Smooth-Bore Tip Diameter for a Target Flow
The tip (bore) diameter a target flow needs at a nozzle pressure.
Example
You enter
- Target flow (gpm) 250
- Nozzle pressure (psi) 50
You get
- Required tip / bore diameter 1.091 in
- Nozzle reaction at that tip 93 lb
Checked against published worked examples from: Fire Engineering (Paul Spurgeon).
Details, formula, and sources
Scoped = sqrt( gpm / (29.7 x sqrt(NP)) ). 250 gpm at 50 psi wants a 1.09 in tip (about 93 lb of reaction); round up to a stocked 1-1/8 in and it is about 99 lb. Answers 'what tip for this flow' instead of the flow from a set tip. Round to a stocked size; incident command and the pump operator govern.
Formula or tablebore_in = sqrt( target_gpm / (29.7 x sqrt(nozzle_pressure_psi)) ), the inverse of gpm = 29.7 x bore_in^2 x sqrt(NP); companion nozzle reaction = 1.57 x bore_in^2 x NP.
Source and editionIFSTA Pumping Apparatus Driver/Operator Handbook smooth-bore discharge form (by name), solved for the diameter; classical orifice discharge, no edition cycle.
Free accessThe discharge relation is public physics; standard nozzle pressures are 50 psi handline / 80 psi master. Incident command and the pump operator govern.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namestarget_gpm, nozzle_pressure_psi, bore_in, reaction_lb
- Discharge coefficient the 29.7 constant bundles the standard smooth-bore discharge coefficient and unit conversion; the tip must be a true smooth boreIFSTA
- Nozzle pressure default 50 psi handline / 80 psi master, editable to the tip in useIFSTA
- Estimate a discharge estimate; incident command governs the flow target and the pump operator sets engine pressureincident command