The Ultimate Guide to Centrifugal Pump: Working Principle and Advanced Concepts

Following is the Complete Outline for Centrifugal Pump for a curious student

• Introduction

• Types of pumps

• Centrifugal Pumps

• Centrifugal Pump Parts

• Centrifugal pump Advanced Concepts

•  What is Affinity Law?

• What are the Pumping terms?

• How Static Head loss is defined, and what are its basic concepts?

• What is Friction Head Loss

• What are the types of Advanced Theories

• Effect of Impeller diameter change

• B.E.P

• Zero- Head Flow rate

• Shutoff Head

• Pump Performance

• Centrifugal pump NPSH Net Positive Suction Head

• What is Pump Priming

• Centrifugal pump curves

• Centrifugal pump Calculations

• Centrifugal Pump Efficient Equipment Operation

• Centrifugal Pump Head Complete understanding

Introduction To Pumps

Credit: Michael-smith-engineers

Simply stated, a pump is a machine used to move liquid through a piping system and raise the liquid's pressure. 

A pump can be further defined as a machine that uses several energy transformations to increase the pressure of this definition. 

The energy input into the pump is typically the energy source used to power the driver. 

Most commonly, this is electricity used to power an electric motor. 

Alternative forms of energy used to power the driver include high-pressure steam to drive a steam turbine, fuel oil to power a diesel engine, high-pressure hydraulic fluid to power a hydraulic motor, and compressed air to drive an air motor. 

Regardless of the driver type for a centrifugal pump, the input energy is converted to rotating mechanical energy, consisting of the driver output shaft, operating at a certain speed, and transmitting a certain torque or horsepower.

How Pumps are classified?/ What are the types of pumps?

There are many ways to classify pumps: according to their function, conditions of service, materials of construction, etc. 

The pump industry trade association, the Hydraulic Instisification, divides pumps as follows:

A. Principle of Energy Addition

The first classification is according to the principle by which energy is added to the liquid. There are two broad classes of pumps, defined below;

1.  Kinetic/ Dynamic Pumps

In a kinetic pump, energy is continuously added to the liquid to increase its velocity. When the liquid velocity is subsequently reduced, this produces a pressure increase. 

Although several special types of pumps fall into this classification, for the most part, this classification consists of centrifugal pumps. 
                          
Types of Dynamic Pumps
1. Rotary Pumps

• Centrifugal Pumps 

• Axial Flow Pumps

• Mixed Flow Pumps

2. Special pumps   

• Jet pumps/ ejectors

• Electromagnetic pumps

• Fluid-actuated: hydraulic ram                          

    2. Positive Displacement Pumps

In a positive displacement pump, energy is periodically added to the liquid by directly applying a force to one or more movable volumes of liquid. 

This causes an increase in pressure up to the value required to move the liquid through ports in the discharge line. 

The important points here are that the energy addition is periodic (i.e., not continuous) and a direct application of force to the liquid.

Centrifugal Pump: Construction Details and Working

• A straightforward machine

• Two main parts

1. A rotary element, IMPELLER
2. A stationary element, VOLUTE

• Filled with fluid & impeller rotated

• Fluid rotates & leaves with high velocity

• Outward flow reduces pressure at the inlet (EYE OF THE IMPELLER), more fluid comes in.

• Outward fluid enters an increasing area region. Velocity converts to pressure

What is the working principle of the Centrifugal Pump?

Swinging pale generates centrifugal force holds water in pale. 

Make a bore in pale, then water is thrown out. Numerically we can have resulted from the following;

• The distance the water stream travels tangent to the circle = f(Vr)

• Volume flow from hole = f(Vr)

• In centrifugal pumps, flow rate & pressure = f(Vr) (tip velocity)

A body will move a distance h = V2/2g, having an initial velocity (V)

What are the parts of the Centrifugal Pump?

There are the following parts of the Centrifugal Pump that will be discussed one by one;

• Casing

• Impeller

• Shaft

• Stuffing box

• Mechanical seal

• Bearings

• Spider

• Strainer

Casing:

Fluid is receiving in casing it is a basic curved funnel that increases in area as it approaches the discharge port and, It converts fluids kinetic energy into pressure.

Casing's Initial area has lower space. Gradually area increases, which sucks more liquid to the impeller eye.

Normally we get caught a question in our mind that 

What are types of Casings? Which casing is more efficient?

1.  Volute casing
2.  Diffuser ring casing

1. Volute casing 

This type of casing is divided into two categories

• Simple Volute Casing
• Vortex Casing

Simple Volute Casing:

In this type of casing, the space between casing and impeller is lower. 

It produces eddy resistance due to the lower initial gap, requiring more energy motor or higher RPM to develop pressure.

Vortex casing:

Vortex type casing is an updated version of volute casing in which a circular chamber is provided, which eliminates eddy resistance.

2. Diffuser Ring Casing

This type of casing is used in turbine-type centrifugal pumps.

There are guide vans around impellers that are in a ring. 

This type of casing Is maximum covert fluid kinetic energy into discharge pressure minimum design losses.

Impeller:

What are the Types of impellers, and what are their functions, limitations, and uses?

1. Open impeller

In this impeller type, blades are directly connected to the impeller eye. This impeller type is used to pump higher viscous liquid like paper pulp & sewage.

Uses - Pumping Highly suspended solids containing liquid

      2. Semi-Open Impeller

In this impeller eye and blades is forger on the base plate. This is used to pump liquid with solid particles.

Uses - Suspended liquids pumping.

3. Closed Impeller

Most efficient impeller wide range of application with normal clean viscous liquid fluid is also known as the shrouded type of impeller 

Uses - Clear liquid pumping

 

Pumping Efficiency : Open impeller < Semi open impeller < Closed Impeller

        4. Non-Clogging Impeller

Used to pump sewage with paper plastic cloths this has a non-chocking design.

      5. Axial Flow Impellers

This impeller type is used to pump two liquids parallel to mixed results. Axis flow pattern means Shaft axis and flow direction is parallel.

      6. Radial Impeller

Radial flow pattern means Shaft axis and flow direction is at 90° Angle

Uses - High head and low flow requirements.

   7. Mixed Flow Impeller

Mixed flow pattern means Shaft axis and flow direction is at 45° - 80° Angle

Uses - High flow High head applications.

Impeller suitability and Performance

Shaft

The shaft is used to connect the shaft of the driver to the pump impeller to transmit power magnetically coupled pump also available to avoid the use of shaft.

Stuffing box

It is used to seal casing with the use of packing material and lantern ring.

Mechanical Seal

A mechanical seal is used to prevent leakage of under pressure liquid into the casing.

Bearings

 

It is used for the smooth operation of pumping generally two bearings are available

1. Drive side

2. Non-drive side

Strainer

The strainer is installed in the pump suction side water tank isolation valve.

 

The intention of Strainer installation is to filter pumping liquid and solid impurities & foreign particles kept away from the pump for efficient pumping of liquid as well as make pump internals safe.

NonReturn Valve -NRV

NRV is installed at the pump discharge side beforehand isolation valve for back backflow prevention to parallel pump.

Another use to install NRV is to prevent priming. For Priming prevention, NRV is installed in the negative suction pump at the suction end which is deep in liquid.

Variable frequency drive - VFD

Variable frequency drive is installed in those pumps which

• Pumps are exceeding flow designed.

• Systems where the flow of liquid flow is required insignificant variations.

Pumps where discharge flow is less required and discharge valve in half close condition loss of energy is there.

A variable frequency drive is installed which controls the frequency of Voltage of the motor.

Reduction in VFD is resulting in Reduction in Pumps motor Rotation RPM reduction.

Reduction in rotation RPM of motor results in lower power consumption.