Air Compressor for Open-Pit Mining

The rig does not decide the compressor — the hammer does

Two rigs with the same hole diameter can need different air if they run different hammers. Always start from the hammer and bit you intend to run.

The hammer is the only component that sets the pressure floor. Its bore, piston mass and porting decide how much air it swallows per blow, and the hole diameter only decides how much of that air is left to carry cuttings out. A 4-inch hammer on a 115 mm bit and a 5-inch hammer on a 130 mm bit are both "110–150 mm class" on paper, yet the second tool may ask for close to twice the volume at the same pressure.

Sizing backwards — buying the compressor the dealer had in stock, then picking a hammer it can feed — is the most common way an open-pit project ends up with poor penetration and short bit life.

Open-pit air demand

DTH rigs for bench blasting typically run 10–25 bar working pressure and consume from about 10 to 40 m³/min depending on hole size. Use the figure for the largest hammer you expect to run, plus margin.

Pressure and volume do different jobs, and neither substitutes for the other:

• Pressure drives the piston. Below the hammer's rated minimum the tool loses blow energy, and penetration rate falls off faster than the pressure gauge suggests.
• Volume cleans the hole. Cuttings must be lifted up the annulus at enough velocity to clear the bit face. Starve the annulus and the bit regrinds its own cuttings, which is the fastest way to destroy a button bit.
• The two figures are quoted together (for example 7.0–19.0 m³/min at 10–25 bar) because the consumption rises with working pressure. Always compare hammers and compressors at the same pressure, never at each one's own best point.

Free air delivery (FAD) on a compressor nameplate is measured at the discharge, typically to ISO 1217. The number that reaches the hammer is lower: hose length, fittings, a blocked filter and altitude all take their cut. On a 30–50 m bench layout with a well-used hose set, plan for a real loss rather than trusting the nameplate.

Open-pit rigs and their air demand

Compressor range

What the rig table actually tells you

Read the two tables together and the fleet splits into three groups, each with a different air strategy.

Rigs that carry their own air. The integrated KT and ZT families are self-contained: the compressor is built into the carrier and sized by the factory for that rig's hole range. Published figures are KT5C at 12 m³/min and 15 bar, KT5H at 13 m³/min and 18 bar, KT11 and ZT11 at 18 m³/min and 20–22 bar, KT12 and KT9D at 20 m³/min and 22 bar, KT15C at 22 m³/min and 24 bar, KT25 at 31 m³/min and 25 bar, and KT30 at 36 m³/min and 35 bar. There is no separate compressor to buy and no hose to drag across the bench; the trade is that the air you have is the air the carrier was built with.

Hydraulic rigs that need no compressed air for drilling. The KL511 drills 64–127 mm to 25 m with a hydraulic rock drill (HC150/HC160 class) and its own 9.7 m³/min at 10 bar screw unit for flushing and dust control. Do not budget DTH-class air for it.

DTH rigs on an external compressor. The KG, KZ and some KT models are built to be fed from outside, and their published air demand is the starting point: KG430 13.0–20.0 m³/min, KG420B 10.0–17.0 m³/min, KG520 15.0–22.0 m³/min. Those ranges already anticipate the hammer, so the compressor is chosen against the upper figure, not the lower one. For a wider comparison of what each surface class will drill, see How to Choose a DTH Drilling Rig and How to Choose a DTH Rig for 110–150 mm Blast Holes.

Matching a hammer to an air supply

Published hammer data is the cleanest way to size air, because the hammer's consumption range and its pressure range are given together. From the current Kaishan hammer range:

Two conclusions follow directly from that table.

First, a 4-inch tool is not a single air demand. K3 bottoms out at 4.8 m³/min at its low pressure point and climbs to 12.6 m³/min when pushed to 2.4 MPa. Size on the low figure and run the hammer at high pressure, and you will be short of air for most of the shift.

Second, large-hole rigs want pressure as much as volume. K80 is a 17–35 bar tool; a 25 bar compressor will run it, but not at the top of its range. For 195–254 mm production holes where the K8 or K80 is the intended tool, the high-pressure machines in the LGCY high-pressure series are the class to compare, while 4- and 5-inch hammers are well served by mid-pressure units such as the LGCY-21/21-23/18 or the KSCY-550/13. Hammer choice has its own logic — piston design, foot valve versus valveless, bit shank and thread — covered in DTH Hammer Selection and DTH Bit Selection; what matters here is that the hammer decision comes first and the compressor follows it.

Model codes, units and pressure drop

The model code carries the two numbers you need, and it is worth converting before comparing. KSCY-550/13 is 550 cfm at 13 bar, published as 15.0 m³/min at 13.0 bar; one m³/min is about 35.3 cfm, so a 600 cfm machine and a 17 m³/min machine are the same machine. KSCY-400/14.5K is 400 cfm at 14.5 bar, published as 11.3 m³/min. The LGCY dual-rated models give two operating points in one machine — LGCY-19/21-21/18 delivers 21 m³/min at 18 bar or 19 m³/min at 21 bar, and LGCY-23/23-25/18 and LGCY-25/23-27/18K follow the same pattern — so always read the flow at the pressure band your hammer will run in.

Air that leaves the compressor at 20 bar does not arrive at the hammer at 20 bar. Losses come from hose length and bore, fittings and quick couplers, and the separating and filtration package as it loads up. Keep the compressor as close to the rig as the blasting pattern allows, match hose bore to flow, and check for restriction before blaming the hammer: a loaded filter element, a partly closed valve or a leaking coupler all look like a weak hammer from the cab. Drilling cost is dominated by metres per hour and downtime rather than by the purchase price of the compressor; those blocks are set out in What Drives Your Drilling Cost per Metre.

High altitude and remote sites

At altitude, free air delivery must be increased for the same hammer. For remote sites, choose a unit with strong local service coverage and a fuel-efficient engine — the compressor runs all day.

The mechanism is air density. A screw element displaces a fixed volume per revolution; at 3,000 m the mass of air in that volume is roughly 30 per cent lower than at sea level, and the hammer responds to mass flow, not to the number on the gauge. A practical planning rule is to add about 15 per cent capacity for every 1,500 m of elevation above sea level, then check the machine's own altitude rating rather than assuming it is derated the same way. Sites above 2,500 m are a separate selection case — the machine often needs a larger displacement for the same rated output, and the diesel engine loses power of its own. The high-altitude drilling page covers that; remote-area drilling covers the logistics side.

Remote sites add three costs that are easy to miss when comparing compressor models: fuel, because the compressor runs for the whole shift whether or not the rig is drilling; service reach, because a machine with no local parts and no trained technician becomes a paperweight the first time an airend or separator element fails; and consumables, because separator elements, oil filters and oil are consumed by running hours.

Selection steps

• Fix the hole programme: largest diameter, largest hammer you intend to run, bench depth, and the pressure band you will run that hammer in. Write the numbers down before talking to any supplier.
• Read the hammer's consumption at that pressure — not at the lowest pressure in its range — and add the margin the annulus and the hose run need.
• Decide whether the rig carries its own air. If the answer is a KT/ZT integrated carrier, the factory figure is your air supply and the question becomes hole range, not compressor size. If the rig is in the KG, KZ or externally fed class, continue.
• Convert every candidate compressor to the same units and the same pressure point. Compare only the flow at the pressure your hammer will actually see.
• Discount the nameplate for altitude, hose length and filter condition. If the discounted figure is below the hammer's demand, step up a size or add a second unit.
• Check the operating envelope: fuel consumption, service interval, road and transport weight, whether the unit can be moved with the face as the pattern advances — and decide on redundancy, because a single compressor feeding a single rig turns a service stop into a production stop.

Common mistakes

• Sizing on hole diameter instead of the hammer. Two rigs drilling the same diameter with different hammers do not share an air demand.
• Using the bottom of the hammer's consumption range. The published range spans its pressure range; take the figure that matches your working pressure.
• Ignoring altitude until the rig is on site. Derating is predictable and cheap to plan for, and expensive to discover.
• Using one oversized compressor to feed two rigs "for efficiency". Air quality, hose runs and a shared single point of failure usually cost more than the second machine.

Checklist

• Largest hole diameter and hammer. 2) Hammer air consumption and working pressure. 3) Altitude of the site. 4) Number of rigs to supply. 5) Fuel and service availability. 6) Whether a second compressor is needed as backup.

Conclusion

Open-pit air supply is a chain: hammer, then air demand, then compressor, then hose. Every link has published numbers, and every link can be checked before anything is ordered. Do the arithmetic on the largest hammer you intend to run, price the altitude and the hose run into the figure, and decide early whether the rig class carries its own air. For quarry and aggregate benches rather than metal mining, the same logic applies with a different duty cycle — see quarry drilling and the open-pit comparison in underground vs surface drilling.