The production of valves is a complicated and simple process. The production cycle of ordinary valves such as gate valves,stainless steel ball valve, 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, but the valve body and bonnet of the valve body and bonnet or corrosion damage shall be tested for strength after repair. For safety valves, the constant pressure and return pressure and other tests shall comply with the specifications and relevant regulations.
(2) The valve installation shall be tested for strength and tightness. 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) Valves in the form of welded joints, when the test is not possible with the slab, the taper 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 strength test and the seal test duration are generally 2-3 min, and the important and special valves 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 valve is generally only used once, and the safety valve, high pressure valve and other raw valves need to be carried out 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 forged steel ball valve, power station valves, marine valves, and lift check valves have different requirements, the leakage requirements should be Execute according to relevant regulations.
(8) The throttle valve shall not be used for the sealing test of the closing member, but shall be used for the strength test and the sealing test at the packing and gasket.
(9) In 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 320 mm, the two are allowed to work together. shut down.
(10) For valves with upper seal, the packing should be taken out for sealing test. After sealing the upper part, check for leaks. When testing with gas, check the water in the stuffing box. When using the packing tightness test, the upper seal is not allowed to be in a tight position.
(11) Where a valve with a drive device is tested for its tightness, the drive device is used to close the valve to perform a tightness test. For manual drives, a seal test using a closed valve should also be performed.
(12) After the strength test and the seal test, the bypass valve installed on the main valve shall be tested for strength and tightness in the main valve; when the main valve closing member is opened, it shall also be opened.
(13) When testing the strength of cast iron valves, tap the valve body and bonnet with a copper hammer to check for leaks.
(14) When the valve is tested, except that the plug valve has provisions to allow the sealing surface to be oiled, stainless steel globe valve are not allowed to apply oil test on the sealing surface.
(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.