A compressor that had reached near the end of its useful life was retained as a spare compressor. The unit sat on standby but rarely ran, except during maintenance periods.
Years ago, a compressed air auditor placed thermal mass flow meters on each of the facilities four compressors. The flow on the standby compressor did not go to zero for some reason when the compressor was not running, and the auditor pressed the site personnel to find out why.
Most thermal mass meters are bidirectional (some can be purchased that aren’t), with a reading that is always the absolute value of the flow. This means the reading of flow into the plant, or into the compressor from the plant shows a positive number on the flow meter display. The auditor, wise to this fact, suspected the compressor was consuming compressed air. A flow of 34 cfm over the 8,760 hours of system operation costs about $6,600 per year in wasted electricity costs at this site.
The plant personnel investigated and found some internal leakage on some tubing and some cracked open drain valves. At some point it its life, the service personnel had bypassed an internal airless condensate drain and manually cracked open a bypass valve, presumably because the drain had failed. For good measure, they also cracked open the manual valve. This is a horrible waste in constantly draining compressed air condensate (that never appears in a compressor that rarely runs).
The leak was repaired and the drain was replaced at a cost of $500. Simple payback on the repair calculates to less than a month. The sharp-eyed auditor earned his keep once again!
