In a catalogue, a piston compressor and a screw compressor of the same power may look interchangeable. They are not. The way they compress air is completely different, and that difference in principle carries through to everything else: duty cycle, noise, air quality, maintenance and electricity consumption.
What happens inside
The piston compressor: compression in cycles
A piston compressor works like a car engine in reverse. An electric motor drives a crankshaft, which moves one or more pistons up and down inside cylinders.
- The piston moves down: air enters through an intake valve.
- The piston moves up: the air is compressed in the cylinder.
- The discharge valve opens: the compressed air flows to the air receiver.
On two-stage models, the air passes through a first cylinder, is cooled, then compressed a second time in a smaller cylinder, which makes it possible to reach a higher pressure.
The air is stored in the air receiver. When maximum pressure is reached, the pressure switch stops the motor; when the pressure drops, it restarts it. A piston compressor therefore works in on/off cycles.
The screw compressor: continuous compression
A screw compressor compresses air between two helical rotors that turn against each other without touching. Air enters on one side, is trapped in the grooves of the screws, and its volume is gradually reduced as it moves forward. It comes out compressed on the other side.
There is no back-and-forth motion and no valves slamming: compression is continuous. In oil-injected screw compressors, the oil injected into the compression stage seals the gap between the screws, lubricates and cools all at once. It is then separated from the air by the air/oil separator.
The practical consequences in the workshop
Duty cycle
This is the most important difference. A piston compressor needs rest periods between cycles: it heats up during compression and has to cool down. It is designed for intermittent use.
A screw compressor is designed to run continuously, all day long. It is the machine for workshops that use air constantly: sanding, painting, production, several workstations at once.
Noise
A piston compressor produces a characteristic hammering sound, caused by the reciprocating motion and the valves. A screw rotates smoothly and the machine is usually housed in a soundproof enclosure. For comparable use, a screw compressor is far more comfortable to have near a workstation.
Air quality
A screw compressor delivers a steady air flow. Combined with a dryer and filtration, it supplies dry, clean air, which is essential for painting and finishing. A piston compressor is perfectly suited to standard air tools, but the air comes out hotter and in pulses, which calls for a good air receiver and, for demanding applications, suitable air treatment.
Maintenance
Both technologies need regular maintenance, but not the same kind:
- Piston: checking and changing the crankcase oil, intake filter, condition of the valves and piston rings, belt tension where applicable.
- Screw: air filter, oil and oil filter, air/oil separator, at intervals based on operating hours. At AIRSTAHL, the parts for a service are grouped into a service kit for each model.
In both cases, the condensate drain on the air receiver is part of routine maintenance.
Electricity consumption
In continuous use, a screw compressor is generally more efficient: it produces air steadily, without the losses caused by repeated starts. For occasional use, a piston compressor remains a sound choice, as it only runs when it is needed.
Purchase price
For comparable power, a piston compressor costs less to buy. A screw compressor costs more up front, but it becomes the obvious choice as soon as the machine runs for a large part of the day.
Which one should you choose?
- Air is used now and then (tyre inflation, tightening, blow gun, small tools): a piston compressor is enough.
- Air is used for a large part of the day, across several workstations, or for painting: choose a screw compressor.
To go further on choosing, read our guide Screw or piston compressor - which one to choose?. And if you are torn between two models, send us the list of your tools in a quote request: we will get back to you with a recommendation.