PUMPS

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Muscatine Power WaterFans, Pumps, Motors, and
Lighting Workshop

• PUMPS
• Energy efficiency and
• improving pumping system performance

Todd Sears
Power Process Equipment Inc.
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• Pumps are the second most
• common machine in use today,
• they are exceeded in numbers only by electric
  motors
• Pump represent 27 of the electricity consumed in
  the manufacturing sector

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Pumping system components

• Typical pumping systems contain five basic
  components
• Pump
• Prime mover
• Piping
• Valves
• End-user equipment
• (e.g. heat exchangers, tanks, other equipment)

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WHAT IS THE PURPOSE OF A PUMP?

• Pumps are designed to move fluid
• Pumps transfer fluid for processing
• In most plants pumps are a critical part of daily
  operation

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Pump terms
-Flow Measured in gallons per
minute -Pressure Measured in PSIG -Head Measu
red in feet -Pump curve Displays flow, head
Eff. -Best efficiency point Relates to energy
consumption -Cavitation Upset condition inside
a pump -Deadhead No discharge flow from a
pump -Suction, Discharge Fluid
connections -Base Foundation for pump and
driver -Alignment lining up pump shaft with
driver
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Pump types

• Positive displacement
• Fixed displacement, fluid is captured in
  cavities within the pump and mechanical energy
  moves it from the inlet to discharge
• Centrifugal
• Velocity is added to fluid by a spinning
  impeller and converted to pressure energy inside
  the pump. Pressure differential moves the fluid
  through the pump

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Positive displacement pumps strengths

• Low flow
• High pressure
• High viscosity
• Self priming
• Metering
• High energy efficiency

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Positive displacement pump concerns

• Not for water thin fluids
• Relief valves required
• Solids can be a problem
• Flow limited by size and speed
• Pulsating flow
• More complicated machine
• May require speed reducers
• Higher initial cost
• Higher repair costs

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Positive displacement pumps
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Centrifugal pump strengths

• High flow capability
• Variable flow rates
  even at constant speed
• Wide range of operation
• Solids handling
• Lower initial cost
• Lower repair costs
• Simple and safe to operate
• Less wear with fewer replacement parts

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Centrifugal pump concerns

• Viscosity limitations
• High pressure may require multiple impellers
• Self priming issues
• Lower energy efficiency
• Piping system back pressure controls flow

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Centrifugal pump operation
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Centrifugal pumps
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Energy efficiency comparison Positive
displacement vs. Centrifugal pumps

• Conditions of service
• 105 GPM
• 48Cps
• 80 PSIG discharge pressure

PD pump -1750 RPM -9.2 HP -15 HP motor

• Centrifugal pump
• -3600 RPM
• 13.2 HP
• 20 HP motor

30 Horsepower difference Potential of over
1300/yr. savings
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Common pump sizing issues

• The importance of pumps to the daily operation of
  many facilities promotes the practice of
  conservatively sizing pumps to ensure that the
  needs of the system will be met under all
  conditions
• In addition to inefficient operation, oversized
  pumps typically require more frequent maintenance
  than properly sized pumps

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Oversized pumps

• Oversizing pumps adds to system operating costs
  both in terms of energy and maintenance
  requirements
• -These costs are often overlooked during the
  system specification process
• Since many of these operating and maintenance
  costs are avoidable, correcting an oversized pump
  can be a cost-effective system improvement

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Indications of an oversized centrifugal pump

• High flow noise
• Highly throttled flow control valves
• Heavy use of bypass lines
• Frequent bearing and seal replacement
• Intermittent pump operation

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High flow noise

• Oversized pumps tend to create high noise levels
• The cumulative damage that results from
  flow-induced pipe vibrations can significantly
  accelerate system wear
• Pump is running at high flow conditions and using
  extra energy

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Throttled flow control valves

• Throttle valves provide flow control in two ways
  by increasing upstream backpressure, which
  reduces pump flow, and by directly dissipating
  fluid energy.
• This dissipating of energy is an inefficiency
  that can be addressed

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Bypass lines

• Bypass lines prevent the buildup of damaging
  pressure differentials
• The energy used to push fluid through bypass
  lines is wasted
• A system that normally operates with a large
  number of open bypass valves indicates that the
  system is performing inefficiently due to
  improper balancing, oversized pumps, or both

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Frequent bearing and seal
replacement

• Excess system flow can extend beyond high energy
  costs
• Oversized pumps often operate far from their Best
  efficiency point (BEP)
• They tend to experience greater bearing and seal
  wear

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Moving towards Shut-Off
BEP
Pump Operating Point
/- 15
Extreme Runout
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Hydraulic loads on the impeller
BEP
Impeller Radial Force
High load
Low load
Capacity
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Simultaneous loads on pump shaft
Impeller Radial Thrust
Impeller Axial Thrust
Hydraulic Induced Forces due to Recirculation
Cavitation
Seal or Packing
Impeller Axial Thrust
Radial Thrust due to Hydraulic Imbalance
Hydraulic Imbalance
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Head flow impact on pump reliability
Head
150
BEP
125
100
Impeller Damage
Low Flow Cavitation
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Suction Recirculation
High Temperature Rise
Bearing Seal Life Reduced
Discharge Recirculation
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High Flow Cavitation
25
0
0
20
40
60
80
100
120
140
160
Capacity
Presented by S. Gopalakrishnan 5th International
Pump Symposium Houston, TX
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Intermittent Pump Operation

• Pumps are often used to maintain fluid levels in
  tanks, either by filling or draining
• Systems with level controls activate the pumps
  automatically
• The cumulative effect of energizing and
  de-energizing a pump shortens the lives of the
  motor controller and the pump assembly

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Ways to control flow of centrifugal pumps

• Discharge throttle valves
• Bypass valves
• Impeller trimming
• Speed control
• Multiple pump arrangements

The most appropriate flow control method depends
on system size and layout, fluid properties, and
system sensitivity to flow rate changes
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Discharge throttle valves

• Throttle valve chokes fluid flow such that less
  fluid can move through the valve, creating a
  pressure drop across it.
• Throttle valves are more efficient than bypass
  valves. As the flow is limited the power required
  by the pump is reduced

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Bypass valves

• Bypass lines allow fluid to flow around a system
  component
• Bypass lines increase system flow and require
  more power
• The power used to pump the bypassed fluid is
  wasted

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Impeller trimming

• Impeller trimming refers to the process of
  machining the diameter of an impeller to reduce
  the energy added to the system fluid.
• Impeller trimming offers a useful correction to
  pumps that are oversized for their application.
• A 2 percent reduction in impeller diameter
  creates about a 2 percent reduction in flow, a 4
  percent reduction in head, and an 8 percent
  reduction in power

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When to consider impeller trimming

• High noise or vibration levels exist indicating
  excessive flow.
• Highly throttled discharge flow control valves.
• Systems bypass valves are open, indicating excess
  flow available.

Note Impeller trim should be limited to 70 of
full diameter
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Variable speed control

• Pump speed adjustments provide an efficient
  means of controlling pump flow.
• By reducing pump speed, less energy is imparted
  to the fluid and less energy needs to be
  throttled or bypassed.

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Multiple pump arrangements

• Multiple pump arrangements are flexible,
  redundant, and have the ability to efficiently
  meet changing flow needs in systems with high
  static head components
• Multiple pumps are usually parallel combinations
  of the same pump model to provide balanced load
  sharing during periods when all the pumps are
  operating

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Systems approach to energy savings

• The systems approach seeks to increase the
  efficiency of electric motor systems by shifting
  the focus from individual components and
  functions to total system performance.
• In addition to energy savings, these improvements
  will yield a number of other economic benefits,
  including increased control over manufacturing
  processes, reduced maintenance, and higher levels
  of quality control.

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Efficient pumping system considerations

• Piping system layout that minimizes pressure
  drops
• Larger pipes create less friction loss
• Minimize unnecessary pressure drops by avoiding
  sharp bends, expansions, contractions, and where
  possible keep piping as straight as possible.
• Use of low-loss components. valves, long sweep
  elbows, and components.

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Pump system Life cycle costs

• A highly efficient pumping system is not merely a
  system with an energy-efficient motor.
• Overall system efficiency is the key to maximum
  cost savings. Often users are only concerned with
  initial cost, accepting the lowest bid for a
  component, while ignoring system efficiency.
• To achieve optimum pumping system economics,
  users should select equipment based on life cycle
  economics and operate and maintain the equipment
  for peak performance.

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References and sources for more information

• Improving Pumping System Performance A
  sourcebook for Industry.
• -Motor Challenge January 1999
• Cameron Hydraulic Data
• -Ingersoll Dresser Pumps
• Pump Principals Manual, Form 07865
• -A.W. Chesterton Company

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Thank you

• Todd Sears
• Power Process Equipment Inc.
• Cell 309-738-3481
• Email todds_at_ppei-mn.com
• Working with Industry to improve reliability