Average demand does not tell the whole story
A tool may consume a large amount of air only briefly. The compressor then replenishes storage between tasks. The assessment must include instantaneous delivery, storage volume and time to replenish storage. The shift average alone does not guarantee that pressure will not drop during a task.
Temperature and starts have their own limits
The permitted duty cycle cannot be circumvented by taking a longer break only at the end of the shift. The length of a single run, starts per hour, ambient temperature and cooling may all be decisive. Continuous industrial operation must be based on the machine's explicit intended duty, not just whether it is labelled piston or screw.
What to check in practice
- Copy the percentage, time basis and applicable conditions from the manual.
- Do not confuse the consumer's duty cycle with the compressor's allowable duty cycle.
- After expanding production, recheck running time, temperatures and starts.
Example scenario
If a particular machine's manual allowed a 60% duty cycle over 10 minutes, this would mean no more than 6 minutes under load and the required rest within that interval. It would not permit six hours of continuous running during a ten-hour shift.
What to watch out for
- Assigning a 100% duty cycle to every compressor.
- Estimating allowable running time from motor size alone.
- Neglecting cooling and high intake temperature.
How can I tell whether operation has changed from the original design?
Signs include longer filling times, more starts, more frequent temperature-limit events or increasing loaded hours. These symptoms may also have a maintenance-related cause, so distinguish increased demand from reduced machine delivery.