Compressor Duty Cycles – What you need to know

When a Good Bargain Isn’t Always a Wise Investment

On the face of it, buying an air compressor seems fairly simple – just match the pressure and flow requirements and bingo, you’ll find the right compressor.

But air compressors are purchased for different reasons by a wide range of individuals and organisations. Having identified the unit that appears to meet your needs for the least possible cost, you might expect that it will run uninterrupted for as long as required.

However, the fact is that most compressors are not designed to run continuously. Therefore, two seemingly innocuous terms that have a great deal of bearing on how you can use your compressor are “run time” and “duty cycle”.

The ‘run time’ is the amount of time an air compressor can be run on full load before it needs a period of rest to cool down.  The amount of run time versus the down time is known as the ‘duty cycle’ which is usually expressed as a percentage. Put simply, duty cycle is the percentage of time that a compressor can run versus how long it needs to rest before it can start compressing air again.

So, during an hour of operation under standard conditions, a compressor specified with a run time of 5 minutes and a duty cycle of 25% would need to operate as follows:

25% duty cycle: 5 minutes on, 15 minutes off, 5 minutes on, 15 minutes off, 5 minutes on, 15minutes off.  This would then make up the hour.

Similarly, a 50% duty cycle with a max runtime of 5 minutes would be: 5 minutes on, 5 minutes off, repeated 6 times to make up the hour.

100% duty cycle – Allows for continuous operation of the compressor with no periods of downtime.

Failure to adhere to the run time and duty cycle of a compressor – the two key pieces of information – can lead to overheating and damage to the motor. Only those air compressors with a 100% duty cycle can run constantly at the specified pressure and flow.

Running an air compressor beyond its duty cycle limit leads to premature wear and tear, higher maintenance costs and, at its most extreme, breakdowns which can shut down production. But if the cooling off time is similarly interfering with operations, then the natural temptation is to push it to the limit, and perhaps beyond.

So, what seems like a good deal on the price of your compressor can actually become an expensive mistake if it can’t operate as required. Understanding the definitions of the terminology is key to keeping your world working.