How this is calculated: friction loss uses the Darcy-Weisbach equation (velocity, Reynolds number, and a laminar or turbulent friction factor at the viscosity and temperature you entered), with the inlet, strainer and each 45°/90° fitting added by the K-factor method. That loss is then converted to feet of your fluid and subtracted from the available suction head: NPSH available = atmospheric head (at your altitude) − vapor pressure head − static lift − friction loss. A size passes only if it clears the assumed pump NPSH requirement with margin and stays under the recommended suction velocity for that fluid's viscosity.

Suction sizing is less forgiving than discharge sizing — a hose that is one size too small cavitates the pump rather than merely running slow. This estimate assumes a typical small transfer pump's NPSH requirement (5 ft) since that figure isn't something most customers have on hand; if you know your pump's actual NPSH-required curve, contact us and we'll confirm sizing against it directly. This estimate covers the inlet, the 45°/90° fittings you entered, and straight hose. Valves, quick couplers, tees, collapsed or kinked hose, and air leaks are not modeled. Hot or water-contaminated oil (common with UCO/WVO) flashes at a far lower temperature than the vapor pressure model here assumes — size up and keep the lift short in that case.