impeller

An impeller, or impellor, is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. Strictly speaking, propellers are a sub-class of impellers where the flow both enters and leaves axially, but in many contexts the term "impeller" is reserved for non-propeller rotors where the flow enters axially and leaves radially, especially when creating suction in a pump or compressor.

An impeller, or impellor, is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. Strictly speaking, propellers are a sub-class of impellers where the flow both enters and leaves axially, but in many contexts the term "impeller" is reserved for non-propeller rotors where the flow enters axially and leaves radially, especially when creating suction in a pump or compressor.

Open

An open impeller has a hub with attached vanes and is mounted on a shaft. The vanes do not have a wall, making open impellers slightly weaker than closed or semi-closed impellers. However, as the side plate is not fixed to the inlet side of the vane, the blade stresses are significantly lower. In pumps, the fluid enters the impeller's eye, where vanes add energy and direct it to the nozzle discharge. A close clearance between vanes and pump volute or back plate prevent most of fluid from flowing back. Wear on the bowl and edge of vane can be compensated by adjusting the clearance to maintain efficiency over time. Because the internal parts are visible, open impellers are easier to inspect for damage and maintain than closed impellers. They can also be more easily modified to change flow properties. Open impellers operate on a narrow range of specific speed. Open impellers are usually faster and easier to maintain. For small pumps and those dealing with suspended solids, open impellers are generally used. Sand locking does not occur as easily as with closed type.

Semi-closed

A semi-closed impeller has an additional back wall, giving it more strength. These impellers can pass mixed solid-liquid mixtures at the cost of reduced efficiency.

Closed or shrouded

The construction of closed impellers includes additional back and front walls on both sides of vanes that enhances its strength. This also reduces the thrust load on the shaft, increasing bearing life and reliability and reducing shafting cost. However, this more complicated design, including the use of additional wear rings, makes closed impellers more difficult to manufacture and more expensive than open impellers. A closed impeller's efficiency decreases as wear ring clearance increases with use. However, adjustment of impeller bowl clearance does not affect the wear on vanes as critically as open impeller. Closed impellers can be used on a wider range specific speed than open impellers. They are generally used in large pumps and clear water applications. These impellers can't perform effectively with solids and become difficult to clean if clogged.

Screw

The screw impeller design aligns more with an axial progressive channel that allows for solids to be openly handled when rotating.

See also

Axial fan design Bladelet (impeller) Centrifugal fan Rim-driven thruster Turbine

References

cs:Rotor

Text derived from https://en.wikipedia.org/w/index.php?oldid=1371500300 under CC BY-SA 4.0; modifications have been made.