Axial Thrust of Single-Suction Semiopen Radial-Flow Impellers
The axial thrust generated in semiopen impellers is higher than that in closed impellers. This is illustrated in Figure 58, which shows that the pressure on the open side of the impeller varies from essentially the discharge pressure at the periphery (at diameter D2) to the suction pressure at the impeller eye (at diameter D1). The pressure distribution on the back shroud is essentially the same as that illustrated in Figure 54, varying from discharge pressure at the periphery to some portion of this pressure at the impeller hub. This latter pressure is, of course, substantially higher than the suction pressure. The unbalanced portion of the axial thrust on the impeller is represented by the cross-hatched area in Figure 58.
Fully open impellers or semiopen impellers with a portion of the back shroud removed produce an axial thrust somewhat higher than closed impellers and somewhat lower than semiopen impellers.