Centrifugal Pump

Maintenance
Presented by: Munam Mushtaq
Mechanical Maintenance Engineer
Email:Munam.mushtaq@klybeck.com
 Centrifugal Pump

• A centrifugal pump is one of the simplest pieces of

equipment
• Its purpose is to convert energy of an electric motor or
engine into velocity or kinetic energy and then into
pressure of a fluid that is being pumped
 Centrifugal Pump

80% pumps in industrial plants are

Centrifugal Pumps
 Centrifugal Pumps

• Relatively inexpensive
• Quite
• Dependable
• Compact
• Simple in construction
• Capacity 5 to 500 gpm
• Head up to 250 ft
• Best for low viscosity fluid
 Centrifugal Pump

Disadvantage
• Capacity reduced when used for heavy oils and viscous
fluids.

• Capacity reduced when pumping solution contain small

amount of vapours.
 Centrifugal Pump

Construction

• The energy changes occur into two main parts of the

pump, the impeller and the volute.
• The impeller is the rotating part that converts driver
energy into the kinetic energy.
• volute is the stationary part that converts the kinetic
energy into pressure.
 Centrifugal Pump

• Centrifugal Force

• Liquid enters the pump suction and then the eye of the impeller. When the impeller rotates,
it spins the liquid sitting in the cavities between the vanes outward and imparts centrifugal
acceleration.

• As the liquid leaves the eye of the impeller a low pressure area is created at the eye allowing
more liquid to enter the pump inlet.

• Because the impeller blades are curved, the fluid is pushed in a tangential and radial
direction by the centrifugal force
 Centrifugal Pump

• Conversion of Kinetic energy into Pressure energy

• The energy created by the centrifugal force is kinetic
energy. The amount of energy given to the liquid is
proportional to the velocity at the edge or vane tip of the
impeller.
• The faster the impeller revolves or the bigger the impeller
is, then the higher will be the velocity of the liquid at the
vane tip and the greater the energy imparted to the liquid.
 Centrifugal Pump

• This kinetic energy of a liquid coming out of an impeller is harnessed by creating a

resistance to the flow. The first resistance is created by the pump volute (casing) that
catches the liquid and slows it down.

• In the discharge nozzle, the liquid further decelerates and its velocity is converted to
pressure according to Bernoulli’s principle.

• Therefore, the head (pressure in terms of height of liquid) developed is approximately

equal to the velocity energy at the periphery of the impeller expressed by the following
well-known formula:
 Centrifugal Pump

One fact that must always be remembered: A

pump does not create pressure, it only provides
flow. Pressure is a just an indication of the
amount of resistance to flow.
 Centrifugal pump
General Components of Centrifugal Pump

Has two main components:

I. Rotating component

Comprised of an impeller and a shaft

II. Stationary component

Comprised of a casing, casing cover, and bearings.

 CENTRIFUGAL PUMP

GENERAL COMPONENTS OF PUMPS

STATIONARY COMPONENTS CASING

Casings are generally of two types: volute and circular. The

impellers are fitted inside the casings.

1. Volute casings build a higher head;

2. circular casings are used for low head and high capacity
1. Volute Casing is a curved funnel increasing in area to the
discharge port. As the area of the cross-section increases,
the volute reduces the speed of the liquid and increases the
pressure of the liquid.
2. Circular casing have stationary diffusion vanes surrounding
the impeller Periphery that convert velocity energy to
pressure energy. Conventionally, the diffusers are applied to
multi-stage pumps.
 CENTRIFUGAL PUMP

The casings can be designed either as solid casings or split

casings.
Solid casing implies a design in which the entire casing
including the discharge nozzle is all contained in one casting or
fabricated piece.

Split casing implies two or more parts are fastened together.

When the casing parts are divided by horizontal plane.
The casing is described as horizontally split or axially split casing.
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP

When the split is in a vertical plane perpendicular to the

rotation axis, the casing is described as vertically split or
radially split casing.
 CENTRIFUGAL PUMP

Suction and Discharge Nozzle

The suction and discharge nozzles are part of the casings itself.
They commonly have the following configurations

End suction/Top discharge

The suction nozzle is located at the end of, and concentric to, the shaft
while the discharge nozzle is located at the top of the case
perpendicular to the shaft. This pump is directly into the impeller eye.

Top suction Top discharge nozzle

The suction and discharge nozzles are located at the top of the case
perpendicular to the shaft. This pump can either be an overhung type
or between-bearing type but is always a radially split case pump
 CENTRIFUGAL PUMP

Side suction / Side discharge nozzles

The suction and discharge nozzles are located at the sides

of the case perpendicular to the shaft. This pump can have
either an axially or radially split case type
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Seal Chamber and Stuffing Box

Both the seal chamber and the stuffing box have the
primary function of protecting the pump against leakage at
the point where the shaft is.
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Rotating Components
Impeller
The impeller is the main rotating part that provides the
centrifugal acceleration to the fluid. They are often classified in
many ways
Based on major direction of flow in reference to the axis
of rotation

• Radial flow
• Axial flow
• Mixed flow
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Radial Flow - A centrifugal pump in which the pressure is
developed wholly by centrifugal force

Axial Flow - A centrifugal pump in which the pressure is

developed by the propelling or lifting action of the vanes of the
impeller on the liquid.

Mixed Flow - A centrifugal pump in which the pressure is developed

partly by centrifugal force and partly by the lift of the vanes of the impeller
on the liquid.
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Based on suction type
• Single-suction: Liquid inlet on one side.
• Double-suction: Liquid inlet to the impeller symmetrically from both sides

Based on mechanical construction

• Closed: Shrouds or sidewall enclosing the vanes.

• Open: No shrouds or wall to enclose the vanes.
• Semi-open or vortex type
 Types of Impellers

Open Semi-Open Closed

 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
SHAFT
Transmit the torques encountered when starting and during

operation while supporting the impeller

SHAFT SLEEVE

Pump shafts are usually protected from erosion, corrosion,

and wear at the seal chambers, leakage joints, internal
bearings, and in the waterways by renewable sleeves
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Coupling:

Couplings can compensate for axial growth of the shaft and

transmit torque to the impeller.
Shaft couplings can be broadly classified into two groups:
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP
Rigid Flexible
Rigid couplings are used in applications where there is absolutely
no possibility or room for any misalignment.

Flexible shaft couplings

Flexible shaft couplings are more prone to
selection,installation and maintenance errors.
Flexible shaft couplings can be divided into two basic groups:
elastomeric and non-elastomeric.
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP

Flexible shaft couplings can be divided into two basic groups:

Elastomeric and non-elastomeric

Elastomeric

couplings use either rubber or polymer elements to achieve

flexibility. These elements can either be in shear or
incompression. Tire and rubber sleeve designs are elastome r in
shear couplings; jaw and pin and bushing designs are elastomer
in compression couplings.
Non-elastomeric
couplings use metallic elements to obtain flexibility.
These can be one of two types:
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP

Lubricated or nonlubricated.
Lubricated designs accommodate misalignment by the
sliding action of their components, hence the need for
lubrication.
The non-lubricated designs accommodate misalignment
through flexing. Gear, grid and chain couplings are examples
of non-elastomeric, lubricated couplings. Disc and diaphragm
couplings are non-elastomeric and nonlubricated
 CENTRIFUGAL PUMP
CENTRIFUGAL Auxiliary Components.
PUMP
Auxiliary components generally include the following piping systems
for the following services:
• Seal flushing , cooling , quenching systems
• Seal drains and vents
• Bearing lubrication , cooling systems
• Seal chamber or stuffing box cooling, heating systems Pump
pedestal cooling systems
Auxiliary piping systems include tubing, piping, isolating valves,
control valves, relief valves, temperature gauges and
thermocouples, pressure gauges, sight flow indicators, orifices, seal
flush coolers, dual seal barrier/buffer fluid reservoirs, and all related
vents and drains.
All auxiliary components shall comply with the requirements as per
standard codes like API 610 (refinery services), API 682 (shaft
sealing systems) etc.
 CENTRIFUGAL PUMP
WEAR RINGS AND RUNNING CLEARANCES
Radial running clearances shall be used to limit internal leakage
and, where necessary, balance axial thrust. Impeller pumping
vanes or close axial clearances shall not be used to balance axial
thrust. Renewable wear rings shall be provided in the pump casing.
Impellers shall have either integral wear surfaces or renewable
wear rings.
Mating wear surfaces of hardenable materials shall have a
difference in Brinell hardness number of at least 50 unless both the
stationary and the rotating wear surfaces have Brinell hardness
numbers of at least 400.
Renewable wear rings, if used, shall be held in place by a press fit
with locking pins, screws (axial or radial) or by tack welding. The
diameter of a hole in a wear ring for a radial pin or threaded dowel
shall not be more than one-third the width of the wear ring.
 CENTRIFUGAL PUMP
CENTRIFUGAL
PUMP RUNNING CLEARANCES
When establishing running clearances between wear rings and
other moving parts, consideration shall be given to pumping
temperatures, suction conditions, the liquid properties, the
thermal expansion and galling characteristics of the materials,
and pump efficiency. Clearances shall be sufficient to assure
dependability of operation and freedom from seizure under all
specified operating conditions.
For cast iron, bronze, hardened martensitic stainless steel and
materials with similarly low galling tendencies, the minimum
clearances given in Table 5 shall be used. For materials with
higher galling tendencies and for all materials operating at
temperatures above 260 °C (500 °F), 125 µm (0,005 in) shall be
added to these diametral clearances.
Cooling Water Pump QP-111C

Cooling Water Pump QP-111C

Cooling Water Pump QP-111C
Damaged Bearings of BFW Pump SP-511
Damaged Bearings of BFW Pump SP-511
Chemical Sewer Pump WP-213
Fire Water Pump PP-512
Belzona Coating in Fire Water Pump
Benfield Solution Pump GM-201
Benfield Solution Pump GM-201
CENTRIFUGAL
PUMP
CAVITATION IN CENTRIFUGAL PUMPS
Cavitation is a common occurrence but is the least understood
of all pumping problems.

Your pump is cavitating if knocking noises and vibrations can

be heard when it is operating. Other sings may be erratic
power consumption and fluctuation or reductions in pump out.

If you continue to oprate your pump when it is cavitating, it will

be damaged. Impeller surfaces and pump bowls will pit and
wear, eventually leading to mechanical destruction
CENTRIFUGAL
PUMP
WHAT IS CAUSE?
When water enters a pump, its velocity increases causing a
reduction in pressure within the pumping unit. If this pressure falls
too low, some of water will vaporise, forming bubbles entrained in
the liquid. Areas of higher pressure creating the noise and vibration
from the pump
CENTRIFUGAL
PUMP

HOW DO AVOID CAVITATION

As cavitation relates only to the suction side of the pump all
prevention measures should be directed at this area.
Suction lift that are too high will only encourage cavitation. As a
general rule, centrifugal pumps located less than 4 metres above
the water level should not experience cavitation
CENTRIFUGAL The following guidelines should be applied to avoid the problem
PUMP
1. minimize the number of valves and bend in the suction line
2. Use eccentric reducers, not concentric ensure the straight side of
the eccentric reducer is installed along the top of the section line.
3. Suction length should be as short as possible.
4. Suction pipe should at least the same diameter as the pump inlet
connection.
5. Use long reduce bend
6. Increase the size of valves and pipe work
7. Do not allow air into the suction line
8. Ensure adequate submergence over the foot valve. The
submergence should be at least 5.3 time the suction diameter.
CENTRIFUGAL
PUMP
ALTERNATIVE SOLUTIONS
One solution may be reduce the required net positive suction head.
This can done by lowering the pump speed. However, this will also
result in reduced output from the pump which may not suit your
system
If pump suction condition cannot be improved, you should seek
expert assistance. It may be that your pumping system needs to be
redesigned.
CENTRIFUGAL
PUMP

ASSISTANCE
Your local official of the department of natural resources and water
may be able to assist you further with this topic or water supply,
irrigation or drainage generally. Call them for details of other fact
sheets. Available services and associated charges
CENTRIFUGAL
PUMP
NO DELIVERED
• Priming Casing and suction pipe not completely filled with liquid

• Speed to slow
• Discharge head too high – check lift and friction loss
• Suction lift too high or suction pipe too small or too long. Causing
excessive friction loss- check with gauge.
• Impeller or suction pipe or suction entry completely plugged
• Wrong direction of rotation
• Air pocket in suction line
• Stuffing box packing worn or water seals plugged, allowing
leakage of air into pump casing
• Air leak in suction line
CENTRIFUGAL NOT ENOUGH DELIVERED
PUMP
• Priming Casing and suction pipe not completely filled with liquid
• Speed to slow
• Discharge head higher than anticipated- check, particularly friction loss.
• Suction lift too high or suction pipe too small or too long, casing excessive
friction loss – check with gauge
• Impeller or suction pipe or opening partially plugged
• Wrong direction of rotation
• Air pocket in suction line perhaps because of sharp vertical bend or
concentric reducer in suction line.
• Stuffing box packing worn or water seal plugged, allowing leakage of air into
pump casing.
• Air leak in suction line
• Foot valve too small
• Foot valve no immersed deep enough
• Mechanical defect – wear rings worn, impeller damage, casing packing
defective.
CENTRIFUGAL
PUMP

NOT ENOUGH PRESSURE

• Speed to low
• Air in water
• Impeller diameter too small
• Mechanical defect- wear ring worn, impeller damaged casing packing defective
• Wrong direction of rotation
• Pressure measured an incorrect point – measure pressure at top of pump case.
CENTRIFUGAL
PUMP

PUMP WORK FOR WHILE THAN QUITS

• Leakage in suction line
• Stuffing box packing worn or water seal plugged, allowing leakage of air
into pump casing
• Air pocket in suction line
• Not enough suction head for hot water or volatile liquid – check carefully
as this is a frequent cause of trouble with hot water, etc
• Air or gases in liquid
• Suction lift to high
CENTRIFUGAL
PUMP

PUMP TAKES TOO MUCH POWER

• Speed too high
• Head lower than rating pump too much water
• Mechanical defect – shaft bent, rotating element binds, stuffing boxes too
tight, pumps and driving unit misaligned
• Wrong direction of rotation.
CENTRIFUGAL
PUMP

PUMPS LEAKS EXCESSIVELY AT THE STUFFING BOX

• Packing worn or not properly lubricated
• Packing incorrectly installed or not properly run in
• Packing type incorrect for liquid handled
• Shaft scored.
CENTRIFUGAL
PUMP
PUMP IS TOO NOISY
• Hydraulic noise (cavitation) – suction lift too high – check with gauge.

• Mechanical defects- shaft bevt; rotating parts bind, are loose or

broken; bearings worn out; pump and driving unit misaligned
CENTRIFUGAL
PUMP
FURTHER INFORMATION
• Should you require assistance or advice on pumps or pumping
generally, please contact your local pump manufacturer or retailer.
• Fact sheet on water and other topics are available from natural
resources and water (NRW) officers and service centres or can be
downloaded at <www.nrw.qld.gov.au/factsheet>.