The screw compressor is the go-to machine as soon as a workshop needs air all day long: truck workshops, body shops, joinery, production plants. This guide brings together the essentials: how it works, what sets it apart from a piston compressor, the different types, how to choose the right size, what it costs and how to maintain it.
What is a screw compressor?
A screw compressor is a rotary air compressor: the air is compressed by two screw-shaped rotors turning against each other, smoothly and without pulsation. It is also called a rotary screw compressor, or an "oil-injected screw compressor" when oil is injected into the screw element, which is the case for every AIRSTAHL compressor.
Unlike a piston compressor, which works in cycles and needs to rest, a screw compressor is designed to run for long periods without stopping. That is why workshops with continuous air demand choose it.
How a screw compressor works
The principle: two screws that shrink the volume of air
The two rotors mesh without touching. As they turn, they trap a pocket of air on the inlet side and push it towards the other end. The volume of this pocket shrinks gradually: the air is compressed continuously, then leaves at the outlet. There is no valve and no piston moving up and down, hence smooth running and less vibration.
The air and oil circuits
In an oil-injected screw compressor, oil is injected into the screw element. It lubricates the rotors and bearings, seals the compression and carries the heat away. At the outlet, air and oil are separated in the separator tank and then in the air/oil separator cartridge: the air goes on to the receiver, while the oil is cooled in the cooler, filtered and injected again. Each circuit, including the electrical side, is explained in our article how a screw compressor works.
Control: variable speed and automatic stop
The controller holds the pressure you have set. On our variable speed models, the frequency inverter matches the motor speed to the air demand: the machine slows down when the workshop uses little air. When the pressure is reached, the compressor stops by itself, then restarts automatically when the network pressure drops. The different control modes are compared in our guide load/unload or variable speed.
Pros and cons
| Screw compressor | Piston compressor | |
|---|---|---|
| Duty | designed to run continuously | works in cycles, with rest periods |
| Noise | generally quieter | louder |
| Air output | steady flow | pulsating flow |
| Maintenance | services based on running hours, with parts kits | simple, but more frequent when it runs a lot |
| Purchase price | higher | lower |
| Best for | workshops using air all day | occasional use, small garage, back-up |
The advantages: continuous running, lower noise, steady air flow, and controlled electricity use when the machine has variable speed.
The limits: a higher purchase price than a piston compressor of the same power, and services to follow by running hours. If your compressor only runs a few minutes per hour, a piston compressor is often still the best choice: our guide screw or piston compressor helps you decide.
The different types of screw compressors
- The standalone screw compressor: the machine on its own, to combine with the receiver and dryer of your choice. This is the S series, from 5.5 to 132 kW, to replace a machine or extend an installation.
- The 4-in-1 screw compressor with dryer: compressor, receiver, refrigerated dryer and filtration on one frame. This is the K series. Set it down, connect it, and the air comes out dry. See 4-in-1 or standalone compressor.
- The high-pressure screw compressor: up to 16 bar, with dryer and precision filtration, for laser cutting. This is the L series. See 10, 13 or 16 bar.
- The mobile screw compressor: mounted on a receiver and wheels, to take the air where the work is. This is the M series.
- Variable or fixed speed: variable speed matches output to demand and avoids running the motor for nothing. See variable or fixed speed.
- Oil-injected or oil-free: oil-free compressors are reserved for uses that require them (pharmaceuticals, some food industries). All AIRSTAHL compressors are oil-injected. When a trade needs very clean air, a suitable dryer and filters are added: see air quality to ISO 8573-1.
How to choose the right size
You do not choose a screw compressor by its power in kW, but by the air flow the workshop needs, at the pressure the tools require.
- Add up the consumption of the tools running at the same time, in litres per minute (l/min).
- Add a margin for leaks and future workstations.
- Check the pressure: 8 bar is enough for most workshops. Some tools and machines need 10 or 13 bar, and laser cutting up to 16 bar.
- Look at the running time: the more the machine runs, the more variable speed saves.
Our guide what size compressor to choose explains the calculation, and the configurator suggests the right model for your trade in a few clicks.
Power supply: our screw compressors up to 22 kW run on 380 V three-phase. See 380 V screw compressor. For a workshop without three-phase power, see single-phase garage compressor.
Screw compressor prices
The price of a screw compressor depends on its power, its pressure and what is built in (receiver, dryer, filtration). Here are the list prices for our whole screw compressor range:
| Model | Power | Pressure | Air flow | Price excl. VAT |
|---|---|---|---|---|
| S 55 — Screw compressor 5.5 kW S Series — screw compressors | 5.5 kW | 8 bar | 0.6 m³/min at 8 bar | From £1,492 excl. VAT |
| K 75 — Screw compressor 7.5 kW 4-in-1 K Series — 4-in-1 compressors | 7.5 kW | 8, 10 or 13 bar, your choice | 1.1 m³/min at 8 bar; 0.95 m³/min at 10 bar; 0.8 m³/min at 13 bar | From £2,408 excl. VAT |
| S 75 — Screw compressor 7.5 kW S Series — screw compressors | 7.5 kW | 8, 10 or 13 bar, your choice | 1.1 m³/min at 8 bar; 0.95 m³/min at 10 bar; 0.8 m³/min at 13 bar | From £1,992 excl. VAT |
| M 75 — Mobile screw compressor 7.5 kW M Series — mobile screw compressors | 7.5 kW | 10 bar | 1.0 m³/min at 10 bar | On quote |
| K 110 — Screw compressor 11 kW 4-in-1 K Series — 4-in-1 compressors | 11 kW | 8, 10 or 13 bar, your choice | 1.7 m³/min at 8 bar; 1.4 m³/min at 10 bar; 1.1 m³/min at 13 bar | From £3,158 excl. VAT |
| S 110 — Screw compressor 11 kW S Series — screw compressors | 11 kW | 8, 10 or 13 bar, your choice | 1.7 m³/min at 8 bar; 1.4 m³/min at 10 bar; 1.1 m³/min at 13 bar | From £2,658 excl. VAT |
| L 110 — 16 bar all-in-one laser cutting compressor 11 kW L Series — 16 bar laser cutting compressors | 11 kW | 8 to 16 bar | 0.8 m³/min | On quote |
| K 150 — Screw compressor 15 kW 4-in-1 K Series — 4-in-1 compressors | 15 kW | 8, 10 or 13 bar, your choice | 2.2 m³/min at 8 bar; 2.0 m³/min at 10 bar; 1.6 m³/min at 13 bar | From £3,825 excl. VAT |
| S 150 — Screw compressor 15 kW S Series — screw compressors | 15 kW | 8, 10 or 13 bar, your choice | 2.2 m³/min at 8 bar; 2.0 m³/min at 10 bar; 1.6 m³/min at 13 bar | From £2,992 excl. VAT |
| L 150 — 16 bar all-in-one laser cutting compressor 15 kW L Series — 16 bar laser cutting compressors | 15 kW | 8 to 16 bar | 1.3 m³/min | On quote |
| S 220 PM — Screw compressor 22 kW permanent magnet S Series — screw compressors | 22 kW | 10 bar | 3.2 m³/min at 10 bar (3.8 at 7 bar; 3.6 at 8 bar; 2.9 at 12.5 bar) | From £3,325 excl. VAT |
| L 220 — 16 bar all-in-one laser cutting compressor 22 kW L Series — 16 bar laser cutting compressors | 22 kW | 8 to 16 bar | 1.8 m³/min | On quote |
| M 220 — Mobile screw compressor 22 kW M Series — mobile screw compressors | 22 kW | 12.5 bar | 2.0 m³/min at 12.5 bar | On quote |
2-year warranty, spare parts available for 15 years. The purchase price is only part of the cost: over a compressor's life, electricity weighs far more than purchase and maintenance. Our guide life-cycle cost explains how to compare two machines.
Installation
A screw compressor is installed in a ventilated, clean and frost-free room, on a flat floor, with space around it for maintenance. The hot air it releases must be able to leave the room. After the compressor come the receiver, which stores the air, then the dryer and filters, which remove water and oil, and finally the network. To go further:
- compressor room installation;
- air receiver sizing;
- connecting the compressor to the network;
- which air dryer to choose.
Maintenance
A screw compressor is serviced by its hour meter. On all AIRSTAHL screw compressors, the first service is at 500 hours, then a service every 1,500 hours: the controller shows the reminder. At each service, the air filter, the oil and the oil filter are replaced and the air/oil separator is checked. Between services: condensate drain, oil level, clean cooler.