One person walks the air lines with a detector and fixes the largest leaks, then the pressure comes down in steps.
Cost
About $2,300 once, then about $800 per year
Payback
About 3 months
Limitation
It pays only if the lines leak or the pressure is spare. Leaks come back, so the walk is repeated each quarter.
What changes
One maintenance person walks the air lines with an ultrasonic detector, a hand-held device that hears escaping air.
Each leak gets a tag, and the largest are fixed first with a new coupling, hose or thread tape.
The compressors' setting then comes down two psi at a time, with a normal shift between steps.
What it costs and could save
A repeat walk each quarter costs about $800 per year, because leaks come back.
After that, the saving is about $8,600 per year if leaks and extra pressure are both there.
The detector and the staff hours cost about $2,300 once, paid back in about 3 months.
Why it works
Mechanism
Every cubic foot of air costs electricity to compress, whether a press uses it or it escapes at a fitting.
A leak that is fixed is air the compressors no longer have to make.
A lower setting means less work on every cubic foot, and less air escapes through any leak that is left.
Math
About $600,000 per year goes on electricity, and we count 12 percent of it for the compressors.
That is about $72,000, or about 720,000 kWh at 10 cents per kWh.
The utility bills by the kWh, short for kilowatt-hour.
Leaks that can be found and fixed take 10 percent of it, about $7,200.
Extra pressure of 6 psi takes 3 percent, about $2,200, at about 1 percent for every 2 psi.
The two add up to about $9,400 per year.
Take off about $800 per year for the repeat walks, in hours and parts, and about $8,600 is left.
The detector and the staff hours cost about $2,300 once, paid back in about 3 months.
Industry evidence
US Department of Energy guidance says leaks often waste 20 to 30 percent of a compressor's output where nobody looks for them, and under 10 percent where they are repaired.
It calls an ultrasonic detector the best way to find them.
Its rule for a system near 100 psi is that a compressor's energy rises about 1 percent for every 2 psi.
All of this is published guidance, and nobody has measured it at this plant.
Limitations
Nothing we saw rules this in or out.
We heard no leak and read no pressure, so both parts are assumed and either could turn out to be zero.
The plant may already walk its air lines for leaks, and then there is little to find.
An idling compressor still uses 15 to 35 percent of its full-load power.
So less air to make does not cut the bill by as much, unless the compressors shut off when idle.
The setting can only come down to what the most demanding press needs.
New leaks open as hoses and fittings wear, so the saving lasts only while the walk is repeated.