Maintenance schedules exist for good reasons — they tell you when to change oil, filters and belts under normal operating conditions. They don't tell you much about the irregular checks and adjustments that separate a well-maintained system from one that just gets its service intervals done.
After fifteen years of working on compressed air systems, here are the items I most consistently find neglected.
Condensate Drain Verification
Float-operated auto drains are fitted to compressors, aftercoolers, dryers and filters to discharge condensed water. They're supposed to work automatically. They often don't.
A float drain that has failed open dumps compressed air continuously — typically 100-400 litres per minute — through the drain port. A float drain that has failed closed lets condensate accumulate until it carries over into the air stream.
Neither failure shows up in a routine service unless someone physically tests the drain. The test takes thirty seconds: observe the drain, isolate and manually open it, verify it discharges properly, and check it reseals. Add this to your monthly checklist.
On a site with ten auto drains, I typically find one or two operating incorrectly. At average compressed air energy costs, a stuck-open drain costs £2,000-5,000 per year. The industry-wide scale of this problem is significant.
Inlet Filter Condition
The inlet air filter protects the compressor from airborne particles. A clogged inlet filter restricts airflow, forces the compressor to work harder to meet demand, and increases energy consumption.
Most compressors have a differential pressure indicator on the inlet filter that shows when restriction is getting high. Many maintenance teams note that the indicator is showing restriction and schedule a filter change — for next month's service. That's too slow.
An inlet filter at maximum recommended differential pressure is adding roughly 5-10% to your energy consumption. Change it when the indicator shows restriction, not when the next service is due.
Cooler Fouling
The aftercooler and oil cooler both need to transfer heat efficiently. Fouled coolers mean higher discharge temperatures, shorter oil life, higher compressor outlet temperatures, and increased condensate carryover.
On compressors in dusty or greasy environments, cooler cleaning should be on the quarterly maintenance schedule, not just the annual one. A visual inspection — if the cooler fins are visible through the access panel — is enough to assess whether cleaning is overdue.
Air-blast cleaning with a low-pressure blowgun is usually adequate for light fouling. Heavy fouling, particularly from oil mist contamination, may need solvent cleaning. A compressor room with a deep fat fryer or spray booth nearby should be on a more frequent cleaning schedule than one in a clean office environment.
Coupling and Belt Alignment
Belt-driven compressors with misaligned belts wear belts prematurely, load bearings unevenly and generate heat. Coupling misalignment on direct-drive machines creates vibration that shortens bearing life.
This is easy to check during routine maintenance but often doesn't happen because the machines are running fine. Fine today doesn't mean fine in six months if misalignment has been developing gradually.
Belt tension and alignment should be checked at every service. On direct-drive machines, a vibration check with a basic accelerometer or vibration pen takes a few minutes and will catch developing bearing problems long before they become failures.
Pressure Drop Across the System
Measuring pressure at the compressor outlet and at your highest-demand point of use tells you the condition of your distribution system. A pressure drop of more than 1 bar across the pipework suggests undersized distribution, excessive filter restriction, or accumulated contamination in old pipework.
Most maintenance schedules don't include this check. Add it to your annual review.