How to choose a screw compressor: power and pressure

If compressed air is needed for hours on end in your workshop or on your production line, the right compressor is a rotary screw one: it is built for continuous duty, which a piston compressor does not handle well. In the AMES collection the power ratings range from 2.2 to over 90 kW, maximum pressures from 7 to 15 bar, and the most common voltage is 400 V three-phase at 50 Hz. For a few workstations a compact model is enough; for a line with several users you move up to the 11 kW classes and above, with a tank and dryer built in if space is short.

The types

• Compact belt-driven: screw unit with belt transmission, small footprint, suited to a workshop starting out with a single compressor. The Fini MICRO and PLUS are of this type, such as the MICRO SE 4.0-08 or the PLUS 8-08. The PLUS 8-15 is 7.5 kW and 15 bar, the PLUS 8-13 is 7.5 kW and 13 bar: same power, different pressure.
• Compact cube version: small units for workshops with medium consumption, such as the MINICUBE 2.2-08 (2.2 kW, 8 bar) or the CUBE 4.0-10 (4 kW, 10 bar).
• With integrated tank and dryer: everything on the same base, ready to connect to the air network. It saves space and fittings, but weighs more. Do not assume from the model code what is on the base: the PLUS 8-13-500 ES and the PLUS 8-13-500 have the same power and pressure, but the data sheet does not say what equipment they have. Ask AMES before ordering.
• Variable speed (VS): the unit adjusts its output to the air demand instead of stopping and restarting. It makes sense when demand changes a lot during the day, because it cuts idle running.
• High power: for lines with high consumption, from the 90 kW class upwards. The K-MAX TS 90-07 VS is a two-stage unit, meaning compression is split into two stages, rated 90 kW and 7 bar.

The versions: Pack, Full Feature, tank-mounted, floor-standing

The catalogue lists the versions as Pack, Full Feature, tank-mounted and floor-standing. The Full Feature has the dryer built in. The tank-mounted and floor-standing versions differ in how the machine is installed. In some of the Fini data sheets we checked, the version is listed as Standard, with no Pack or Full Feature option, so before ordering ask AMES which configuration matches the code you have chosen.

How to choose according to the job

The features to look at

Air flow. This is the figure that really matters: it tells you how much air the machine delivers per minute or per hour. Add up the consumption of the tools you use together and add a margin. Look for it in the data sheet of the individual model, because it is not the same thing as power.

Power (kW and HP). In the collection you find 2.2, 4, 5.5, 7.5, 11, 15, 22, 37 kW and the higher classes up to over 90. Remember that 1 HP is about 0.75 kW: 7.5 kW is about 10 HP. For the same required flow, more power simply means a compressor bigger than necessary.

Maximum pressure. You find 7, 7.5, 8, 10, 13 and 15 bar. Take the pressure the most demanding tool needs, plus the loss along the network. If you have no special tools, 8-10 bar is fine; 13-15 bar are for specific uses.

Cooling. Air-cooled in most cases, and then the room must be well ventilated; water-cooled where it is very hot or where there is no room for ventilation.

Tank. If present, it smooths consumption peaks and reduces starts.

Voltage and weight. 400 V three-phase at 50 Hz is the Italian standard; some Abac GA models are also available at 460 V and 60 Hz for other markets, so check that the voltage matches the mains at your site. Net weight ranges from 68 kg for the MINICUBE 2.2-08 to 3,050 kg for the K-MAX TS 90-07 VS: check the floor and the access route.

How to think about sizing. Start from the list of tools and machines that will use air, write down the consumption of each and add up only those that run at the same time. Add a margin for network losses and possible expansion. The result is the minimum air flow: power and size come after, not before. A compressor that is too small always runs at its limit; one that is too big costs more and, unless it is variable speed, spends a lot of time running idle.

Standards and documents to ask for

The data sheets of the Fini PLUS in the collection list three references, and it is worth knowing what they are for.

• Directive 2014/68/EU (PED): covers pressure equipment, that is the tanks and pressurised parts of the compressor.
• Machinery Directive 2006/42/EC: the basis of the CE marking and of the machine's declaration of conformity. From 20 January 2027 Regulation (EU) 2023/1230 applies and replaces it: for a purchase today, it is best to ask for the declaration of conformity for the specific model.
• ISO 1217: describes the acceptance tests for displacement compressors, including the measurement of the air flow delivered. If you compare two models, check that the flow is declared with the same method.

Installation and maintenance

The compressor goes in a ventilated technical room, on a flat floor and away from heat sources, with free space around it for cooling and maintenance. Pressure and operating mode (load or variable speed) are set from the control panel. After that it needs little, but it must be done regularly: drain the condensate, watch the alarms on the panel and carry out the scheduled services at the operating hours given in the manual, that is oil level and quality checks, filter replacement and cleaning of the air intakes, preferably with an authorised technician. It pays to plan them in advance, so as not to stop production.

Common mistakes

• Choosing on motor power rather than on the air flow you need.
• Installing the machine in a closed or hot room with no air change: it overheats and stops on alarm.
• Forgetting air treatment: without a dryer and filters, condensate and impurities reach the tools.
• Connecting the compressor to the network without a tank when consumption comes in peaks.
• Ignoring the mains voltage and frequency at the site.
• Leaving no space around the panels and then being unable to do maintenance.
• Skipping the scheduled maintenance at the operating hours given in the manual.

Frequently asked questions

When does it make sense to move from piston to screw?

When the compressor runs for many hours a day or over several shifts. A piston used like that wears out quickly; the screw is designed for continuous duty. For occasional use the piston costs less and is enough.

Is a tank always necessary?

No, but it helps cover the peaks. If the network is long or consumption is irregular, a tank, integrated or separate, makes the pressure more stable.

Is a dryer needed?

If the air has to be dry (painting, sensitive instruments), yes. The Full Feature has the dryer built in; for the other versions ask AMES whether it is included, otherwise it has to be added to the system.

How do I calculate the air flow I need?

Add up the consumption of the tools that run at the same time, add a margin for losses and expansion, and compare it with the flow stated in the data sheet.

Which pressure should I choose?

The one required by the most demanding tool, with a small margin. 8-10 bar is almost always enough.

Is single-phase supply suitable?

The standard voltage in the collection is 400 V three-phase at 50 Hz, and some Abac GA models are also available at 460 V and 60 Hz. You need a three-phase line suited to the power.

You find the models in the Industrial screw compressors collection: if you have doubts about flow and pressure, ask for a quote or advice from the AMES technicians.