What is 35 bar portable air used for?
Most borewell compressors in Telangana and Andhra Pradesh work at 200–400 psig (13.8–27.6 bar) and 600–1,500 cfm. 35 bar, 507.6 psig, sits above that as a special class for jobs where back-pressure or tooling demands it. Typical duties include:
- Very deep borewells, especially where heavy water ingress adds a tall column of water above the hammer.
- Exploration, geothermal and reverse-circulation drilling with high-pressure tooling.
- High-pressure DTH work in very hard rock, where the hammer is designed for higher pressure.
- Feed air to process and nitrogen equipment that needs a high inlet pressure.
- Pipeline and well-service support on oil and gas projects, within the client’s engineering procedures.
Because so few machines reach this pressure, a 35 bar enquiry deserves more care than a standard hire. The pressure category helps shortlist equipment; it does not prove that a particular unit will deliver the air you need at the hammer.
35 bar and 500 psi: getting the units right
| Stated pressure | Equivalent (approximately) | Comment |
|---|---|---|
| 35 bar(g) | 508 psig | True equivalent of 35 bar |
| 500 psig | 34.5 bar(g) | About 0.5 bar below 35 bar |
| 400 psig | 27.6 bar(g) | Top of the normal borewell band |
| 35 bar(a) | 34.0 bar(g) | Absolute includes about 1 bar of atmosphere |
If the work has a firm minimum of 35 bar at a defined point, a 500 psig machine does not meet it, and a machine must never be set above its rated maximum to close the gap. Where the requirement is approximate, say so in the enquiry so that both parties work to the same number.
How 35 bar machines are built
Reaching about 35 bar from atmospheric air in a towable package usually needs a two-stage oil-injected screw airend, or a compressor plus booster arrangement. The diesel engine is large, the oil cooler and aftercooler are sized for a high pressure ratio, and the separator vessel, safety valve and piping are rated for the higher pressure.
Many such machines are variable-pressure units. Some variable-pressure portable models are rated for 22–35 bar with a flow figure at maximum pressure, and a separate, higher flow in a “flow-boost” mode at minimum pressure. Those two flows describe different operating conditions. The higher figure is not available at 35 bar.
About 7% more power is needed for every extra bar, so a 35 bar setting is expensive in fuel. Run at the lowest pressure that does the work: if a hole drills well at 28 bar, there is no benefit in running at 35 bar.
Start with the acceptance question
Before asking which machine is available, decide what must be proven. Is the need a compressor with a published 35 bar capability, or a complete temporary-air arrangement delivering a stated flow at a defined point? The two need different evidence. A useful acceptance question is:
What will show that this supply arrangement delivers the agreed pressure, flow and air quality at the agreed point, under the stated operating conditions?
- Record the required pressure with unit, gauge or absolute basis and location.
- Record the flow at that pressure, in cfm or m³/min of free air, with its reference conditions.
- Record air quality needs, such as water removal or an ISO 8573-1 class for process feed.
- Record the duty pattern, hours per day and project length.
- Record who owns the receiving equipment’s requirements and who will accept the supply.
Four kinds of evidence, kept separate
| Evidence | What it answers | What it does not answer |
|---|---|---|
| Maker’s published data | What duty is published for this configuration? | Whether the offered unit matches it |
| Offered-unit identification | Which machine (make, model, serial, fitted options) will come? | Whether it meets the agreed duty |
| Complete supply review | How compressor, treatment, hoses and connections work together | Who is responsible for the receiving application |
| Agreed site record | What was demonstrated, where and under what conditions | Whether those conditions cover all intended work |
A brochure helps shortlist; a unit-specific response confirms the offer; a site record shows what was seen. None should quietly stand in for another during approval.
What a site demonstration should establish
Agree the purpose before arranging a demonstration. Showing the controls, inspecting condition and assessing performance are different activities. For a performance check, the responsible technical parties set the method, measurement points, instruments and acceptance criteria, following the maker’s instructions and an approved procedure.
Ask for a record that still makes sense later: equipment identity, configuration, agreed duty, ambient conditions, readings, observations and the reviewer’s conclusion. In a 40–45 °C summer, a machine that performs in the morning may behave differently at mid-day, so note the conditions.
Safety and site practice at 35 bar
- Every hose, valve, manifold and coupling must be rated above the maximum working pressure and safety-valve setting; standard construction hoses are not suitable.
- Fit whip checks or restraints on every joint and keep people out of the line of pressurised hoses.
- Depressurise fully before breaking connections, including any trapped section between a compressor and booster.
- Check shutdowns for high discharge temperature, low engine oil pressure and high coolant temperature before mobilisation.
- Use the correct high-pressure compressor oil and keep coolers clean; dust and heat leave little margin at high pressure ratios.
- Pneumatic pressure testing at this pressure stores very high energy; the client’s engineer and approved procedure govern any test.
Sizing flow for a deep, high-pressure hole
Pressure overcomes back-pressure; flow cleans the hole. A DTH hammer needs enough free air at its working pressure to cycle properly and to lift cuttings up the annulus between the drill pipe and the borehole wall. If uphole velocity is too low, cuttings fall back, regrind and wear the bit, and penetration slows however high the pressure is set.
Start from the hammer maker’s consumption at the working pressure, check the uphole velocity for the bit and pipe sizes, then add foam or water injection, any rig functions that use the same air, and hose losses between the compressor and the rig. Compare the total with the compressor’s free air delivery at the required discharge pressure, never with its flow-boost figure. Wet, clay-rich or fractured formations often need extra flushing air, so leave margin for the conditions actually met underground.
Where both pressure and flow are at the edge of what one machine offers, two compressors manifolded together, or a compressor with a booster, may be the sounder arrangement. Each option should be compared against the same delivered duty.
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 35 bar work we supply new and used/refurbished high-pressure portable compressors and boosters; rent from our own fleet (50–2,000 cfm, 2–30 bar, diesel and electric), arranging special high-pressure units up to about 35 bar where the project needs them; and service, overhaul and supply spares for high-pressure machines already in your fleet. We identify the actual unit, check the flow at the duty pressure and the rating of every hose and fitting, and tell you plainly where an offer falls short. Operators can come from our team of over 20 service engineers and technicians, and for long projects we can supply brand-new machines to site.
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 with unit, basis and point of use
- Flow required at that pressure and duty pattern
- Hammer or process equipment make and model
- Depth, formation and water conditions for drilling
- Project duration, location and access
- For existing machines: make, model, serial number and nameplate photo
Frequently asked questions
Is 500 psi the same as 35 bar?
Not exactly. 500 psig is 34.5 bar(g), while 35 bar(g) is 507.6 psig, a difference of roughly half a bar. For approximate work this rarely matters, but where a firm 35 bar minimum applies, a 500 psig machine does not meet it. Compare both values on the same gauge basis and record the exact requirement.
When do I need a 35 bar compressor for borewell drilling?
Most borewells are drilled at 200–400 psig (13.8–27.6 bar). A 35 bar unit is a special choice for very deep holes, heavy water ingress or high-pressure hammers in hard rock. Running higher than necessary wastes fuel, roughly 7% more power per extra bar, so confirm that the depth and tooling really need it before hiring one.
Why is the flow lower at 35 bar than in flow-boost mode?
Variable-pressure compressors have a fixed engine power. At minimum pressure the machine can deliver more air; at maximum pressure it delivers less, because each cubic metre takes more energy to compress. A flow-boost figure applies only at the lower pressure stated, so always use the flow published at the pressure you will actually run.
Can I rent a 35 bar portable compressor in India?
Units in this class are specialist, so availability must be checked for each project. Our rental fleet covers up to 30 bar and 50–2,000 cfm, and special high-pressure units up to about 35 bar can be arranged for projects. We serve Telangana and Andhra Pradesh and supply across India. Send us the depth, hammer and duty details.
What hoses are safe for 500 psi air?
Use hoses, couplings and valves rated above the compressor’s maximum working pressure and its safety-valve setting, with the maker’s safety factor. Ordinary construction hoses rated for 10 bar are not suitable. Fit whip checks on every joint, inspect for cuts, bulges and damaged ends before each shift, and replace damaged hose rather than repairing it.
How do I check that a 35 bar compressor will deliver on site?
Agree beforehand what must be proven: pressure, flow and air quality at a defined point. Then confirm the actual unit’s make, model and serial against published data, review the full arrangement including hoses and treatment, and, if needed, agree a site check with a defined method and record. Keep the record with its operating conditions.
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.
Annular area and return velocity
In drilling, the air must lift the cuttings up the annulus. Check the return velocity from the hole and rod size.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Hole diameter (mm): 115
- Rod outside diameter (mm): 89
- Free air supplied (m³/min): 12
- Bottom-hole back pressure (bar g): 1
- Target return velocity (m/s): 15
Result
- Annular area: 41.7 cm²
- Return velocity: 24.16 m/s = 4,757 ft/min
- Free air needed for the target velocity: 7.45 m³/min = 263 cfm at 15 m/s
- Assessment: Within the commonly quoted range
Method. Annular area = π/4 × (D_hole² − D_rod²). Actual flow at the back pressure = free air × (P_atm / (P_back + P_atm)). Velocity = actual flow ÷ area. A return velocity often quoted for efficient cuttings lift is around 15–25 m/s; confirm for your material.
What to take from it. Low return velocity leaves cuttings in the hole; very high velocity wears the rods and hammer. Both are warnings, not verdicts.