Could some one explain what is meant by a bubble tight valve? How is the test done for bubble tightness?We used to test critical valves used for equipment isolation by putting pressure on the upstream side (normal operating pressure) and checking for leakage through the valve. We'd essentially do a hydrotest on the upstream valve and check for leakage past the seat.If you want to use compressed gas, you can put a flange with a connection going into a water filled tube so you can check for bubbles showing leakage is occuring (I'm not crazy about using compressed gas for high pressures).I am not familiar with a test procedure or standard which defines "bubble-tight". ANSI/FCI 70.2 provides testing and leakage rates for control valves, but the tightest valve, Class VI has an allowable leakage rate. It must be a mutually defined and accepted criteria between vendor and customer. If anyone knows otherwise, I'd also be interested.

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