What is a centrifugal pump and where is it used

What is a centrifugal pump

A pump is a device that can convert the mechanical energy into hydraulic energy a centrifugal pump is a mechanical device that can move the liquid by using rotational energy and this energy is created with the help of impellers. A centrifugal pump is a non-positive displacement pump, the NPDP’s discharge reduces with the increase in pressure. So in this type of pump, the moving part would run at high speed and transfers its kinetic energy to the liquid and with this kinetic energy, the liquid will travel from the inlet to the outlet. So basically the operation of this pump is based on the principle of centrifugal force and this force will act on the liquid and by using the impeller this force is created.

What are the types of pump

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How does a centrifugal pump work

The energy for the rotation of the impeller will be received from an engine or a motor. The rotation of the impeller causes the liquid to enter the eye of the impeller to get impelled towards the outside diameter of the impeller. The impeller will rotate inside a casing, during the impeller rotation the liquid that is around the impeller will also rotate with it, and because of this centrifugal force is induced in the liquid and the liquid moves to the output. The casing would convert some of the kinetic energy into pressure in the casing a foot valve is also used to prevent the flow back of liquid in the reverse direction, the major function of the foot valve is to retain liquid in the suction pipe and casing.

What are the main parts of centrifugal pump and how centrifugal pumps are constructed

  • Casing
  • Impeller
  • Wear rings
  • Shaft & shaft sleeves
  • Volute

Casing

The casing in a centrifugal pump is the housing that covers the impeller, there are two types of casing they are circular casing and volute casing. The circular casing is for low head and high capacity and the volute casing is for high head and medium capacity.

Impeller

The major part of the centrifugal pump is the impeller it is the moving or rotating part the impeller consists of curved vanes and this impeller is mounted on a shaft that is connected to the shaft of an electric motor.

Impeller types

Closed type impeller – this type has two cover plates, one on either side of the vanes, this type of impeller is mostly used for clear and thin liquids

Semi-closed impeller – In this type, it has only one cover plate on any one side of the vanes and this type is suitable for liquids charged with some amounts of suspended solid particles

Open type impeller – this type has no cover plates and they are suitable for liquids with more amount of debris

Shaft & Shaft sleeves

The shaft sleeves are mostly used in a pump to protect the shaft from erosion and corrosion. This is commonly used as a stuffing box, leakage joints, and bearings. This device would also transmit the torques encountered when starting and during operation while supporting the impeller and other rotation parts.

Wear rings

The impeller and casing joint would be subjected to heavy wearing, so the wear ring will provide an easily renewable leakage joint between the impeller and the casing.

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What are the characteristics and functions of a centrifugal pump

  • This type of pump is a non-positive displacement pump
  • Flow variation is depended on pressure
  • NPSHR in centrifugal varies with the flow and it is determined by the pressure
  • Centrifugal pumps are efficient in high flow conditions
  • These pumps are commonly used to move liquid through a piping system

How can we reduce the cavitation in centrifugal pump

  • High speed can reduce the pressure below the vapor pressure and it can cause cavitation, so we must not run it in high speed
  • Cavitation can also happen because of high static suction head, which would reduce the pressure below the vapor pressure, in order to prevent it, mount the pump nearer to the water
  • Cavitation can also happen due to the leakage in the suction pipe, so we must seal the leakage in the suction pipe
  • Vortex formation can also cause cavitation it can be prevented by submerging the suction pipe inside the water
  • Length of the suction pipe can also cause cavitation, so we must keep the length as less as possible

Cavitation effects

  • Power loss can happen because of friction
  • Heat will generate because of friction
  • Efficiency will be reduced
  • Noise and vibration
  • Surface damage of vanes
  • Machine life will be reduced and regular maintenance will be needed

How to select a centrifugal pump

  • It must be selected according to the available net positive suction head(NPSH)
  • Required delivery head
  • Required rate of flow
  • Type of liquid to be pumped
  • According to the available power source
  • Speed vibration and permitted noise
  • Size of the pump
  • Size of the mating parts such as base, shaft, flange, etc

How to install a centrifugal pump

The pump must be located closer to water and it must be accessible for service and maintenance. The pipe must be aligned properly with the pump and the pipe should be independently supported. The pump unit must be properly anchored to the foundation. In order to connect the suction pipe to the pump inlet, an eccentric reducer should be used. Make sure that the suction pipe inlet is submerged and no valve must not be installed in the suction piping.

What is the priming of the centrifugal pump and why is it required

It is a process in which liquid will be filled into the casing and suction pipe in case if there is no liquid inside before starting the pump. If there is no liquid in the casing then the impeller won’t be able to transfer its kinetic energy to the liquid and the pump won’t be able to operate.

Priming can be done by adding water into the casing of the pump, or it can also be done by connecting the casing priming valve to other sources of liquid

Why the centrifugal pump is the most common fire pump

Centrifugal pumps are widely used and it is the chief pump in the class of kinetic pump. A centrifugal pump is a non-positive displacement pump and because of this, it has better running clearance than the positive displacement pump. This pump can run at high speed and won’t need much maintenance, these pumps are compact in design and it can also handle high flows.

What are the advantages of centrifugal pump

  • The discharge rate of this pump is steady and not pulsating
  • This pump is suitable for high flow rates
  • This pump is suitable for corrosive fluids or fluids that contain solids
  • This pump can also be used as a metering pump to a certain extent if the drive can be controlled
  • Its size is small when compared to other pumps with the same output
  • It can operate at high speed with less maintenance

What are the disadvantages of centrifugal pump

  • No vapor or air should not be allowed to accumulate in the pump
  • It cannot be used for high discharge pressures
  • The pump is less suited for low flow rates and accurate metering
  • Maintenance issue can be caused by close-fitting parts as parts wear out
  • It can develop cavitation

What are the applications of the centrifugal pump

  • Energy and oil – refineries, power plants
  • Building services – pressure boosting, heating installation, air conditioning
  • Chemical and process industries
  • Water engineering – boiler feed applications, irrigation, wastewater management
  • Textile and food industry
  • Agriculture industry
  • Steel industry