Most premature pump failures trace back to one moment: the day someone guessed the duty point. Sizing well takes ten minutes and three numbers.
Start with flow, honestly
Use the real process requirement, not a comfort margin on top of a comfort margin. Oversized pumps run off-curve, cavitate and shake themselves to bits — the opposite of the safety the margin was meant to buy.
Calculate head, don’t estimate it
Static lift plus friction losses at design flow plus delivery pressure. Friction tables take minutes and remove the biggest source of error, especially on long or elderly pipe runs.
Respect NPSH
Compare what the installation makes available with what the pump requires at your flow — with margin. Hot media, suction lift and altitude all eat into it faster than intuition suggests.
Then look at the curve
Pick the pump whose best-efficiency point sits at or just right of your duty. If the numbers are unusual, send them to a manufacturer’s engineer — good ones will tell you when a smaller pump is the better answer.
