Fire Hydrant and Hose Reel Systems
Hydrants, hose reels and water supply
Hydrant design is about available flow at a usable residual pressure, not static pressure alone. A flow test records static pressure, residual pressure and pitot flow; the results are extrapolated to a reference residual, commonly 20 psi (1.4 bar). Hydrant spacing, nozzle size, valve type and access determine whether the fire service can use the supply. Hose reels are first-aid appliances: they need a defined hose length, reel size, nozzle and minimum running pressure, and they must be positioned so the hose reaches the risk without passing through fire doors. Friction loss, elevation and hose diameter all reduce nozzle pressure.
Traps include using static pressure as the design pressure; applying a hydrant flow formula without correcting for the test residual; assuming a 30 m hose reel provides 30 m of horizontal reach; ignoring friction loss in small-bore hose; and sizing a pump from hydrant flow without checking the system curve.
Worked example: a hydrant flow test gives static 70 psi, residual 50 psi at 1000 gpm. Estimate flow at 20 psi: Q₂ = Q₁ × √[(Pstatic − 20) ÷ (Pstatic − Presidual)] = 1000 × √(50 ÷ 20) = 1000 × 1.58 = 1580 gpm. Use the result with the local utility data and a safety margin; do not treat it as a guaranteed supply.