M.S.E. – Baripada

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Dept. of Automobile Engineering

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4^th Semester, Summer - 2022

CENTRIFUGAL PUMP

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Prepared by :

Er. Sourin Mohanty

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Contents

1. INTRODUCTION
2. CONSTRUCTION
3. CLASSIFICATION
4. WORKING
5. HEADS LOSSES & EFFICIENCIES
6. ADVANTAGE & DISADVANTAGE
7. APPLICATION

INTRODUCTION

CONSTRUCTION

• Sump
• Strainer
• Foot valve
• Vanes
• Impeller
• Suction pipe
• Delivery pipe
• Casing
• Delivery valve

CLASSIFICATION

• According to working head
• According to casing
• According to number of entrances to the impeller
• According to types of impeller
• According to number of stages
• According to shape of the vanes
• According to disposition of shaft

• According to working head
• Low head centrifugal pump – working head developed by these pumps is up to 15m.
• Medium head centrifugal pump – working head developed by these system is 15m<H<45m.
• High head centrifugal pump – working head developed by these pumps is more than 45m.

According to casing

• Volute Casing
• In this casing, the impeller is surrounded by the spiral casing.
• The casing is such shaped that it’s c/s area gradually increases from tongue to delivery pipe.
• Due to impact of the high velocity water leaving the impeller (shock losses), efficiency of conversion of K.E. into P.E. is very less.

• Vortex Casing
• In this casing, an annular space known as vortex or whirlpool chamber is provided b/w the impeller and volute casing.
• Liquid from the impeller flow with free vortex motion in vortex chamber where it’s velocity is converted into pressure energy.
• It is more efficient than a volute casing.

• Diffuser Casing or Casing with guide vanes
• In this casing , the guide vanes are arranged at the outlet of the impeller.
• The guide vanes are shaped to provide gradually enlarged passage for flow of liquid.
• The kinetic energy of the liquid coming out from the impeller is converted into the pressure energy during flow in guide vanes (increasing area).

• According to number of entrances to the impeller
• Single suction pump

Liquid enters from a suction pipe to impeller only from one side.

• Double suction pump Liquid enters to both the sides of impeller.

• According to types of impeller
• Closed impeller

if the vanes of the impeller are covered with plates on both sides, it is called a closed impeller. It is made of cast iron, stainless steel, cast steel, gun metal.

• Semi open impeller

if the vanes of the impeller are covered with plate on one side, it is called semi open impeller. It has less number of vanes, but it’s height is more than that of closed impeller.

• Open impeller

If the vanes of the impeller are without covered plate, it is called open impeller. These are generally made of forged steel. It has less life, as they have to perform very rough task.

• According to number of stage
• Single stage

In a single stage pump, only one impeller is used on the shaft.

 Multi stage

In a multi stage pump, more than one impeller is used on the same shaft and enclosed in the same casing. It is used to raise high head.

• According to shape of the vanes
• Curved forward vanes

The outlet tip of the vane is curved forward in the direction of rotation of the impeller. The impeller having such vanes is called slow speed impeller. This type of the impeller has low efficiency about 75%.

• Radial vanes

These vanes have outlet tips in radial direction. The impeller having such vanes is called medium speed impeller. The efficiency of this type of impeller varies from 80% to 85%.

• Curved backward vanes

The outlet tip of the vane is curved backward in the direction of rotation of the impeller. The impeller having such vanes is called fast speed impeller. This type of impeller gives highest efficiency about 85% to 90%.

• According to disposition of the shaft

• Horizontal pump

In this type of pump, the impeller shaft is used horizontal.

• Vertical pump

In this type of pump, the impeller shaft is used vertical.

Priming

Necessity of priming

Methods of Priming

Manual Priming

Self Priming

Working

• Impeller in rotating motion forces water out towards the circumference due to centrifugal force effects.
• Due to this, negative pressure gets generated at the centre of the pump so water is sucked from the sump via suction pipe which is connected to the pump.
• The kinetic energy of high velocity water is converted into pressure energy because of diverging passage of casing.

Heads

The heads of a pump may be expressed as:

• Suction Head
• Delivery Head
• Static Head
• Manometric Head
• Total Head
• Euler’s Head

• Suction Head (h_s): It is the vertical distance b/w liquid levels in the sump and the centre line of the pump. Usually, it is kept 7 to 8 m to avoid cavitation.
• Delivery Head (h_d): It is the vertical height of the liquid surface in the overhead tank to which the liquid is delivered above the centre line of the pump.
• Static Head (h_st): It is the vertical distance b/w liquid levels in the sump and the overhead tank. It is the sum of suction head and delivery head. (h_st=h_s+h_d).
• Manometric Head (H_m): The available head against which a centrifugal pump has to work is known as the manometric Head.
• Total Head (H): It is the total head which has to be developed by a pump to deliver the liquid from the sump into the overhead tank.

 Euler’s Head (H_e): It is defined as the head developed by the impeller. It is denoted as H_e.

Losses

Energy losses in centrifugal pumps may be classified as follows:

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1. Hydraulic Losses
2. Mechanical losses
3. Leakage Losses`

• Hydraulic Losses: There are two types of hydraulic losses which may occur in a pump.
1. Pipeline Losses: Major (due to friction) and minor (due to pipe bend) losses in pipes.
2. Pump Losses: Eddy or shock losses, frictional losses in impeller, guide vane/diffuser, casing.
• Mechanical Losses: Losses due to friction of main bearings and glands.
• Leakage Losses: slipping back of part of liquid through the clearance between the impeller and casing due to pressure difference b/w inlet and outlet. Energy carried by these liquid is ultimately wasted and this loss of energy of liquid is known as leakage losses.

Efficiencies

 Mechanical Efficiency (Ƞ_M):

 Volumetric Efficiency (Ƞ_V):

 Hydraulic Efficiency (Ƞ_H)

 Overall Efficiency (Ƞ_O)

Advantages

• Small in size & space saving.
• Output is very steady and consistent.
• Easy for maintenance.
• No danger creates if discharge valve is closed while starting.
• Deal with large volume.
• Able to work on medium to low head.
• Able to work on medium to low viscous fluid.
• Almost no noise

Disadvantages

• Extra priming process requires.
• Cannot be able to work on high speeds.
• Cannot deal with highly viscous liquid.

Application

• Agriculture and irrigation purpose.
• Pumping of water in buildings.
• Transfer raw material.

THANK YOU