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Back Fins

Back fins, thrust fins or anti thrust vanes are often used on the rear of the impeller back plate.

Applicable only to single width fans they are used for 3 purposes.

1) To reduce the axial thrust and improve bearing life. (Centrix halves the calculated thrust when back fins are used).

2) To reduce dust build up on the back of the impeller.

3) To reduce gas or dust leakage through the casing seal.

Whilst it is possible to design back fins to eliminate axial thrust completely this can only be achieved at a single duty and through extensive testing. Using half the usual axial thrust provides a more conservative value to use in bearing life calculations.

Note : The use of back fins tends to increase the power absorbed and becomes more significant with narrow impellers. Centrix makes no power allowances when back fins are used.

If an estimate of back fin power is required the following is suggested.

1) Obtain the zero flow power from the performance curve.

2) Multiply this value by the back fin width and divide by the blade tip width.