate valves with nominal diameters below DN32mm.

② Another method is to open the gate to raise the test pressure of the valve to the specified value; then close the gate, open one end of the blind plate, and check whether the sealing surface is leaking. Then turn the head down and repeat the above test until it is qualified.

The sealing test of the pneumatic gate valve packing and gasket should be carried out before the gate sealing test.

3. 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 valve.

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.

② Sealing 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 1.6 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.

4. Pressure test method of plug valve

① When carrying out the strength test of the plug valve, the medium is introduced from one end, the rest of the passages are closed, and the plug is rotated to each working position of the fully open one by one for the test. If no leakage is found in the valve body, it is qualified.

② During the tightness test, the straight-through cock should keep the pressure in the cavity equal to that of the passageway, 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 valves The pressure in the cavity and one end of the passage should be kept equal, the plugs are rotated to the closed position in turn, the pressure is introduced from the right-angle end, and the inspection is carried out from the other end at the same time.

A layer of non-acid thin lubricating oil is allowed to be coated on the sealing surface in front of the plug valve test bench, and it is qualified if no leakage and enlarged water droplets are found within the specified time. The test time of the plug valve can be shorter, generally 1-3 minutes according to the nominal diameter.

The plug valve for gas shall be subjected to an air tightness test at 1.25 times the working pressure.

5. 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 medium flow end, the butterfly plate should be opened, the other end should be closed, and the injection pressure should reach the specified value; after checking that there is no leakage at the packing and other seals, close the butterfly plate, open the other end, and check the butterfly valve. It is qualified if there is no leakage at the plate seal. Butterfly valves used to regulate flow may not be tested for sealing performance.

6. Pressure test method of diaphragm valve

Diaphragm valve strength test Introduce the medium from either end, open the disc, and close the other end. After the test pressure rises to the specified value, it is qualified if there is no leakage from the valve body and bonnet. Then reduce the pressure to the tightness test pressure, close the valve disc, open the other end for inspection, and if there is no leakage, it is qualified.

7. 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.

8. Pressure test method of safety valve

① The strength test of the safety valve is the same as other valves, and it is tested with water. When testing the lower part of the valve body, the pressure is introduced from the inlet I=I end, and the sealing surface is closed; when testing the upper part of the valve body and the bonnet, the pressure is introduced from the outlet El end, and the other ends are closed. It is qualified if there is no leakage of the valve body and bonnet within the specified time.

② For tightness test and constant pressure test, the generally used medium is: steam safety valves use saturated steam as the test medium; valves for ammonia or other gases use air as the test medium; valves for water and other non-corrosive liquids use water as the test medium medium. Nitrogen is often used as the test medium for safety valves in some important positions.

The sealing test is carried out with the nominal pressure value as the test pressure, and the number of times is not less than two. If there is no leakage within the specified time, it is qualified. There are two ways to check for leaks: one is to seal the joints of the safety valve, and use butter to seal the thin paper on the outlet flange. Plastic board or other boards are pasted on the lower part of the outlet flange, water is poured to seal the disc, and it is qualified if there is no bubble in the water. The number of constant pressure and reseating pressure tests of the safety valve shall not be less than 3 times, and it is qualified if it meets the regulations.

For various performance tests of safety valves, see GB/T 12242 "Safety Valve Performance Test Methods".

9. 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 strength test is carried out with air at 1.5 times the maximum pressure after the pressure reducing valve.

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 highest 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 be changed sensitively and continuously within the range of maximum and minimum values without stagnation or jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the cut-off valve after the valve is closed, the outlet pressure is the highest and the lowest value, within 2 minutes, the rise of the outlet pressure should meet the regulations, and at the same time, the volume of the pipeline behind the valve meets the regulations. ; For water and air pressure reducing valves, when the inlet pressure is set 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.