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Leakage valve refers to flow through a valve that is set to 'off'.
The importance of valve leakage depends on what controls the valve. For example, a dripping faucet is less significant than a leak from a six-inch tube carrying high-pressure radioactive vapor.
In the United States, the American National Standards Institute assigns six different leakage classes, with "leakage" defined in terms of full open valve capacity:
- Class I valve, or 'dust-tight', is meant to work but has not been tested
- The Class II valve has a leak of no more than 0.5% with a pressure of 50psi (or less if operating less) at the operating temperature
- Class III valves do not have more than 0.1% leakage under those conditions; this may require a soft valve seat, or a grounded metal surface
- The Class IV valve has no leakage of more than 0.01% under such conditions; this tends to require some graphite piston rings or a single Teflon piston ring, and a winding metal seat.
- The Class V valve leaks less than 5 * 10 ^ -12 cubic meters, per second, per bar pressure differential, per millimeter of port diameter, water when tested at service pressure.
Class VI valves are slightly different because they are needed (at 50psi pressure or operation, which is less) to have less leakage rate in milliliters per minute:
Video Valve leakage
References
- "Control Valve Leak Classification" (PDF) . SFV Flow Controls, Inc . Retrieved March 15, 2012 .
Source of the article : Wikipedia
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