Blower Sizing
Estimate brake horsepower and the next NEMA motor for a low-pressure blower from airflow and differential pressure.
BHP ≈ (CFM·ΔP)/(229·η) with ΔP in psi (in wg ÷ 27.68). This isothermal estimate ignores heat of compression, for ΔP above ~1 psi (≈28 in wg) confirm adiabatic head and discharge temperature with the blower curve.
Pump-Down Time
Estimate the time a mechanical vacuum pump needs to draw a closed volume from start pressure to a target vacuum.
Target is in the rough-vacuum band (>1 torr), a single mechanical pump and the V/S·ln(P1/P2) estimate apply.
t = (V/S)·ln(P1/P2), the ideal volumetric model. It assumes constant pumping speed and a leak-free, dry system, real pump-down is longer once outgassing, conductance, and reduced speed near base pressure take over. Treat the result as a floor.
Motor Wire Sizer
Size branch-circuit conductors and inverse-time breaker for a motor from horsepower and voltage using NEC 430 full-load amps.
Conductor is sized at 125% of motor FLA and protection per NEC 430. Verify termination temperature rating and voltage drop on long runs.
Conductor at 125% of motor FLA (NEC 430.22) on 75°C copper ampacity (310.16); inverse-time breaker up to 250% of FLA (430.52), rounded up to a standard rating (240.6). Apply ambient/fill derating and check voltage drop on long runs.