Under normal circumstances, industrial valves are not subjected to a strength test when in 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 set pressure and return 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. The pressure testing methods for 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 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 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 tightness 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 tightness at various positions.

2. Pressure test method 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 method of pressure reducing valve
① The strength test of the pressure reducing valve is generally assembled after a single piece test, and it can also be tested after assembly. The duration of the strength test: 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. For the steam pressure reducing valve, after the inlet pressure is adjusted, the valve is shut off and the outlet pressure is the highest and lowest value. Within 2 minutes, the rise in the outlet pressure should meet the requirements in Table 4.176-22. At the same time, the pipeline behind the valve The volume meets the requirements in Table 4.18 as 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 and the tightness test is performed. No leakage within 2 minutes is qualified.

4. 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.

5. Pressure test method of plug valve
① During the strength test of the plug valve, the medium is introduced from one end, the remaining passages are closed, and the plug is rotated to the fully open working positions for the test. The valve body is qualified if no leakage is found.
② During the sealing test, the straight-through cock should keep the pressure in the cavity equal to that of 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; three-way or four-way plug valve The pressure in the cavity and one end of the passage should be kept equal, the stopper should be rotated to the closed position in turn, the pressure should be introduced from the right-angle end, and the other end should be inspected at the same time.
Before the plug valve test, it is allowed to apply a layer of non-acid dilute lubricating oil on the sealing surface, and no leakage or enlarged water droplets within the specified time are qualified. The test time of the plug valve can be shorter, generally 1~3min according to the nominal diameter.
The plug valve for gas shall be tested for air tightness at 1.25 times the working pressure.

6. Pressure test method of diaphragm valve
In the diaphragm valve strength test, the medium is introduced from either end, the valve flap is opened, and the other end is closed. After the test pressure rises to the specified value, it is qualified to see that the valve body and bonnet 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.

7. Pressure test method of stop valve and throttle valve
In the strength test of the stop valve and the throttle valve, the assembled valve is usually placed in a 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 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.

8. Pressure test method of Gate Valve
The strength test of the gate valve is the same as that of the stop valve. There are two methods for the sealing test of the gate valve.
① Open the gate to increase the pressure in the valve to the specified value; then close the gate and immediately take out the gate valve to 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 the sealing test of gate valves with a nominal diameter below DN32mm.
② Another method is to open the gate to increase the test pressure of the valve to the specified value; then close the gate and open one end of the blind plate to check whether the sealing surface is leaking. Reverse the head and repeat the test above until it is qualified.
The sealing test of the packing and gasket of the pneumatic gate valve shall be carried out before the sealing test of the gate.

9. Pressure test method of safety valve
① The strength test of the safety valve is the same as that of other valves. 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. The valve body and bonnet are qualified without leakage within the specified time.
② For sealing tests and constant pressure tests, the general media used are: safety valves for steam 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. For safety valves in some important positions, nitrogen is often used as the test medium.
The sealing test shall be conducted with the nominal pressure value as the test pressure, and the number of times shall not be less than twice, and no leakage within the specified time is considered qualified. There are two leak detection methods: one is to seal the JOINTs of the safety valve, and use butter to seal the thin paper on the flange of the outlet. The plastic plate or other plate seal is attached to the lower part of the outlet flange, and the valve disc is sealed with water. It is qualified to check that the water does not bubble. The number of constant pressure and return pressure tests of the safety valve shall not be less than 3 times, and it shall be qualified if it meets the requirements. The various performance tests of safety valves refer to GB/T 12242-1989 Safety Valve Performance Test Methods.

Valve pressure test management regulations
1. All valves should be visually inspected after unpacking, including complete nameplates on the valve body, product quality certification documents, valve in a closed state, no other damage such as blue surface, no dirt, and protective covers at both ends.
2. The operator should be familiar with the operation of the pressure test bench.
3. The valve pressure test JHA is perfect, and the operator should be familiar with the safety hazards of the valve pressure test, reverse transportation and other processes and have corresponding preventive measures.
4. The valve pressure test process is: valve shell strength test, upper seal test, and seal test.
(1) The test medium for the strength of the valve shell is water, the pressure is 1.5 times the nominal pressure of the valve, and the pressure holding time is 5 minutes. No drip or moisture is qualified.
(2) The sealing test medium on the valve is water, the pressure is 1.5 times the nominal pressure, the pressure holding time is 15s for DN≤50, 60s for 65≤DN≤300, and 120s for DN≥350. No leakage is qualified.
(3) Valve sealing test: Low pressure sealing test is carried out. The test medium is air (gate valve), the pressure is 0.6MPa, the holding time is 15s for DN≤50, 60s for 65≤DN≤150, and 120s for DN≧200. The requirement is qualified.
(4) After the pressure test is qualified, the water in the valve cavity should be blown dry with compressed air in time.
(5) Valves that pass the pressure test are marked √ on the valve body, and valves that are unqualified are marked ×.
(6) After the pressure test, the valves should be stacked separately according to the type and specifications of the device, and the unqualified products should be stacked separately; each stacking area should be erected with a clear sign. After the pressure test, the valve should be closed back and covered with a colored strip of cloth for protection in the stacking area.
(7) After the valve is pressure tested, the "Valve/Pipe Fitting Test Record" should be filled out in time according to the device, and the model column should be filled in with the purchase contract number on the valve body.
(8) For valves that have passed the test, the valve "Valve Issuance Record" must be filled in and signed by both the issuing and receiving parties.
(9) Unqualified valves need to establish a separate "Unqualified Valve Information Ledger"