Small industrial rotary screw compressors

Where do small screw compressors fit?

A small screw compressor sits between the workshop piston compressor and the larger plant machines of 30 kW and above. It is designed for duty that piston compressors handle poorly: air needed for many hours a day, at stable pressure, in a space shared with people.

Typical users include:

• CNC machining centres and tool rooms, for tool changers, spindle air, chip blowing and door actuators.
• Automotive service centres and body shops, for impact tools, tyre changers, lifts and spray painting.
• Packaging and printing units, for cylinders, grippers, vacuum generators and cutters.
• Small textile, garment and plastics units, for looms, presses and moulding machines.
• Food processing support, bakeries and small dairies, with suitable air treatment.
• Laboratories, hospitals and small pharmaceutical units, often with oil-free machines.

In and around Hyderabad, many such users are in industrial estates such as Balanagar, Jeedimetla, Cherlapally, Uppal and Patancheru, and in the growing manufacturing clusters across Telangana and Andhra Pradesh.

Screw or piston for a small plant?

As a rule of thumb, if your piston compressor runs more than about half the working day, or you have added receivers to keep it from overheating, a small screw compressor is worth evaluating.

How to size a small screw compressor

1. List every user. Note each machine’s air consumption and required pressure from its manual or nameplate.
2. Estimate simultaneous use. Not every tool runs at once. Multiply each consumption by how often it is in use, then add the results. A CNC shop with five machines may need far less than five times one machine’s peak.
3. Allow for leaks and growth. Older systems lose a significant share of air through leaks; fix them first, then add a realistic margin for planned expansion.
4. Set the pressure. Take the highest point-of-use pressure, add losses through dryer, filters and piping, and choose the nearest pressure variant, typically 7.5, 8.5 or 10 bar (about 110, 123 or 145 psig). Every extra bar adds about 7% to power.
5. Use FAD, not displacement. Compare free air delivery at working pressure, measured to ISO 1217.
6. Choose the control. Fixed speed with a well-sized receiver suits steady demand; variable speed suits varying demand and avoids long unloaded running.

Oversizing is the most common mistake in small plants. A compressor much larger than the demand spends long hours unloaded, still drawing a significant part of its full-load power, and may run so little that moisture builds up in the oil.

Package options to consider

• Base-mounted: the compressor stands on the floor and feeds a separate receiver and dryer. Flexible and easy to service.
• Tank-mounted: the compressor sits on its own receiver, saving floor space. Good for compact rooms.
• Integrated dryer: a refrigerated dryer built into the package, delivering air with a pressure dew point typically around +3 °C. Simplifies installation for CNC and painting.
• Belt or direct drive: belt drives are common and easy to adjust; direct drives remove belt maintenance.
• Oil-injected or oil-free: oil-injected with filtration suits most workshops; oil-free scroll or screw machines suit labs, medical and sensitive food uses.

Air treatment for small systems

Small plants often skip air treatment, then suffer water in tools, rust in cylinders and rejected paint finishes. A sensible minimum is:

• Refrigerated dryer for general plant air, or a desiccant dryer (−20 or −40 °C pressure dew point) where air lines run outdoors or the process is moisture-sensitive.
• General-purpose and coalescing filters to the ISO 8573-1 class the equipment manufacturer specifies.
• Oil–water separator for condensate, so oily water is not drained to the ground.

Hyderabad’s monsoon humidity and hot summers mean a compressor can produce many litres of condensate a day. Without a dryer, much of that ends up in the pipework.

Installation in Indian conditions

A small screw compressor rejects nearly all its motor power as heat. In a closed room in a 40–45 °C summer, temperatures rise quickly and the machine trips on high discharge temperature. Good practice includes:

• A clean, shaded, ventilated location away from boilers, ovens and dust sources such as grinding or cutting.
• Hot-air ducting from the cooler outlet to outside, and a cool-air inlet low on the opposite wall.
• Clearance around the package for service access, as given by the manufacturer.
• Correct cable size, protection and a stable supply; low voltage raises motor current and temperature.
• Piping sized for low pressure drop, preferably a loop, with drops taken from the top of the header.

Common problems in small screw systems

Running costs: why energy matters even on a small machine

On a small compressor, the purchase price feels like the main cost. Over the life of the machine, electricity usually costs far more. A 15 kW compressor running loaded for 4,000 hours a year uses roughly 60,000 kWh, before counting unloaded running. That is why a few simple habits pay back quickly.

• Lower the pressure to what the machines actually need. Running at 8 bar instead of 9 bar saves about 7% of compressor power.
• Fix leaks at quick couplings, hoses, drain valves and fittings. In small plants they often run day and night, even when production has stopped.
• Switch off after hours, or isolate the compressor from the network with a valve so leaks do not keep it running overnight.
• Avoid open blowing with plain pipe ends; use engineered nozzles or reduce blowing time.
• Keep filters clean, since a blocked intake or line filter forces a higher discharge pressure.
• Check load and unload hours on the controller each month. A rising load ratio with the same production usually means leaks or wear.

Measuring specific power in kW per m³/min once a year gives a clear picture of whether the compressor still delivers the air it should for the power it draws.

How Reddy Compressors helps

Reddy Compressors has supplied and serviced compressors since 2002 from our office at Tarnaka, Secunderabad. As an independent multi-brand specialist, not an authorised dealer, we sell new and used/refurbished small screw compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, with dryers, receivers and filters. We have tie-ups with all major and reputed brands.

• We size the compressor from your actual machines and shifts, and advise whether a screw, piston or oil-free machine suits you.
• We supply complete packages: compressor, receiver, dryer, filters and drains, with guidance on room layout and piping.
• Our team of over 20 service engineers and technicians provides service, AMC and breakdown repair across Telangana and Andhra Pradesh.
• We supply spares across India, identified from the nameplate and serial number with fit confirmed before quoting.
• We can provide a rental compressor while your machine is under repair.

What to send us

• List of machines and tools using air, with their pressure and consumption if known.
• Number of shifts and hours of operation.
• Details of the existing compressor: make, model, nameplate photo and any problems.
• Photos of the proposed compressor location, showing ventilation.
• Air-quality needs, such as painting, food contact or instrument air.
• Your power supply: voltage, and whether a DG set is used.

Frequently asked questions

What size screw compressor do I need for a CNC shop?

Add up the air consumption of each CNC machine from its manual, estimate how many run at once, include blowguns and other users, and allow for leaks. Then check the highest pressure any machine needs. Many CNC shops find a 7.5–15 kW machine with a refrigerated dryer adequate, but the real answer comes from the machine data and shift pattern, not the number of machines alone.

When should I replace a piston compressor with a screw compressor?

Consider a screw compressor when your piston machine runs for most of the working day, overheats, passes oil into the lines, or cannot keep up with demand. Screw compressors are designed for continuous duty and keep their output steadier over time. If air is needed only occasionally for short periods, a piston compressor may still be the more economical choice.

Do small screw compressors need a dryer?

For most industrial uses, yes. Compressed air leaves the compressor saturated with moisture, and in Hyderabad’s humid months this means a lot of water in the pipes. A refrigerated dryer, giving a pressure dew point typically around +3 °C, protects tools, cylinders and paint finishes. Many small compressors are available with a built-in dryer to simplify installation.

Can a small screw compressor be installed inside the workshop?

Often yes, because enclosed screw packages are much quieter than piston compressors. The location still needs good ventilation, protection from dust and heat, and service clearance. Duct the hot cooling air outside, especially in summer, and keep the compressor away from grinding, welding and painting areas, whose dust and fumes clog filters and coolers quickly.

Is a variable-speed drive worth it on a small compressor?

It can be, when demand varies widely through the day and the compressor would otherwise spend long periods unloaded. On a steady load near full output, a fixed-speed machine with a well-sized receiver is cheaper and works well. Running a check of load and unload hours on the existing machine shows which pattern your plant has.

How often should a small screw compressor be serviced?

Follow the manufacturer’s service intervals for the intake filter, oil, oil filter and separator, and shorten them in dusty or very hot conditions. Check drains and filter indicators weekly, and clean coolers before summer. A planned service or AMC keeps the machine reliable and avoids the overheating and oil problems that most small plant breakdowns start with.

Related pages

• Medium industrial rotary screw compressors
• Tank-mounted rotary screw compressors
• Integrated compressor and dryer packages
• Rotary screw vs reciprocating air compressors
• Compressor capacity selection and sizing
• Rotary screw compressors hub