• Valve pressure test precautions

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Valve pressure test precautions

  • 07 02, 2019
The production of valves is a complicated and simple process. The production cycle of ordinary valves such as gate valves, ball valves, globe valves, butterfly valves and check valves is generally three days. The production of manufactured valves must pass various performance tests. The most important test is the pressure test. The pressure test is to test whether the pressure value that the valve can withstand meets the production requirements. Generally, the valve pressure test must comply with the following principles and precautions:
 
1. Under normal circumstances, the valve is not tested for strength. However, the valve body and bonnet should be tested for strength after repair, as well as corrosion-damaged valve bodies and bonnets. For safety valves, the constant pressure and return pressure and other tests shall comply with the specifications and relevant regulations.
 
2. The strength and sealing test should be carried out before the valve is installed. The low pressure valve is checked by 20%. If it is not qualified, it should be 100% inspection; the medium and high pressure valves should be checked 100%.

3. When testing, the valve installation position should be in the direction of easy inspection.

4. For the valve in the form of welded connection, when the pressure test is not possible with the blind plate, the cone pressure seal or O-ring seal can be used for pressure test.

5. The valve air should be excluded as much as possible during the hydraulic test.
 
6. The pressure should be gradually increased during the test, and it is not allowed to pressurize sharply and suddenly.

7. The duration of the strength test and the seal test is generally 2-3 min, while for some important and special valves, it should last for 5 min. The test time of the small-diameter valve can be correspondingly shorter, and the test time of the large-diameter valve can be correspondingly longer. During the test, the test time may be extended if in doubt. During the strength test, the body and bonnet are not allowed to sweat or leak. For the sealing test, the common valve is only tested once, and important valves such as safety valves and high pressure valves need to be performed twice. During the test, a small amount of leakage is allowed for low-pressure, large-diameter unimportant valves and valves that are allowed to allow leakage; since general-purpose valves, power station valves, marine valves, and other valves have different requirements, the leakage requirements should be executed according to relevant regulations.

8. The throttle valve is not tested for the tightness of the closure, but the strength test and the tightness test at the packing and gasket are to be performed.

9. During the pressure test, the valve closing force only allows one person's normal physical strength to close; it must not be applied by means of a lever or the like (except the torque wrench). When the diameter of the hand wheel is greater than 320mm, the two people are allowed to close together. .

10. For valves with upper seals, the packing should be taken out for sealing test. After the upper seal is closed, check whether there is leakage or not. When testing with gas, add the water in the stuffing box for the test. When the packing tightness test is carried out, the upper seal is not allowed to be in a tight position.

11. For valves with a drive device, when the seal is tested, the drive device is used to close the valve to make the seal test. For manual drives, a seal test of the manual shut-off valve should also be performed.

12. After the strength test and the tightness test, the bypass valve installed on the main valve should also be opened when the main valve closing member is opened during the strength and tightness test of the main valve.

13. When testing the strength of cast iron valves, use a copper hammer to tap the valve body and bonnet to check for leaks.

14. When the valve is tested, except that there is any provision permitting the plug valve to be oiled on the sealing surface, other valves are not allowed to be applied oil on the sealing surface for the test.

15. When the valve is pressure tested, the pressing force of the blind plate to the valve should not be too large, so as to avoid deformation of the valve and affect the test effect (the cast iron valve will be damaged if it is pressed too tightly).

16. After the pressure test of the valve is completed, the water in the valve should be removed and cleaned in time, and the test record should be made.

Valve pressure test precautions
 
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