Total pressure requirement
1. Fluid and boundaries
One steady liquid flow passes through every section in order. Enter actual inside diameters, including the bore used to define each fitting’s K.
Outlet pressure is gauge pressure at the selected outlet boundary. Required inlet pressure uses the same gauge reference. Reservoir boundaries have zero velocity. Add entrance and exit fitting losses explicitly (typically K = 0.5 and 1, respectively); choosing a reservoir does not add them.
2. Sections in flow order
For reservoir boundaries, include the elevation difference to the liquid surfaces in the section elevation changes. Positive elevation change rises in the direction of flow; negative falls. A diameter change’s irreversible loss is separate from static pressure recovery. Any reducer around a smaller fitting also needs its own loss entry.
3. Section breakdown
Method, assumptions and checks
ΔP required = Σ(pipe + fitting + equipment + transition losses) + ρgΣΔz + ½ρ(αout Vout² − αin Vin²). Required inlet gauge pressure = outlet gauge pressure + ΔP required. Head is ΔP required / (ρg). A negative result is preserved.
Pipe losses use the Darcy factor: ΔP = f(L/D)ρV²/2. Laminar f = 64/Re; turbulent f solves Colebrook; Re 2300–4000 uses a linear interpolation with a warning. Fitting loss = quantity × K × ρVfitting²/2. Each K must use the displayed fitting bore as its reference diameter. Fanning factors cannot be entered as Darcy factors.
The first section begins at the inlet boundary. Subsequent rows include the velocity change and reducer at their entrance, then their pipe, fittings, equipment and elevation. The final outlet boundary correction is shown separately. Intermediate kinetic energy terms telescope, so diameter changes are not counted twice. α defaults to 1; use appropriate coefficients for laminar or nonuniform flow.
Sudden expansion uses Borda–Carnot ΔP = ½ρ(Vup − Vdown)². Custom transition K uses the smaller bore’s velocity. No-loss transitions represent ideal recovery; real contractions need manufacturer or reference K. Equipment ΔP is the irreversible loss at the entered flow, not a pump rise or a value automatically scaled from another flow.
Typical fitting presets are screening estimates from EPA EPANET; geometry, opening and Reynolds number affect actual K. Prefer manufacturer data. No branches, compressible gas, two-phase flow, water hammer, pump curves, cavitation or NPSH calculation. Endpoint pressure does not prove safe minimum pressure at every local restriction.
Pipe schedules / inside diameters · Pipe roughness · K-factor guide · Darcy vs Fanning · Branched network solver
Sources: EPA EPANET and user manual (Darcy losses and typical fitting K); Princeton: Bernoulli equation (pressure, velocity and elevation balance).