API598 Valve Low-Pressure Sealing Test
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I have some doubts regarding the low-pressure sealing test for valves as specified in the valve standard API598, and I am seeking guidance. API598 “6.4.4 The test of sealing air or gas in the chamber between the two sealing surfaces of a wedge-type single-plate (rigid or elastic) gate valve, followed by sealing it with water or checking for leaks at the seals using soapy water, does not constitute an acceptable low-pressure sealing test. “ As far as I have seen, in valve manufacturing, for valves with small diameters, the aforementioned method is used: the valve is closed to seal the air within the chamber between the two sealing surfaces, and then it is placed in water for low-pressure sealing. Is there any explanation for why the standard stipulates this?
During a hydrostatic test, the results are inaccurate when gas is present, as gas is more compressible than liquid; in other words, gas can be compressed more easily. Therefore, the provisions in the standards are reasonable and must be taken into account during pressure testing.
I didn’t quite understand your reply. This is a low-pressure gas sealing test: the gas under pressure is sealed inside the intermediate chamber, and then the chamber is placed in water. If there is a leak in the seal, bubbles will form. I’m not sure what about this method isn’t accepted by the standards Moreover, the previous requirement was limited to wedge-type single gate plates; does that mean this method can be used for other types of gate plates as well?
I’m sorry, I mistook it for a hydrostatic test; it’s my fault! :L