NFPA 20 Check Valves in Sensing Line
NFPA 20 Check Valves in Sensing Line
(OP)
Guys,
Any reason why NFPA requires 2 check valve in the pressure sensing line and why is it require to be separated by 1.50meters.
Thanks!
Any reason why NFPA requires 2 check valve in the pressure sensing line and why is it require to be separated by 1.50meters.
Thanks!





RE: NFPA 20 Check Valves in Sensing Line
The purpose for (2) checks is to dampen the pressure surge through the sensing line. The pressure surge will hit the first orifice, slow down significantly (we are talking a 3/32" hole), lose pressure from friction through the 5' of pipe, hit the second orifice, reduce again and be at a manageable pressure when it gets to the transducer. The 5' between the checks is likely not an exact science, but deemed acceptable enough to be an across-the-board requirement for all NFPA 20 fire pump installations.
Also, check valves aren't the only way to do it. NFPA 20-2010 4.30.4.2 states "Where the water is clean, ground-face unions with non corrosive diaphragms drilled with a nominal 0.09375" orifice shall be permitted in place of the check valves.
RE: NFPA 20 Check Valves in Sensing Line