First, quality requirements
Each standard puts forward the relevant requirements for valve quality. 1 The chemical composition and mechanical properties of the valve body material comply with the requirements of the relevant material standards. 2 The deviation of the shape and size of the valve casting conforms to the drawings. 3 Non-machining surfaces of valve castings shall be smooth, smooth, free of sticky sand, free of oxide scale, non-porous, non-sanding, and crack-free. The cast mark is clear and the gate and riser should be flush with the casting surface after cleaning. 4 All parts of the valve should be firmly connected, no loose phenomenon. 5 The results of the pressure test and sealing performance test of the valve comply with the requirements of the relevant test standards. 6 The operation of the valve should be under the condition of nominal pressure and specified pressure difference, and there should be no jamming in the opening and closing operation. 7 has a certain number of operations and service life. 8 has a large flow capacity (ie after the valve, the pressure loss at the valve is smaller).
Second, inspection and test methods
1 casting quality
The shape and size of the casting should meet the requirements of the technical drawing or the requirements of the buyer. If there is no requirement for dimensional deviation in the sample, the relevant materials for JB/T 2580, GB/T 6414, and GB/T 2121 shall be specified for the material. The minimum wall thickness of each part of the valve, the deviation of the structural length, and the displacement of the gate wear shall not be less than the relevant technical standards of the product or the requirements of the product drawings. The surface of valve blanks and valve finished pressure shells shall not have defects such as cracks, cold septa, sand inclusions, and pores. The sticky sand, gates, risers, and oxide scale on the casting surface shall be removed. Casting should be clear. The pressure shell shall be subject to shell tests at 115 times the nominal pressure specified in GB/T 13927. The result shall be no visible leakage and no structural damage. The chemical composition and mechanical properties of castings are in accordance with the requirements of GB/T 12225, GB/T 12226, GB/T 12227, GB/T 12229 and GB/T 12230.
2 pressure test
Pressure test is the most basic test of the valve. Each valve must be pressure tested before leaving the factory. Test pressure and duration According to the provisions of GB/T 13927, the test items include shell test and seal test. When the valve has an upper seal structure, it needs to be sealed. During the test, no external force that affects the test results shall be applied to the valve. The test pressure should remain unchanged during the holding pressure and testing period. When using a liquid as a test medium, the air in the valve body should be excluded. The valve should be closed in the manner given by the design. The relevant standards for the tests are GB/T 13927, MSS SP61, ISO 5208, DIN 3230, API598, NFM 872401, ANSI B16134, J IS B2003, BS 5417 and BS 6755.
The shell test of the valve is a pressure test of the entire valve housing formed by connecting the valve body and the valve cover. The purpose is to check the tightness of the valve body and the valve cover, that is, the pressure resistance of the entire housing including the connection between the valve body and the valve cover. Prior to shell testing, the valve was not allowed to be painted and other leak-proof coatings were used. When the user checks the inventory valve, the existing coating is no longer removed. The shell test requires that the housing, including the connection between the valve body and the valve cover, must not leak, and must not have structural damage.
The seal test is a test to verify the performance of the opening and closing parts and the sealing body of the valve body. Sealing test is divided into high pressure liquid sealing test and low pressure gas sealing test. Prior to the seal test, except for valves sealed by grease, the oil on the seal faces should be removed, but no more than no protective agent can be applied. During the test, for the valve that regulates the flow direction of the medium, pressurizes according to the specified flow direction, and the check valve is pressurized from the outlet end.