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The Practical Pumping Handbook ........................................ -~ _ ::: ;~:-iiiiiiiiiiii~ii~iiiiiiiiiiiiiilu~L;~---=~

thus permitting the suction source to be emptied to a theoretical zero
NPSH available.
Many of these pumps use a solid shaft motor with the coupling located
in the discharge head assembly above the stuffing box. Frequently the
pump will also be supplied with the thrust bearing in the same area,
although this increases the total height of the installation which could
aggravate vibration problems.

These vertical can pumps can be modified to handle temperature
sensitive liquids. For example, sulfur can be handled by jacketing the
entire length of the pump and using steam or hot oil in the jacket. In
addition, heat transfer fluid pumps can be built to withstand the forces
caused by temperature variations and pipe strain. The bowls and
impellers in these pumps are usually made out of 300 series stainless
steel.
The typical vertical turbine pump is made to order and consists of three
major components; the Bowl Assembly which uses a variety of standard
parts, the Column and the Discharge Head. In view of this, a high level
of communication is essential between the end user and supplier to
ensure that the best equipment is selected and supplied for the
application.

9.2.1 Vertical pump bowl assembly
The Bowl Assembly consists of the impeller and the bowl. As in the
horizontal pumps, the impellers can cover the entire spectrum of
specific speed as discussed in Chapter 1.4.1. Most commonly used in
the larger vertical pumps however, are the mixed flow or axial flow
designs. As these styles usually develop relatively low heads, the use of
multistage pumps is common where higher pressures are required.
These impellers are all keyed to a common shaft or secured by means of
tapered colletts.
The pump bowl contains the axial diffuser vanes to direct the flow of
liquid from one impeller to the next or into the pump column. They
also convert the velocity energy as it is leaving one impeller, to the
pressure energy at the inlet of the next impeller. These bowls can be
either flanged or screwed together, depending on the particular pump
design. The bowls also contain the sleeve bearings which act
predominantly as guide bushings only, as the axial diffuser design
minimizes radial thrust from the impellers.
In the larger pumps the inlet to the bowl assembly is fitted with a
suction bell which provides a smooth flow transition into the first stage
from an open pit type of application. This also applies to those pumps
used as main intake pumps from a well screened sump. Other designs
include a suction casing fitted with a suction strainer or with a longer