Mining compressed air: drilling, tools and site systems

Where is compressed air used in a mine?

Compressed air in mining is rarely one network. It is a set of separate duties spread across the pit, the haul roads, the workshop, the coal handling or beneficiation plant and, in underground mines, the working sections. Each duty has its own pressure, flow pattern and tolerance for dirty or wet air.

The point of the table is that one compressor sized for the biggest number on site will serve none of these duties well. Drilling needs pressure and mobility. The workshop needs dry, steady air. The plant needs reliability and clean instrument air. Good mine-air design starts by separating them.

Typical system architecture for surface and underground mines

Most Indian surface mines run a hybrid arrangement that changes as benches advance and new areas open.

• Portable diesel compressors at the drill. Drilling faces move every day. A towable or skid-mounted diesel unit, often a high-pressure package, travels with the rig. For DTH blast-hole and exploration drilling the usual band is 600–1,500 cfm at 200–400 psig (13.8–27.6 bar), with special units up to about 35 bar (507.6 psig).
• Medium portables for tool work. 250–600 cfm units at 7–10 bar run breakers, rock drills and secondary breaking near crushers, haul-road and drain work, and maintenance jobs away from power.
• Fixed electric screw stations. Workshops, washeries, crushing and screening plants and coal handling plants are better served by electric rotary screw compressors with a receiver, dryer and filters, because grid power is cheaper per cubic metre than diesel and the duty is stationary.
• Dedicated instrument-air branch. Where a plant has control valves and analysers, a separately dried and filtered branch, ideally with its own receiver, protects control air from workshop demand surges.
• Underground mains. In underground mines, air is commonly generated on the surface or near the shaft or incline and piped in. Long runs mean pressure loss, condensate collection at low points and leak exposure. Local boosters or section compressors are considered where the pipe budget cannot carry the pressure to the face.

The architecture should be reviewed every time the mine plan changes: a deeper bench, longer haul, new seam or relocated plant can turn a sound layout into an undersized or wasteful one.

How to size air for drilling and tools

Drilling is the largest and most demanding mining air duty. Two numbers matter: pressure at the hammer and flow for hole cleaning.

1. Start from the hammer and bit. The DTH hammer’s data sheet gives air consumption against operating pressure. Higher pressure gives more impact energy and faster penetration, but only if the compressor can deliver the flow at that pressure.
2. Check up-hole velocity. Cuttings must be lifted out of the annulus between the drill pipe and the hole wall. Flow needed rises with the square of hole diameter less pipe diameter, so a bigger bit on the same pipe needs much more air. Wet holes and sticky clay need more margin.
3. Add losses. Hoses, couplings, the rotary head, lubricators and any booster all take pressure. Allow for altitude and high ambient temperature, which reduce the mass of air the compressor delivers.
4. Think in free air delivery (FAD). Compare compressors on FAD at the working pressure under ISO 1217 reference conditions, not on piston displacement or a brochure maximum.
5. For tools, use diversity. Add the rated consumption of each breaker or rock drill, then apply a realistic usage factor for how many run at once. A 250–400 cfm class unit typically runs two to four breakers or rock drills; a 400–600 cfm unit covers crawler drills or several tools together.

Remember that every extra bar of discharge pressure costs about 7% more power. Running a 24 bar compressor for 7 bar tool work wastes fuel and wears the machine. Keep high-pressure units on drilling and use a separate medium-pressure machine for tools.

Air treatment in a dusty, hot mine

Mine air treatment is less about purity classes and more about protecting equipment from water, oil and dust.

• Intake protection. Mine dust is fine and abrasive. Heavy-duty or two-stage intake filters, cyclonic pre-cleaners on portables, and regular checking of the restriction indicator are the first line of defence for the airend and engine.
• Aftercooling and water separation. Air leaves an oil-injected screw at about 75–95 °C and carries a lot of water vapour. On portables used for drilling or blasting, an aftercooler and moisture separator remove most of the free water before it reaches hammers and tools.
• Line lubricators for tools. Breakers and rock drills need lubricated air. Lubricators must be filled and adjusted; a dry tool fails early.
• Dryers for fixed plants. Workshop and plant air normally needs a refrigerated dryer (PDP about +3 °C). Outdoor instrument lines exposed to cold nights or long pipe runs may justify a desiccant dryer (PDP −20 °C or −40 °C).
• Condensate handling. Drains at receivers, dryers, filters and pipe low points must work, and oily condensate should go to an oil-water separator, not into the ground.

Heat, dust and the Indian mining climate

Telangana and Andhra Pradesh host large mining activity: the Singareni coal belt along the Godavari valley in Telangana, and limestone, iron ore, barytes, manganese and other mineral mining across Andhra Pradesh. Across India, the same conditions recur in coal, iron ore and limestone regions. Summer ambient temperatures of 40–45 °C, and above 45 °C in open pits, with radiated heat from benches and haul roads, push compressors towards their thermal limits.

Practical consequences:

• Coolers clog with dust and coal fines, discharge temperature climbs and the machine trips on high discharge temperature or high coolant temperature.
• Engine air filters on portables load quickly; restriction rises and fuel consumption increases.
• Hot intake air reduces mass flow, so a compressor that met the drilling demand in winter may fall short in May.
• Fixed stations in plant buildings need ventilation and hot-air ducting; a compressor that recirculates its own exhaust air will run hot whatever its rating.
• Power quality at remote sites can be poor, with voltage dips and imbalance. Electric compressors need proper protection, and diesel units are often the practical answer away from the plant grid.

Specify high-ambient capability for any machine going to a mine, plan cooler cleaning into the service routine, and park portables where they can breathe, away from blasting fumes and drill dust.

Reliability, criticality and standby cover

When the drill compressor stops, the blast schedule slips, and the excavators and dumpers that depend on it wait. In plants, loss of air can stop crushers, conveyors and dust collectors. Rank each duty by consequence:

Rental is a practical form of standby. A hire compressor can cover a breakdown, an overhaul, a planned shutdown or a peak in drilling while the owned fleet is serviced. Safety shutdowns on mine compressors (high discharge temperature, low engine oil pressure, high coolant temperature, low fuel) must be kept working and never bypassed to keep a machine running.

Energy and fuel

Diesel is usually the largest running cost of a mine-air fleet. Fuel used depends on load, pressure setting and engine condition, so there is no fixed litres-per-hour answer, but the levers are well known:

• Run at the lowest pressure the duty needs. Do not set a drilling unit to maximum pressure for tool work.
• Avoid long idle running. A portable left unloaded for hours still burns fuel.
• Keep intake and fuel filters clean; restriction costs fuel and power.
• Fix hose and coupling leaks. Leaks on a drilling string or tool manifold waste air the engine has already paid for.
• Where the duty is stationary and grid power is available, an electric screw compressor normally costs less per cubic metre than a diesel portable.
• For plant stations, measure specific power and demand before adding compressors; an air audit often shows leaks and poor control are the real problem.

Common problems in mine compressed-air systems and their fixes

Worked example: air demand for an underground development section

The demand calculator on this page suits a surface workshop or plant. Underground, the method is the same but the users, the duty pattern and the allowances are different. The example below is for a single development section of an underground limestone or metal mine (illustrative). Tool figures are typical consumptions at about 6 bar(g) at the tool; always replace them with the data sheets of the tools actually in use.

The diversity factors reflect the cycle: drills and the loader rarely run flat out together because mucking follows drilling, while dewatering pumps and air movers run almost continuously.

1. Diversified demand: 288 + 150 + 96 + 200 + 25 = 759 cfm.
2. Leakage allowance for a long, frequently extended underground main: 15% × 759 = 113.9 cfm, giving 872.9 cfm.
3. Margin for wear and for the next heading: 10% × 872.9 = 87.3 cfm, giving about 960 cfm.
4. In metric terms: 960 ÷ 35.315 = 27.2 m³/min, or about 453 l/s free air delivery.

Note what does not change the answer: buying more compressor will not fix a pipe that is too small. The 960 cfm must still arrive at 6 bar(g) at the face, which is the subject of the next section.

Pressure drop over long underground pipe runs

Underground mains are long, extended in stages, and often a size smaller than the flow now needs. A common empirical estimate for pressure drop in straight steel pipe is:

Δp = 450 × q^1.85 × L ÷ (d⁵ × p), where Δp is the drop in bar, q is free air flow in l/s, L is the equivalent pipe length in metres, d is the inside diameter in mm and p is the mean absolute pressure in bar(a).

Worked example (illustrative). The 960 cfm (453 l/s) section above is fed by a main of 1,800 m down the incline and along the drive. Bends, valves and tees are allowed for by adding 10%, so L = 1,980 m. The tools need 6.0 bar(g); allowing 0.3 bar for the hose and fittings at the face, the main must deliver 6.3 bar(g) at its far end. Solving the formula with the mean pressure in the pipe gives:

Check for the 100 mm line: mean pressure ≈ (7.24 + 6.30) ÷ 2 + 1.013 = 7.78 bar(a); 450 × 453^1.85 × 1,980 ÷ (100⁵ × 7.78) ≈ 0.94 bar.

The 100 mm main costs 7.24 − 6.43 = 0.81 bar more pressure than the 150 mm main. At about 7% more power per bar, a station drawing 170 kW (illustrative) uses 170 × 0.07 × 0.81 ≈ 9.6 kW extra. Over 6,000 hours a year that is about 57,600 kWh, or about ₹4.9 lakh at an assumed ₹8.50/kWh (illustrative tariff). The larger pipe usually pays for itself well within the life of the drive.

Practical points for underground mains:

• The formula assumes clean pipe. Old, scaled or dented pipe and undersized hose couplings can double the real drop, so measure it: one gauge at the shaft top and one at the face, read together with all tools running.
• Keep velocity in the main below about 6–8 m/s; above that, drop rises steeply and water is carried along to the tools.
• Lay the main with a slight fall and fit drain legs with traps at every low point and at the bottom of each shaft or incline. Air cools to rock temperature underground and drops its water there.
• Where the main runs a long way to a single district, a parallel main or a local compressor near the load (where permitted) can be cheaper than raising the whole station’s pressure for every user.

Surface station or portable units underground?

The choice is mostly decided by ventilation, fire risk, distance and how often the load moves. In practice most mines use a fixed surface station for the main and limit underground compressors to cases where the regulator, the ventilation plan and the mine’s own risk assessment allow them.

Diesel portables belong on the surface: at opencast benches, at the shaft top or at an adit mouth feeding a pipe in. Taking a diesel engine underground is a separate approval question, not a compressor selection question.

Air quality and safety underground

Compressed air underground is a fire and air-quality hazard as well as a utility. Three risks matter most.

• Carbon monoxide from the compressor. If discharge temperature runs high, lubricating oil can crack and leave carbon deposits in the discharge pipe, aftercooler and receiver. These deposits can smoulder or ignite and produce carbon monoxide that travels down the main. Defences: working high-temperature trips that are tested, the oil grade the manufacturer specifies, clean coolers, regular inspection and cleaning of discharge pipework, and a CO monitor where air is used near people.
• Oil mist. A worn separator or overfilled sump sends oil mist to the face, where it is breathed in and coats surfaces. Lubricated tools add more. Keep separator pressure drop and oil carry-over within the manufacturer’s limits, and never use tool air for blowing down clothing or skin.
• Fire at the compressor. Oil-soaked dust on a hot engine or airend, a leaking oil hose and electrical faults are the usual causes. Keep the compressor chamber clean, ventilated with intake air, fitted with suitable extinguishers, and free of stored fuel and rags.

Compressed air from an ordinary compressor is not breathing air. Air supplied for respirators, refuge chambers or self-rescue must be treated and monitored to a breathing-air specification; ISO 8573-1 classes describe contaminants but do not by themselves make air breathable.

In India, compressors and pneumatic equipment in mines fall under the Mines Act, 1952, the Coal Mines Regulations, 2017 for coal mines and the Metalliferous Mines Regulations, 1961 for metal and other non-coal mines, together with circulars and equipment approvals issued by the Directorate General of Mines Safety (DGMS). Gassy coal seams bring extra rules on flameproof electrical equipment and on any diesel engine taken underground. The mine manager and the mine’s safety management plan decide what is permitted at a given location; compressor selection must start from those requirements.

Dust and heat at Indian coal, limestone and granite mines

The heat section above covers climate in general. The dust differs a great deal from one mineral to the next, and so does the maintenance it demands.

Heat compounds the dust. A machine sized on a 25 °C morning delivers less useful air in a 45 °C afternoon because the air is less dense: (273.15 + 25) ÷ (273.15 + 45) = 0.937, so about 6% less mass of air for the same cfm. At the same time, part-blocked coolers push discharge temperature towards the trip point. On Indian sites both peak together in April and May, which is when cooler cleaning and filter checks should be at their most frequent. Shade over the unit, a clear 1–2 m around the cooler inlet, and siting away from hot exhaust and haul-road dust all help.

How Reddy Compressors helps

Reddy Compressors is an independent multi-brand compressed-air business based at Tarnaka, Secunderabad, serving industry since 2002. We sell, rent and service compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and others; we are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.

• Sales: new portable diesel and high-pressure drilling compressors, electric screw compressors for workshops and plants, dryers, filters and receivers; brand-new machines supplied to site for long-term mining projects.
• Used and refurbished machines where they suit the duty and budget.
• Rental: our own fleet, 50–2,000 cfm and 2–30 bar, diesel and electric, for drilling campaigns, breakdown cover, shutdowns and peak demand. On hire jobs we change oil and service at every 300 running hours.
• Service and AMC: over 20 service engineers and technicians cover all of Telangana and Andhra Pradesh, with project-based site support elsewhere in India where feasible.
• Spare parts: identified from the make, model, serial number, nameplate photo or old part, with fit confirmed before we quote. Supplied across India.
• Air audits for fixed plant stations: demand, pressure and leak surveys.

Our track record. We have supplied compressors to leading companies in mining across Telangana, Andhra Pradesh and beyond – new and used machines, long-term rental, and breakdown cover for drilling and plant air – backed by our own service team.

What to send us

• Mine type and location (surface or underground, mineral, district and state).
• Duties: drill model, hammer and bit size, hole depth; number and type of tools; plant air users.
• Required pressure and flow, or the equipment data sheets.
• Existing compressors: make, model, serial number, running hours, nameplate photo.
• Diesel or electric preference, power available, shift pattern and expected duration.
• Your contact name, phone or WhatsApp and email.

Call +91 99590 60718 or +91 92468 88812, WhatsApp +91 99590 60718, or email reddycompressors@gmail.com. Office: Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017.

Frequently asked questions

What size compressor is needed for blast-hole drilling in a mine?

It depends on the hammer, bit diameter, drill pipe size and depth. DTH blast-hole and exploration drilling typically uses 600–1,500 cfm at 200–400 psig (13.8–27.6 bar). Start from the hammer’s air consumption at the chosen pressure, check up-hole velocity for cuttings removal, then add margin for hose losses, wet ground and high summer ambient. Send us the rig and hammer details for a firm recommendation.

Should a mine use diesel or electric compressors?

Use diesel where the work moves or there is no reliable power, such as drilling faces, haul-road work and remote exploration. Use electric screw compressors where the duty is stationary and grid power is available, such as workshops, washeries and crushing plants. Electric air usually costs less per cubic metre. Many mines run both, matched to each duty rather than one machine for everything.

Why does my mine compressor trip on high temperature in summer?

The usual causes are dust-blocked oil and aftercoolers, low or degraded oil, a faulty thermostatic valve, or the machine drawing in its own hot exhaust air. Summer ambient in Telangana and Andhra Pradesh reaches 40–45 °C, and above 45 °C in open pits, which leaves little margin. Clean coolers on a routine, check oil and the thermal valve, and park the unit in clean, moving air.

How do I stop water reaching rock drills and DTH hammers?

Fit an aftercooler and moisture separator at the compressor outlet and make sure the drains are working. Hot compressed air carries a lot of water vapour that condenses in hoses. Drain receivers and hose low points, and keep line lubricators filled so tools are protected. For workshop air, add a refrigerated dryer with a pressure dew point of about +3 °C.

Can I hire a compressor for a mining drilling campaign?

Yes. Reddy Compressors rents diesel and electric compressors from 50 to 2,000 cfm and 2 to 30 bar, including high-pressure units for drilling. Hire suits short campaigns, breakdown cover, overhauls and peak demand. Tell us the drill, hammer, depth, duration and site location, and we will advise on the unit, hoses and servicing, which on hire jobs is done every 300 running hours.

Do you service mining compressors outside Hyderabad?

Yes. Our service teams cover the whole of Telangana and Andhra Pradesh, including coal and mineral mining districts, and we supply compressors, rentals and spare parts across India with project-based site support where feasible. We work on multi-brand machines. Send the make, model, serial number and fault description so the service engineer arrives with the right parts.

What compressed air system does a mine need for heavy-duty equipment?

Most mines need two systems, not one. Heavy-duty drilling uses diesel portable compressors at 14–28 bar(g), sized from the hammer’s air requirement and moved with the rig (see DTH drilling compressors). Pumps, air movers, workshop tools and plant use a fixed electric screw station at about 7 bar(g), feeding a main sized for the full flow. Add aftercooling and drains for water, two-stage intake filtration for dust, and standby capacity for any duty whose loss would stop production or dewatering.

Which air compressor is used for underground mining equipment?

Usually none is used underground at all: a fixed electric screw compressor station on the surface feeds rock drills, loaders and pumps through a pipe main at about 7 bar(g). Underground compressors are used only where the distance is too great or the work temporary, and then subject to the mine’s ventilation plan, fire precautions and the approvals required under Indian mining regulations. Diesel units underground need specific approval, and gassy coal mines need flameproof electrical equipment.

How much pressure is lost in a long underground air pipe?

It depends on flow, pipe bore and length. For about 960 cfm through 1,980 m of equivalent pipe, a 100 mm main loses about 0.94 bar, a 125 mm main about 0.32 bar and a 150 mm main about 0.13 bar. Old, scaled pipe and small couplings can double these figures. Measure with two gauges, one at the shaft top and one at the face, while all tools are running, and size the main so velocity stays below about 6–8 m/s.

Is compressed air from a mine compressor safe to breathe?

No, not without dedicated treatment and monitoring. Ordinary compressor air can carry oil mist, water, particles and, if the compressor has overheated, carbon monoxide from cracked oil and carbon deposits. Air for respirators, refuge chambers or self-rescue must be filtered, purified and checked against a breathing-air specification, with continuous CO monitoring. Tool air should also never be used to blow dust off clothing or skin.

Related pages

• Industrial applications of compressed air
• DTH drilling compressors
• High-pressure portable compressors
• Diesel portable compressors
• Compressor rental engineering
• Quarry compressed air