1.1 Types and nomenclature
Kinetic pumps may be classified by such methods as impeller or casing configuration, end application of the pump, specific speed or mechanical configuration. The method used in Figure (1.1), is based primarily on mechanical configuration.
This Standard is for centrifugal and regenerative turbine pumps of all industrial/commercial types except vertical single and multistage diffuser types. It includes types and nomenclature.
1.1.2 Definition of a centrifugal pump
A centrifugal pump is a kinetic machine converting mechanical energy into hydraulic energy through centrifugal activity.
1.1.3 Types of kinetic pumps
Centrifugal pumps are most commonly typed by their general mechanical configuration. The broadest characteristics, which include virtually all centrifugal pumps, are the following:
18.104.22.168 Overhung impeller type
In this group, the impeller (or impellers) is mounted on the end of a shaft that is cantilevered or "overhung" from its bearing supports.
These pumps are either close coupled, where the impeller is mounted directly on the driver shaft; or separately coupled, where the impeller is mounted on a separate pump shaft supported by its own bearing.
22.214.171.124 Impeller between bearing type
In this group, the impeller (or impellers) is mounted on a shaft with bearings at both ends. The impeller is mounted "between bearings."
These pumps are further separated as single stage and multistage configurations.
126.96.36.199 Regenerative turbine type
A low rate of flow, high head pump utilizing peripheral or side channel vanes or buckets on a rotating impeller to impart energy to the pumped liquid. The liquid travels in a helical pattern through the impeller vanes and accompanying flow passages, with the liquid pressure increasing uniformly through the passages from inlet port to outlet port.
188.8.131.52 Special variations
In addition to the mechanical configuration described previously, there are some special variations of pumps that are included in these general types but which stand separately because of some special characteristic. Examples of these are:
1. a) Sewage pumps with nonclog impellers;
2. b) Abrasive pumps which may be made of hard metals or may have rubber lining;
3. c) Heating circulating pumps which are fractional horsepower units for home heating systems;
4. d) Canned motor or magnetic drive pumps which do not require mechanical seals or packing.
1.1.4 Impeller designs
Impeller designs are grouped as either radial flow, mixed flow, or axial flow depending on their hydraulic geometry. These are further described as follows:
184.108.40.206 Specific speed
To understand impeller groupings better, a discussion of specific speed may be helpful.
Specific speed is a correlation of pump rate of flow, head, and speed at optimum efficiency, which classifies the pump impellers with respect to their geometric similarity.
Specific speed is a number usually expressed as:
NS = Pump specific speed;
n = Rotative speed in revolutions per minute;
Q = Rate of flow in m 3 /h (gpm) at optimum
H = Total head in meters (feet) per stage
The specific speed of an impeller is defined as the revolutions per minute at which a geometrically similar impeller would run if it were of such a size as to discharge one m3/hr (gpm) against one meter (foot) head.
Specific speed is indicative of the shape and characteristics of an impeller. It has been found that the ratios of major dimensions vary uniformly with specific speed. Specific speed is useful to the designer in predicting proportions required and to the application engineer in checking suction limitations of pumps. Proportions vary with specific speed as shown in Figure 1.2.
Pumps are traditionally divided into three types: radial flow, mixed flow, and axial flow. However, it can be seen from Figure 1.2 that there is a continuous change from the radial flow impeller, which develops pressure principally by the action of centrifugal force, to the axial flow impeller, which develops most of its head by the propelling or lifting action of the vanes on the liquid.
In the specific speed range of approximately 1200 to 7000 (1000 to 6000), double suction impellers are used as frequently as single suction impellers.
220.127.116.11 Suction specific speed
Suction specific speed is an index number for a centrifugal pump similar to discharge specific speed and is used to define its suction characteristic. See HI 1.3-2000 Section 18.104.22.168.15.
22.214.171.124 Radial flow
Pumps of this type with single inlet impellers usually have a specific speed below 4900 (4200), and with double suction impellers, a specific speed below 7000 (6000). In pumps of this type, the liquid enters the impeller at the hub and flows radially to the periphery (see Figure 1.3).
126.96.36.199 Francis vane
Radial flow impellers with double curvature of the vanes at the inlet.
188.8.131.52 Mixed flow
This type of pump has a single inlet impeller with the flow entering axially and discharging in an axial and radial direction. Pumps of this type usually have a specific speed from 4900 to 10,500 (4200 to 9000) (see Figure 1.4).
184.108.40.206 Axial flow
A pump of this type, sometimes called a propeller pump, has a single inlet impeller with the flow entering axially and discharging nearly axially. Pumps of this type usually have a specific speed above 10,500 (9000) (see Figure 1.5).