Why is the valve always faulty, quality problem or wrong operation?

- Apr 29, 2018-

Why is the valve always faulty? In the design, manufacture, installation, operating conditions, operation, maintenance throughout the process, each step should not be lax. How do you determine if the valve is in the factory or after the complete installation? This needs to be checked by the appearance test and certain performance tests. Through the results of these tests, the defects can be exposed and adjusted accordingly, only after all the tests have been qualified can be put into use. So what are the details of the appearance test?

What do the performance tests include?

Appearance inspection

1, the valve body inside and outside the surface has no sand holes, cracks and other defects.

2, the valve seat and valve body joint is firm, spool and valve seat is consistent, sealing surface has no defects.

3, valve stem and spool connection is flexible and reliable, the stem has no bending, the thread has no damage, corrosion.

4, filler, gasket aging damage, valve open whether flexible.

5, the valve body should be nameplate, valve body and nameplate should include: Manufacturer name, valve name, nominal pressure, nominal size, such as identification.

6, Valve transport when the opening and closing position should meet the following requirements:

(a) gate valve, cut-off valve, throttle valve, butterfly valve, bottom valve, control valve should be in full closed position.

(b) Plug valve, ball valve closure should be in full open position.

(c) The diaphragm valve should be in a closed position, must not be closed too tight to prevent damage to the diaphragm valve.

(d) The disc of the check valve shall be closed and fixed.

7, the spring type safety valve should have the seal, lever type safety valve should be heavy hammer positioning device.

8, check valve disc or spool action should be flexible and accurate, no eccentricity, displacement or skew phenomenon.

9, lining glue, lining enamel and lined with plastic valve inside surface should be smooth, lining and the substrate with solid, no cracks, bubbling and other defects.

10, flange sealing surface should meet the requirements must not have radial scratches.

11, valve shall not have damage, missing parts, corrosion, nameplate off and other phenomena, and the valve body must not be dirty.

12, the valve at both ends should have protective cover protection, handle or handwheel operation should be flexible, no card astringent phenomenon.

13. The valve quality certificate shall contain the following contents:

(a) Manufacturer name and date of manufacture.

(b) Product name, model and specification.

(c) Nominal pressure, nominal size, applicable medium and applicable temperature.

(d) The basis of the standards, inspection findings and date of inspection.

(e) Factory numbering, inspectors and the person responsible for the inspection of the signature.

Performance test

Shell Strength test

Valve can be regarded as a pressure vessel, solid to meet the pressure of the medium and not leakage of the requirements, so the valve body, bonnet and other parts of the blanks should not have the impact of strength of the cracks, porosity, slag and other defects. The strength test is usually carried out after the final assembly. Tests are usually carried out at room temperature, and the test pressure p is typically 1.25-1.5 times times the nominal pressure PN to ensure safe use. The valve is open at the test, one end is closed, the other is injected into the media and pressure is exerted. Check the shell (body, cover) exposed surface, require the prescribed test duration (generally not less than 10 minutes) without leakage, can be considered the valve strength test qualified.

In order to ensure the reliability of the test, the strength test should be done before the valve is painted, and the air in the cavity should be cleaned when the water is the medium.

Leakage of the valve, such as technical conditions allow repair welding can be made according to technical specifications for repair, but repair welding must be renewed strength test, and appropriate extension of the duration of the test.

Seal test

Out of the throttle valve, whether it is to cut off the valve or adjust the valve, should have a certain close sealing, solid valve in the factory to be one by one seal test, with a sealed valve to carry out the seal test. The tests are usually performed at ambient temperature at nominal pressure pn, and the SU valve is under 1.1 times times the PN pressure.

Water as a test medium, easy to make valve rust, usually according to technical requirements to control water quality, and in the test after the residual water blown dry or drying. Gate valve and ball valve as there are two sealing pairs, it is necessary to carry out two-way sealing test. In the test, first the valve opened to the end of the channel seal, pressure from the other side, to the pressure rise to the specified value when the valve closed, and then the sealing end of the pressure gradually removed, and checked. The other end also repeats the experiment.

Another test method of gate valve is to maintain the test pressure in the body cavity to check the double seal of the valve from both ends of the channel.

When the check valve is tested, the pressure should be introduced at the outlet end and inspected at the inlet. When sealing test, the closing moment of valve shall be determined by nominal pressure and nominal diameter. Manual valves are usually only allowed to be closed with normal physical strength, and may not be assisted by other auxiliary devices, when the handwheel diameter is greater than or equal to 320mm allow two people to close. A valve with a driving device. Should be tested in the case of the use of a driving device.

If the requirement of closing moment is stipulated in the technical requirement, the force wrench is needed to measure the closing moment.

The sealing test should be carried out after the strength test of the valve assembly, because not only the sealing of the valve should be inspected, but also the sealing of the filler and the flange gasket should be inspected. The upper seal test is usually carried out in the strength test.

When the test and the stem raised to the limit position, so that the valve stem and bonnet sealing surface close contact, the filler pressure Guesson Open after inspection of its sealing. Specification for valves or drawings for use in gaseous media the valves for low-pressure gas seal tests shall be carried out in accordance with the standard specifications of the test, nitrogen or dry clean air.

The test pressure is 0.6MPa.

Action Performance Test

The test medium with the shell strength test and the seal test, after the shell strength test and the seal test is qualified.