Closing the head budget: total dynamic head (static + friction + minor + equipment + residual), the hydraulic grade line, and a worked, line-by-line head budget that sets the pump duty.
The pressure-drop budget is where everything reconciles. Every metre of static lift, every length of friction, every fitting K and every piece of equipment back-pressure is added up from inlet to outlet so the selected pump delivers the design flow at every operating point — not just on paper. A closed, honest head budget is the single document that proves the hydraulics work; a missing line item is how plants end up flow-starved on commissioning day.
The pump must supply the total dynamic head (TDH) — the sum of every demand on the route:
Hstatic = elevation + pressure differenceΣhf = straight-pipe friction (Darcy–Weisbach)Σhm = minor (fitting/valve) losses (ΣK·v²/2g)Σhequip = equipment drops (filters, membranes, heat exchangers, instruments)Hresidual = required delivery pressure at the outletPlotting the running head against distance gives the hydraulic grade line (HGL) — it must stay above the pipe profile everywhere, or the line goes sub-atmospheric and risks air ingress, column separation and collapse.
| Line item | Head (m) | Basis |
|---|---|---|
| Static lift (suction → delivery) | 12.0 | Elevation survey |
| Straight-pipe friction (250 m, DN200) | 1.6 | Darcy–Weisbach |
| Fittings & valves (ΣK) | 1.1 | K·v²/2g |
| Cartridge filter | 3.0 | Vendor curve (clean→dirty) |
| Control valve (authority) | 6.0 | 0.6 bar allocated |
| Residual delivery pressure | 10.0 | Process requirement |
| Total dynamic head | 33.7 | Pump duty at 40 L/s |
The pump is selected for 40 L/s @ 33.7 m, then re-checked at minimum and peak flow (friction and filter drop scale with Q² and fouling). A fouled-filter allowance and a margin keep the duty point inside the BEP window across the envelope.
Quantify each friction and fitting line item that feeds the budget.
Reynolds & Bauhm sizes pipework, pumps and valves and closes the head budget as part of a gated, fully documented bespoke design — every figure traceable from flow to fabrication.
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