A correctly sized compressor alternates between running and stopping, or slows down when the workshop uses little air if it has variable speed. If it runs all the time, even at night, or restarts every two minutes, something is wrong. Both symptoms are costly in electricity and wear.
It runs without ever stopping
Leaks in the network
This is the most frequent cause. Listen to the network when all machines are stopped: hissing means air, and therefore electricity, is escaping. A simple test: see whether the pressure in the receiver drops during a break, with no air being used. See detect and repair leaks, and our calculator to put a figure on what they cost.
Demand higher than the machine's output
An extra workstation, a hungry new tool, a sandblaster: demand has gone beyond what the compressor can deliver. It runs continuously without reaching its pressure. Add up the consumption of the tools used at the same time and compare it with the machine's air flow: see what size compressor to choose.
Pressure set too high
The higher the required pressure, the longer the machine works, and the more air the leaks lose. Set the pressure to what the tools really need, with a small margin.
A drain left open
A forgotten manual drain or an automatic drain stuck open lets air escape continuously.
A machine that is wearing
A clogged air filter or a separator at the end of its life reduces the air actually delivered. If the service is overdue, start there: see when to service.
It restarts too often
Receiver too small
The receiver is the reserve. Too small, it empties in a few seconds and the compressor starts again and again. See air receiver sizing.
Too small a gap between stop and restart
If the restart pressure is set just below the stop pressure, the machine starts at the slightest draw of air. The setting is made on the controller, or on the pressure switch of a piston compressor, within the limits of the manual.
Leaks, again
Even small leaks empty the receiver during breaks and cause restarts at regular intervals, including at night.
Why it matters
- Electricity: a compressor running to feed leaks costs money every hour. Our article cost of compressed air per m³ helps you put a figure on it.
- Wear: repeated starts tire the motor and contactors, and a compressor that never gets warm enough builds up water in its oil.
- Protections: in the end the machine stops on a fault (see compressor tripping).
A variable speed compressor limits both problems: it slows down instead of stopping and restarting. See variable or fixed speed. For a full check of the network, there is also the compressed air audit.
Other symptoms are covered in our compressor troubleshooting guide.