Best Compressor for DTH Drilling

Two numbers decide the compressor

Discharge pressure must cover the hammer working pressure. Free air delivery must cover the hammer air consumption plus a margin for leakage and altitude. A bigger compressor is not automatically better — it costs fuel and money.

Those two numbers come from the hammer, not from the rig and not from the drill string. A DTH hammer is a piston driven by compressed air: pressure sets how hard the piston hits, and volume sets how often it hits and how well the cuttings are flushed out of the annulus. Buy pressure without volume and the hammer strikes hard but slowly while the hole loads up with cuttings; buy volume without pressure and air bypasses the piston through the exhaust without doing work. Both mistakes look the same on site — poor penetration, and no obvious fault to point at.

The hammer side of the equation

Start from the hammer you intend to run. Our own figures for the families most often used with mobile compressors:

• L2 class (68–88 mm holes): 5.0 m³/min at 5.0 bar. Low pressure, small air package.
• K3 / K30C (90–105 mm): 4.8–12.6 and 8.5–14.0 m³/min at 10 bar.
• M30C / M3A / M3AK (90–110 mm): 5.5–12.0 m³/min at 6 bar.
• K4 / K40 / K46 (105–130 mm): 5.0–14.0 and 6.0–15.0 m³/min at 10–12 bar.
• K5 / K50 (135–165 mm): 7.0–19.0 m³/min at 10 bar.
• K6 (155–190 mm): 9.0–26.0 m³/min at 10 bar.
• K8 / K80 (195–254 mm): 12.0–31.0 and 12.0–35.0 m³/min at 10 and 17 bar.
• K10 (254–311 mm): 22.0–65.0 m³/min at 10 bar, up to 30 bar.

Read those ranges carefully: they are quoted across the hammer's working band, not at one setting. A K5 at 19 m³/min needs a different compressor than the same K5 run at the low end of its band, and the choice is made by the rock, not by preference. Hard rock wants the top of the band.

Practical consequences:

• Never size from the nominal model number of the compressor. A machine badged by its air delivery at 8 bar does not deliver that flow at 18 bar. Compression is a trade: the same air end moves more volume at low pressure and less at high pressure.
• The margin is real, not marketing. Use 10–20% on top of the hammer figure for leaks at joints, hose losses and filter restriction, and more at altitude. A hammer that gets exactly its rated flow on paper will be starved in practice.
• Pressure rating of the hose and the joints must match the machine. A 35 bar compressor feeding 20 bar rated hose is a hazard, not a configuration.

Current range with published figures

The table below lists our compressor models with working pressure and free air delivery. Note that pressure and flow are not interchangeable: a 25 bar / 21 m³/min unit and a 18 bar / 25 m³/min unit serve different hammers.

Our compressor range (published parameters)

Beyond the standard band: high pressure and dual-mode machines

Dual-mode machines deserve a note because their nameplate is easy to misread. LGCY-45/25-37/35 delivers 45 m³/min at 25 bar and 37 m³/min at 35 bar; LGZJ-36/30-41/20 gives 41 m³/min at 20 bar and 36 m³/min at 30 bar. The conservative figure is the one to use when the rock is hard and the hammer runs at the top of its band, because that is where the machine will spend its working life on a production bench. Below roughly 25 m³/min both numbers usually matter little; at 35 bar and above the difference decides whether an 8 inch hammer gets its rated flow.

What sits behind the nameplate

Two practical readings from that table. First, engine power and weight rise steeply with pressure: the 8 bar KSCY-220/8X weighs 1.4 t with a 75 HP engine, while a 25 bar 33 m³/min machine such as the LGCY-33/25 carries 6.8 t and a 560 HP engine. That is fuel burn, transport and service access, not just purchase price. Second, dual outlets are the normal arrangement above 18 bar: one G2 port for the rig and one G3/4 port for a second consumer or for blowing down the line, which saves a manifold on site.

Matching compressor class to hole range

The cleanest way to close the sizing loop is to work backwards from the hole:

• 90–115 mm, one rig, mid-pressure hammer: 12–15 m³/min at 15–18 bar is enough. KT5C carries 12 m³/min at 15 bar; a KSCY-400/14.5K at 14.5 bar and 11.3 m³/min covers the same band as a separate unit.
• 115–165 mm with a 4–5 inch hammer: 17–22 m³/min at 18–22 bar. This is where the LGCY-17/18-18/15T, LGCY-19/21-21/18 and LGCY-21/21-23/18 sit.
• 155–203 mm with a 6 inch hammer: 22–31 m³/min at 21–25 bar. The LGCY-23/23-25/18 and LGCY-25/23-27/18K serve this band.
• 195–254 mm with an 8 inch hammer: from 26 m³/min upward, and at working pressure. The LGCY-26/25 and LGCY-33/25 are here, with the 35 bar LGZJ-30/35-35/25 for the hardest ground.
• 254–311 mm: 33–65 m³/min. In practice this is either a large single machine, such as the LGCY-39/25, or two machines running in parallel into a common manifold.

If you run a fleet rather than a single rig, the arithmetic changes. One 25 m³/min machine feeding three split rigs on the same bench costs less per hole than three machines idling between holes, provided the drill pattern and hose runs allow it.

How to pick

• Read the hammer working pressure. 2) Read the hammer air consumption at that pressure. 3) Add a margin (typically 10–20%, more at altitude). 4) Choose the smallest compressor that still satisfies both. 5) Check the service network in your country.

Two additions to that list, both learned the expensive way:

• Check the duty cycle, not just the peak. A machine sized to the bare minimum runs at 100% load all shift, which raises fuel consumption per cubic metre and shortens airend life. Sizing the air package 15% above the hammer requirement is normal practice on production benches.
• Check how you will move it. A 6.8 t machine needs a different trailer, road and loading arrangement than a 2.4 t one. On a site that relocates weekly, that can outweigh the air advantage.

Altitude and temperature

At altitude the air is thinner, so the same hammer needs more volume. If your site is above roughly 1,500 m, size the compressor up or confirm the derating with an engineer.

The same applies to ambient temperature, in the opposite direction on the cooling side: a machine working at 45 °C ambient loses effective capacity and needs its cooling package and oil specification checked. Sites in high-altitude cold climates hit both problems — thin air and cold starts — and the answer is usually one machine size up plus a cold-weather starting package, not a different hammer.

Altitude is also where the margin stops being optional. A hammer fed exactly its rated flow at sea level will be short of volume at 2,500 m, and the symptom is not a hard failure: the rig simply drills slower, the bit runs hotter and button life drops. For those sites, tell us the altitude with the hole diameter and we will size the air package together with the rig; our high-altitude drilling page covers the configuration choices in more detail.

Common mistakes

• Sizing from the rig instead of the hammer. The rig does not consume air; the hammer does.
• Reading a dual-mode nameplate as a single figure and assuming the top number always applies.
• Ignoring the pressure drop along a long hose run. Thirty metres of undersized hose can cost more pressure than a change of compressor model.
• Choosing a compressor whose outlet port and hose rating do not match the hammer's working pressure.
• Running a compressor flat out with no margin for filter restriction and leaking joints.
• Forgetting the altitude correction, then blaming the hammer for slow penetration.
• Buying a high-pressure machine for a low-pressure hammer (or the reverse) because the price difference looked small. Pressure and flow are matched to the hammer, not to the budget.

Conclusion

Pressure first, volume second, margin third — then check altitude, hose, outlet and transport. Most quarry and open-pit work in the 115–165 mm band is well served by a 18–22 bar machine delivering 17–22 m³/min, which is exactly where the LGCY-17/18-18/15T, LGCY-19/21-21/18 and LGCY-21/21-23/18 sit. Above 155 mm the 6 inch and 8 inch hammers move the requirement to 25–35 m³/min and 25–35 bar, and the LGCY-33 and LGZJ families take over. The compressor is not an accessory to the rig; it is half of the drilling system. Send us the hammer model, hole diameter and site altitude and we will quote the air package that matches it, together with the rig and tooling.

Next steps: DTH hammer selection guide and how to choose a DTH drilling rig, plus the compressor ranges at diesel screw air compressors, drilling air compressors and high-pressure air compressors.