Precautions for valve pressure test

The production of valves is a complex and simple process. The production cycle of ordinary valves such as gate valve, ball valve, globe valve, butterfly valve and check valve is generally three days. The manufactured valves must undergo various performance tests, of which the most important one is pressure test. Pressure test is to test whether the pressure value that the valve can withstand meets the requirements of production regulations. Generally, the pressure test of valves must comply with the following principles and precautions:

1. Generally, the strength test is not conducted for the valve, but the strength test shall be conducted for the valve body and bonnet after repair or the valve body and bonnet with corrosion damage. For the safety valve, its constant pressure, reseating pressure and other tests shall comply with the provisions of its instructions and relevant regulations.

2. The strength and sealing test shall be conducted for the installation of the valve. 20% of low-pressure valves shall be randomly inspected, and 100% of them shall be inspected if they are unqualified; Medium and high pressure valves shall be 100% inspected.

3. During the test, the valve shall be installed in the direction easy to check.

4. For the valve in the form of welded connection, if the blind plate pressure test fails, the conical seal or O-ring seal can be used for pressure test.

5. During the hydraulic test, exhaust the valve air as much as possible.

6. During the test, the pressure shall be increased gradually, and sharp and sudden pressurization is not allowed.

7. The duration of strength test and sealing type test is generally 2-3min, and important and special valves shall last 5min. The test time of small-diameter valves can be shorter, and that of large-diameter valves can be longer. In case of doubt during the test, the test time can be extended. During strength test, sweating or leakage of valve body and bonnet is not allowed. Generally, the sealing test is only conducted once for valves, and twice for safety valves, high-pressure valves and other important valves. During the test, minor leakage is allowed for unimportant valves with low pressure and large diameter and valves with specified leakage; Due to different requirements for general valves, power station valves, marine valves and other valves, the leakage requirements shall be implemented in accordance with relevant regulations.

8. The throttle valve shall not be subject to the sealing test of the closing parts, but shall be subject to the strength test and the sealing test at the packing and gasket.

9. During the pressure test, the valve closing force only allows one person's normal physical strength to close; It is not allowed to apply force with tools such as lever (except torque wrench). When the diameter of hand wheel is greater than 320mm, two people are allowed to close it together.

10. For the valve with upper seal, the packing shall be taken out for sealing test. After the upper seal is closed, check whether there is leakage. When testing with gas, check with water in the stuffing box. During the packing tightness test, the upper seal is not allowed to be in the tight position.

11. When testing the tightness of valves with driving device, the sealing test shall be conducted by closing the valve with driving device. For manual driving devices, the sealing test of closing the valve with power shall also be carried out.

12. The bypass valve installed on the main valve after strength test and sealing test shall be tested on the main valve; When the closing part of the main valve is opened, it shall also be opened.

13. During the strength test of cast iron valve, tap the valve body and bonnet with a copper hammer to check whether there is leakage.

14. During the valve test, except that the sealing surface of plug valve is allowed to be oiled, other valves are not allowed to be oiled on the sealing surface for test.

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

16. After the pressure test of the valve is completed, the accumulated water in the valve shall be removed and cleaned in time, and the test records shall be made.