Preventive Maintenance: The Scheduled Approach
Preventive maintenance is work done at fixed intervals of time, cycles or running hours, whatever condition the equipment is in. The intervals usually come from the manufacturer, the plant's own failure history or a regulation.
Typical preventive tasks:
- Replacing drive belts and filters on a schedule.
- Re-greasing bearings at fixed intervals.
- Re-torquing electrical connections.
- Calibrating instruments on a regular cycle.
Strengths
- Simple to plan and schedule.
- Needs no monitoring equipment.
- Works well where wear is predictable.
- Meets the fixed intervals regulators and insurers set.
Weaknesses
- Parts get replaced with plenty of life left in them.
- A schedule does not catch a random failure between two intervals.
Predictive Maintenance: The Condition-Based Approach
Predictive maintenance watches the equipment: vibration, temperature, oil condition, electrical signatures, ultrasound. When the data shows a component wearing out, you plan the repair before it fails.
Common predictive techniques:
- Vibration analysis on rotating equipment.
- Infrared thermography on electrical panels and motors.
- Oil analysis for hydraulic systems and gearboxes.
- Ultrasound for compressed air leaks and bearing condition.
- Motor current signature analysis for rotor and mechanical faults.
Strengths
- Parts are replaced when they show wear, so they run their full life.
- A developing fault is caught early and the repair can be planned.
- Over time the data shows how each asset behaves.
Weaknesses
- It takes instruments and people who can read the results.
- Not every failure gives a warning the instruments can see.
- It only works if the data is collected and acted on every time.
- The first months tell you little, until baselines exist.
Which Strategy for Which Assets?
Match the strategy to how critical the asset is and how it fails.
Critical Assets
Large motors, gearboxes, compressors
High-Wear Consumables
Filters, belts, lubricants
Safety-Critical Systems
Emergency shutdowns, safety interlocks
Non-Critical Assets
Equipment where a failure has little impact
Scheduling Preventive Maintenance for Large Mechanical Systems
A large system, such as a long conveyor line, a press line or a plant with many gearboxes, is easier to keep up when the schedule is built from its parts. Start with the manufacturer's maintenance manual for each component, then adjust the intervals to what the plant's own records show.
- List every component with its tasks and its interval, by calendar time, running hours or cycles
- Rank the components by how much a failure would stop production
- Group tasks that need the same stop into one planned window, so the machine is down once
- Write down what each visit finds, and move an interval when the records say it is too short or too long
Planned stops are the cheapest place to do this work. See planned shutdown staffing for covering a large stop, and mechanical repair vs. maintenance for what each kind of visit includes.
When External Specialists May Help
Most predictive techniques need instruments and people who can read the results. For one plant that is hard to justify in-house. Advanced vibration analysis, thermography, oil analysis and high-voltage partial discharge testing, for a start.
A plant can bring a specialist in for periodic visits instead: a quarterly vibration route, a yearly thermographic survey, or a diagnostic visit when a machine starts to sound wrong. On FindFST each visit is a mission you post when you need it. No long-term commitment.
Disclaimer: This guide is general information, not professional or legal advice. Maintenance intervals and inspection duties depend on your equipment, its manufacturer and the rules that apply to your site. FindFST accepts no liability for decisions made on the basis of this guide.
From the field
Fault-finding stories from FST Life that go with this guide.
15 Oct 2026
The limit switches on this gearbox exist for one reason. To stop it destroying itself.
A fault was suspected on them. Instead of troubleshooting it, someone unplugged them and carried on. Classic... No fault. No protection. Just a gearbox...
24 Sep 2026
Would you replace this motor coupling?
Motor's been running like this for who knows how long. Went in to replace the motors. Pulled the couplings and found them cracked through. New motors...
17 Sep 2026
When it comes to engineering, more is not always better.
Machine calls for cooled water between 15 and 20 degrees. Customer was feeding it 5. From their side that's a free win, colder water, faster cooling, no...
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