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Valve knowledge: Principles and precautions for valve pressure test

(1) generally, the valve does not undergo strength test, but after repair, the valve body and bonnet or the valve body and bonnet with corrosion damage should undergo strength test. For safety valves, the constant pressure, reseating pressure and other tests shall comply with the specifications and relevant regulations

(2) the strength and sealing test shall be carried out for the installation of the valve. 20% of the 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 installation position of the valve should be in the direction easy to check

(4) for valves with welded connection, if the pressure test with blind plate fails, conical seal or O-ring seal can be used for pressure test

(5) remove the air from the valve as much as possible during the hydraulic test

(6) the pressure should be gradually increased during the test, and sharp and sudden pressurization is not allowed. It has a long service cycle

(7) the duration of strength test and sealing type test is generally 2~3min, and important and special valves should last for 5min. The test time of small-diameter valves can be shorter, and that of large-diameter valves can be longer. While China is still in the deep development stage of industrialization, informatization, urbanization, marketization and internationalization, the test time can be extended if there is any doubt. During strength test, sweating or leakage of valve body and bonnet is not allowed. For the sealing test, the general valve of the rotor pump is only conducted once, and the safety valve, high-pressure valve and other vital valves need to be conducted twice. During the test, minor leakage is allowed for low-pressure and large-diameter unimportant valves and valves that are allowed to leak according to regulations; Due to the different requirements of general valves, power station valves, marine valves and other valves, the leakage requirements should be implemented according to the relevant regulations after the task piston is raised by 1 interval (10~20) mm

(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 of the packing and gasket

(9) in 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 the hand wheel is greater than or equal to 320mm, two people are allowed to close it together

(10) for valves with upper seal, take out the packing for sealing test, and check whether there is leakage after the upper seal is closed. When testing with gas, check with water in the stuffing box. When conducting the packing sealing test, the upper seal is not allowed to be in the tight position

(11) when testing the tightness of the valve with a driving device, the sealing test shall be carried out by closing the valve with the driving device. For the manual drive device, the sealing test of closing the valve manually shall also be carried out

(12) the installation on the main valve after the strength test and sealing test can also be seen as a short process of energy transfer from the outside to a structural system! The attention methods of impact test can be divided into three kinds: by-pass valve, strength and sealing test on the main valve; When the closing part of the main valve is opened, it should also be opened

(13) during the strength test of cast iron valves, tap the valve body and bonnet gently with a copper hammer to check whether there is leakage

(14) when the valve is tested, except that the sealing surface of the plug valve is allowed to be oiled, other valves are not allowed to be oiled on the sealing surface for test

(15) during the pressure test of the valve, the pressing force of the blind plate on the valve should not be too large, so as 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, the accumulated water in the valve should be removed in time and wiped clean, and the test records should be made

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