This partial calculator applies an entered piston-area ratio and selected transfer multiplier to entered steam pressure, then converts the resulting selected water pressure to equivalent freshwater head. It does not predict an actual steam fire engine's flow, losses, power, capacity or safety.
Steam Fire Engine - Selected Pressure-Transfer Ledger
Explore entered pressure, selected piston-area ratio and transfer-factor arithmetic.
Equation Used
- Steam pressure, piston-area ratio and transfer multiplier are entered values.
- The area ratio is steam piston area divided by water piston area.
- The selected multiplier is not inferred from machine construction.
- Head is equivalent freshwater pressure head using 2.31 ft/psi.
- Flow, dynamics, thermodynamics, losses and safety are excluded.
The secondary figure is an abstract pressure-transfer ledger, not a steam fire engine design.
Selected pressure-transfer ledger
Ideal static pressure transfer is entered steam pressure times selected steam-to-water piston-area ratio. The selected output pressure multiplies that value by the entered transfer factor. Their difference is arithmetic reduction. Equivalent freshwater head uses 2.31 ft per psi.
What the calculator determines
Use it to inspect selected pressure, area-ratio and multiplier arithmetic. It cannot size or rate a pump or fire stream.
Selected relationships
P_ideal=P_s(A_s/A_w); P_selected=eta P_ideal; reduction=P_ideal-P_selected; freshwater head=2.31 P_selected.
Selected-input example
At 100 psi entered steam pressure, area ratio 1.00 and selected multiplier 95%, ideal transfer pressure is 100 psi, selected water pressure is 95 psi, arithmetic reduction is 5 psi and equivalent freshwater head is 219.45 ft.
Not a fire-engine performance model
Cycle timing, steam expansion, condensation, friction, leakage, valve losses, water flow, nozzle, hose, suction lift, cavitation, boiler capacity and safety are excluded.
Questions
Is the entered multiplier a measured efficiency?
Not unless the user supplies independently established data; it is only a selected arithmetic factor.
Is head a discharge height prediction?
No. It is pressure-equivalent freshwater head before dynamic losses.
Does this determine fire flow?
No. No flow-path or demand inputs are present.
Authoritative references
- U.S. Fire Administration, Water Supply Systems Volume II — gives h=2.31P for freshwater head in feet from psi.
- USGS pressure-transducer guide — tabulates pressure and freshwater-head conversion and notes density dependence.
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