Water Pumps

How Centrifugal Pumps Work

A centrifugal pump uses a rotating impeller to add velocity to water. The casing then converts part of that velocity into usable pressure.

Operating principle

How a Centrifugal Pump Moves Water

Labeled centrifugal-pump operating diagram showing suction, the impeller eye and impeller, the volute casing, increasing pressure, and discharge flow.

Typical centrifugal-pump operating principle. Actual configurations vary by pump type and application.

Key takeaways

What to Know

Scan the main ideas first. Open “Key points” only when you want the supporting details.

Swipe the cards to continue

01

Water Reaches the Suction Inlet

Before pumping can begin, the casing and suction line must contain water unless the selected pump is specifically self-priming. Atmospheric or supply pressure then moves water toward the lower-pressure region created at the impeller eye.

Key points 3
  • A short, adequately sized suction line helps reduce losses
  • Air leaks, blocked strainers, or insufficient inlet pressure can interrupt flow
  • The available inlet pressure must remain high enough to avoid cavitation
02

Water Enters the Impeller Eye

Water enters axially at the center of the rotating impeller. The eye is the low-radius entry area shown in the diagram, where the liquid begins following the rotating vanes.

Key points 3
  • The impeller eye is the central inlet region of the rotating impeller
  • Water should reach the eye with as little swirl and air as practical
  • Restricted inlet conditions can reduce performance and increase cavitation risk
03

The Impeller Adds Velocity and Energy

As the vanes rotate, they guide water outward from the eye toward the impeller perimeter. The increasing radius and blade motion raise the liquid’s velocity and total energy.

Key points 2
  • Impeller diameter and rotational speed strongly influence the developed head
  • Vane geometry affects efficiency and the range of stable operation
04

The Volute Converts Velocity Into Pressure

Water leaving the impeller enters the expanding volute passage. The growing flow area slows part of the high-velocity water and converts part of that velocity energy into static pressure.

Key points 3
  • The volute collects flow around the impeller perimeter
  • Its expanding passage converts part of the water’s velocity into pressure
  • Casing geometry and operating point influence hydraulic efficiency and internal forces
05

Pressurized Water Leaves the Discharge

The collected flow exits through the discharge outlet and enters the connected pipe system. The actual operating flow occurs where the pump performance curve and the resistance of the complete system meet.

Key points 3
  • A partly closed discharge valve increases system resistance and reduces flow
  • A system with lower resistance generally allows more flow
  • Operation should remain within the manufacturer’s approved range