SCR Screw Compressors: Technology for the cheapest air

Six machines from the SCR range side by side — from a compact unit to a large cabinet

8 SCR series

SCR builds its compressors around a single figure — what a cubic metre of air costs over the whole time the machine runs. The programme has eight series from 2.2 to 280 kW: oil-free scroll units for a doctor’s surgery, compact screw machines for the workshop and two-stage cabinets for plants that never stop. This page does not explain why a screw compressor — the overview of screw compressors is there for that. It is about which SCR series to take.

2.2 – 280 kWmotor rating

200 – 60,000 l/minair output

7 – 12.5 barworking pressure

8series in the programme

Before you start choosing, answer four questions

Each one narrows down what the previous one left — after the fourth answer you are usually left with two of the eight series.

How much air do you use?

A compressor is chosen by litres per minute, not by kilowatts. Add up the consumption of the tools and machines that can run at the same time and put a reserve on top for leaks in the pipework. The SCR programme covers 200 to 60,000 l/min, so the first question rules most of the series out straight away.

Does the demand fluctuate through the shift?

When the consumption changes — everything runs for a while, then nothing — a variable-speed drive pays off: the machine holds the pressure with its speed instead of cycling empty. With an even demand at full output, fixed speed is cheaper to buy and uses just as much.

May the air meet oil?

Food production, beverages, pharmaceuticals, medicine, electronics and paint shops need air that oil has no way of getting into. Only the oil-free series can do that — the XA scroll in small volumes and the G/GV screw in large ones. Filtration behind an oil-lubricated machine is a substitute, not the same thing.

How many hours a day will it run?

On one shift the purchase price decides. On two and three shifts the electricity bill outgrows it so far that two-stage compression and an IE4 motor with permanent magnets pay off — the higher series, that is. The difference is not counted in years, but in months of running.

Eight series and what sets them apart

The series are ordered by motor rating, which is the way a machine is really chosen. Each one says what kind of plant it is built for.

SCR-XA

2.2 – 29.6 kW · 200 – 3,520 l/min — Oil-free air in small quantities. A doctor’s surgery, a laboratory, a small paint shop or a food line — anywhere the air meets the product and there must not be a trace of oil in it. Two scrolls compress it without ever touching each other, so there is no lubricant in the compression chamber at all. The output is set by switching individual blocks in and out, not by a variable-speed drive.

SCR-APM Mini

3.7 – 5.5 kW · 320 – 696 l/min — The smallest screw machine for the workshop. A car workshop, a joinery, a smaller assembly shop. It replaces a piston compressor where its stop-start running is no longer enough, but a large cabinet would be a waste. Also sold as an assembly with an air receiver and a dryer in one frame.

SCR-APM Maxi

7.5 – 15 kW · 950 – 2,000 l/min — Workshop and smaller production. A typical engineering workshop or an assembly line taking around a thousand litres a minute. The same technology as the Mini, only one size up — and with assemblies that carry filtration besides the air receiver and the dryer.

SCR-PM2 run-out

7.5 – 15 kW · 950 – 2,000 l/min — Run-out of the previous generation. The predecessor of the APM Maxi series in the same power band. The machines are new and complete, it is only the rest of the stock that is being sold off — so it pays to compare the price with the Maxi before you decide.

SCR-EPM

15 – 45 kW · 2,300 – 9,500 l/min — Production on two shifts. The middle band, where the energy already counts. Direct drive without belts, an IE4 motor with permanent magnets and a variable-speed drive that holds the pressure in the system instead of cycling empty. The SCR9000 controller can run a weekly schedule.

SCR-G / GV

37 – 280 kW · 5,700 – 47,000 l/min — Oil-free air in quantity. Food production, beverages, pharmaceuticals, electronics, glassworks — plants that need air without oil in volumes a scroll machine cannot cover. Two screw stages with no lubrication in the compression chamber, cooled by air or by water. The GV version has a variable-speed drive on top of that.

SCR-EPM2

55 – 160 kW · 10,000 – 33,500 l/min — Large industrial plant. The main machine of the compressor room in a production plant. A new generation in an anthracite finish, a variable-speed drive with vector control and controlled speed on the cooling fan as well — so the power input falls with the load twice over.

SCR-H / HPM

132 – 280 kW · 28,500 – 60,000 l/min — Continuous duty, the lowest specific consumption. The most powerful machines in the range, for plants that never stop — laser cutting, textiles, power generation, large metalworking. The air is compressed in two stages with intercooling, so the same cubic metre costs less electricity. The only series that also does 12.5 bar.

A comparison of the eight SCR series
Series	Rating (kW)	Output (l/min)	Pressure (bar)	Lubrication	Speed control	Typical role
SCR-XA	2.2 – 29.6	200 – 3,520	7 – 10	oil-free	in steps, by blocks	Oil-free air in small quantities
SCR-APM Mini	3.7 – 5.5	320 – 696	10	oil-lubricated	variable-speed drive	The smallest screw machine for the workshop
SCR-APM Maxi	7.5 – 15	950 – 2,000	10	oil-lubricated	variable-speed drive	Workshop and smaller production
SCR-PM2	7.5 – 15	950 – 2,000	10	oil-lubricated	variable-speed drive	Run-out of the previous generation
SCR-EPM	15 – 45	2,300 – 9,500	7 – 10	oil-lubricated	variable-speed drive	Production on two shifts
SCR-G / GV	37 – 280	5,700 – 47,000	7 – 10	oil-free	G fixed speed, GV variable-speed drive	Oil-free air in quantity
SCR-EPM2	55 – 160	10,000 – 33,500	7 – 10	oil-lubricated	variable-speed drive	Large industrial plant
SCR-H / HPM	132 – 280	28,500 – 60,000	7 – 12.5	oil-lubricated	H fixed speed, HPM variable-speed drive	Continuous duty, the lowest specific consumption

The output is the rated volume flow to ISO 1217; on machines with a variable-speed drive it is the upper limit of the control range. The exact figures for a particular model are given with the product.

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Which series for which plant

The overview is a shortcut, not a rule — borderline cases are settled by working the demand out. If your plant is not in the table, or if it fits two rows at once, write to us.

Which series for which plant
Plant	What decides	Series
Dental surgery, laboratory, small paint shop	oil-free air in small quantities	SCR-XA
Car workshop, joinery, smaller assembly shop	300 – 700 l/min, one shift	SCR-APM Mini
Engineering workshop, assembly line	around 1,000 – 2,000 l/min	SCR-APM Maxi
Production on two shifts	fluctuating demand, 15 – 45 kW	SCR-EPM
Compressor room of a production plant	main machine 55 – 160 kW	SCR-EPM2
Food production, beverages, pharmaceuticals, electronics	oil-free air from 5,700 l/min	SCR-G / GV
Laser cutting, textiles, power generation	continuous duty 132 – 280 kW	SCR-H / HPM
Glassworks, cement plant	a large amount of air at a low pressure	low-pressure versions on request

The industries that come to us most often

Biscuits on the conveyor of a packing line — Food production — the air meets the product and the packaging

Blisters of tablets on the conveyor of a pharmaceutical plant — Pharmaceuticals — air purity is part of the manufacturing specification

Glass bottles in a forming machine above the flame of a glass furnace — Glassworks — large volumes of air, often at a lower pressure

A laser cutting machine cutting steel sheet — Metalworking — laser cutting runs without a break

Car bodies on an assembly line — Automotive industry — assembly, bolting and painting

Robots populating printed circuit boards — Electronics — board assembly will not take oil mist

Five technologies the saving rests on

Most SCR series are fitted with them, and the higher up the programme, the more of them the machine carries. They are what makes the difference between a compressor that is cheap to buy and a compressor that is cheap to run.

Two-stage compression — the air is compressed in two goes with intercooling, so the same cubic metre costs less electricity than on a single-stage machine.
Direct 1:1 drive — the block sits on the motor with no belts and no gearbox, so nothing is lost in the transmission and nothing is spent on tensioning and changing belts.
IE4 motors with permanent magnets — they hold a high efficiency at part load as well, which is exactly where an ordinary asynchronous motor falls away.
Motor cooling by oil or by liquid — the winding temperature stays low, which spares the insulation and the bearings and holds the efficiency for the whole life of the machine.
Speed control of the motor and of the fan — the speed follows the actual consumption, so a machine that happens to be running at a third is not cooled flat out.

How a screw compressor works

A pair of rotors turns against each other and the space between their teeth shrinks steadily on the way from the intake to the outlet — that is what compresses the air, with no valves, no pulsation and no breaks. It is why a screw machine takes the continuous running that would cook a piston compressor. A scroll compressor does the same thing differently: pockets of air travel between a fixed and an orbiting scroll towards the centre and shrink on the way. It is gone into in more detail in the advice section.

Four stages of air compression between the fixed and the orbiting scroll — The scroll principle — the air is compressed between two scrolls that never touch. There is therefore no lubricant in the compression chamber.

The screw principle — a pair of rotors reduces the volume of the air steadily, with no valves and no pulsation.

A two-stage screw block — both stage sections on a common gearbox — The two-stage block — the air goes through two stages with cooling between them, so the same cubic metre costs less energy.

A variable-speed drive with vector control inside the compressor cabinet — A variable-speed drive changes the speed with the consumption instead of letting the machine cycle between full output and running empty.

The SCR9000 controller with a colour display and a diagram of the machine — The SCR9000 controller watches the pressure, the temperatures and the service intervals, and can run a weekly schedule.

A look inside a two-stage compressor at the screw block and the electric motor — The layout of a large machine — block, motor, cooling and separator in one sound-insulated cabinet.

A compressor room with a row of cabinet compressors and upright air receivers

There is more to it than the compressor

The machine on its own makes air, but it is the rest of the compressor room that makes it usable. An air receiver evens out the peaks, so that the compressor does not switch on at every draw. Drying removes the water that would otherwise condense in the pipework and in the tools. Filtration tunes the purity to what the air is for. The pipework decides how much pressure you lose on the way. On the smaller series the air receiver and the dryer can be bought in one frame with the compressor; on the large ones the compressor room is put together to measure.

Ventilek advises

Do not buy a compressor by the kilowatts on the plate. What decides is how many litres a minute the machine gives at your pressure and how much it takes to do it — and on two machines with the same motor that can easily differ by a quarter. In a multi-shift plant the purchase price is only a fraction of what the compressor will cost you in the end; the rest is electricity. If you are not sure, send us your demand and your running hours and we will work it out for you.

Common questions about choosing

Is a variable-speed drive worth it, or is fixed speed enough?: It comes down to whether the demand fluctuates. A fixed-speed machine can only run and unload — and an unloaded machine still takes roughly a third of its power. When a plant has peaks and lulls, a variable-speed drive takes that idle running away. When a line runs evenly at full output, the VSD has nothing to save and all that is left of it is the higher purchase price. Most SCR series have a VSD as standard; on the G and H series you choose between the version with one and the version without.
What is the difference between oil-free and filtered air?: On an oil-lubricated compressor the oil is right there in the compression chamber and filtration behind the machine reduces what is left of it. On an oil-free machine the oil has no way of getting into the compressed air, because there is none in the chamber. For plants where the air meets food, a medicine or a painted surface, that is the difference between a precaution and a certainty.
Why two-stage compression?: Compressing air in one go from atmosphere to ten bar means a high outlet temperature, and a loss with it. Split it into two stages with a cooler in between and the same cubic metre uses less energy. That is why the most powerful series have it, where the saving is multiplied by the hours worked.
How many bar should I choose?: Most air tools and machines manage on 7 or 8 bar. Every extra bar costs roughly 7% of the power input, so buying pressure “just in case” does not pay. Ten bar makes sense on long pipe runs and with machines that reduce the pressure themselves; 12.5 bar is done by one series only — the SCR-H.
Do I need anything else besides the compressor?: Almost always an air receiver, so that the machine does not switch on at every draw, and drying, so that water does not condense in the pipework. On the smaller series both can be bought in one frame with the compressor; on the large ones they are dealt with separately, to suit the compressor room.
Does more kW mean more air?: Only within one series. Between series it does not — a two-stage machine makes more air from the same power input than a single-stage one, and an oil-free machine makes less, because it compresses without a lubricated sealing film. So compare litres per minute at a given pressure, not kilowatts.

The ranges given apply to the whole SCR programme; individual models differ. The output figures come from the manufacturer’s data and the flow measurement follows ISO 1217. Prices of the large machines depend on the particular assembly and version, which is why they are given on request.