Maintenance of Pumps and Motors
Maintaining pumps and motors can be critical to keeping the collection system operating at an optimum rate. In addition to good system operation, maintaining the pumps and motors can prevent costly repairs and replacements. Before doing work on pumps or other equipment it is important to practice lock out tag out principles. The equipment should be locked in such a way that it can only be turned back on by the person working on the equipment. Also a tag identifying who locked the equipment out and the type of maintenance being performed on the equipment should be placed on the lock to identify the problem and so the proper person can be contacted about the maintenance.
1. Check the condition of the motor for dirt, dust, moisture, air circulation obstructions, and excessive leakage of grease from the bearings.
2. Observe any unusual conditions including noise, excessive heat, vibration, intermittent to continuous sparking of brushes, or sluggish operation. A stethoscope is sometimes used to check for bearing whines, gratings, or uneven noises. Cavitation can be a reason for a pump to run noisy or sound like a marble is trapped in the volute.
3. Keep close watch on the amperage being pulled by the motors. A sudden increase could be indicative of a pumping restriction while a sudden decrease may be the result of a drop in pumping head caused by a break in the discharge line.
4. When restarting a pump after maintenance or repair, you should calibrate it to verify that it is operating in accordance with its design parameters.
For motors wound for 3-phase current, periodically check to insure equal distribution across all three phases. If one phase cuts out while in operation the motor may overheat and become damaged unless it is stopped by a thermal control device.
Pump Operating Problems & Causes of Failure or Reduced Operating Efficiency Causes for pump not starting:
1. Blown fuses or circuit breakers due to:
2. Rating of fuses or circuit breakers not correct
3. Switch (breaker) contacts corroded or shorted
4. Terminal connections loose or broken somewhere in the circuit
5. Automatic control mechanism not functioning properly
6. Motor shorted or burned out
7. Wiring hookup or service not correct
8. Switches not set for operation
9. Contacts of the control relays dirty and arcing
10. Fuses or thermal units too warm
11. Wiring short-circuited
12. Shaft binding or sticking due to rubbing impeller, tight packing glands, or clogging of pump
13. Loose connection, fuse, or thermal unit
Causes for reduced pump discharge rates:
1. Pump not primed
2. Mixture of air in the wastewater
3. Speed of motor too low
4. Improper wiring
5. Defective motor
6. Discharge head too high
7. Suction lift higher than anticipated
8. Impeller clogged
9. Discharge line clogged
10. Pump rotating in wrong direction
11. Air leaks in suction line or packing box
12. Inlet to suction too high, permitting air to enter
13. Valves partially or entirely closed
14. Check valves stuck or clogged
15. Incorrect impeller adjustment
16. Impeller damaged or worn
17. Packing worn or defective
18. Impeller turning on shaft because of broken key
19. Flexible coupling broken
20. Loss of suction during pumping may be caused by leaky suction line, ineffective water or grease seal
21. Belts slipping
22. Worn wearing ring
Causes for high power requirements:
1. Speed of rotation too high
2. Operating heads lower than rating for which pump was designed, resulting in excess pumping rates
3. Check valves open, draining long force-main back into wet-wall
4. Specific gravity or viscosity of liquid pumped too high
5. Clogged pump
6. Sheaves on belt drive misaligned or maladjusted
7. Pump shaft bent
8. Rotating elements binding
9. Packing too tight
10. Wearing rings worn or binding
11. Impeller rubbing
Causes for noisy pump operation:
1. Pump not completely primed
2. Inlet clogged
3. Inlet not submerged
4. Pump not lubricated properly
5. Worn impellers
6. Strain on pumps caused by unsupported piping fastened to the pump
7. Foundation insecure
8. Mechanical defects in pump
9. Misalignment of motor and pump where connected by flexible shaft
10. Rags or sticks bound (wrapped) around impeller