Mining Pumps

Mining Pumps are pumps specially designed for the mining industry.  Almost all types of pumps are
used in the mining industry.  These include centrifugal pumps, borehole pumps, magnetic drive pumps, submersible pumps, etc.

These pumps will have to handle slurry, corrosive substances, metal tailings, reagent dosing, etc.

Wetted parts of a pump

The Wetted parts of a pump are the parts which come into contact with the medium.  These include
the casing, the impeller and the seals.

In the case of pumps which have to handle corrosive substances such as slurries, acids and alkalis, the wetted parts are covered by a protective layer made of special plastic.  These protective layers can be replaced during maintenance.

Diffuser Rings in Centrifugal Pumps

A Diffuser Ring is a set of  specially designed vanes which are constructed in the casing of a

centrifugal pump.  Diffuser rings are present only in pumps of high capacity as they are expensive to manufacture.

Diffuser rings help in converting the dynamic energy of the moving liquid into static pressure energy.

Acid and Alkali Pumps

Pumps required to pump corrosive substances such as acids and alkali have special modifications.
These include impellers made with chemically resistant materials.  The casings will also have special protective liners.  These liners can be replaced at regular intervals.

These pumps are used in industries related to electroplating, pharmaceuticals, and metallurgy.

Slurry Pumps - An Overview

Slurry Pumps are pumps used to pump solid particle mixtures.  These pumps can handle different types of slurries such as chemical slurry, metal tailing slurry.

The impellers of slurry pumps are made of materials resistant to corrosion by the medium.  The choice of the material depends on the nature of the slurry the pumps will handle.

The casing of the slurry pumps have protective liners made from elastomers such as rubber to protect the casing from the medium.

Centrifugal, pumps, gear pumps and peristaltic pumps can be used as slurry pumps.

Single Stage and Multistage Centrifugal Pumps - An Overview

A single stage centrifugal pump consists of an impeller and a volute.  The liquid is drawn inside at the centre of the impeller and discharged radially.

Multistage centrifugal pumps have more than one impeller and volute. A three stage multistage pump will have three impellers and three volutes.  The output of the first impeller will be fed to the input of the second impeller and so on.

The multistage pump can generate more pressure than a single stage pump.

For a given output pressure, the multistage pump will have impellers of smaller diameter.  The efficiency of a multistage pump will also be greater than a single stage pump.

It is possible to retrofit a single stage pump assemble with a multistage assembly with minimal rework in the piping.

In certain multistage pumps, there are provisions to by pass an impeller.  This may be useful for applications such as in firefighting where the pressure of the liquid will be different at different situations (based on the height of the building).  In such cases, the last impeller may be bypassed and the output can be drawn before the last impeller.

Multistage pumps will have more vibration than single stage pumps.

Useful Link

What is the eye of the impeller in Centrifugal pumps ?

In Centrifugal pumps, the impeller rotates and drives the water to the periphery towards the casing. The vortex thus creates has a low pressure region in the center.

This low pressure region is called the eye of the impeller.

What is the Specific Speed of a Pump ?

The Specific Speed of a Pump is a method of describing a pump by parameters such as the speed, head and flow rate.  The Specific Speed helps in deciding the type of pump for a specific application.  It also helps in comparing different types of pumps against a single requirement.

The Specific Speed is the speed at which a geometrically similar pump would have to run to deliver a flow rate of 1 liter of fluid at a head of 1 meter.

The Specific Speed can be calculated using the following formula

where 

n is the speed in rpm

Q is the flow rate and 

h is the head in metres

How is the capacity of the pump expressed ?

The Capacity of the pump refers to the discharge rate of the pump at a specific head.

It is generally expressed in cubic metres per hour, second or minute.  Sometimes, it is also represented in litres per second or hour.

Vibration in Pumps

Vibration is a very vital parameter in pump operation.  Excessive vibration can seriously damage the pump and the connected fittings.  Hence it is necessary that any increase in vibration be investigated
and corrective action taken.

Excessive vibration can

• damage the Impeller, bearings and bush rings
• damage the packing
• affect the wear rings and the setting of the impeller.
• loosen the fastening bolts of the pump and the motor
• damage the coupling
• affect the motor and its bearings

There are many causes for pump vibration.  Some of the causes are mechanical in nature such as alignment, balancing and loose fitment.  There are also hydraulic causes such as water hammer and turbulence.

Causes of Pump Vibration

Pump vibration can be caused by a number of causes.  Many of these cause are related to the fluid
being handled and issues such as pressure fluctuations in the line.  These are called hydraulic causes.

The Hydraulic causes of pump vibration are

• Operation the pump away from the Best Efficiency Point (BEP)
• Turbulent flow in the lines
• Fluid getting recirculated
• Low Net Positive Suction Head Available (NPSHA)
• Water Hammering

Mechanical Causes

• Aligment between the pump and the motor
• Unbalanced shaft
• Loose parts and fitment
• Vibration from other equipment nearby

Hammering issues in pump

Hammering is caused due to pressure fluctuations in the lines.  These fluctuations are caused when the flow is suddenly decreased or interrupted.  Hammering can cause vibrations in the lines.  It can
cause pipes to burst, damage the pipe supports.  It can rupture seals and cause leakage.  Hammering should be immediately investigated.  Water Hammering is also known as Hydraulic Shock.

Some of the causes of Hammering in pump lines are

Faulty pulsation damper in positive displacement pumps.
Operating the pump at the critical speed
malfunctioning of the check valves in the line

Some methods of minimizing hammering are

Reducing the velocity of the fluid.
Adding pressure absorbing devices such as accumulators or surge tanks.
Use of Pressure Relief Valves.
Using softstarters in motors which gradually increase the speed of the pump and provide a smoother rise in pressure.

Isolation Valves - An Overview

Isolation Valves are valves which are used to isolate a pipeline.  Any type of valve can be used as an isolation valve.  They are named after their functionality.

Consider a skid with two pumps with only one pump running at any given time.  The other pump is a standby pump.  The suction line of both the pumps will be  common.  There will be an isolation valve in the suction line of each pump.

The isolation valve of the main pump will be in the open condition while the isolation valve of the standby pump will be in the closed condition.  The position of the valves needs to be reversed if the standby pump is to be run and the main pump is to be taken offline for maintanence.

Isolation valves can also be provided around measuring instruments such as manometers.  The valve can be opened to connect the instrument to the line and then closed to take it off line.

NPSHA and NPSHR

Operating a pump at

low pressure will result in reduced efficiency and damage due to cavitation and pressure fluctuation.

NPSHA stands for Net Positive Suction Head Available.

NPSHA gives the absolute head available at the suction port.  The NPSHA is based on the system.  It is calculated by taking into account factors such as the atmospheric pressure, the vertical distance from the water level to the centerline of the pump, the friction in the suction piping, etc.

NPSHR stands for Net Positive Suction Head Required.  This is given by the pump manufacturer. This value gives the Net Positive Suction Head which should be made available at the pump suction point.

The NPSHA should be made to match the NPSHR value given by the manufacturer.

Noise in Pumps

Noise in Pumps occurs when the waves created by the impeller strike the casing.  This results in vibration of the casing causing the sound which we hear.  In addition, Noise can also come from vibration between the pump and the fittings such as pipes and clamps.


Cavitation Noise

This is caused when the bubbles formed in a low pressure region collapse when the pressure increases.  This causes a sharp, crackling noise.  This can also result in vibrations.

Noise and Vibration are critical parameters.  If the noise or vibration show any abnormal increase, they can cause damage to the pump components such as the impeller and can damage the pipelines.  Hence, it is necessary to monitor the noise and vibration.

Vibration Analysis of the pump will help decompose the vibration into specific frequencies.

These frequencies can be analyzed.  Specific frequencies may be related to specific causes.  This will help analyse the cause of the vibrations.

Pulsation Dampers in Pumps

Pulsation Dampers are sometimes needed at the outlet of positive displacement pumps.  In positive displacement pumps such as reciprocating pumps, the output of the pumps is not steady but is pulsating.


These pulsations are caused by the nature of the pump itself, which sucks water and expels it.  The velocity of the fluid discharged from the pump is thus constantly changing.  The acceleration and deceleration of the fluid are converted to fluctuations in pressure due to the momentum of the fluid.

Pulsation Dampers are devices which absorb the fluctuations.  They are usually constructed as a container which contains a gas such as nitrogen.  The container is connected to the line carrying the fluid.  When the pressure of the fluid increases in the line, the nitrogen in the damper gets compressed and absorbs the pressure.  Thus, there is a compression and decompression of the gas for every stroke of the pump.

The nitrogen gas is separated from the medium by means of a membrane.  This prevents the gas from being absorbed by the fluid.

What is a Hydraulic Ram Pump ? How does it work ?

A hydraulic ram pump is a pump which is powered by water.  The pump works by using the momentum of a large quantity of water flowing downhill to raise the water uphill.  Water is allowed to flow downhill.  The water flows through the waste water outlet.

At this time, the valve V1 is closed and V2 is open.  As the water flows, valve V2 gradually closes interrupting the flow of water.  The momentum of the water is converted into pressure energy which opens the valve V1 and pushes the water through the outlet.  The outlet is of a small cross section as compared to the inlet.

As the water is discharged, the pressure energy reduces and the valve V1 closes and V2 opens and the cycle starts over again.    Thus, only a small quantity of water is discharged.  The cylinder C1 serves as a pulsation damper which absorbs the fluctuations during each cycle.

Submersible Pumps - An Overview

Submersible pumps, as the name suggests are pumps which can be immersed in the water.  They are useful in situations where the water is from a deep source.  The submersible pump is a compact and hermetically sealed assembly containing the motor and the impeller in a single body.  The motor and the impeller are placed in a  single vertical shaft.  A centrifugal impeller is used.  The water enters the pump from an opening in the bottom.  It is pressurized and is conducted through the casing of the pump upwards to the surface.


The submersible pump should always be below the water level as the water is used to cool the pump.  The pump can get overheated if the water level falls or if the pump is operated out of the water.

Submersible pumps should never be used in water where people may swim.  There is a risk of electricity leaking and people may get electrocuted.


Advantages of submersible pumps over jet pumps.

Submersible pumps are more efficient.
They do not require priming
They are quieter.
They do not require any extra space.

Disadvantages of submersible pumps

High initial cost
Risk of current leakage in water

Air Lift Pump

An Airlift pump is a pump with no mechanical parts.  It is used in applications where the medium is corrosive and not free flowing such as slurry or muddy water.

The pump has a simple construction.  It consists of a source of compressed air such as a cylinder or a compressor.  The compressed air is fed to the bottom of a vertical pipe which is immersed in the medium.

The pump works by mixing air with the muddy water or slurry.  This creates a region of less density which rises to the surface.  The high density material then enters the pipe.  The process continues.

The Air Lift pump is simple and reliable.  It is also cheap.    However, it cannot be used where high heads are required.  It is also less efficient than other types of pumps.

The Air lift pump can even pump liquds which contain solids suspended in them.

What are Axial pumps ? How do they work ?

Axial pumps are pumps with a rotary impeller.  The impeller drives the water as a result of which the water gains kinetic energy.  In this aspect, it is similar to a centrifugal pump.

The Axial pump differs from the centrifugal pump in the direction of the water flow.  In a centrifugal pump, the water is radially moved towards the casing.  Here, however, the water is moved axially. That is, it is moved in a direction parallel to the axis of the impeller.  The water is not radially displaced.

The impeller of the axial pump is designed like a curved propeller which pushes the water upwards.

Selecting a pump coupling

A coupling is a critical part of a motor pump assembly.  The coupling conveys the torque generated by the motor to the pump.

Some of the important criteria to be kept in mind while selecting a pump coupling are

Power Rating
Having a coupling of the right power rating is necessary.  If the power rating of the coupling is lower than the required rating, the coupling may fail during operation.

Operating speed
The operating speed of the coupling determines the centrifugal force it can withstand.  Hence, the speed rating of the coupling should be suited to the operating speed.

Physical dimensions
The coupling will have to be fitted in a specific amount of space.  The coupling should be checked with the other parameters such as the gap between the shafts, the location of the bolts in the shafts, etc.

Tolerance for misalignment
The coupling should be able to tolerate minor misalignments between the shafts.

Thermal Growth

Thermal Growth refers to the increase in dimensions of a component or machine due to increase in temperature during operation.  It is also known as Thermal Expansion.  For instance, the dimensions of a turbine operating at high temperature can change.  This can affect the issues such as bearing clearances and alignment.

When machines are designed, thermal growth is taken into account and the components and clearances are decided keeping in mind the operating temperature.

Adjustments and settings need to be done taking into consideration the thermal growth.  For instance, the alignment of a turbine needs to be done assuming the dimensional change which may occur at the operating temperature.

Critical Speed in pumps

Critical Speed is the speed at which the dynamic forces caused by rotation make a shaft to rotate in its natural frequency.  The vibrations produced as a result can cause serious damage to the equipment.  Hence, rotating equipment should be operated above or below the critical speed to avoid the risk of damage.

Pumps, being rotating equipments, also have a critical speed.  The speed is dependent on factors such as the stiffness, length and mass.  The details of the critical speed for each pump will be provided by the manufacturer.

The operating speed of the pump is mentioned in the nameplate details.  Low speed pumps will have a operating speeds below the critical speeds such as 1440 rpm.  High speed pumps, on the other hand, will have their operating speeds above their critical speeds.

When these pumps are started, they will have to cross the critical speed  to reach the operating speeds.  Operators will gradually ramp the speed of these pumps to a value below the critical speeds and then rapidly cross the critical speed range to reach the operating speed.

Pipe Strain

Pipe strain refers to the strain caused by the pipes on a device such as a pump.  If the piping system is not supported properly or if the piping system is under stress, the stress can cause loading on the connected equipment such as a pump or a heater.  This can causing loading of components such as the flange.  Pipe Strain is a factor which affects the alignment of pumps and consequently pump operation and the life of its components.  Pipe strain causes radial loading of the bearings and produces stress on the flanges.  This may lead to failure over a period of time.

Pipe Strain is caused by

Improper supports for the pipe
Thermal expansion which results in stress
Improper installation or fitment of machinery

Pipe strain can result in misalignment of couplings.  It can also result in excessive radial loading of bearings, gears, seals.

Pipe Strain can be categorized into two major types

Static Pipe Strain which occurs when the machine is at room temperature and it at rest.  Static Pipe Strain can be measured by disconnecting the pipe flanges and measuring the misalignment

Dynamic Strain occurs when the the machine is running. Dynamic Strain is caused by thermal expansion (thermal growth),  inadequate supports for the pipeline or the mass of the liquid flowing during operation.

Common symptoms of pipe strain are excessive vibration, frequent failures of bearings and wear around supports.

Throttling of Pumps

Pumps come in standard sizes and discharge rates.  The actual flow required in a system may differ from the designed discharge rate.  For example, a filter may have a flow rate which is lesser than the discharge rate of the pump connected to its output.  In such situations, it may be necessary to reduce the discharge rate.

A commonly used practice is to throttle the pump with a valve.  Sometimes, orifice plates are also used.  Throttling creates an obstruction in the flow.  This leads to a drop in the efficiency of the pump.  The backpressure developed due to the restriction placed on the flow can stress the pump affecting its life.

Throttling is, therefore, not advisable.

Alternatives to Throttling

Variable Frequency Drives

Variables Frequency Drives or VFDs are devices which control the speed of the motor (the prime mover) by varying the frequency applied to the motor terminals.  VFDs can be used to regulate the speed.  VFDs also help save energy.  VFDs can make quick changes in speed and thereby the discharge pressure.  VFDs are gaining in popularity in speed control.  However, they may be expensive to install.

Trimming the Impeller

This method can be used if the discharge rate is to be permanently reduced.  The impeller is trimmed by reducing its circumference.  This affects the output pressure of the pump.  This method may not be suitable if the discharge pressure has to be constantly adjusted.

Installing multiple pumps

In this method, more than one pump can be connected in parallel.  These pumps can have discharge rates.  The pumps can be brought on line and taken offline depending on the required pressure.  This method, however, is expensive and may require modification in the system which may not be possible.

Sometimes, a combination of the three methods is used.

Wetted Perimeter

Wetted perimeter refers to the perimeter of the surface of the pipe in contact with the medium.  If the pipe is circular, the wetted perimeter will be 2pir

If the pipe has a square cross-section, the wetted perimeter will be 4a.

Wetted Area of a Trapezoidal channel in Red

The wetted perimeter for regular geometric shaped conduits can be calculated using standard formula.

For irregular conduits such as rivers and channels, the wetted perimeter has to be calculated manually.  To measure the wetted perimeter of rivers, a long chain is suspended across the river from either bank.  Using a boat, the depth of the river is measured every 50 cms and the values are noted.  This data can be drawn and the wetted area can be calculated.

What is an Orifice ? How are orifices classified ?

An orifice is a small opening through which a fluid is made to flow.  Orifices are used to measure the rate of flow or to restrict the flow in a pipe or a vessel.  In vessels, orifices can be provided in the side or in the base.

Orifice Plate

An orifice plate is a plate with a hole in the centre of a specific diameter.  Orifice plates can be introduced in pipelines to reduce the flow or for measurement.

Classification or orifices.

Orifices can be classified on certain criteria.

On the basis of shape

Triangular orifices
Circular orifices
Rectangular orifices

According to the nature of discharge

Fully submerged orifices
Partially submerged orifices

Friction Losses in Laminar and Turbulent Flow

When a fluid flows through a pipe, there will be frictional losses.  Theses losses are due to the shear stress between the fluid molecules and the walls of the pipe.

When the flow is laminar
If the flow through the liquid is laminar, the losses will be proportional to the velocity.
The frictional losses are inversely proportional to the temperature of the fluid and to the pipe area.

When the flow is turbulent
In turbulent flow, the losses are proportional to the square of the velocity.  In turbulent flow, a layer of eddies and vortices is formed near the pipe surface.  The roughness of the pipe surface also has a bearing on the losses in turbulent flow.  If the pipe surface is rough, the losses will be more.  In turbulent flow, the losses are proportional to the density of the fluid.

Hydraulic Gradient Line and Energy Gradient Line

Consider a horizontal pipe carrying a fluid.  If a vertical pipe is connected as shown, the water will rise to a certain level due the pressure.  This line is known as the Hydraulic Gradient Line.

The Hydraulic Gradient Line is the differene of the total head available to the device and the velocity head.

Hydraulic Gradient Line = Total Head - Velocity Head


What is the Energy Gradient line

The Energy Gradient Line refers to the total head available to a fluid.  Consider a horizontal pipe carrying a fluid.  If a pitot tube is connected in the line as shown in the figure, the fluid will rise to a particular height in the pitot tube.

This height is called the Energy Gradient line.

Wetted Perimeter and Hydraulic Depth

Wetted Perimeter

In Fluid dynamics, wetted perimeter refers to the perimeter of the cross sectional area of the pipe in contact with the medium.  If the pipe is circular, the wetted perimeter will be 

If the pipe has a square cross-section, the wetted perimeter will be 4a.

Hydraulic depth

Hydraulic depth refers to the length through which the liquid flows through the pipe.

Hydraulic depth = Area of the flow / wetted perimeter.

What are Hydraulic Coefficients

In Fluid dynamics, the following four coefficients
are known as Hydraulic Coefficients.  They are

Coefficient of Contraction

This is the ratio of the area of the jet at Vena Contracta to the area of the orifice.

Coefficient of Velocity

This is the ratio of the actual velocity of the jet at vena contracta to the theoretical velocity of the jet

Coefficient of resistance

This is the ratio of loss of head in the orifice to the actual head.  This loss of head is due to the frictional losses when the fluid passes through the orifice.

Coefficient of Discharge

This is the ratio of the actual discharge to the theoretical discharge.

An orifice meter is a device which is used to measure the flow through a pipe.  The construction of the orifice meter is simple.

It consists of a circular plate with an orifice in the center.  The plated is fitted in the middle of the pipeline.  The orifice offers resistance to the flow of water.  This results in a drop in pressure after the orifice.

The static pressure is measured