Multi-stage impeller pumps have substantially increased heads over single-impeller
types. In the model shown, there are five rotating impellers in sequence,
with the intake from the lower hole on the left and the outlet at the lower right.
The upper two holes connect to the lower holes, balancing intake and outlet pressures
on the shaft.
The liquid swirls (not shown here) with the rotation of the pump. As many as 12
separate impellers are often connected together to increase flow rates and head.
In many models the fluid enters at either end and works towards the middle,
or enters one end and immediately after the first impeller, is sent to the opposite
end to the second impeller, then back to the first end, and so on, exiting in
the middle.
The advantages of such a system are improved pressure balance
on the shaft and relatively low pressure around the seals. On the pump shown the
right-hand seal has the pressure of four stages pushing against it.
(This is a still representation and possibly also a low-resolution
image of a pump which is fully animated in the CD-ROM version of this glossary.)
