John, the maintenance manager of a wood products company, was very proud of his Number 3 compressor. It has been operating for years, racking up more than 200,000 run hours — and was so trouble free, it was almost scary. Of course, John kept it maintained, changing oil and filters on a regular basis, fixing any leaks, and keeping it sparkling clean by cleaning up any collected dirt and oil.
He was particularly proud of the fact that it was the coolest compressor of his four units, never overheating once, even on the hottest days. From time to time, his compressor service company would stop by and try to sell him a new, more efficient replacement but he always put them off, because his existing Number 3 was a dream … he wanted to keep it forever.
One day, the power utility offered to do a free checkup of John’s system. The inspector placed instruments on the air compressors, measuring pressure, power, and flow. He eagerly awaited the results, predicting his system would pass the inspection with flying colors. But the power company had bad news. His dream was about to turn into a nightmare: his compressors were running poorly. In fact, on average they were consuming about 2.5 times the energy than they should, and the worst of the bunch was the Number 3 compressor!
The power company report showed that the Number 3 compressor was running with its inlet valve almost totally closed, due to a mechanical malfunction. Thus, it was consuming about 70% power, but putting out very little air. Adding to this, the other three compressors were running in “modulation mode,” the absolute least efficient way to run lubricated screw compressors: loaded on average 40% and consuming twice as much energy as they needed.
The power company estimated, based on system loading, that the Number 3 compressor didn’t need to be running at all, and had wasted more than $50,000 per year in electricity costs, more than enough to pay for a new compressor many times over. Furthermore, two more of his four compressors were running unnecessarily. Big changes in John’s control strategy were required.
To sooth John’s disappointment, the power company offered to help John improve his compressors with a fat six-figure incentive. First on John’s list to things to do is to call the compressor salesman back for a talk!
Monitoring the flow from a compressor seems to be one of the more important ways to keep track of it’s condition.. Not the very simplest but certainly important. I am guessing that monitoring the discharge air temperature might provide similar information.