7.2 Preventive Maintenance, Pumps, Motors & Mechanical Equipment
Key Takeaways
- A preventive maintenance program is built on an equipment inventory, manufacturer-specified tasks and intervals, a scheduling system, and completed work records — the same four elements whether it is a card file or a computerized maintenance management system.
- Bearing life is destroyed primarily by contamination, over-greasing, and misalignment; grease until fresh grease appears at the relief, never until the housing is packed solid.
- Vibration, temperature, and motor current trends are predictive tools — a rising vibration amplitude at one times running speed usually indicates imbalance, while two times running speed commonly indicates misalignment.
- Valve exercising programs prevent the classic emergency in which a main break cannot be isolated because the valve has not been turned in twenty years.
- Lockout/tagout under 29 CFR 1910.147 applies to every maintenance task on energized or stored-energy equipment, and the person who applies the lock is the only person who may remove it.
7.2 Preventive Maintenance, Pumps, Motors & Mechanical Equipment
1. The four elements of a maintenance program
- Equipment inventory. Every pump, motor, blower, valve, meter, and analyzer with its make, model, serial number, nameplate data, installation date, and location.
- Task list and intervals taken from the manufacturer's O&M manual — lubrication, belt tension, packing adjustment, oil changes, filter changes, alignment checks, exercising.
- A scheduling mechanism that generates the work when it is due, whether a card file, a spreadsheet, or a CMMS.
- Completed work records, which are what let an operator see that a pump has needed a seal every four months and should be rebuilt.
Terminology to keep straight: corrective (fix on failure), preventive (time or runtime based), predictive (condition based — vibration, thermography, oil analysis), and reliability-centered (prioritizing tasks by consequence of failure).
2. Lubrication
- Grease: apply with the correct grease for the bearing, at the specified interval, until fresh grease appears at the relief port — then stop. Over-greasing churns, overheats, and fails bearings and blows out seals just as reliably as under-greasing. Never mix incompatible thickeners.
- Oil: maintain the level at the sight glass midpoint; change on schedule or on analysis. Water in the oil shows as a milky appearance and destroys bearings rapidly.
- Contamination control: wipe fittings before greasing, cap open oil ports, and store lubricants sealed and labeled.
3. Alignment and coupling care
Misalignment is a leading cause of premature bearing and seal failure. Straightedge and feeler gauge methods are acceptable for small equipment; dial indicator or laser alignment is standard for anything of consequence. Align after the unit reaches operating temperature where thermal growth is significant, check soft foot before aligning, and record final readings.
Vibration signatures worth knowing:
| Dominant frequency | Typical cause |
|---|---|
| 1 × running speed | Imbalance |
| 2 × running speed | Misalignment or looseness |
| Vane pass frequency (vanes × rpm) | Hydraulic — flow far from BEP, volute clearance |
| Random broadband, gravel-like sound | Cavitation |
| High-frequency bearing defect bands | Bearing wear |
4. Pump and motor troubleshooting
| Symptom | Check first |
|---|---|
| No flow, motor running | Prime, suction valve, clogged impeller or foot valve, wrong rotation |
| Reduced flow and head | Worn wear rings, partially plugged impeller, air entrainment, closed discharge valve |
| Noise like gravel, fluctuating discharge | Cavitation — raise suction head, clean strainer, reduce speed |
| Packing leaking excessively | Adjust gland one flat at a time, replace packing if the sleeve is grooved |
| Mechanical seal weeping | Seal faces damaged — replace; never run the seal dry |
| Motor overheating or tripping | Amps versus nameplate, voltage balance across phases, ventilation blocked, bearing failure |
| Frequent short-cycling | Wet well or tank volume, control differential, waterlogged pressure tank |
Packing versus mechanical seals: compression packing is intended to leak a small, controlled amount — commonly cited as roughly 10 to 60 drops per minute — because that flow cools and lubricates the sleeve. A mechanical seal is designed for no visible leakage and fails quickly if run dry.
5. Valve exercising
A distribution or plant valve that has not been operated in years will not close when a main breaks. A valve exercising program:
- Locates and cleans the valve box, verifies the valve on the map, and records the number of turns to close and the direction of operation (most North Carolina systems are open-left, but legacy open-right valves exist and must be flagged in the records).
- Operates the valve through its full travel and back to fully open, backing off if it binds rather than forcing it.
- Records condition, turns, and any leakage — which becomes the basis for a replacement program.
The same logic applies inside the plant: exercise basin drain valves, blowdown valves, and bypass valves before you need them in an emergency.
6. Spare parts and documentation
Stock parts by consequence of failure and lead time, not by cost: seals and packing, gaskets, bearings, coupling elements, fuses and contactors, chemical pump repair kits, and at least one complete spare for any unit whose failure stops treatment. Keep O&M manuals, wiring diagrams, valve and hydrant maps, and as-built drawings where the on-call operator can reach them at 2 a.m.
7. Maintenance safety
- Lockout/tagout (29 CFR 1910.147): identify all energy sources — electrical, hydraulic, pneumatic, gravity, stored rotational energy — shut down, isolate, lock, tag, release stored energy, and verify zero energy before work. Each worker applies a personal lock, and only the person who applied a lock may remove it.
- Confined spaces: wet wells, digesters, clearwells, and basins are permit-required confined spaces when entered.
- Machine guarding: couplings, belts, and chain drives get guards back on before the unit is returned to service.
- Electrical work on energized equipment requires qualified personnel and arc-flash-rated PPE under NFPA 70E; operators de-energize.
[!NOTE] Why the exam cares. The needs-to-know composition tables list Maintenance as a scored category on every A and B drinking water exam, and the Grade 2 biological course devotes an hour to "Mechanical & Maintenance Operations." Questions are practical: what a bearing failure sounds like, when to stop greasing, why a valve is never used for throttling, and who may remove a lock.
An operator is greasing a motor bearing. What is the correct stopping point?
A vibration analysis shows a dominant peak at two times the pump's running speed. What is the most likely mechanical cause?
Under the lockout/tagout standard, who may remove a personal lock applied to an isolated energy source?