Quick answer: when a DTH hammer appears to use too much air, do not begin by turning pressure down or replacing the hammer. First separate five different causes that can produce the same symptom: compressor delivery limits, pressure loss in hoses and fittings, extra flushing demand from the hole, a change in drilling efficiency, and internal hammer leakage from wear or an incorrect rebuild. Compare the system under the same hammer, bit, operating pressure, hole diameter, formation, and depth before calling the change “excessive air consumption.”
This guide is for quarry, mining, construction, water-well, and drilling-service teams diagnosing a hammer that now demands more compressor capacity, causes a larger pressure drop, or drills fewer metres for the same air supply.
1. What “Excessive Air Consumption” Actually Means
Air consumption can mean two different things in the field. The first is instantaneous airflow, normally expressed as m³/min, L/s, or cfm at a defined operating condition. The second is air used per drilled metre, which combines airflow with penetration rate.
If airflow is Q in m³/min and penetration rate is v in m/min, a useful diagnostic indicator is:
Air intensity = Q / v, in m³ of air per drilled metre.
This is not an OEM discard limit. It is a comparison metric. A hammer can consume roughly the same air per minute while air per metre rises sharply because the bit is worn, the rock has changed, flushing is poor, or penetration rate has fallen. Conversely, a higher airflow reading may be expected when operating pressure or hammer configuration has changed.
OEM data reinforces this point. Epiroc publishes hammer airflow at stated pressure points rather than as one pressure-independent number, and its AirROC documentation notes that additional flushing air varies with drilling depth and rock formation. Therefore, diagnose the complete air path and drilling condition before blaming the hammer itself.
2. Start by Identifying the Symptom
| Observed symptom | First area to check | What it may indicate | Next step |
|---|---|---|---|
| Compressor pressure is normal unloaded but drops heavily as drilling begins | Delivered air capacity and air path | System demand exceeds delivered flow, or a restriction/leak becomes significant under full flow | Verify compressor output, hose size/length, couplings, valves and pressure at more than one point |
| Airflow demand is higher than the historical baseline at the same pressure and similar hole conditions | External leakage and hammer condition | Air-line leak, altered hammer configuration, assembly issue, or internal leakage from wear | Check the external system first, then inspect the hammer to model-specific limits |
| Airflow per minute is stable but air used per metre rises | Penetration efficiency | ROP has fallen because of bit wear, rock change, poor feed/rotation balance or hole-cleaning problems | Compare penetration rate, bit condition and cuttings return before changing compressor settings |
| Air demand changes mainly as the hole gets deeper or enters broken/wet ground | Flushing requirement | More air is being used to transport cuttings or overcome a difficult return path | Separate flushing demand from hammer operating demand |
| Problem started immediately after a rebuild or part replacement | Assembly and configuration | Incorrect component, clearance, orientation or hammer setup | Stop using generic assumptions and check the exact service manual and parts list |
3. Step 1 — Verify the Compressor at the Actual Operating Point
A compressor should be judged by the air it can actually deliver at the required operating pressure, not simply by engine size or a maximum-flow headline. Record the compressor model, rated free-air delivery (FAD), rated pressure, current service condition, ambient conditions, and the pressure observed while drilling.
Then compare that available air with the hammer manufacturer's requirement at the intended pressure, plus the air needed for flushing and any other consumers on the rig. A pressure gauge that looks normal before the hammer opens does not prove the compressor can maintain the required flow under load.
Do not use one universal pressure or flow target. Epiroc's current DTH documentation shows model-specific working ranges and configurations, and its COP M-series can be adapted for different compressor air pressures and volumes. The correct reference is the exact hammer configuration being operated.
4. Step 2 — Check the External Air Path Before Opening the Hammer
A hammer cannot receive air that is lost or restricted upstream. Check the system from compressor outlet to hammer inlet in a fixed order:
- Hoses: confirm the correct internal diameter, inspect for collapse, ageing, abrasion, cracking, internal damage, and excessive length.
- Quick couplings and fittings: inspect seals, damaged faces, loose joints and components smaller than the main air line.
- Valves and manifolds: confirm they open fully and are not contaminated or partially obstructed.
- Connections at the rotary head and drill string: check for audible or visible leakage using the site's approved high-pressure-air inspection method.
- Pressure comparison: where the rig design allows safe measurement, compare pressure near the compressor and farther downstream while the hammer is operating.
Never search for a high-pressure leak with bare hands. Isolate and depressurize the system before touching suspect hoses or fittings, and follow the compressor and rig manufacturer's safety procedure.
Epiroc's COP M6 operating instructions also emphasize clean, dry compressed air and regular air-hose checks. Old or damaged hoses can introduce contamination as well as create an air-supply problem, so an air-path inspection is both a performance and maintenance check.
5. Step 3 — Separate Hammer Air Demand from Flushing Air
Compressed air has more than one job in DTH drilling. It drives the hammer and carries cuttings back up the annulus. Those two requirements should not be treated as a single fixed number.
Epiroc's AirROC documentation explicitly notes that published hammer air consumption is the volume required for the hammer or drilling component to function, while additional flushing air depends on drilling depth and rock formation. This distinction explains why a system can appear to “consume more air” in deeper, fractured, wet, collapsing, or high-cuttings-load holes without the hammer having developed an internal leak.
Look at cuttings return. If the hole is not cleaning, increasing total airflow may be solving a transport problem rather than an impact problem. If the return is strong but compressor demand has risen unexpectedly under otherwise comparable conditions, investigate the air path and hammer condition more closely.
6. Step 4 — Confirm Pressure and Hammer Configuration
Air consumption must always be interpreted at the pressure where it was measured. In Epiroc's AirROC D50 technical table, the same DTH hammer examples are listed with increasing air consumption as operating pressure increases. That does not mean “higher pressure is always better”; it means flow and pressure are linked operating variables.
Before comparing two shifts, two rigs, or two hammer rebuilds, record:
- hammer make, model, size and current internal configuration;
- bit shank and bit diameter;
- working pressure during drilling;
- compressor FAD / delivered-air specification;
- hole depth and formation;
- whether water, foam, or another flushing medium is injected.
If any of those changed, a simple “before vs after cfm” comparison can be misleading.
7. Step 5 — Measure Drilling Efficiency, Not Just Airflow
A well-supplied hammer can still be an expensive drilling system if penetration rate has collapsed. Record airflow and pressure together with metres drilled per minute or per hour. The most useful field comparison is usually air demand under similar drilling conditions plus the production achieved with that air.
If air used per metre is rising, inspect the factors that lower penetration:
- bit buttons and gauge wear;
- incorrect rotation relative to penetration rate;
- excessive or insufficient feed;
- poor flushing and recutting of cuttings;
- formation changes, fractures, moisture or voids;
- hammer lubrication and contamination;
- hole deviation or side loading.
Mincon's current blast-hole guidance treats hammer-to-bit matching, airflow balance, feed and rotation as an interacting system. A compressor change cannot compensate for every mechanical or drilling-parameter problem.
8. Step 6 — Check Internal Wear and Leakage
After compressor capacity, external leakage, flushing demand and drilling efficiency have been checked, internal hammer wear becomes a stronger suspect.
Mincon's current maintenance guidance is explicit about this mechanism: critical wear parts must stay within the manufacturer's specified tolerance. Running components outside tolerance can increase air leakage, reduce hammer efficiency and lower impact energy. In practice, worn internal running clearances can allow more compressed air to bypass the intended working cycle instead of being converted effectively into piston impact.
Do not diagnose internal leakage from sound alone, and do not reuse a generic piston-to-cylinder or sleeve clearance from another hammer. During scheduled service:
- clean and identify all components;
- measure the model-specific critical wear parts at the locations stated in the manual;
- inspect piston, inner cylinder / distributor components, wear sleeve, chuck, bit shank, check valve and seals or O-rings where applicable;
- verify the correct rebuild parts and orientation;
- replace components that are outside the exact model's wear limits;
- lubricate and assemble according to the hammer instructions.
If the air-demand change appeared immediately after a rebuild, treat assembly, component match and clearances as high-priority checks before continuing to drill.
9. An 8-Step Troubleshooting Sequence
- Define the baseline. Compare against the same hammer, bit class, pressure, hole diameter, depth and similar ground whenever possible.
- Record pressure, flow and penetration rate. Do not diagnose from compressor pressure alone.
- Verify delivered compressor capacity. Confirm the actual operating point and whether the compressor is already at full load.
- Inspect the complete external air path. Hoses, couplings, valves, manifolds and drill-string connections come before hammer disassembly.
- Check cuttings return and hole conditions. Separate additional flushing demand from hammer operating demand.
- Compare operating pressure and configuration. Confirm that the hammer has not been changed to a different air-consumption setup.
- Check penetration efficiency and bit condition. If airflow is stable but production falls, solve the drilling problem before chasing airflow.
- Inspect internal wear to the exact manual. Only after upstream and drilling-condition checks should the hammer be dismantled and measured.
10. Common Diagnostic Mistakes
| Mistake | Why it creates a wrong conclusion | Better check |
|---|---|---|
| Comparing cfm at different pressures | Hammer airflow is specified at operating conditions; pressure changes can change demand | Compare like-for-like pressure and configuration |
| Blaming the hammer before checking hoses | External leakage or restriction can create pressure loss and low hammer performance | Inspect the air path first |
| Calling deeper-hole flushing demand a hammer leak | Additional flushing air can change with depth and formation | Check cuttings return and ground conditions |
| Reducing pressure only to “save air” | Moving outside the model's intended operating range can reduce impact and penetration | Use the hammer manufacturer's pressure/flow data |
| Looking only at air per minute | Production may have fallen even when flow is unchanged | Track air per drilled metre and penetration rate |
| Using a universal internal wear limit | Critical dimensions are hammer-model specific | Measure against the exact service manual |
11. What to Record Before Service or an RFQ
If technical support or replacement parts are needed, send evidence that allows the air-system problem to be reproduced on paper:
- hammer manufacturer, exact model and nominal size;
- bit shank, bit diameter and current bit condition;
- compressor make/model, rated FAD and rated pressure;
- actual working pressure during drilling;
- measured airflow, if available, and where it was measured;
- main hose internal diameter and approximate length;
- hole diameter, depth and drilling orientation;
- rock type, fracture condition, moisture and water/foam injection;
- current penetration rate and previous normal penetration rate;
- when the air-demand change began;
- whether the hammer was recently rebuilt and which parts were changed;
- photos of worn components and any recorded dimensional checks.
For current PerfoMax options, review the DTH Tools collection and the DTH Tools collection. For a project-specific check, send the operating data above through the Request a Quote page.
12. Frequently Asked Questions
Can a worn DTH hammer consume more air?
Yes. When critical internal components run outside their specified wear tolerances, internal air leakage can increase and useful impact energy can fall. The correct response is to measure the exact hammer's critical parts against its service limits rather than applying a universal clearance number.
Why does air pressure look normal until drilling starts?
Once the hammer opens and full airflow begins, compressor capacity, hose restrictions, fittings, leakage and hammer demand all become part of the loaded system. A normal no-flow or low-flow gauge reading does not prove the system can maintain pressure at the required delivered airflow.
Does higher DTH pressure always improve drilling?
No. Higher operating pressure can change airflow and impact performance, but the hammer must remain within its model-specific operating range and the complete system must have enough delivered air. Penetration also depends on bit condition, rock, feed, rotation and flushing.
Why can air used per metre rise when compressor airflow has not changed?
If penetration rate falls while airflow stays similar, the same air is spread across fewer drilled metres. Check bit wear, drilling parameters, flushing and formation changes before concluding that the hammer itself is consuming more air.
Can deep, wet or fractured holes need more air without a hammer failure?
Yes. OEM drilling documentation distinguishes hammer operating air from additional flushing air, and flushing demand can vary with depth and rock formation. Poor cuttings return, water and broken ground should therefore be checked as part of the diagnosis.
Technical References
- Mincon — How to Optimise Blast-Hole Drilling: 8 Expert Tips: critical wear, air leakage, impact-energy loss and component measurement.
- Mincon — Extend DTH Hammer Life in Blast-Hole Drilling: hammer-to-bit matching, lubrication, airflow balance, feed, rotation and wear monitoring.
- Epiroc — AirROC T35 & D50 brochure: model-specific DTH air consumption at stated operating pressures and additional flushing-air note.
- Epiroc — Secoroc COP M6 operator instructions: compressed-air cleanliness, air-hose inspection, lubrication and maintenance practices.
Next Step: Diagnose the System Before Buying More Compressor
Excessive air demand is best treated as a system diagnosis, not a single-component verdict. Establish a comparable baseline, separate hammer demand from flushing demand, verify compressor delivery and line losses, check production efficiency, and only then measure internal wear. That sequence reduces unnecessary parts replacement and makes the final service or procurement decision much more defensible.