Oil-injected and oil-free designs
In an oil-injected machine, oil helps seal and remove heat. It is separated downstream of the airend and returned to the circuit. An oil separator does not, however, guarantee the required purity at the point of use. In oil-free designs, oil is not introduced into the compression chamber; some use dry compression, others water injection, for example.
Control matters, not just size
With variable consumption, a suitable option may be speed control, while a properly selected fixed-speed machine can serve a stable base demand well. Minimum delivery and behaviour below it also matter. Long unloaded running of an oversized package can significantly worsen operating costs.
What to check in practice
- Compare delivery and input power at the required pressure.
- Provide maintenance access, air supply and heat removal.
- Design air treatment for the consumer, not just the compressor type.
Example scenario
Production steadily consumes 4 m³/min, but demand almost disappears for an hour during shift change. The design must address that break too. A daily average of 3.5 m³/min alone does not show the required maximum delivery or low-demand costs.
What to watch out for
- Automatically choosing VSD without knowing consumption.
- Assuming a screw compressor does not need a dryer.
- Blocking cooling to reduce noise.
Is a screw compressor also suitable for a small workshop?
It can be, if it matches the operating profile. For very short, infrequent demand, a piston machine is also worth comparing. Workshop size alone is not decisive; air requirements and operating patterns are.