Pump types & load curves

Pumps can be classified by their method of the fluid displacement. Two overviews of pump types is presented in Fig. 1 and 4 (at the bottom of this page), though there are many alternative overviews and classifications.

Fig.1. Pump classification.¹

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 $T\sim n^2$ (Fig.2)
• Positive displacement pumps have constant load curve $T\sim const$ (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.

Fig.4. Pump types with illustrations.²

¹ (Source of the classification) ² (Source of the classification)