Impeller

An impeller is a rotor inside a tube or conduit to increase the pressure and flow of a fluid.

Impellers in pumps

An impeller is a rotating component of a centrifugal pump, usually made of iron, steel, aluminum or plastic, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid radially, and a splined center to accept a driveshaft.

Impellers in water jets

Some impellers are similar to small propellers but without the large blades. Among other uses, they are used in water jets to power high speed boats.

Since impellers have no large blades to turn, they can spin at much higher speeds than propellers. The water forced through the impeller is channelled by the housing, creating a water jet that propels the vessel forward. The housing is normally tapered into a nozzle to increase the speed of the water, which also creates a Venturi effect in which low pressure behind the impeller pulls more water towards the blades, tending to increase the speed.

To work efficiently, there must be a close fit between the impeller and the housing. The housing is normally fitted with a replaceable "wear ring" which tends to wear as sand or other particles are thrown against the housing side by the impeller.

Vessels using impellers are normally steered by changing the direction of the water jet.

Compare to propeller and jet aircraft engines.

Impellers in agitated tanks

Impellers in agitated tanks are used to mix fluids or slurry in the tank. This can be used to combine materials; solids, liquids, gas. Mixing the fluids in a tank is very important if there are gradients in conditions such as temperature or concentration.

Example: If one heats a pot of tomato soup on the stove the pot will develop a temperature gradient, (warmest on the bottom and cooler at the surface). Mild agitation will increase the rate of heating by dissipating the heat through the entire pot. See: Law of cooling (which also applies to heating). Severe agitation may however decrease the rate of heating.

Impellers in washing machines

Some constructions of top loading washing machines use impellers to agitate the laundry during washing.

Firefighting rank badge

Fire services in the United Kingdom and many countries of the Commonwealth use a stylized depiction of an impeller as a rank badge. Officers wear one or more on their epaulettes or the collar of their firefighting uniform as an equivalent to the "pips" worn by the army and police.