The principles and precautions for valve pressure testing are as follows:
(1) Under normal circumstances, valves are not subject to strength tests, but valve bodies and valve covers that have been repaired or damaged by corrosion should be subject to strength tests. For safety valves, their constant pressure, backseat pressure and other tests should comply with the instructions and relevant regulations.
(2) Strength and sealing tests should be carried out before the valve is installed. 20% of low-pressure valves shall be randomly inspected. If they are unqualified, 100% shall be inspected; medium and high-pressure valves shall be inspected 100%.
(3) During the test, the valve should be installed in a direction that is easy to inspect.
(4) For valves with welded connections, when the pressure test using the blind plate is not possible, the cone seal or O-ring seal can be used for pressure test.
(5) During the hydraulic test, remove as much air from the valve as possible.
(6) The pressure should be gradually increased during the test, and rapid and sudden pressure increases are not allowed.
(7) The duration of strength test and sealing test is generally 2~3 minutes, and important and special valves should last 5 minutes. The test time for small-diameter valves can be correspondingly shorter, and the test time for large-diameter valves can be correspondingly longer. During the test, if there is any 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 conducted 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 low-pressure, large-diameter unimportant valves and valves with regulations that allow leakage; because general valves, power station valves, marine valves and other valves have different requirements, the leakage requirements Should be implemented in accordance with relevant regulations.
(8) The throttle valve is not subject to a sealing test of the closing parts, but a strength test and a sealing test of the packing and gasket are required.
(9) During the pressure test, the valve closing force is only allowed to be closed by the normal physical strength of one person; no tools such as levers are allowed to apply force (except torque wrenches). When the diameter of the handwheel is greater than or equal to 320mm, two people are allowed to work together. closure.
(10) For valves with an upper seal, the packing should be removed for a sealing test. After the upper seal is closed, check for leaks. When testing with gas, fill the stuffing box with water for inspection. When conducting the packing sealing test, the upper seal is not allowed to be in the tight position.
(11) For valves with a driving device, when testing their tightness, the driving device should be used to close the valve and conduct a tightness test. For manually driven devices, a sealing test for closing the valve manually should also be carried out.
(12) After the strength test and sealing test, the bypass valve installed on the main valve shall be tested for strength and sealing on the main valve; when the closing part of the main valve is opened, it shall also be opened accordingly.
(13) During the strength test of cast iron valves, tap the valve body and valve cover lightly with a copper hammer to check for leaks.
(14) When testing valves, except for plug valves that have regulations that allow the sealing surface to be coated with oil, other valves are not allowed to apply oil to the sealing surface.
(15) When testing the pressure of the valve, the pressing force of the blind plate on the valve should not be too large to avoid deformation of the valve and affecting the test effect (cast iron valves will be damaged if they are pressed too tightly).
(16) After the valve pressure test is completed, the accumulated water in the valve should be removed and wiped clean in time, and test records should be made.