TROUBLE SHOOTING - CENTRIFUGAL PUMPS

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS

• Areas to be covered
• Quick introduction to pump design
• Quick system overview
• No flow or incorrect flow
• Over heating - bearings
• Over heating - seal housing/stuffing box
• Premature failure of mechanical seals
• Inability to align pump and motor shaft
• Vibrations
• Motor tripping out
• These issues will addressed both for new and
• existing pump installations.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Typical Centrifugal Pump Designs
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Typical Pump Design Overview
1- protective wear element 2- volute (casing) 3-
radial vane open impeller 4- stuffing box/seal
housing 5- shaft and sleeve 6- bearings 7- power
frame
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
System Overview
Valves
Piping
Pump
Drive Gear
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 1. Confirm there is power available to the
  motor.
• 2. Are the pump and motor connected?
• Ensure that the coupling or V-belt drive gear is
  connected and installed correctly.
• Confirm that the motor speed is correct.
• Confirm that the pump output speed is correct. If
  a VFD is being used check the speed range. If
  V-belts are being used confirm reduction ratio.
• These items seem obvious but it happens!

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 5. Pump rotation
• Confirm that the pump is operating in the
  correct rotation.
• Pumps will produce a reduced flow and head when
  operating in reverse.

Flow direction arrow is often present
For this picture clockwise rotation when viewed
from motor end
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 6. Pump is not primed.
• Required discharge head is higher than
  anticipated.
• Suction lift too high. (Suction lift must be
  added to discharge head to determine total pump
  head (TDH)).
• Insufficient Net Positive Suction Head (NPSH).
• Not enough suction head for hot or volatile
  liquids (NPSH).
• For existing pumps have the operating conditions
  changed (ie. higher TDH)?
• Centrifugal pumps respond to the system.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow
1,800 usgpm _at_ 50 TDH
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 12. Excessive air leaks in suction pipe or
  stuffing box.
• This is from operation with a vacuum on the
  suction.
• 13. Excessive leakage from seal housing.
• Worn out packing and/or the packing shaft
  sleeve, or a failed mechanical seal can cause
  excessive leakage.

Bad ?
Good ?
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 14. Valve position or condition.
• Ensure that the valves are 100 open and
  operating correctly.
• 15. Plugged suction or discharge lines.
• Large solids, rags, etc. maybe caught up on
  valving or plugging up the line.
• Operating with insufficient line velocities
  can result in solids settling out in the line.
• 16. Build up on inside of piping effectively
  reducing pipe diameter.
• Some fluids contain product that can build
  up on pipe walls (i.e. grease) which effectively
  reduces the pipe size and can increase discharge
  heads, or suction lifts or reduce suction heads.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow
17. Slugs of air/gas. Or simply gas bubble build
up in the eye of the impeller. Incorrect
piping can allow for gas pockets to occur.
Some sludge contains air which can amass in
suction line. Gas build up in the low
pressure zone of the impeller will
prevent flow.
Bad ?
Incorrect allows air pocket
Correct
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow
18. Plugged pumps. Solids larger than the
pump can pass may be in the process fluid.
Solids may build up in the pump choking off flow
through the pump. Operating the pump with a
wide range in flows can result in low suction
velocities allowing solids to settle out. These
solids can amass into a larger mass of solids
(birds nest). When higher suction velocities
occur this mass of solids will be suspended and
brought into the pump.
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow

• 19. Incorrect impeller diameter, or worn wet
  end components.
• As clearances open up in most pumps flow
  will be reduced.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow
20. For submersible pumps pump flange to
discharge elbow flange does not connect correctly
or is damaged.
poor mating connection
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
No Flow or Incorrect Flow
21. Struvite is formed under anaerobic
conditions. Struvite typically forms in piping
or pumps in high turbulent zones. It simply
builds and builds and will either choke off the
flow or render an impeller useless!
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Increased Clearances
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Overheating - Bearings

• Misalignment between pump and motor.
• Make sure direct coupled units are aligned
  to manufacturers
• standards.
• Make sure V-belt sheaves are aligned to
  acceptable standards.

Bad ?
Parallel Misalignment
Angular Misalignment
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Overheating - Bearings

• Misalignment (continued)
• If the pumps are running in a high
  temperature service the alignment should be
  checked after pumps have run for a while and
  heated up (as the metal heats it expands and this
  can affect the alignment).
• Lubrication.
• Make sure all bearings are lubricated before
  start-up.
• Make sure bearings or lubricants are not
  contaminated.
• Defective or worn out bearings.
• Bent shaft.
• Binding rotating equipment. Ensure pump
  rotates freely.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Overheating Stuffing Box/Seal Housing

• Loss of sealing liquid to stuffing box/seal
  housing.
• With packing, excessive gland pressure.
• should have 30-60 drips per minute out of
  gland.
• For existing pumps a change in packing type. Make
  sure packing is compatible with the pumpage and
  that it requires the same flushing rates.
• For existing pumps the lantern ring position.
  When replacing
• packing make sure to remember that the lantern
  ring must be lined
• up with the flush connection.
• If the seal flush water is supplied by a pump,
  over time this pump
• will also wear. This may increase the
  recirculation within the pump
• reducing the flow output to the
  packing/seal.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Overheating Stuffing Box/Seal Housing
Reminder! Packing must always be monitored
and adjusted to ensure that there is sufficient
water flow going across the sleeve
Good ?
Bad ?
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Premature failure of mechanical seals

• Pump runs dry and there is no fluid at seal.
• Loss of sealing liquid to seal gland. This
  could be due to water pump failure, line
  flow/pressure failure, plugged flush piping
  strainer.
• Applications where abrasives are present and soft
  seal faces are used (i.e. carbon vs. ceramic).
  For abrasives hard faces, Silicon Carbide or
  Tungsten Carbide, should be used.
• Applications involving corrosive fluids. Ensure
  that all seal components are compatible.
• For double mechanical seal systems insufficient
  flush pressure. Should have at least 15 psi above
  discharge pressure.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Premature failure of mechanical seals

1. For vertical dry pit pumps has the pump seal
   chamber been vented.
2. Seal faces are cocked when initially installed
   or when seal replaced.
3. Pump is cavitating or thrusting due to lack of
   inlet pressure or flow. This results in excessive
   loading on seal faces greatly reducing their life.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Premature failure of mechanical seals
Good ?
Plug must be opened to vent air
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Inability To Align Pump and Motor
Ensure that the base plate and pump assembly is
level over its length and width by adjusting
leveling shims, wedges or jacking bolts.
Before tightening anchor bolts, align unit.
Anchor bolts must not be tightened such that they
distort the base.
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Inability To Align Pump and Motor
After pre-alignment of pump motor the base
plate should be grouted. Once the grout has cured
recheck alignment ensuring that there is no more
than 0.002 movement on dial indicators. Then
connect piping. There is to be no pipe loading
upon pump. Check alignment again.
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Inability To Align Pump and Motor
If the pump assembly is grouted in prior to
alignment the base can be locked into a distorted
position. This makes it virtually impossible
to align the pump and motor shafts.
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations / Noise

• Misalignment between pump and motor.
• Make sure direct coupled units are aligned
  to manufacturers
• standards.
• Make sure V-belt sheaves are aligned to
  acceptable standards.

Bad ?
Parallel Misalignment
Angular Misalignment
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations / Noise

• 2. Loose equipment or parts.
• Make sure that foundation bolts are tight
  (do not distort base).
• Make sure pump and motor are bolted down
  correctly.
• 3. Grouting. Make sure base platess are securely
  installed and supported. For most pumps this
  means that the bases are grouted in. Ensure that
  all of the air is allowed to escape so that there
  will be no air pockets in the grout. Air pockets
  can set up a slight vibration that will grow as
  the grout breaks down and the base plate flexes
  more.
• Bent pump shaft. It is possible with older
  existing pumps that damage has occurred to the
  shaft.
• Worn bearings or parts. As bearings wear over
  time this can allow for some movement in the pump
  which can cause vibration.
• Suction pipe misalignment. There should be zero
  loading upon the suction flange.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations - Grouting
Good ?
Bad ? Wheres the grout?
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations / Noise

• Cavitation. On the suction side due to
  insufficient NPSH available. Pump may be running
  out at the end of the curve (providing too much
  flow and cavitating).
• Closed suction or discharge valve. Pump is being
  starved (suction) or throttled too far back
  (discharge)
• Blockage in suction or discharge piping. Same
  results as above with pump either being starved
  or throttled too far back.
• Binding rotating equipment. Incorrectly set
  clearances or tramp material can result in
  binding, noise, potential thrusting of the pump.
  

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations

• 11. System piping issues
• - Too much flow turbulence on suction of pump.
  Ideally there should be at least 10
  diameters of pipe between the suction of the
  pump and the first elbow.
• - Eliminate pipe loading upon the pump. Pumps
  typically are not designed to handle pipe
  loading. Pipe from the suction flange to the
  pipe rack, not the other way around.
• - Ensure there is sufficient piping support.
• - Reducers. Make sure eccentric reducers are
  not installed upside down at the pump suction.
  The top of the reducer should go straight into
  the suction flange.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations / Noise incorrect piping
Air can be trapped in this section which
eventually works its way into the pump.
Bad ?
Good ?
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Vibrations / Noise

• 11. System piping issues (cont.)
• - Fluid line velocities. Keep flow turbulence
  down. Maximum recommended velocity in the
  suction line is 2.4 m/s (8.0 fps). Velocities
  may be increased at the pump suction flange by
  the use of a gradual reducer. Higher velocities
  are acceptable providing the piping design
  delivers a smooth inlet flow to the pump
  suction.
• 12. Air leaks. Make sure that suction piping is
  kept free of air leaks. Many times suction lines
  are under vacuum conditions and can draw air
  through pipe connections, valving, etc. This
  entrained air will enter the pump.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Motor Tripping Out

• Motor size / speed. Make sure that the motor has
  the required minimum horse power for the
  operating conditions. Also make sure that the
  motor speed is correct. If the motor is running
  at a higher speed it can put the pump into a run
  out condition which can cause the motor to trip
  out on high amp draw and/or cause cavitation.
• Voltage. Make sure that the motor has the correct
  voltage. Some motors are dual voltage. Many
  plants have more than one voltage in use.
• Pumping at run out. If the pumps are trying to
  operate at the run out condition (pumps are not
  normally sized to operate at run out) this may be
  cause for high amp draws and tripping out.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Motor Tripping Out
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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Motor Tripping Out

• VFD operation. Pumps that are operating with
  Variable Frequency Drives have normally had the
  motors sized to operate in a specific speed
  range. By running beyond this range it will
  change the condition point and may cause the
  motor to trip out on high amp draw. By running
  below a minimum speed range it may allow the
  motor to overheat and trip out on thermal
  overload (high temperature).
• Fluid Viscosity or Density. If the fluid is
  different than what was designed for then the
  motor may be undersized. Pump performance curves
  are based on a water like viscosity (1.0 cps) and
  density (1.0 s.g.). This is particularly
  relevant when dealing with slurries.

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TROUBLE SHOOTING - CENTRIFUGAL PUMPS
Motor Tripping Out