Centrifugal Pump

What Is a Centrifugal Pump

A centrifugal pump converts rotational energy from a motor into kinetic energy in a fluid, then into pressure energy. It does this through an impeller — a rotating set of vanes that accelerates the fluid outward, and a casing that collects the high-velocity fluid and decelerates it, converting velocity head into pressure head.

Centrifugal pumps dominate industrial fluid handling. They account for roughly 80% of all pumps in process plants, water systems, and power stations. Their popularity comes from simplicity, reliability, and the ability to handle large flow rates at moderate heads with relatively compact equipment. Designs range from small chemical-metering pumps handling a few liters per minute to massive cooling-water pumps moving tens of thousands of cubic meters per hour.

How a Centrifugal Pump Works

Fluid enters the pump through the suction nozzle into the eye of the impeller. The rotating impeller blades accelerate the fluid radially outward by centrifugal force. The fluid leaves the impeller at high velocity and enters the casing. In a volute casing, the gradually expanding spiral shape slows the fluid, converting velocity to pressure. In a diffuser (turbine) pump, stationary vanes around the impeller perform the same diffusion function.

The pressure increase across the pump — called total head — depends on the impeller diameter, rotational speed, and the number of stages. A single-stage pump produces one increment of head. Multistage pumps stack several impellers in series on a common shaft to achieve much higher discharge pressures.

Before a centrifugal pump can operate, the suction line and impeller eye must be filled with liquid — the pump must be primed. If air or vapor occupies the eye, the pump cannot generate enough centrifugal force to lift liquid. Some installations use a flooded suction (pump below the liquid source) to ensure priming; others rely on priming systems or self-priming pump designs.

Key Components

Impeller Types

Impeller vanes can be radial, backward-curved, or forward-curved. Backward-curved vanes are by far the most common in industrial pumps because they produce a non-overloading power characteristic — motor current peaks at the design point and falls off at higher flow, protecting the driver.

Casing Designs

• Volute: A single spiral-shaped casing that collects fluid around the impeller. Simple, cost-effective, and by far the most common design for single-stage pumps.
• Diffuser (Turbine): Stationary diffuser vanes surround the impeller. More efficient at the design point, but more expensive and sensitive to off-design operation. Common in multistage and vertical turbine pumps.
• Barrel (Can):