Blower and motor maintenance on a vapor recovery unit is often scheduled by calendar because it is simple to administer. Calendar scheduling works reasonably well on continuous duty, and poorly on the intermittent duty that many fuel depot units actually see. The alternative is to set intervals from running hours and observed condition, which takes a little more effort to set up and considerably less effort to live with.
Why calendar intervals drift away from reality
A unit that runs four hours a day accumulates wear at roughly one sixth the rate of a continuously running unit, yet both receive the same service on the same date. Conversely, a unit working through a hot season with frequent cycling can accumulate more than calendar time suggests. Running hours, start-stop frequency and duty temperature are the variables that actually drive wear.
What drives wear on the blower side
Blowers handling hydrocarbon vapour see three things that matter: liquid carryover, particulates, and operating temperature. Carryover is the most damaging and the least predictable, because it depends on upstream separation performance. A unit that has had a knock-out drum event will show accelerated wear in the blower regardless of its scheduled hours.
Setting intervals that reflect duty
| Component | Primary driver of wear | Recommended basis for interval |
|---|---|---|
| Blower bearings | Running hours and operating temperature | Running hours, with a shorter interval if temperature is high |
| Blower seals | Carryover events and vapour composition | Condition based, checked after any carryover event |
| Drive belt or coupling | Start-stop frequency | Counted starts rather than calendar time |
| Motor bearings | Running hours and ambient temperature | Running hours, adjusted for duty cycle |
| Motor insulation | Temperature history and starts | Periodic measurement plus visual inspection |
| Filters and strainers | Particulate loading and hours | Pressure differential, not a fixed date |
Condition checks that repay the time
- Log running hours and start counts, so intervals can be based on duty rather than dates;
- Record blower and motor temperatures at steady state to establish a normal baseline;
- Check pressure differential across filters and strainers and trend the readings;
- Listen to and record the unit’s normal sound at commissioning, for later comparison;
- Inspect after every carryover event, not only at scheduled intervals;
- Review the log quarterly and adjust intervals where the trend justifies it.
Spares and consumables worth holding
Which spares to hold follows from the interval decisions. Components with short intervals and long lead times should be on the shelf, while those that can be sourced quickly do not need to be. Bearings, seals, belts or couplings and filter elements form the usual short list, with quantities set by how many units are in service and how quickly deliveries arrive.
Frequently asked questions
How often should blower bearings be replaced?
There is no single interval that fits all units. Base it on running hours with a temperature adjustment, and shorten it after any carryover or abnormal temperature event rather than waiting for the scheduled date.
Is condition monitoring necessary on a small unit?
Full monitoring is not, but simple condition records — running hours, temperatures, sound and differential pressure — cost very little and give a clear basis for decisions.
What is the most common maintenance error on these units?
Servicing to the calendar while ignoring what the unit has actually been through. A unit that has been running intermittently and has never seen carryover is often over-serviced; one that has seen carryover events is usually under-inspected.
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