What's an LRK?

If the valve is in gas service and you can show that from max operating pressure the gas can't create pressure bother than the valve design pressure die to temperature increase then no, I don't believe it needs a pressure relief. But liquid yes.

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Also: If you get a response it's polite to respond to it.

Cavity relief is a default requirement if trapping of fluid is required, UNLESS OTHERWISE AGREED. This does not care if it's liquid or gas, it's just that for liquid, it's faster for the trapped pressure to build up due to lack of compressibility.

Thus, the answer is NO, it's not always required, but it's highly desirable.

Luke | Valve Hax | https://valvehax.com/

Thanks guys. Hitokiri you are correct the 'unless otherwise agreed' clause exempts gas (as does the compressibility of gas as you would have to overpressure piping to overpressure valve cavity...) - classic vague code where they say fluid but gas is essentially always exempt.

Hitokiri, there are lots of issues we are experiencing associated with tubing (namely tubing relief commonly occuring and the valve becoming essentailly a DBB afterwards as pressure is required on both sides of the seat to hold and oftgen the tubing is being ran to the incorrect side; U/S vs. D/S confusion, tubing freezing, plugging, leaking etc.) so we are trying to avoid DIB-1 valves as they don't add any value in standard applications/operations when the relief tubing is either piped u/s or d/s..