Foam Eductor Back-Pressure / Hose-Lay Limit
In-line eductor limit: max_back_pressure = 0.65 x inlet; max hose length = (0.65 x inlet - nozzle - 0.434 x elevation) / (C x (Q/100)^2) x 100. If the back-pressure exceeds ~65% of inlet the eductor stops drawing foam concentrate entirely (not less, none) while water keeps flowing. A planning aid, not incident command.
Formula and source
max_back_pressure = 0.65 x inlet_pressure; FL_per_100 = hose_coefficient x (eductor_flow / 100)^2; max_length = (max_back_pressure - nozzle_pressure - 0.434 x elevation) / FL_per_100 x 100 (0 if the budget is non-positive).
IFSTA / eductor manufacturer data (TFT/Elkhart) in-line foam eductor back-pressure limit, by name.
Audience
This tile is built for fire-ground and the adjacent professions in the Fire-Ground Engineering group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.