Centrifugal Pump
Troubleshooting Guide
(taken from the
Pump System Design Manual)
Problem 1: Pump does not reach design
flow rate.
A. Probable Cause: Insufficient
NPSH ( Noise may or may not be present).
Recommended Remedy:
Recalculate NPSH available. It must
be greater than NPSH required by pump at desired flow rate. If not:
1. Refer to Chapter 18
2. Re-design suction piping, holding number of elbows and number of number of
planes to a minimum to avoid adverse fluid rotation as it approaches the impeller.
B. Probable Cause: System head is
greater than anticipated.
Recommended Remedy:
Reduce system head by increasing pipe
size and/or reducing number of fittings.
Increase impeller diameter.
C. Probable Cause: Plugged
impeller, suction line, or casing: product fibrous or contains large size solids.
Recommended Remedy:
For fibrous materials:
1. Reduce length of fiber when
possible
2. Reduce consistency when possible.
3. Consider oversized pump.
For solids:
If solid's size exceeds the maximum
allowable sphere published for the pump a larger pump may be required.
Refer to: A.J. Stepanoff, Pumps and
Blowers, Two Phase Flow,
John Wiley & Sons, Inc. New York 1965.
D. Probable Cause: Entrained
air-leak from atmosphere on suction side.
Recommended Remedy:
1. Check the suction line gaskets and
threads for tightness.
2. Properly repack the stuffing box.
3. If vortex formation is observed in suction tank, install vortex breaker.
4. Check for minimum submergence, See Chapter 18.
E. Probable Cause: Entrained gas
from process.
Recommended Remedy:
Process generated gases may require a
larger pump.
F. Probable Cause: Speed too low.
Recommended Remedy:
Check motor speed against design
speed.
G. Probable Cause: Direction of
rotation wrong
Recommended Remedy:
Reverse any two of three leads on a
three phase motor.
H. Probable Cause: Impeller too
small
Recommended Remedy:
Replace with proper diameter
impeller.
I. Probable Cause: Impeller
clearance too large.
Recommended Remedy:
Reset Impeller
Problem2: Pump not reaching design
head(TDH)
A. Probable Cause: Check all items
listed under "Pumps not reaching design flow rate".
Recommended Remedy:
Refer to remedies listed under
Problem 1.
Problem 3:No discharge or
flow--pump running
A. Probable Cause: Not properly
primed.
Recommended Remedy:
Repeat priming operation, recheck
instructions.
B. Probable Cause: Suction lift too
high.
Recommended Remedy:
1. Rearrange piping.
2. Increase suction head if possible.
3. Determine if larger impeller would be better.
4. Select new pump to handle higher suction lift.
C. Probable Cause: Impeller,
suction line, or casing is plugged
Recommended Remedy:
For fibrous materials
1. Reduce length of fiber when
possible.
2. Reduce consistency when possible.
3. Consider oversized pump.
For solids:
If solids size exceeds the published
maximum allowable sphere for the pump, a larger pump may be required.
Refer to: A.J. Stepanoff, Pumps and
Blowers, Two Phase Flow,
John Wiley & Sons, Inc., New Your 1965
D. Probable Cause: Direction of
rotation wrong.
Recommended Remedy:
Reverse any two of three leads on a
three phase motor.
E. Probable Cause: Entrained
air-leak from atmosphere on suction side.
Recommended Remedy:
Refer to recommended remedy under
Problem 1-D
Problem 4: Pump operates for short
period, then loses prime.
A. Probable Cause: Insufficient
NPSH
Recommended Remedy:
Recalculate NPSH available. It must
be greater than NPSH required by pump at desired flow. If Not:
1. Refer to Chapter 18 of the
Pump Design Manual
2. Re-design suction piping, holding the number
of elbows and number of planes to a minimum to avoid adverse fluid rotation as it
approaches the impeller.
B. Probable Cause: Entrained
air-leak from atmosphere on suction side.
Recommended Remedy:
Refer to recommended remedy under
Problem 1-D
Problem 5: Excessive
noise--wet end
A. Probable Cause:
Cavitation-Insufficient NPSH available.
Recommended Remedy:
Refer to Recommended remedy under
Problem 1-A
B. Probable Cause: Abnormal fluid
rotation due to complex suction piping.
Recommended Remedy:
Re-design suction piping holding
number of elbows and number of planes to a minimum to avoid adverse fluid rotation as it
approaches the impeller.
C. Probable Cause: Impeller
rubbing.
Recommended Remedy:
1. Check and reset impeller
clearance.
2. Check outboard bearing assembly for axial end play.
Problem 6: Excessive noise--power end
A.
Probable
Cause: Overloading bearing which is indicated by
flaking or spalling of the bearings raceway.
Recommended Remedy:
Check to be sure that actual
operating conditions do not exceed the maximum allowable specific gravity.
B. Probable Cause: Bearing
contamination appearing on the raceways as a scoring, pitting, scratching or rusting
caused by adverse environment and entrance of abrasive waste materials from the
atmosphere.
Recommended Remedy:
1. Work with clean tools
in clean environment.
2. Remove all outside dirt from housing before exposing bearings.
3. Handle with clean dry hands.
4. Treat a used bearing as carefully as a new one.
5. Use clean solvents and flushing oil.
6. Protect dissembled bearing from dirt and moisture.
7. Keep bearings wrapped in paper or clean cloth while not in use.
8. Clean inside of housing before replacing bearings.
9. Check oil lip seals and replace as required.
10. Check all plugs and tapped openings to make sure that they are tight.
C. Probable Cause: Brinelling of
bearing identified by indentations on the ball races, usually caused by incorrectly
applied forces in assembling the bearing or by shock loading such as hitting the bearing
or shaft with a hammer.
Recommended Remedy:
When mounting the bearing on a shaft
use a proper size ring and apply the pressure against the inner ring. When mounting in a
housing, press against the outer ring. Be sure when mounting a bearing to apply the
mounting pressure slowly and evenly.
D. Probable Cause: False Brinelling
of bearing identified again by either axial or circumferential indentations usually caused
by vibration of the balls between the stationary bearing.
Recommended Remedy:
1. Correct the source of vibration.
2. Where bearings are oil lubricated and employed in units that may be out of
service for extended periods, the shaft should be turned over periodically to relubricate
all bearing surfaces at intervals of one to three months.
E. Probable Cause: Thrust overload
on bearing identified by flaking ball path on one side of the outer race or in the case of
maximum capacity bearings, may appear as a spalling of the races in the vicinity of the
loading slot. These thrust failures are caused by improper mounting of the bearing or
excessive thrust loads.
Recommended Remedy:
1. Follow correct mounting procedures
for bearings.
2. Check pump literature to be sure that actual conditions do not exceed the
maximum allowable specific gravity or suction pressure limitations of the of the
particular pump.
F. Probable Cause: Misalignment
identified by fracture of ball retainer or a wide ball path on the inner liner and a
narrower cocked ball path on the outer race. Misalignment is caused by poor mounting
practices or improperly machined shafts. .For example, shaft shoulders not square with the
shaft centerline, initial shaft bowed due to grinding inaccuracies, or possibly a bent
shaft due to improper handling.
Recommended Remedy:
Check housing bore dimensionally to
be sure that shoulders are square with the shaft centerline and that all shoulder steps
are concentric and straight.
G. Probable Cause: Bearing damaged
by electric arcing identified as electro-etching of both inner and outer ring as a pitting
or cratering. Electrical arcing is caused by a static electrical charge emanating from
belt drives, electrical leakage or short circuiting..
Recommended Remedy:
1. Where current shuning through the
bearing cannot be corrected, a shunt in the of a slip ring assembly should be
incorporated.
2. Check all wiring, insulation and rotor windings to be sure thay they are sound
all connections are properly made.
3. Where pumps are belt driven, consider the elimination of static charges by
proper grounding or consider belt material less generative.
H. Probable Cause: Bearing damage
due to improper lubrication, identified by one or more of the following.
1. Abnormal bearing temperature rise.
2. A stiff cracked grease appearance.
3. A brown or bluish discoloration of the bearing races.
4. Failure of the ball retainer.
Recommended Remedy:
1. Be sure that the lubricant is
clean.
2. Be sure proper amount of lubricant is used. The constant level oiler supplied
with Durco pumps will maintain the proper oil level if it is installed and operating
properly. In the case of grease lubricated bearings, be sure that there is space adjacent
to the bearing into which it can rid itself of excess lubricant, otherwise the bearing may
overheat and fail prematurely.
3. Be sure the proper grade of lubricant is used. Generally speaking for oil
lubrication, use a SAE 30 weight oil. For grease lubrication a general purpose ball
bearing grease with an operating temperature of -15F. to 250F. is satisfactory. For more
specific advice or if the bearing temperature exceeds 200F. consult the local Durion
office.
Problem 7: Excessive leakage at stuffing
box-packed pump
A.
Probable Cause:
Loose packing gland
Recommended Remedy:
Adjust packing gland while pump is
running.
B. Probable Cause: Packing excessively worn or improperly lubricated.
Recommended Remedy:
Replace worn packing and check for
proper lubrication. If the packing is being lubricated by the pumpage itself, it is
mandatory that there be no solids in the pumpage.
C. Probable Cause: Shaft Bent
(Resulting in whipping action)
Recommended Remedy:
Replace bent shaft.
D. Probable Cause: Shaft or shaft
sleeve severely scored.
Recommended Remedy:
Replace shaft or shaft sleeve.
|