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Understanding centrifugal pump

In industry today, centrifugal pumps are one of the most commonly used types. It is used to transport fluid by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. This energy typically comes from an engine or electric motor.

Today you’ll get to know the definition, functions, applications, components, classifications, types, history, diagram, and how centrifugal pump works. You’ll also get to know the advantages and disadvantages as well as factors to be considered while selecting a centrifugal pump.

centrifugal pump

What is a centrifugal pump?

Just as mentioned in the introduction, a centrifugal pump is a mechanical device designed to move or transport fluid by the means of the transfer of rotational energy from one or more driven rotors known as impellers.

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Fluid enters the rotating impeller along its axis and it is cast out by centrifugal force along its circumference through the impeller’s vane tips. The effectiveness of the impeller increases the fluid’s velocity and pressure which also direct it toward the pump outlet.

In the design of a centrifugal pump, the casing is capable of constricting fluid from the pump inlet. It will direct it into the impeller and then slow and control the fluid before discharging.

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The first machine considered a centrifugal pump was designed for lifting mud. It appeared in early 1475 in a treatise by the Italian renaissance engineer. The true centrifugal pump was developed in the late 17th century when Denis Papin built one using straight vanes. In 1851 John Appold who was a British inventor introduced the curved vane version. This is a brief history of a centrifugal pump.

The function of a centrifugal pump is specified for higher flows and pumping of lower viscosity liquids. It does this down to 0.1 cP. in most chemical

Applications of centrifugal pump

In most chemical plants, 90% of pumps used are centrifugal pumps. Although there is a number of applications for which positive displacement pumps are preferred. Below are some applications of centrifugal pumps.

  1. Centrifugal pump is often used in oil and energy factories. It is used for pumping crude oil, slurry, mud, etc. it is also used by refineries, and power generation plants.
  2. The fire protection industry also makes good use of this pump in heating and ventilation, boiler feed applications. it is used in pressure boosting, and fire protection sprinkler systems.
  3. Applications of a centrifugal pump are vast in waste management, agriculture, and manufacturing. Wastewater processing plants, municipal industry, drainage, gas processing, irrigation, and flood protection.
  4. Pharmaceutical, chemical, and food industries also used this pump. It works on paints, hydrocarbons, petro-chemical, sugar refining, food and beverage production, cellulose.
  5. Finally, various industries including manufacturing, industrial, chemicals, pharmaceutical, food production, aerospace, etc. they make use of centrifugal pumps for the purpose of cryogenics and refrigerants.

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Major components of centrifugal pump

Below are the major components of a centrifugal pump.

Impeller

The diagram below shows a full diagram of different impellers including Open, Semi Enclosed, and Enclosed Impeller. It is a wheel or rotor that is designed with a series of backward curved blades or vanes. It is mounted on a shaft that is powered by an external source of energy. This external source imparts the liquid energy to the impeller which thereby makes it rotate.

impeller

Casing

The casing is another major part of a centrifugal pump. It is a pipe that is connected at the upper end to the inlet of the pump towards the center of the impeller. This part is also known as the eye. In double end reaction pump two suction pipe is connected to the eye from both sides. The liquid is lifted through the lower end as it’s dipped into it. This lower end is fitted into the foot valve and strainer. The three types of casing commonly used in centrifugal pumps are volute casing, vortex casing, and casing with guide blades.

Delivery Pipe

A delivery pipe is mounted at the lower end of the outlet of the pump. It delivers the liquid to the required height. There is a valve close to the outlet of the pump on the delivery pipe. This valve controls the flow from the pump into the delivery pipe.

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Suction Pipe with Foot Valve and Strainer

The suction pipe is connected with the inlet of the impeller while the other end is dipped into the source of liquid. At the end of the pipe, there is a foot valve and strainer. This foot valve is a one-way valve that opens in an upward direction. The strainer is used to filter the unwanted particles present in the liquid to prevent the centrifugal pump from blockage.

Centrifugal Pump Diagram:

diagram of centrifugal pump

Classifications and types of centrifugal pump

Below are the classifications of centrifugal pump and their types:

Classification based on a number of impellers in the pump:

  1. Single-stage pump
  2. Two-stage pump
  3. Multi-stage pump

Based on the orientation of case-split:

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  1. Axial split Pump
  2. Radial split Pump

Based on the type of impeller design

  1. Single suction Pump
  2. Double suction Pump

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Based on the type of volute

  1. Single volute Pump
  2. Double volute Pump

Based on where the bearing support

  1. Overhung
  2. Between-bearing

Based on shaft orientation

  1. Horizontal Pump
  2. Vertical Pump

Based on the basis compliance with industry standards

  1. ANSI pump – (American National Standards Institute)
  2. API pump – (American Petroleum Institute)
  3. DIN pump – DIN 24256 specifications
  4. ISO pump – ISO 2858, 5199 specifications
  5. Nuclear pump – ASME (American Society of Mechanical Engineers) specifications

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Working principle

Just as earlier mentioned, centrifugal pumps are used to induced flow or raise liquid from low to a high level. Its working is very simple and can be easily understood because it has a very simple mechanism. Centrifugal pump converts rotational energy that often got its power from the motor. This energy is then used to move the fluid.

There are two important parts in the centrifugal pump responsible for the conversion of energy. These parts are impeller and casing. The impeller was earlier explained as a rotating part of the pump and the airtight passage surrounding the impeller.

In the working of a centrifugal pump, fluid enters into the casing and then falls on the impeller blades. The fluid drops at the eye of the impeller. The impeller is powered whirled tangentially and radially outward until it leaves the impeller to the diffuser part of the casing. As the fluid passes through the impeller, it gains both pressure and velocity.

working of a centrifugal pump

Watch the video below to learn more on the working of centrifugal pump:

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Factors that can affect the performance of a centrifugal pump

The following are factors that can affect the performance of a centrifugal pump. These factors must be considered while selecting or choosing a centrifugal pump.

Working fluid viscosity:

This can be defined as resistance to shear when energy is applied. Generally, centrifugal pumps are suitable for low viscosity fluids because the pumping action creates high liquid shear.

Net Positive Suction Head (NPSH) and Cavitation:

The term NPSH refers to the pressure of a fluid on the suction side of a pump. This helps to determine if the pressure is high enough to avoid cavitation. Cavitation is the formation of bubbles or cavities in a liquid, which are developed in areas of relatively low pressure around an impeller. This can cause serious damage to the impeller and lead to decreased flow/pressure rates. The net positive suction head available (NPSHA) must be greater than the pump’s net positive suction head required (NPSHR).

Vapor pressure of the working fluid:

The word vapor pressure of the working fluid means the pressure at a given temperature. That is the pressure at which a fluid will change to a vapor. This must be determined so that cavitation must be avoided. Also, bearing damage is caused by dry running when the fluid has evaporated.

Operating temperature and pressure:

This is another factor to be considered in pumping operation. For example, high-temperature pumping may require special gaskets, seals, and mounting designs. Also, a properly designed pressure retaining casing may be needed for high-pressure conditions.

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Specific density and gravity of working fluid:

The density of a fluid is determined by its mass per unit of volume. So, a fluid’s mass per unit volume and gravity of a fluid is the ratio of a fluid’s density to the density of water. This directly affects the input power needed to pump a particular liquid. When a centrifugal pump is to be used with a fluid other than water, one must consider the specific density and gravity. This is because the weight directly affects the amount of work performed by the pump.

Advantages and disadvantages of centrifugal pump

Advantages:

Below are the benefits of centrifugal pumps in their various applications.

  • Centrifugal pumps work well with large volumes of fluid transfer – this is why it is often used for transferring water, chemicals, and light fuels. This is because a large amount is often transferred.
  • Simplicity in design, working, and mechanism. Centrifugal pump does not require valve and piston and their moving parts are minimal.
  • Centrifugal pumps are comparatively compact. with this concept, the pump doesn’t take a lot of space. I think this is one of reason centrifugal pump is widely used.

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Disadvantages:

Despite the great advantages of centrifugal pumps, some limitations still occur. below are the disadvantages of centrifugal pumps in their various applications.

  • The net positive suction head (NPSH) of the system is too low. This is known as cavitation.
  • Wearing of the impeller, which can be worsened by suspended solids.
  • Fluid properties can cause corrosion inside the pump.
  • A low flow rate will cause overheating.
  • Leakage along the rotating shaft.
  • Centrifugal pump must be filled with fluid to be a pump in order to operate; else lack of prime occurs.
  • Viscous fluid cannot be used
  • Surge
  • For a very high head application, a centrifugal pump is not suitable.

Conclusion

Centrifugal pump is a great pump that is widely used today, it offers a variety of advantages even though some limitation still shows up. However, the pump is still the best choice for pumping in various fields. it works using casing and impeller. In this article, we’ve examined the definition, applications, function, components, classifications, and types of centrifugal pumps. We’ve also examined the factors to be considered before choosing this pump. The advantages and disadvantages of the centrifugal pump were also discussed.

I hope you learned a lot from this post, if so, kindly share with other technical students. Thanks for reading! See you next time.

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