In the design, manufacture, installation, working conditions, operation and maintenance of the whole process, every step should not be relaxed. How do you determine if there is a problem with the valve before or after the complete installation? This needs to be checked by visual inspection and certain performance tests. Through these test results, the defects can be exposed and adjusted accordingly, and only after all the tests are qualified can they be put into use. So, what details do you need to pay attention to? What are the performance tests included?
Visual inspection:
- the inside and outside surface of body has no blisters, cracks and other defects.
- whether the valve seat and the valve body are firm, whether the valve core and the valve seat match, the sealing surface has no defects.
- stem and spool connection is flexible and reliable, valve stem bending, thread damage or corrosion.
- packing, gaskets are aging damage, valve opening is flexible, etc..
- the body should have a nameplate, the body and nameplate should include: manufacturer name, valve name, nominal pressure, nominal diameter and other signs.
- The opening and closing position of the valve shall comply with the following requirements:
- Gate valve, globe valve, throttle valve, butterfly valve, foot valve, regulating valve, the valve is in full closed position.
- Plug valve, ball valve closed parts should be in full open position.
- Diaphragm valve should be in the closed position, must not be closed too tight to prevent damage to the diaphragm valve.
- The disc of the check valve shall be closed and secured.
- spring-loaded safety valve should be sealed, positioning lever type safety valve should have the weight of the device.
- check valve disc or spool movement should be flexible, accurate, no bias, displacement or skew phenomenon.
- lining, lining, enamel and plastic lined valve, the inner surface should be smooth and smooth, lining and solid combination of the base, no cracks, bubble and other defects.
- the flange sealing surface should meet the requirements, shall not have radial scratches.
- the valve shall not be damaged, missing parts, corrosion, nameplate shedding and other phenomena, and the valve body shall not be dirty.
- both ends of the valve should be protective cover, handle or hand wheel operation should be flexible, must not be stuck phenomenon.
- The valve quality certificate shall contain the following contents:
- Manufacturer name and date of manufacture.
- Product name, model and specification.
- Nominal pressure, nominal diameter, applicable medium and applicable temperature.
- Standard, inspection conclusion and date of inspection.
- Serial number, inspection personnel and signature of surveyor.
Shell strength test:
- Valve can be seen as a pressure vessel, solid to meet the pressure to withstand the media without leakage requirements, so the body, valve cover and other parts of the rough should not affect the strength of cracks, loose pores, slag and other defects.
- Strength tests are usually performed after assembly. Test is usually carried out at room temperature, in order to ensure the safety of use, the test pressure P is generally PN times the nominal pressure 1.25-1.5. During testing, the valve is in open position with one end closed, injected into the medium at the other end, and applied pressure. Check the shell (body, cover) exposed surface, requiring the prescribed test duration (generally not less than 10 minutes) without leakage, it can be considered that the valve strength test qualified. In order to ensure the reliability of the test, the strength test shall be done before the valve is painted, and the air in the inner cavity shall be discharged when the water is used as the medium.
- Leakage of the valve, such as technical conditions permit welding, welding can be repaired according to technical specifications, but repair welding must re test the strength, and appropriate to extend the duration of the test.
Sealing test:
- a throttle valve, whether it is cut off or adjust the valves with the valve should be closed with a certain degree of tightness, solid valve sealing test before delivery to one by one, with the valve seal and seal test.
- The test is usually done under nominal pressure PN at room temperature, under 1.1 times PN pressure. Water as the test medium, easy to cause corrosion of the valve, usually according to technical requirements to control water quality, and after the test will be residual water drying or drying.
- gate valve and ball valve due to two sealing pairs, it is necessary to conduct two-way sealing test. During the test, the first valve open to one end of the channel blocked, the pressure from the other end of the pressure to be elevated to the specified value when the valve is closed, and then the sealing end of the pressure gradually lifted, and check. The tests were repeated at the other end. Another test method for gate valves is to maintain test pressure in the chamber and check the double tightness of the valve from both ends of the channel.
- When testing the check valve, the pressure should be introduced at the exit and inspected at the entrance.
When sealing test, the closing moment of valve shall be determined by nominal pressure and nominal diameter. Manual valves are normally closed only with normal physical strength, not with other assistive devices, and are allowed to be closed with two hands when the diameter of the handwheel is greater than or equal to 320mm. Valve with drive device. The test should be done with the actuating device. If the technical requirements specify the closing torque, the torque wrench shall be used to measure the closing torque. - sealing test should be carried out after the valve assembly strength test, because not only to check the sealing of the valve, but also to test the sealing of the packing and the middle flange gasket.
- Sealing test is usually carried out in strength test. During test, the stem is raised to the limit, so that the stem and the valve cover face are tightly contacted, and the packing gland is released to check the tightness.
- Valves used in gas medium or drawing technical specifications requiring valves for low pressure sealing test must be carried out according to the test standard. The test medium is nitrogen or dry clean air. The test pressure is 0.6MPa.
Performance test:
- test the same strength and sealing test of the same shell, after the strength test of the shell and the sealing test.
- Manual valve performance test
- the valve is open, the valve cavity pressure to the test pressure for the moment to close the valve, the valve in the pressure side, in order to establish the differential pressure valve opening in the most unfavorable direction, then the moment to open the valve, so at least three times more than the complete load cycle, in order to check the valve opening and closing operation is normal, the action is flexible, open and close position indicator is right.
Check valve performance test:
- Under the provisions of the pressure difference valve in the open test, the test is not less than 3 times.
- Electric and pneumatic valve performance test, according to the provisions of the technical specifications of the valve, no clear provisions of technical specification for valve, actuator valve operation should be rated to complete three full load cycle, in the test, the valve must be stable, flexible, open and close the valve position indicator must must be in place. Right.
Vacuum sealing test:
- a high sensitivity sealing test method.
- vacuum test usually in the valve strength, sealing test after qualified. In order to ensure the accuracy of the test, the valve to be tested has a high degree of cleanliness and processing of fine sealing surface. Moreover, the body, valve cover should be used in general forgings.
- helium mass spectrometry leak detection: the valve will be measured by vacuum pump to the specified vacuum, the valve was measured outside the application of helium. If there is a leak of helium will enter the valve under test, helium leak detector system can be displayed, the calculation of leakage rate.
Leak test:
- in recent years, with the strengthening of people’s awareness of environmental protection, the world’s various agencies on the valve sealing more stringent requirements, especially for the use of medium for strong corrosion, strong radiation, highly toxic. Valve micro leakage requirements is one of them. Valve micro leak detection is mainly to check the valve flange and stuffing box at the level of micro leakage, belonging to a valve shell seal test.
- micro valve leak detection is the basic principle: the valve is in a semi closed state to open the valve internal pressure of the helium to provide communication with good leakage rate has been adjusted with the suction probe helium leak detector to detect stuffing in the cavity and on site, to see if the site meets the specified leak rate user.
