Impeller Diffuser, Multi-Stage (from Internet Glossary of Pumps)
Impeller-Diffuser, Multi-Stage
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.

Above photos of Grundfos multistage pump by the author.

Vertical multistage pump drawings courtesy Afton Pumps.

(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.)

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Last modified February, 2002
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