Pump power calculator

Hydraulic (useful) power is P_h = ρ·g·Q·H, where ρ is the fluid density, g gravity, Q the flow, and H the total head. In practical form, P_h [kW] = Q[m³/h]·H[m]·relative density / 367. Shaft power (what the motor must deliver) is higher: divide the hydraulic power by the pump efficiency. FB engineering checks both against the model curve at the duty point.

Hydraulic power is transferred to the liquid. Shaft power also accounts for pump losses and depends on efficiency at the duty point. The motor must meet required power and torque across the intended range. Motor rated power, efficiency and service factor are distinct information.

Efficiency is the ratio of hydraulic power to shaft power. Read the value on the model curve at the intended flow and speed. BEP identifies the maximum on that curve; selection must consider duty point and operating range, without assigning one percentage to the whole FBCN series.

Select the motor using the absorbed-power curve, starting torque, duty and installation conditions. Confirm margin and rated power against pump and motor manufacturer criteria. Do not treat service factor as a universal 10%, 15% or 25% addition to a calculation.

Check whether the document uses kW, metric CV or mechanical HP. Rounded NIST factors are 1 CV ≈ 0.735499 kW and 1 HP ≈ 0.745700 kW. To convert kW, use approximately 1.35962 CV or 1.34102 HP per kW. Record the unit alongside the value and verify power on the nameplate and curve.

Yes, directly. Hydraulic power is proportional to density: pumping a fluid denser than water (a brine, for example) requires more power for the same flow and head; a lighter oil requires less. That is why engineering asks for the water temperature (which sets the density) or the informed density for other fluids. Note: head in meters of column is already independent of density — what density scales is the energy per meter. According to the Hydraulic Institute, a specific gravity of 1.1 requires 10% more power than 1.0.

BHP (brake horsepower) is the power the pump shaft receives, expressed in hp. It adds the pump losses to the hydraulic power: BHP = hydraulic power ÷ efficiency. On the model curve, absorbed power varies with flow, so a BHP value applies to one duty point. In CV, BHP × 1.0139; in kW, BHP × 0.7457.

When the known value is pressure, as with positive displacement pumps, use P_h = Q × Δp. With Q in m³/h and Δp in kgf/cm², P_h [kW] = Q × Δp ÷ 36.71; with Δp in bar, ÷ 36. Example: 10 m³/h and 7 kgf/cm² give 10 × 7 ÷ 36.71 = 1.91 kW of hydraulic power. Shaft power is that value divided by the efficiency at the duty point, which engineering checks for the fluid and speed.