I'm curious where you heard this. Considering they are required to be listed there is practically no chance of failure when they are properly maintained and installed. In some instances, standpipes, their use is unavoidable.
On Thursday we received a call from a hospital because our competition was refilling a system and the PRV would not set. Additionally the PRV assembly was not installed per code so there was no bypass. At the end of the day there was something caught in the valve so flushing it fixed the problem. But the hospital and the competition had a very long frustrating night. So yes, they do fail. Install per code in case they do. (Two in parallel with control valves).
Sorry, that's not a failure A failure would be that if fails to regulate pressure.
Pressure reducing valves or other mechanical appurtenances which are subject to mechanical failure are prohibited in main suction supplies to fire pumps.
Since the code dictates a flow rate of 500 gpm at 100 psig residual at the hydraulically most remote standpipe, while flowing 250 gpm at 65 psig at all other standpipes, up to a maximum of 1,000 gpm for hydraulically calculated sprinkler systems in light hazard occupancies, the result is that all the fire hose connections between the hydraulically most remote standpipe requires a pressure restrictor to limit the residual pressure at 100 psig max. .
...for 1-1/2" outlets, correct?
PRV valves do fail in both the open and shut position. Most manufactures recommend a minor rebuild (rubber parts replacement) every 3 years for diaphragm style valves. For this reason if valves are to be installed to regulate a stand pipe system its best if there is a control valve on both sides of the PRV so the rebuild can be a smooth process.
If there is no bypass, what is the use of the downstream valve?
Recommend to identify the residual pressure to maintain below the maximum test pressure of the components and accordingly you may be able to calculate pressure loss on height of the building and pressure loss on friction of the components where you may be able find the height in relation the above and thereafter having another mechanical room where you can position another pump set with water tank.
In that way, you may be able to maintain the pressure requirement of Standpie system as er NFPA 14.without using PRVs.
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