What does a 25 bar portable compressor do?
Most portable compressors on Indian construction sites work at 7–10 bar (101.5–145 psig). That is enough for breakers, rock drills and blasting. A 25 bar machine sits in a different class: it is built for jobs where the air has to overcome a large back-pressure, such as a column of water and cuttings in a deep borehole, or where the tool itself is designed for high pressure.
To reach 25 bar efficiently, these machines normally use a two-stage oil-injected rotary screw airend, or a single-stage high-ratio airend with heavy-duty bearings, driven by a large diesel engine or an electric motor. The compression heat is higher than on a 7 bar unit, so the oil cooler, aftercooler and cool-box airflow are sized generously, and the safety system includes high discharge temperature, low engine oil pressure and high coolant temperature shutdowns.
Many high-pressure portables are variable-pressure machines. The operator can select a lower pressure and the control system trades pressure for flow, so the same unit can give more cfm at 17 bar than at 25 bar. That flexibility is useful, but it also means a brochure flow figure must always be read with the pressure it belongs to.
25 bar, 350 psi and 363 psi: why the numbers matter
Pressure labels get rounded in commercial conversations. A rig owner asks for “25 bar”, a supplier offers a “350 psi machine” and both assume they are talking about the same thing. They are not. With 1 bar = 14.5 psi, the gauge-pressure conversions are:
| Stated pressure | Equivalent (approximately) | Comment |
|---|---|---|
| 25 bar(g) | 363 psig | The true equivalent of a 25 bar requirement |
| 350 psig | 24.1 bar(g) | About 0.9 bar short of 25 bar |
| 363 psig | 25.0 bar(g) | Matches 25 bar on the same gauge basis |
| 300 psig | 20.7 bar(g) | Common drilling rating, well below 25 bar |
| 25 bar(a) | 24.0 bar(g) | Absolute pressure includes about 1 bar of atmosphere |
Two further points catch buyers out. First, gauge and absolute pressure differ by roughly one bar at sea level, so “bar(a)” in a process document is not the same as the “bar” on a compressor gauge. Second, the pressure that matters is the pressure at the point of use. A compressor set to 25 bar at its discharge valve will deliver less at the hammer after hoses, couplings, a moisture separator and a lubricator have taken their share.
If the application has a firm minimum, for example a hammer that will not cycle properly below a certain pressure, write that minimum down with its unit and location. An offer at 350 psig does not meet a firm 25 bar(g) minimum, however close the numbers look, and a machine should never be set above its rated maximum to close the gap.
Where is 25 bar air used?
Typical duties for this pressure class in India include:
- Deep borewell and water-well drilling with DTH hammers, where depth and water ingress raise the back-pressure the air must overcome. Our borewell range runs from 600–1,500 cfm at 200–400 psig (13.8–27.6 bar), so 25 bar sits in the upper working band.
- Exploration and geotechnical drilling where reverse-circulation or high-pressure DTH tooling is specified.
- Oil and gas well services and pipeline work, such as drying and nitrogen-unit feed, always under the client’s engineering procedures.
- Quarry and mining drilling with high-pressure hammers chosen for penetration rate in hard rock such as the granites of the Deccan plateau.
- Feed air for high-pressure boosters where the final duty is above 25 bar.
Pneumatic pressure testing of pipelines and vessels with high-pressure air carries a serious stored-energy hazard. Where a 25 bar compressor is used for testing support, the client’s engineer and approved test procedure govern the work, the exclusion zone and the test medium.
How to size the flow at 25 bar
Pressure only tells half the story. A DTH hammer needs a certain volume of air at its working pressure to lift cuttings and keep the bit clean. Too little flow and the hole is not cleaned; cuttings regrind, the bit wears and penetration falls.
Sizing works from the bottom of the hole upward:
- Take the hammer maker’s air consumption at the intended working pressure, in cfm or m³/min of free air.
- Check the annular uphole velocity needed to lift cuttings for the bit and drill-pipe diameters. Larger bits in soft, wet or clay-rich formations need more air.
- Add allowances for foam or water injection, rig functions that use compressed air and dust collection if fitted.
- Allow for hose and fitting losses so that the compressor discharge pressure is high enough to deliver the required pressure at the hammer.
- Select a machine whose published free air delivery at that discharge pressure covers the total, with margin for wear and high ambient temperature.
Free air delivery is normally measured to ISO 1217 at the compressor outlet. Make sure the flow you compare is stated on that basis and at the pressure you need, not at the machine’s lowest selectable pressure. About 7% more power is needed for every extra bar of discharge pressure, so running at 25 bar when the job needs 20 bar costs diesel for no benefit.
Choosing between pressure classes
| Class | Pressure | Typical flow band | Typical work |
|---|---|---|---|
| Standard portable | 7–10 bar (101.5–145 psig) | 100–600 cfm | Breakers, rock drills, blasting, construction |
| Medium-high | 12–14 bar (174–203.1 psig) | 400–900 cfm | Crawler drills, quarry work, shallower DTH |
| High pressure | 17–21 bar (246.6–304.6 psig) | 800–1,200 cfm | Medium-depth borewells, exploration drilling |
| Very high pressure | 21–28 bar (304.6–406.1 psig) | 1,000–1,500 cfm | Deep borewells, hard rock, wet holes |
| Special units | Up to 35 bar (507.6 psig) | Project specific | Very deep or specialist drilling |
These are typical bands from our own work, not the rating of any one model. A 25 bar requirement usually leads to a machine in the very-high-pressure class, often a variable-pressure unit that can also run at lower pressure for shallower holes.
What to check in a 25 bar offer
- Maximum working pressure stated in bar(g) or psig, for the exact configuration offered.
- Free air delivery at 25 bar, not only at minimum pressure or in a flow-boost mode.
- Make, model, serial number and year, so the specification can be traced to the actual unit.
- Engine power, fuel tank capacity and running hours, or motor rating and starting method for electric units.
- Aftercooler and moisture separator if the air feeds a hammer that dislikes water, or treatment for any downstream process.
- Pressure rating of the hose, manifold, valves and couplings: every component must be rated above the compressor’s maximum pressure and safety-valve setting.
- Condition of the safety valve, shutdown sensors and whip checks on hose joints.
- Who services the machine on hire and at what interval; on our hire jobs we change oil and service every 300 running hours.
When two documents for the same model disagree, for example an older brochure and a regional data sheet, ask the supplier which one applies to the unit being offered. Do not combine the highest pressure from one with the highest flow from the other.
Operating 25 bar machines in Indian conditions
Summer ambient temperatures of 40–45 °C in Telangana and Andhra Pradesh, including Rayalaseema, and above 45 °C on open sites, push high-pressure compressors hard. Discharge temperature rises with pressure ratio, and a partly blocked cooler quickly turns into a high-temperature shutdown at mid-day. Keep cooler cores clean, check the cool-box seals and park the machine so that hot exhaust and dust are not drawn back into the air intake.
Dust from drilling sites loads air filters faster than service schedules assume. Check restriction indicators daily and change elements on condition. Use the correct high-pressure compressor oil; an oil not suited to the higher temperature and pressure can varnish and shorten separator life.
High-pressure air also means higher stored energy. Bleed the system before breaking any connection, use whip checks on every hose joint and keep people out of the line of a pressurised hose.
How Reddy Compressors helps
We sell (new and used/refurbished), rent and service portable compressors of ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and other makes as an independent multi-brand specialist, not an authorised dealer of any brand; brand names and trademarks belong to their owners. We have tie-ups with all major and reputed brands.
For 25 bar duties we sell new and used/refurbished high-pressure portable compressors, rent machines from our own fleet (50–2,000 cfm, 2–30 bar, diesel and electric), and service, overhaul and supply spares for units already on your rig. With over 20 service engineers and technicians, we can send a machine with operators and look after its servicing on site. For long-term drilling or project work we can supply brand-new compressors to site.
Before quoting, we check the pressure basis, the flow at the duty pressure and the hose and accessory ratings, and we tell you plainly if a proposed machine falls short of your stated minimum.
Our office is at Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017, and we have served industry since 2002. Call +91 99590 60718 or +91 92468 88812, WhatsApp +91 99590 60718, or email reddycompressors@gmail.com. Our service teams cover the whole of Telangana and Andhra Pradesh, and we supply compressors, rentals and spare parts across India.
What to send us
- Required pressure at the tool, with unit (bar(g) or psig) and any firm minimum
- Hammer or tool make and model, bit size and drill-pipe size
- Expected depth, formation and water conditions
- Daily running hours and project duration
- Site location in Telangana, Andhra Pradesh or elsewhere in India
- For an existing machine: make, model, serial number and a nameplate photo
Frequently asked questions
Is a 350 psi compressor the same as 25 bar?
350 psig converts to about 24.1 bar(g), so it is roughly 0.9 bar below 25 bar. For work without a firm minimum the difference may not matter, but if a hammer or procedure requires at least 25 bar at a defined point, a 350 psig machine does not meet it. The true equivalent of 25 bar(g) is 362.6 psig. Always compare both figures on the same gauge basis.
How much cfm do I need from a 25 bar compressor for borewell drilling?
It depends on the hammer, bit diameter, drill-pipe size, depth and water ingress. Start with the hammer maker’s consumption at the working pressure, check uphole velocity for cuttings lift, then add allowances for foam injection and hose losses. Deep borewell work in our experience typically uses machines from about 1,000 to 1,500 cfm in the 300–400 psig (20.7–27.6 bar) band.
Can I set my compressor higher to reach 25 bar?
Only within the maker’s rated maximum working pressure for that configuration. Setting a compressor above its rating overloads the airend, engine and separator vessel, and can lift the safety valve or damage components. If the machine is rated below 25 bar, the right answer is a different machine or a booster arrangement, not a higher setting. We can check the rating from the nameplate.
Why does a high-pressure compressor give less cfm at 25 bar than at 17 bar?
Many high-pressure portables are variable-pressure machines with a fixed engine power. Compressing to a higher pressure takes more energy per cubic metre, roughly 7% more power for each extra bar, so at maximum pressure the available flow falls. That is why a flow figure quoted at minimum pressure or in a flow-boost mode cannot be assumed at 25 bar.
Do you rent 25 bar portable compressors in Hyderabad?
Yes. Our own rental fleet covers 50–2,000 cfm and 2–30 bar in diesel and electric versions, and we deliver from our Tarnaka, Secunderabad office across Telangana and Andhra Pradesh and to projects elsewhere in India. Operators can be provided, and on hire we service the machine every 300 running hours. Send us the duty and site details for a firm proposal.
What hose rating do I need for 25 bar air?
Every hose, coupling, valve and manifold must be rated above the compressor’s maximum working pressure and its safety-valve setting, with the maker’s safety factor. A hose rated for a 10 bar construction compressor is not suitable. Use whip checks on joints, inspect hoses for cuts and bulges before each shift, and replace damaged sections rather than repairing them on site.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Pressure unit and gauge/absolute conversion
Convert between bar, psi, kPa and MPa and between gauge and absolute pressure. A mix-up between gauge and absolute is a classic cause of wrong sizing.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Pressure: 7
- Unit: bar g
Result
- bar gauge: 7
- bar absolute: 8.01
- psi gauge: 101.5
- psi absolute: 116.2
- kPa gauge: 700
- MPa gauge: 0.7
Method. Absolute pressure = gauge pressure + atmospheric (1.01325 bar at sea level). 1 bar = 14.504 psi = 100 kPa = 0.1 MPa. Hyderabad is about 540 m above sea level; atmospheric pressure there is roughly 0.95 bar, so enter the local value in the flow tool if it matters.
What to take from it. A 7 bar gauge system is 8.01 bar absolute. Ratio and flow-conversion work uses absolute pressure.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.
DTH hammer duty against two compressors
Check whether each of two compressors can supply a DTH hammer’s documented air consumption at the pressure the hammer needs, after hose, string and water-column losses, and with what margin.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Hammer working pressure at the hammer (bar g): 21
- Hammer air consumption at that pressure (cfm): 950
- Pressure loss from compressor to hammer (bar): 1
- Water column above the hammer to be lifted (m): 0
- Compressor A: maximum working pressure (bar g): 17
- Compressor A: data-sheet flow at the required pressure (cfm): 1150
- Compressor B: maximum working pressure (bar g): 24
- Compressor B: data-sheet flow at the required pressure (cfm): 1000
- Site derating of delivered flow: heat, altitude, condition (%): 0
Result
- Hammer working pressure: 21 bar g = 305 psig
- Water column allowance: 0 bar
- Required compressor discharge pressure: 22 bar g = 319 psig
- Hammer consumption: 950 cfm = 26.9 m³/min
- Compressor A: Fails: cannot reach 22 bar g (maximum 17 bar g); its flow does not count
- Compressor B: flow available at 22 bar g: 1,000 cfm = 28.3 m³/min
- Compressor B: margin: +5.3 % (covers the duty)
- Result: Only compressor B covers the duty
Method. Required discharge pressure = hammer working pressure + pressure loss from compressor to hammer (hose, swivel, drill string, check valves) + water column to be lifted (0.0981 bar per metre of water). A compressor whose maximum working pressure is below the required pressure fails, whatever its flow. Available flow = data-sheet flow at the required pressure × (1 − site derating). Margin (%) = (available flow − hammer consumption) ÷ hammer consumption × 100. Use the same flow basis (FAD or scfm) for hammer and compressor. 1 bar = 14.504 psi; 1 m³/min = 35.31 cfm. Hole cleaning (annular velocity) is a separate check.
What to take from it. Compare flows at the same pressure. More cfm at a lower pressure does not run a hammer that needs higher pressure.