Relief valve required between two closed valves?
Relief valve required between two closed valves?
(OP)
Hi Everyone:
Someone once told me that ASME B&PV Code had an exception stating that UV stamped relief valves were NOT required if you are protecting against thermal releif or liquid expansion between two closed valves. Is this true?? Does B31.3 say anythign like this?
Thanks
Someone once told me that ASME B&PV Code had an exception stating that UV stamped relief valves were NOT required if you are protecting against thermal releif or liquid expansion between two closed valves. Is this true?? Does B31.3 say anythign like this?
Thanks





RE: Relief valve required between two closed valves?
A relief valve is needed going all the way back to the original steam engines in 1795: Continuous Additional Energy going in = more heat in the pipe = more steam (or water pressure = busted pipe, boiled off steam boiler = fire, flooding, feast (not!) and famine.
but note the difference: In an isolated pipe, the "extra" energy going in is going to come from what? Ambient energy into the pipe is going to be limited to solar heat on the pipe, room heat through the insulation from other nearby operating lines or burners, and not much else. If anything, your pipe is going to cool off, the liquid or gas or vapor inside cool down, possibly condense, and the new pressure actually become a vacuum until leakage builds up through the isolation valves. So a classic PRV can't (won't) protect your system against vacuum. And, if you have a vacuum relief valve, then you can't refill the system until that valve is isolated.
If leakage is the source of the pressure between the two valves, the only source of leakage is from the (otherwise isolated) operating system. Which is protected by the PRV's in the two operating loops against maximum operating pressure.
RE: Relief valve required between two closed valves?
RE: Relief valve required between two closed valves?
The extreme nature of your "liquid nitrogen heating to room temperature" problem (again) exceeds my experience in power plant systems, so (again) I will not guess. 8<)
RE: Relief valve required between two closed valves?
A.
RE: Relief valve required between two closed valves?
Years ago I worked on a Chlorine Plant and we had to install relief valves everyplace a section of line could be "Blocked in". I think the requirement for this came from the Chlorine Institute Standards.
prognosis: Lead or Lag
RE: Relief valve required between two closed valves?