Concept reference

Pump Types for Water and Wastewater

C.1Plain-language definition

Pump type is a response to the liquid and duty. Clean-water machines can prioritise hydraulic efficiency and close passages; raw-sewage machines must pass solids or deliberately cut them. Centrifugal pumps trade head against flow along a curve, while positive-displacement machines move nearly fixed volume per cycle and demand different protection.

C.2Governing relation or decision logic

For any pump, useful hydraulic power is ρgQH. A centrifugal machine’s Q is set by its curve intersection; a positive-displacement machine’s flow is tied more directly to displacement and speed, with slip. A relief path is essential where a positive-displacement discharge can be blocked.

C.3The failure to name

“Non-clog” does not mean immune to wipes, stringy material or poor wet-well geometry. Selecting on peak duty alone can leave a pump cycling, ragging or operating far left of BEP at the common flow that dominates run hours.

C.4Field review checklist

• Describe liquid, solids size/shape, grit, gas, temperature and corrosivity.
• Map minimum, normal and peak flow-head duty plus expected run hours.
• Verify solids passage or cutting strategy with the actual hydraulic passage.
• Review access, lifting, seal arrangement, maintenance history and failure consequence.

C.5Where it fits in the course

§6.3 compares hydraulics and solids passage; §8.2 follows what arrives with sewage.