Testing of valves
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A 150LB 20-inch gate valve. The high-pressure sealing test pressure is 2.2 MPa. The standard testing method involves sealing one end while leaving the other end open to the atmosphere, and then checking for leaks at the sealed end. My question is: if, for example, this valve starts to leak at a low pressure of 4 kilograms, but no leaks are observed even when the pressure is increased to 15 kilograms, does this mean the valve is still considered qualified?
“Leakage started at 4 kilograms, but no visible leakage was observed even after increasing the pressure to 15 kilograms. This can’t be possible!
That’s strange – low pressure leaks but high pressure doesn’t? That’s highly unlikely! Please, the original poster, explain the details...
I’m not quite sure what that means
It leaks under low pressure but not under high pressure – how is that possible? If that were the case, it would be clear that it doesn’t work already at 4 kilograms of pressure; why bother applying more pressure then?
It is possible that the seal is compressed only when the operating pressure is reached; this is normal, and the valve should be qualified.
What the poster means is that the air was already completely exhausted at 4 kilograms, so by 15 kilograms there was no air left to be exhausted. This situation shouldn’t happen; there should be some sensation when there’s a leak, right?
“Leakage started at 4 kilograms, but no visible leakage was observed even after increasing the pressure to 15 kilograms. This can’t be possible!
The handling procedures vary depending on the medium used in the sealing test; if gas is used as the testing medium, such a phenomenon should be considered a failure. If it is a liquid, it is qualified. Because once a gas medium leaks, it is not possible to ensure a steady increase in pressure.
Keep the valve in a semi-open position. Seal both ends of the ball with flange covers equipped with pipe fittings. Introduce the test medium at one end; the test medium is clean nitrogen or air. The other end fitting is blocked. Gradually increase the pressure to 5.6 bar, then close the intake valve to stop air intake. (Turn the ball several times and then close the ball valve (operate the actuator)); open the plug of the pipe fitting on the other end (the end that is not used for introducing the test gas) to reduce the pressure in that chamber to atmospheric pressure. At the test pressure (5.6 bar), the pressure in the intake chamber must not drop over a period of more than 5 minutes. The pressure gauge to be used should be of grade 0.4 with a range of 10 bar. At the same time, use soapy water to check for external leaks at all connection flanges and gasket areas; no bubbles that keep appearing should be present. Then, the test medium is introduced from the other end, and the above experiment is repeated. After passing the test, blow away any remaining soapy water using compressed air. Remove the flange covers at both ends, and clean away any residual seal material from the sealing surfaces at those ends of the ball valve. If any residue remains inside the valve bore, it must be removed and the area cleaned thoroughly.
Dear experts, what are double-sealed ball valves like? What are their characteristics? Could you provide a detailed introduction? Thank you!
Open the valve, clean the sealing surface, and do it again to see if the problem you mentioned will occur again It’s unlikely to happen.