Principles and precautions for valve pressure testing

The principles and precautions for valve pressure testing are as follows. ⑴ Valve strength test ① Generally, the valve is not subjected to strength test, but the repaired valve body and bonnet or the valve body and bonnet damaged by corrosion should be subjected to strength test. For the safety valve, its constant pressure, reseating pressure and other tests shall comply with the requirements of its manual and relevant regulations. ② The strength and tightness test should be done before the valve is installed. 20% random inspection of low-pressure valves, 100% inspection if unqualified; 100% inspection of medium and high pressure valves. ③ The tightness test of the closing parts is not required for the throttle valve, but the strength test and the tightness test of the packing and gasket shall be carried out. (2) Pay attention to the strength and tightness test of the valve ① During the test, the installation position of the valve should be in the direction that can be easily checked. ② For valves in the form of welded connection, when the pressure test with the blind plate fails, conical seal or O-ring seal can be used for pressure test. ③ The valve air should be excluded as much as possible during the hydraulic test. ④ During the test, the pressure should be gradually increased, and rapid and sudden pressure increase is not allowed. ⑤ During the pressure test, the closing force of the valve is only allowed to be closed by one person's normal physical strength; it is not allowed to use tools such as levers (except torque wrenches) to apply force. When the diameter of the handwheel is greater than or equal to 320mm, two people are allowed to close together. ⑥ When testing the valve, it is not allowed to apply oil on the sealing surface of other valves, except for the plug valve which is specified to allow oiling on the sealing surface. ⑦ For any valve with a driving device, when testing its tightness, the driving device should be used to close the valve and then carry out the tightness test. For manually actuated devices, a seal test for manually closed valves shall also be carried out. (3) Test time and leak detection ① The duration of strength test and tightness test is generally 2 to 3 minutes, and important and special valves should last for 5 minutes. The test time of small-diameter valves can be correspondingly shorter, and the test time of large-diameter valves can be correspondingly longer. During the test, if in doubt. The test time can be extended. During the strength test, the valve body and valve cover are not allowed to sweat or leak. The sealing test is only performed once for general valves, and twice for important valves such as safety valves and high-pressure valves. During the test, a small amount of leakage is allowed for unimportant valves with low pressure and large diameter, as well as valves with regulations that allow leakage; due to the different requirements for general valves, power station valves, marine valves and other valves, the leakage requirements are different. It should be implemented in accordance with relevant regulations. ② For valves with upper seals, the packing should be taken out for a tightness test. After the upper seals are tightly sealed, check for leakage. When testing with gas, check with water in the stuffing box. When doing the packing tightness test, the upper seal is not allowed to be in the tight position. ③ During the strength test of cast iron valves, tap the valve body and bonnet with a copper hammer to check for leakage. ⑷ Post-test treatment ①For the bypass valve installed on the main valve after the strength test and the tightness test, the strength and tightness test of the main valve shall be carried out; when the main valve closing part is opened, it shall also be opened. ② During the pressure test of the valve, the pressing force of the blind plate on the valve should not be too large, so as not to deform the valve and affect the test effect (if the cast iron valve is pressed too tightly, it will be damaged). ③ After the pressure test of the valve is completed, the accumulated water in the valve should be removed in time and wiped clean, and the test record should be made.
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