Backward inclined, backward curved blades
Backward inclined, backward curved blade is a highly efficient impeller design. Its employed to handle air and also used for gas medium containing lighter amounts of dust particles and at high temperatures. Reinforcements and surface hardening are done for extra strength, if required.
Backward inclined, flat blades
An efficient and strong shape, this design is a cost-effective alternative to the backward curved design but with flat blades instead of curved and radial tipped. This results in a slightly lower efficiency, compensated by handling moderate dust particles.
Backward inclined, forward curved blades
Mostly known as radial tipped blades, this design reduces the potential for dust build-up on the underside of the blades in applications with light or moderate amounts of gas-borne dust. Backward inclined, forward curved blade is an intermediate design for volume and pressure.
Backward inclined, aerofoil blades
Aerofoil bladed impellers are most commonly used in applications handling large volumes at low pressures. This highly efficient design of fan is used in clean air or with gases containing small amounts of erosive particles.
Blades running from hub to impeller tip without any curve or inclination essentially a large paddle wheel. This design results in a relatively inefficient fan with power consumption higher than that using the much more common backward inclined blade.Its mechanical strength and resistance to wear makes the fan to handle applications when high quantities of abrasive dust are present in the gas stream or when very high temperature in the gas is expected.
Single or double inlet
A double inlet impeller consists of two single inlet impellers back to back on the shaft may or may not sharing a common back plate, providing almost double the flow of a single inlet fan. The selection of a double inlet fan results in a smaller diameter, compact compared to two single inlet fans. Hence a centrifugal fan has a descriptive term as SISW (Single inlet single width) or DIDW (double inlet double width).
Single or multiple stages
A multi-stage fan consists of two or more impellers mounted on the same shaft. The air or gas flow passes through each one in turn, with a consequent increase in pressure.