Brochure
2323
1.2.7 Return channel and outer sleeve
To increase the pressure rise over the pump, more impellers can be connect-
ed in series. The return channel leads the fluid from one impeller to the next,
see figure 1.22. An impeller and a return channel are either called a stage or
a chamber. The chambers in a multistage pump are altogether called the
chamber stack.
Besides leading the fluid from one impeller to the next, the return channel
has the same basic function as volute casing: To convert dynamic pressure
to static pressure. The return channel reduces unwanted rotation in the fluid
because such a rotation aects the performance of the subsequent impeller.
The rotation is controlled by guide vanes in the return channel.
In multistage inline pumps the fluid is lead from the top of the chamber
stack to the outlet in the channel formed by the outer part of the chamber
stack and the outer sleeve, see figure 1.22.
When designing a return channel, the same design considerations of impel-
ler and volute casing apply. Contrary to volute casing, a return channel does
not create radial forces on the impeller because it is axis-symmetric.
Figure 1.22: Hydraulic components in an
inline multistage pump.
Guide vane
Impeller blade
Return channel
Impeller
Annular
outlet
Outer
sleeve
Chamber
Chamber
stack