Page 87 - Root Cause Failure Analysis

78 Root Cause Failure Analysis
In relatively small, general-purpose pumps, the impellers normally are designed to
provide radial flow and the choices are limited to either an enclosed or open design.

Enclosed impellers are cast with the vanes fully encased between two disks. This type
of impeller generally is used for clean, solid-free liquids. It has a much higher effi-
ciency than the open design.

Open impellers have only one disk and the opposite side of the vanes is open to the
liquid. Because of its lower efficiency, this design is limited to applications where
slurries or solids are an integral part of the liquid.

Impeller Orientation
In single-stage centrifugal pumps, impeller orientation is fixed and not a factor in
pump performance. However, it must be carefully considered in multistage pumps,
which are available in two configurations: in-line and opposed. These configurations
are illustrated in Figure 7-1.

In-Line Configuration

<----
300psi

100
100 psi--) + psi

100 psid 100 Psid
Opposed Configuration

Figure 7-1 Impeller orientation of multhge cenhifugal pumps.