Loss of efficiency due to recirculation

Balance holes may be drilled in the blade wheel to reduce the loading caused by this effect. This has the effect of increaseing the amount of recirculation, introduces a stress raiser and increases windage losses. To try to elleviate soem of this the bore is carefully radiused and polished
A certain amount of reaction is put on the blade by casuing a pressure drop across the blade to equal that caused by the eduction effect-approxiamtely 10% ( Degree of reaction = Enthalpy drop over blade/enthalpy drop over stage)