Research And Insight

# Pump curves

The efficiency curve shows the η (efficiency) of the pump. Efficiency is measured in %. All pumps have a ‘best point’ (ηmax), indicating where the pump is working most efficiently. The efficiency of the pump depends on the pump size and the quality of the construction/production. Small pumps normally have a lower efficiency than large pumps.

**The pump performance curve** shows the correlation between media flow (Q) and the pressure differential or head (H) that the pump creates.

The units for Q are normally [m^{3}/h] or [l/s]

The unit for H is normally [m]

H (head) can be recalculated to p (pressure) by using the following equation:

p = ρ x g x H [pa]

p = pressure [pa]

ρ = density [kg/m^{3}]

g = acceleration due to gravity [m/s^{2}]

H = head [m]

Flow is normally given in m^{3}/h or l/s. Pressure differential or head is given in kPa or mws (meter water column). For variable-speed pumps, the performance curve is given at minimum and maximum RPM.

When several pumps are connected, the final performance curve is achieved by combining the characteristics of the individual pumps.

Parallel-connected pumps are added horizontally to increase Q. For two identical pumps, the maximum Q will double, yet maximum H will be the same. This principle is commonly used in pump systems.

Series-connected pumps are added vertically to increase H. For two identical pumps, the maximum H will double. Maximum Q will remain the same. This principle is commonly used in multi-stage pumps.

The performance curve is used together with the system characteristics when dimensioning and selecting pumps.

Use the sizing tool to find a specific pump’s efficiency curve and performance curve.