15.2 Preventive & Corrective Maintenance Programs

Four Strategies, Chosen by Consequence

A treatment plant cannot afford predictive monitoring on every asset and cannot afford reactive failure on the raw water pumps. The operator judgment being tested is matching the strategy to the consequence of failure, which is precisely why the examinations ask candidates to differentiate between preventive and corrective work and to assign work to the proper trade.

Lubrication: The Most Commonly Botched Task

• Grease is oil held in a soap thickener; it stays in place and seals against contamination. Oil carries away more heat and is used in high-speed or high-temperature service.
• Never mix incompatible greases. Mixing a lithium complex with a polyurea can break down the thickener and release the oil, leaving a dry bearing.
• Over-greasing fills the bearing cavity so completely that the grease churns rather than flows, generating heat, and the excess pressure pushes out seals and lets contamination in. The symptom is a bearing running hot shortly after service.
• Under-greasing produces metal-to-metal contact, rising temperature and a rising high-frequency vibration signature.
• Purge fittings and wipe them before applying a gun so that grit is not injected with the grease.
• Motors with sealed-for-life bearings must not be greased at all; the fitting simply is not there, and adding grease through a drain plug is a common and damaging error.

Bearings, Seals and Packing

Bearing failure modes an operator should recognize: fatigue spalling from normal end of life, contamination from failed seals or dirty grease, lubrication starvation, overheating, misalignment loading, and electrical fluting from stray shaft currents on drive-fed motors.

Packing versus mechanical seal is a distinction that appears repeatedly:

The classic operator error is tightening a packing gland until it stops dripping, which removes the lubricating film and destroys the sleeve within hours.

Alignment and Balance

Coupled equipment must be aligned in two ways: angular, where the shaft centerlines meet at an angle, and parallel (offset), where they are parallel but displaced. Both load bearings and seals continuously. Alignment is verified with dial indicators or a laser alignment tool, and it must be checked after the base is grouted and after piping is connected, because pipe strain pulls a pump out of alignment even when it was perfect on the shop floor. Soft foot, a base condition where one mounting foot does not sit flat, distorts the casing when bolted down and must be corrected before alignment is attempted.

Imbalance in a rotating assembly produces vibration at running speed and is corrected by cleaning or balancing the impeller or rotor.

Predictive Tools

• Vibration analysis identifies imbalance, misalignment, looseness and bearing defects by their characteristic frequencies, and rising overall vibration is an early warning long before noise is audible.
• Infrared thermography finds hot electrical connections, overloaded motors, failing bearings and steam or air leaks.
• Oil analysis on gearboxes detects wear metals, water intrusion and additive depletion.
• Ultrasonic testing locates compressed air and gas leaks and detects early bearing distress.

Spares, Records and the Inspector

A maintenance program that exists only in an operator's head fails the first inspection and the first retirement.

1. Equipment inventory listing every asset with make, model, serial number and nameplate data.
2. Scheduled task list with frequencies stated in calendar time or runtime hours.
3. Work order history recording what was done, when, by whom, with what parts.
4. Critical spares list covering items whose failure stops treatment and whose lead time exceeds the tolerable outage, for example a raw water pump seal kit, chlorinator repair kit, blower belt set or a spare turbidimeter.
5. Operation and maintenance manuals and standard operating procedures kept current and accessible on every shift.

Under Chapter 302 the certified operator is accountable for the process control decisions that keep the facility in compliance, and maintenance records are the evidence that equipment was capable of supporting those decisions. When a plant loses a filter, a blower or a chlorinator during a compliance event, the maintenance history is the first document reviewed.