12 bar portable compressors: uses, sizing and air demand

What is a 12 bar portable compressor?

It is a mobile compressor, usually diesel-driven and towable, whose maximum working pressure is about 12 bar gauge (174 psig). Most are oil-injected rotary screw machines in the 185–750 cfm range (about 5.2–21 m³/min). Many are sold as dual-pressure or variable-pressure machines that can run at 7, 10 or 12 bar, giving more flow at the lower settings and less at the top setting.

The 12 bar figure is the compressor’s rating, not a promise of 12 bar at the tool. Pressure falls along the hose, through couplings and through any aftercooler, separator, dryer or filter. A machine set at 12 bar may deliver noticeably less at the end of a long, narrow hose under full flow.

Where is 12 bar air used?

• Fibre-optic cable blowing – telecom and utility contractors across Telangana and Andhra Pradesh use 10–14 bar air to carry cable through ducts; higher pressure helps on longer or more difficult routes within the duct and cable limits.
• Sandblasting with long hoses – extra compressor pressure helps hold the target nozzle pressure where hose runs are long.
• Light drilling – some rock drills and small hammers in favourable ground.
• Pipeline drying and purging support – under the client’s approved procedure.
• Tools and process equipment rated for higher inlet pressure – where the maker specifies it.

Twelve bar is not automatically better. Each extra bar of discharge pressure takes about 7% more power for the same flow, so a job that only needs 7 bar at the tool should not run at 12 bar.

How do you total the air demand?

Many machines that use compressed air have more than one consumer. A cable-blowing machine, for example, uses air to carry the cable through the duct and may also use an air motor to drive the feed mechanism. A blast set uses air at the nozzle and sometimes for remote controls. Add every consumer.

1. List each consumer: main process, air motors, feed drives, controls and any auxiliary tools.
2. For each, record the flow and the pressure at which that flow applies.
3. Check whether the maker’s “compressor requirement” already includes the motor or feed drive, or whether that must be added. If the document does not say, ask the maker before selection.
4. Note conditional figures, such as motor consumption at a stated cable speed, and do not treat them as fixed for all speeds.
5. Add the simultaneous demand, then allow a working margin for wear, leakage and higher ambient temperatures.
6. Compare the total with the compressor’s free air delivery at its 12 bar setting, not its lower-pressure rating.

A common mistake is to compare a demand figure with a compressor whose quoted flow only just exceeds it. Two figures a few cfm apart, measured on different bases, do not prove a match. Check the reference conditions and allow margin.

A worked demand example

Suppose a crew plans to blow cable through a duct and the blowing machine’s documents give a duct-related compressor range plus a separate air-motor consumption at a stated cable speed. The documents do not say whether the motor is included in the range. For this illustration only, assume the duct needs 300 cfm at 12 bar and the motor needs 35 cfm.

• If the motor is included, the demand stays at 300 cfm.
• If it is not, the demand becomes 335 cfm, before any margin.
• Add a working margin, and also allow for pressure drop through the aftercooler, separator and hose.

A compressor rated at, say, 320 cfm at 12 bar would pass the first reading and fail the second. That is why the inclusion question must be answered by the equipment maker before a machine is reserved, rather than settled by whichever interpretation suits the compressor that happens to be available. These figures are illustrative, not a recommendation for any duct or route.

Flow at 12 bar versus lower settings

On a variable-pressure portable, flow falls as pressure rises because the engine power is shared between pressure and volume. A machine that delivers a given cfm at 7 bar may deliver noticeably less at 12 bar. Always ask for the free air delivery at the setting you will actually use.

Air quality: cool, dry and clean

Air leaving a portable compressor is hot and saturated with moisture. For general tool use this is acceptable with a drain trap and lubricator. For cable blowing, coating work and pipeline drying it often is not.

• Aftercooler – cools discharge air close to ambient so moisture condenses before it reaches the work.
• Moisture separator – removes the condensed water and drains it automatically.
• Dryer – where the work needs a lower dew point; a refrigerated dryer typically gives a pressure dew point around +3 °C.
• Filtration – to reduce oil aerosol and particles where the receiving equipment requires cleaner air.

Every treatment item adds pressure drop. Include it when you work out the compressor setting, and confirm each item is rated for the full working pressure.

Hoses and connections at 12 bar

Check the working-pressure rating of the complete hose assembly, including the end fittings, not just the hose marking. Every joint should have a rated coupling and a restraint or whip check. Choose hose bore by flow and length: a narrow hose on a long route can waste much of the pressure you paid for. Keep the hose run as short and straight as the job allows, and keep a gauge at the point of use.

Common problems on 12 bar jobs

Standard safety shutdowns on diesel portables include high discharge temperature, low engine oil pressure and high coolant temperature. Normal oil-injected screw discharge temperature is about 75–95 °C.

Buy, buy used or hire?

Contractors who run cable-blowing or blasting crews most of the year often buy, either new or used and refurbished. Project work, seasonal peaks and trials usually suit hire. On hire jobs we service machines every 300 running hours, including oil change, so the crew can concentrate on the work.

How Reddy Compressors helps

Reddy Compressors, based at Tarnaka, Secunderabad, has supported industry since 2002 as an independent multi-brand specialist. We sell new and used or refurbished 12 bar portables, rent from our own fleet of diesel and electric machines (50–2,000 cfm, 2–30 bar), and service and supply spares for ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and other makes. We are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.

We help you total the demand from the receiving equipment’s documents, choose the pressure setting, and supply hoses, aftercoolers, moisture separators and dryers where the work needs them. Our team of over 20 service engineers and technicians covers all of Telangana and Andhra Pradesh, and we supply machines, rentals and spares across India.

What to send us

• Application and the receiving equipment’s make, model and air-demand document.
• Pressure and flow required, including air motors or feed drives.
• Hose length, route and any treatment needed.
• Site location, working hours and expected job duration.
• Whether you want to buy new, buy used or hire.

Frequently asked questions

What is 12 bar in psi?

12 bar is 174 psi, using 1 bar ≈ 14.5 psi. Compressor ratings are normally gauge pressure, so 12 bar gauge means 12 bar above atmospheric. Check whether specifications are gauge or absolute, because the difference is about 1 bar and can cause a mismatch when you compare compressors, hoses, dryers and receiving equipment.

What size compressor do I need for fibre-optic cable blowing?

It depends on the duct diameter, cable, route length and the blowing machine’s own requirement. Typical practice uses 10–14 bar air with flow chosen from the duct size, often in the 185–750 cfm range. Add any air motor consumption if it is not included in the maker’s figure, and use an aftercooler and separator for cool, dry air.

Can I run a 12 bar compressor at 7 bar?

Yes. Many 12 bar portables are variable-pressure machines that can run at lower settings, and they usually deliver more flow at lower pressure. Running at the lowest pressure the job needs saves fuel, because each extra bar takes about 7% more power. Check the controls and the free air delivery at each setting before choosing.

Why does my 12 bar compressor show lower pressure at the tool?

Pressure is lost through the hose, couplings, filters and treatment equipment, and leaks add to the loss. A narrow or very long hose at full flow is the most common cause. Fit gauges at both ends, check the hose bore and filter condition, and fix leaking joints before assuming the compressor itself is weak.

Do I need a dryer with a 12 bar portable compressor?

Not always. General tools need only drainage and sometimes lubrication. Cable blowing, coating work, pipeline drying and instrument duties often need cool, dry air, so an aftercooler and moisture separator are the minimum and a dryer may be needed. Tell us what the air is for, and we will suggest a suitable treatment train.

Can I hire a 12 bar compressor in Hyderabad?

Yes. We rent diesel and electric compressors from our own fleet from our base at Tarnaka, Secunderabad, for work across Telangana and Andhra Pradesh, and we supply rentals across India. Send us the duty, hose run and hire period, and we will propose a machine with hoses and treatment as needed.

Related pages

• 10 bar portable compressors
• 14 bar portable compressors
• Fibre-optic cable blowing air
• Variable-pressure portable compressors
• Portable aftercoolers
• Portable air compressors