A pump with a rated capacity of 3,000 gpm (11,335 L/min) should have what size circulation relief valve?

NFPA 1901, Standard for Automotive Fire Apparatus, assigns minimum inside diameters for the pump-to-tank circulation (cooling) relief line in order to prevent pump overheating when water is not being discharged. Table 16.13.3 (2016 ed.) requires a 1.5 in. (38 mm) line — and therefore a relief valve of the same size — for pumps whose rated capacity is 2,251–3,000 gpm (11 335 L/min). A 3,000 gpm pump therefore must be equipped with a 1.5 in. circulation relief valve.

A. 0.5 in. line is only permitted for pumps ≤750 gpm; too small for 3,000 gpm.

B. 0.75 in. applies to 751–1,500 gpm pumps; inadequate for 3,000 gpm.

C. 1.0 in. is the minimum for 1,501–2,250 gpm pumps; still undersized here.

1. NFPA 1901: Standard for Automotive Fire Apparatus, 2016 Edition, Table 16.13.3 “Minimum Size of Pump-to-Tank Circulation Line”.

2. NFPA 1901: 2016, §16.13.2–16.13.4 (pp. 134–135) – requirements for automatic pump circulation relief valves and sizing criteria.