Regenerative machines are those machines that can allow high heads at small flow rates and performance curves with very stable features. Unfortunately, the efficiency of regenerative blowers are not high, it is usually less than 50 %, thus this book aims to study the effect of inlet blade angle and blades number for improving efficiency by minimizing the losses as much as possible. An incidence loss is one of these losses that appears usually at the blade inlet regions. The increase of angle of attack (AOA) leads to the increase of the incidence loss (Shock loss). Since decreasing the effect of the shock losses and vortices could be obtained by changing the inlet blade angle and the blade numbers, the present work focuses on the study of the effect of inlet blade angles of (90 , 115 , 125 and 135 ), and blades numbers of (21, 31, 41 and 51) on the performance of regenerative blower at different rotational speeds of (1000, 2000, and 3000 rpm). The investigations are carried out analytically using two different 1-D models, experimentally, and numerically by the CFD. sakriti opis