Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)
9 by Erik B. Fiske BW/JP International, Inc. Pump Division Vertical Pumps This chapter discusses radially split bowl pumps that are typically mounted vertically. In older literature these pumps are often, but improperly, referred to as vertical turbine pumps. This pump type is unique in that designs with optimum efficiency can be obtained over the full specific speed range, normally with values from 1,500 to 15,000. In the upper specific speed range, the pumps are referred to as axial flow or propeller pumps. The impeller profile changes with the specific speed as shown in Figure 9-1. The hydraulic performance parameters, including efficiency, compare favorably with centrifugal pumps of the volute and diffuser type. However, except for highly specialized designs, vertical pumps are seldom used for high speed applications above 3,600 rpm. Vertical pumps can be designed mechanically for virtually any application and are the only suitable configurations for certain applications such as well pumping. They are commonly used for handling cryogenic liquids in the minus 200°F to minus 300°F range as well as for pumping molten metals above 1000°F. The radially split bowl design lends itself to safe, confined gasketing. For high pressure applications, typically above 1,0(30 psi discharge pressure, an outer pressure casing can be employed, similar to that which is used for double-case, horizontal pumps. Except for conventional well pumps, the mechanical design for the majority of vertical pumps is customized in accordance with the application requirements. This requires close cooperation between the pump manufacturer and the architect/engineers responsible for the pump mounting structure and system piping. 113
114 Centrifugal Pumps: Design and Application Figure 9-1. Specific speed and impeller profiles. Configurations There are three primary types of vertical pump configurations that are used for a broad range of applications. Well Pumps Designed to be installed in cased wells, these pumps consist of a multistage pumping element or bowl assembly installed at sufficient depth below the dynamic water level (the water level when the pump is operating) and with sufficient NPSH to preclude cavitation. The subject of NPSH is dealt with in detail Chapter 8. The bowl assembly, as illustrated in Figure 9-2, consists of a series of impellers mounted on a common shaft, and located inside diffuser bowls. The number of stages is determined by the height to which the liquid must be raised to the surface plus the design pressure required at the surface. The bowl assembly is suspended from a segmented column pipe mat directs the flow to the surface where the column pipe is attached to a discharge head. The column also houses the lineshaft with bearings for transmitting the torque from the driver to the bowl assembly. The discharge head, in addition to providing the required connection to the customer's piping, also serves as the base for the driver. The driver can either be a direct electric motor drive, typically of hollow shaft construction, see Figure 9-3, or a right angle gear drive powered by a horizontal engine or turbine. The discharge head must be supported on a foundation adequate to carry the water-filled weight of the pumping unit plus the driver weight. However, the hydraulic thrust developed by the pump impellers is not transmitted to the foundation.
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114 <strong>Centrifugal</strong> <strong>Pumps</strong>: <strong>Design</strong> <strong>and</strong> <strong>Application</strong><br />
Figure 9-1. Specific spe<strong>ed</strong> <strong>and</strong> impeller profiles.<br />
Configurations<br />
There are three primary types of vertical pump configurations that are<br />
us<strong>ed</strong> for a broad range of applications.<br />
Well <strong>Pumps</strong><br />
<strong>Design</strong><strong>ed</strong> to be install<strong>ed</strong> in cas<strong>ed</strong> wells, these pumps consist of a multistage<br />
pumping element or bowl assembly install<strong>ed</strong> at sufficient depth below<br />
the dynamic water level (the water level when the pump is operating)<br />
<strong>and</strong> with sufficient NPSH to preclude cavitation. The subject of NPSH is<br />
dealt with in detail Chapter 8. The bowl assembly, as illustrat<strong>ed</strong> in Figure<br />
9-2, consists of a series of impellers mount<strong>ed</strong> on a common shaft, <strong>and</strong><br />
locat<strong>ed</strong> inside diffuser bowls. The number of stages is determin<strong>ed</strong> by the<br />
height to which the liquid must be rais<strong>ed</strong> to the surface plus the design<br />
pressure requir<strong>ed</strong> at the surface. The bowl assembly is suspend<strong>ed</strong> from a<br />
segment<strong>ed</strong> column pipe mat directs the flow to the surface where the column<br />
pipe is attach<strong>ed</strong> to a discharge head. The column also houses the<br />
lineshaft with bearings for transmitting the torque from the driver to the<br />
bowl assembly. The discharge head, in addition to providing the requir<strong>ed</strong><br />
connection to the customer's piping, also serves as the base for the driver.<br />
The driver can either be a direct electric motor drive, typically of hollow<br />
shaft construction, see Figure 9-3, or a right angle gear drive power<strong>ed</strong> by<br />
a horizontal engine or turbine. The discharge head must be support<strong>ed</strong> on<br />
a foundation adequate to carry the water-fill<strong>ed</strong> weight of the pumping<br />
unit plus the driver weight. However, the hydraulic thrust develop<strong>ed</strong> by<br />
the pump impellers is not transmitt<strong>ed</strong> to the foundation.