Pumps play a vital role in the ways our world functions today. Industrial pumps, for example, are a part of most manufacturing processes. Commercial pumps ensure that office buildings remain functional for businesses. Similarly, municipal pumps provide fresh water for our cities and clear wastewater from our drainage systems.
While pumps are available in several types, centrifugal pumps are the most common in operation today. These pumps find applications across a vast set of residential, commercial, municipal, and industrial processes. They are the ideal choice for meeting various pumping requirements owing to their wide range of capacity and head, high efficiency, design simplicity, smooth flow rate, and ease of operation and maintenance. Centrifugal pumps are also ideal for pumping lower viscosity (thin) liquids and in applications that demand high flow rates.
Although centrifugal pumps come in a variety of configurations, choosing the correct pump depends on several factors. Some of these include the pump's construction, its application, the fluid being pumped, fluid pressures and temperatures required, compliance, and service.
Types of Centrifugal Pumps
While the general principle behind how centrifugal pumps work is the same, they can be classified into more specific categories as follows:
Flow type
This category classifies pumps according to how the fluid flows through the pump. Pumps in this category include:
Radial Centrifugal Pumps
The fluid enters the suction line in radial flow pumps and takes a 90-degree turn to enter the first stage. The design of these pumps facilitates an outward motion flow, which speeds up with the use of impellers. The fluid entering the horizontal suction flange exits through a vertical discharge flange. As such, the discharge in radial centrifugal pumps is perpendicular to the pump shaft. Such a design helps in increasing the discharge pressure while keeping the fluid flow rate lower. Radial pumps are more common in the oil & gas industry.
Axial Centrifugal Pumps
The fluid flow in axial pumps is parallel to the pump shaft. These pumps produce flow from the propelling motion of the impeller vanes (via a lifting effect). Axial pumps are capable of handling a large amount of fluid while keeping the pressure head low. These pumps find applications in irrigation and dewatering systems, fluid circulation in power plants, and evaporators.
Number of Stages
This category classifies pumps on the number of stages a pump has. A stage determines the number of impellers within a centrifugal pump.
Single Stage
These pumps utilize a single impeller, which makes their design simple and easy to maintain. This design typically works best for low-pressure and large-flow-rate installations. For the most part, this pump services a low to moderate total dynamic head and high flow.
Multistage
As the name implies, this pump has multiple (two or more) impellers connected in series. Each stage increases the fluid pressure further to meet the desired outlet pressure head requirements. Evidently, multistage pumps are useful for applications requiring a high head at discharge. For example, these pumps are ideal for pumping boiler feed water, boosting water supply, irrigation, reverse osmosis, and fire fighting. For more info, see our post on multistage pumps explained.
Design Code
Many centrifugal pumps need to meet specific industry standards established by bodies such as the American National Standards Institute (ANSI) and American Petroleum Institute (API). There are also DIN, ISO, and ASME specifications for pumps used in nuclear applications.
ANSI
Regardless of the manufacturer, ANSI pumps are identical in interface and envelope to meet the dimensional standards set by ANSI. As a result, these pumps are also easy to interchange with similar-rated pumps. Ideal for low fluid flow rates, ANSI pumps are single-stage centrifugal pumps that find applications in process plants, food processing, textile industries, and manufacturing units.
API
While ANSI standards define the dimensional requirements, API emphasizes the design, construction, and structural integrity of the pumps. As a result, these pumps are usually preferred for heavy-duty applications and in handling toxic fluids. Industries that employ API pumps include oil and gas, petrochemical, and other processing units.
Shaft Orientation
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Centrifugal pumps can also be classified by shaft orientation:
Horizontal
In this type, a shaft is at a horizontal plane and includes a minimum of two or more impellers. They are widely used for pumping services due to their easy maintenance.
Vertical
Vertical centrifugal pumps are also known as cantilever pumps. These are usually installed where the available space is limited. Borewell pump and sump collection are some examples of this type.
Pump Casing
In some cases, it is useful to classify a pump based on their casing:
Number of Volutes
A volute is a space inside the pump casing with an increased area near the discharge point of the pump. A pump casing either consists of a single volute or a double volute. A single volute casing is simple in design consisting of a single cutwater to guide the flow out of the impeller. In comparison, double volute casings feature two cutwaters located 180-degrees from each other. This volute type balances the radial load acting on the impeller and allows equal pressure distribution in the volute.
Casing Design
A pump casing can be split open for maintenance in either a radial split or an axial split. This type of casing opens parallel to the impeller(s) and perpendicular to the shaft axis. In comparison, an axially split pump casing splices into two halves that get separated horizontally or parallel to the shaft axis.
Other Classifications
Pumps can also be classified on various other factors such as the number of suction lines it has, single or double. When the flow rate is very high, a single-suction pump will not be adequate; hence a double suction pump will be used. Even in a double suction pump, there is a single suction line, but the impeller design of these pumps lets fluid enter from both sides.
Common Applications of Centrifugal Pumps
Centrifugal pumps find applications in:
Need Help Finding The Right Centrifugal Pump?
The types and applications of centrifugal pumps are closely related to each other. Let our expert engineers assist you in choosing the correct pump based on the application, design, and other important parameters. Hayes is the oldest and largest pump distributor in the Northeast, offering the broadest line of pump products from over 20 different manufacturers. Get in touch with our engineers to select the right centrifugal pump for your unique application.