Pump types and load curves

Pumps can be classified by their method of the fluid displacement. There are many classifications, one of them is presented in Fig. 1.

Fig.1. Pump classification.

There are two basic types of pumps: positive displacement and centrifugal (rotodynamic). Load curves (torque-speed characteristics) of these two types of pumps are different:

• Centrifugal pumps have quadratic load curve (QT) $T \sim n^2$ (Fig.2)
• Positive displacement pumps have constant load (CT) curve $T~const$ (Fig.3)

Fig.2. QT curve.

Fig.3. CT curve.

Quadratic loads are often approximately represented by assuming that the torque required is proportional to the square of the speed, giving rise to the terms square-law load.