Centrifugal Pumps are the most popular and commonly used type of pump for the transfer of fluids. In simple words, it is a pump that uses a rotating impeller to move water or other fluids by using centrifugal force. These are the undisputed pump choice especially for delivering liquid from one location to another in numerous industries including agriculture, municipal (water and wastewater plants), industrial, power generation plants, petroleum, mining, chemical, pharmaceutical, and many others.
Centrifugal Pumps are useful since they can generally handle large quantities of fluids, provide very high flow rates (which may vary with the changes in the Total Dynamic Head (TDH) of the particular piping system) and have the ability to adjust their flow rates over a wide range.
Centrifugal pumps are generally designed and suitable for liquids with a relatively low viscosity that pours like water or light oil. More viscous liquids such as 10 or 20 wt. oils at 68-70 deg F will require additional horsepower for centrifugal pumps to work. For viscous liquids of more than 30 wt. oils, positive displacement pumps are preferred over centrifugal pumps to help lower energy costs.The following information shall help you to understand more about these pumps and enable you to select the best kind of pump for your operations.
Applications of Centrifugal Pumps
The fact that centrifugal pumps are the most popular choice for fluid movement makes them a strong contender for many applications and as mentioned previously, they are used across numerous industries. Supplying water, boosting pressure, pumping water for domestic requirements, assisting fire protection systems, hot water circulation, sewage drainage and regulating boiler water are among the most common applications. Outlined below are some of the major sectors that make use of these pumps:
Oil & Energy - pumping crude oil, slurry, mud; used by refineries, power generation plants
Industrial & Fire Protection Industry - Heating and ventilation, boiler feed applications, air conditioning, pressure boosting, fire protection sprinkler systems.
Waste Management, Agriculture & Manufacturing - Wastewater processing plants, municipal industry, drainage, gas processing, irrigation, and flood protection
Pharmaceutical, Chemical & Food Industries - paints, hydrocarbons, petrochemical, cellulose, sugar refining, food and beverage production Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production, Aerospace etc.) - for the purposes of cryogenics and refrigerants.
Types of centrifugal pumps
Centrifugal pumps can be classified into several types depending on factors such as design, construction, application, service, compliance with a national or industry standard, etc. Therefore, one specific pump can belong to different groups and at times pump is known by its description itself. Some of these groups have been highlighted below:
Depending on the number of impellers in the pump, pumps can be classified as per the following:
– A one impeller pump, single stage pump has a simple design and easy maintenance. Ideal for large flow rates and low-pressure installations. They are commonly used in pumping services of high flow and low to moderate TDH (Total Dynamic Head).
– This type of pump has two impellers operating side by side which are used for medium head applications.
– pump has three or more impellers in series; for high head service.
What is Pump Head? In simple words, the pump head is pressure defined as the height to which the pump can raise the fluid to. It is important as it evaluates a pump’s capacity to do its job. The most important specifications of a pump are its capabilities regarding flow and pressure.
Type of case-split
The Orientation of case-split is another factor used to categorize Centrifugal pumps:
Axial split – In these kinds of pumps, the volute casing is split axially and the split line at which the pump casing separates is at the shaft’s center-line. Axial Split Pumps are typically mounted horizontally due to ease in installation and maintenance.
Radial split – Here, the pump case is split radially; the volute casing split is perpendicular to the shaft center-line.
Categorized by type of impeller design
– This kind of pump has a single suction impeller that allows fluid to enter the blades only through one side; It has a simple design but impeller has a higher axial thrust imbalance due to flow coming in on one side of impeller only.Double suction – This particular type of pump comes with a double suction impeller that allows fluid to enter from both sides of the blades and has lower NPSHR than a single suction impeller. Split-case pumps are the most common type of pump with a double suction impeller.
If a pump has more than one impeller, the design of the first stage impeller will determine if the pump is of a single or double suction type.
On the basis compliance with industry standards
While choosing a centrifugal pump, the buyers should be selective based on the quality standards they have to achieve. They need to check for the following:
– (American National Standards Institute) - ANSI standards refer to dimensional standards. The pumps are also required to meet ANSI B73.1 standards, also known as ASME B73.1 – (American Society of Mechanical Engineers). The objective of this standard is to ensure interchangeability of ANSI process pumps of similar sizes. These centrifugal pumps are horizontal, end suction, single stage pumps and are comparable regardless of manufacturer.
– (American Petroleum Institute) API’s standard refers to the parameters of pump’s construction, design, and ability to handle high temperatures and pressures. API 610 specifications and a variety of API types include API VS4, API VS7, API OH3, API OH2, API OH1, API BB1, API BB2, API BB3 etc. Centrifugal pumps must meet the requirements of the American Petroleum Institute Standard 610 for General Refinery Service.
– DIN 24256 specifications. Centrifugal pumps satisfying these standards are used in installations requiring large flow rates, abnormally high working pressures or very high temperatures. Rarely used in mechanical building services.
ISO pump – ISO 2858, 5199 specifications, the international standard ISO 5199 specifies the requirements for class II end suction centrifugal pumps of single-stage, multistage, horizontal or vertical construction, with any drive and any installation for general application.
– ASME (American Society of Mechanical Engineers) specifications
By type of volute
Centrifugal pumps can also be categorized based on volute namely Single volute and Double volute:
– This kind of pump Is usually used in small low capacity pumps where a double volute design is impractical due to a relatively small size of the volute passageway which makes obtaining good quality commercial casting difficult. Pumps with single volute design have higher radial loads.
– This kind of pump volute has two partial volutes which are located 180 degrees apart resulting in balanced radial loads; most centrifugal pumps are of double volute design.
Depending on where the bearing support is
Bearing support is also often used to categorize Centrifugal Pump:
– where the impeller is mounted on the end of a shaft, supported by bearings on only one side. Further, the overhung pump type has a horizontal orientation of shaft or can be vertical in-line with bearing bracket.
where the impeller is mounted on a shaft that has bearing support on both ends, thus impeller is located in between-bearings. Examples are Axial Split Vertical Split Case
Depending on shaft orientation
Shaft orientation is another characteristic which distinguishes the type of Centrifugal pump:
– These are pumps with the shaft the in horizontal plane; popular due to ease of servicing and maintenance. It is sometimes overhung or placed between bearing design.
– Vertical centrifugal pumps have their shaft in the vertical plane. They utilize a unique shaft and bearing support configuration that allows the volute to hang in the sump while the bearings are outside the sump. it is generally an overhung and of radial-split case type design.
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