Step 1
Delivery line
The hose or pipe carrying water from the site supply to the rack. Its inner diameter and length set how much pressure is lost to friction; the vertical lift sets how much is lost to elevation.
Step 2
Equipment on the rack
Add one row per type of equipment on the manifold — nozzle banks, oscillating wands, whatever's plumbed in. Name each row yourself; there's no fixed list and no limit on how many you add.
Why the minimum required pressure isn't a sum: equipment sharing one manifold is a parallel hydraulic circuit, not a series one. The manifold only has to clear the single highest per-unit minimum operating pressure among everything connected to it — adding a second nozzle's minimum pressure on top of the first would overstate what the supply actually needs to deliver. This calculator uses the maximum across rows for that figure, and sums only the flow rates, which really do add.
| Equipment | Qty | GPM / unit | Min. psi / unit | Remove |
|---|---|---|---|---|
Step 3
Site conditions
What's actually available at the hose bib or hydrant, plus an optional inline booster pump if the raw site pressure falls short.
Where the booster figures come from: small inline centrifugal booster pumps in the 1/2–1 HP class typically publish shutoff/low-flow heads in roughly the 45–100 ft range on their pump curves, which is about 20–43 psi (using the psi = ft ÷ 2.31 conversion below). This tool uses +20 psi for the 0.5 HP tier and +40 psi for the 1 HP tier as round, representative figures for that class of pump at low flow — not a lookup from any specific manufacturer's curve. Swap in a real pump curve for anything beyond a rough check.
Advanced Hazen-Williams roughness coefficient (C)
C describes how smooth the inside of the hose or pipe is — higher C means less friction for the same flow. 150 is a standard textbook value for new, smooth-wall PVC or rubber spray hose and is the default this calculator uses everywhere above. Older or rougher pipe runs lower; leave it at 150 unless you have a reason to change it.
Result
Flow, pressure, and pump sizing
Each figure below shows the formula it comes from, with your current inputs plugged in, so nothing here is a black box.
Total flow required
— GPM
Σ (quantity × GPM per unit), across every equipment row
Elevation head loss
— psi
0.433 × vertical lift (ft) — 1 ft of water column = 0.433 psi
Friction loss through hose
— psi
Hazen–Williams (US customary, psi form):
psiloss = 4.52 × L × Q1.852 ÷ (C1.852 × d4.8655)
L = hose length (ft), Q = flow (GPM), d = inner diameter (in), C = roughness coefficient. Standard form of the Hazen–Williams equation used throughout fire-protection and irrigation hydraulics.
Min. required equipment pressure
— psi
MAX(minimum operating psi), across every equipment row — not a sum. See the note in Step 2.
Total system pressure required
— psi
Min. equipment pressure + friction loss + elevation head loss
Available pressure = site pressure + booster boost, compared against total system pressure required above.
Pump sizing verification
If the rack needs its own pump rather than relying on site pressure, here's roughly what that pump has to be rated for to hit the total system pressure required above, at the total flow required above.
Total head
— ft
Total system pressure required (psi) × 2.31 — the psi-to-feet-of-water conversion (the reciprocal of the 0.433 used above; 1 ÷ 0.433 = 2.309…, conventionally rounded to 2.31 in pump-sizing references).
Hydraulic horsepower
— HP
(Total flow GPM × Total head ft) ÷ 3960 — the standard hydraulic-horsepower formula for water (specific gravity = 1); 3960 = 33,000 ft·lb/min per HP ÷ 8.33 lb/gal.
Estimated brake horsepower
— HP
Hydraulic HP ÷ 0.5 — a rough rule-of-thumb estimate assuming ~50% overall pump efficiency at this flow and head, not a real pump's published efficiency curve.