DTH Air Pressure vs Airflow: What Bar, PSI, CFM, and m³/min Mean

Quick answer: air pressure and airflow describe different parts of a DTH drilling system. Pressure, usually stated in bar or PSI, is the pressure level available to operate the hammer. Airflow, usually stated in CFM or m³/min, is the quantity of air delivered over time. A DTH hammer needs both at the same operating point, which is why serious OEM data is written as a flow requirement at a stated pressure rather than as one number by itself.

For buyers, quarry managers and drilling contractors, the practical rule is simple: never approve a hammer-compressor match from “350 PSI” alone or from “900 CFM” alone. Confirm the exact hammer model, its approved pressure range, its air consumption at that pressure, the hole and flushing demand, and the compressor's available flow at the same working pressure and actual site conditions.

1. Pressure and airflow are not the same specification

The easiest way to avoid confusion is to separate the questions each number answers.

In a DTH hammer, higher pressure within the manufacturer's approved range can change the energy available to the pneumatic cycle, but the exact response of impact energy and frequency depends on hammer design. Airflow must also be sufficient to keep that operating pressure stable under load and to move cuttings out of the hole. This is why “more pressure” and “more CFM” are not interchangeable solutions.

2. What bar, PSI, MPa, CFM and m³/min actually mean

Pressure units can be converted directly:

• 1 bar = 100 kPa = 0.1 MPa ≈ 14.5 PSI.
• 10 bar ≈ 145 PSI.
• 24 bar ≈ 348 PSI.

Airflow units can also be converted:

• 1 m³/min ≈ 35.31 CFM.
• 1 CFM ≈ 0.02832 m³/min.

But converting the unit is not enough. The reference condition matters. Atlas Copco explains that compressor Free Air Delivery (FAD) is measured at the compressor outlet and then recalculated to the compressor's inlet conditions. Other terms such as SCFM or actual volumetric flow can use different reference conditions. If a hammer sheet and a compressor sheet use different bases, two numbers that look compatible may not be directly comparable until the supplier confirms the reference basis.

Gauge pressure vs absolute pressure

Another common source of confusion is gauge pressure versus absolute pressure. A drill-site pressure gauge normally reads pressure relative to the local atmosphere. Absolute pressure includes atmospheric pressure. This distinction matters most when engineering compressor pressure ratios or working at high altitude. For normal purchasing conversations, use the pressure convention shown by the hammer and compressor manufacturers and do not silently mix gauge and absolute values.

If the project is at significant elevation, see the related guide: DTH Drilling at High Altitude: Compressor Derating, Airflow, and Hammer Setup.

3. Why OEM datasheets state airflow at a pressure

A hammer does not simply “consume 700 CFM” in every condition. Air consumption changes with operating pressure, hammer architecture and configuration. OEM specifications therefore pair the two values.

Current manufacturer data shows the pattern clearly. Sandvik lists the Leopard DI560's nominal flushing-air capacity as 24.4 m³/min at 24 bar. Mincon's HDD pilot-hammer tables likewise state minimum air as paired values such as 11.3 m³/min at 17.2 bar or 25.5 m³/min at 24.1 bar, depending on model and drilling condition. These are manufacturer-specific examples, not universal PerfoMax requirements, but they demonstrate the correct way to read pneumatic specifications: flow and pressure belong together.

4. What happens when pressure is sufficient but airflow is not

A system can briefly reach the target pressure on a gauge and still be unable to sustain the hammer under drilling load. Typical reasons include an undersized compressor, restricted hose or drill-pipe passages, leakage, another large air consumer on the same system, or a compressor whose available flow falls as working pressure rises.

Possible field symptoms include:

• pressure falls when the hammer begins drilling;
• hammer operation becomes weak or unstable under load;
• cuttings return at the collar is poor;
• the compressor remains at maximum load with little reserve;
• penetration falls as hole depth or diameter increases;
• performance worsens when another air user is connected.

These symptoms do not prove that airflow is the only cause. Bit wear, internal hammer wear, lubrication, blocked flushing passages and changing ground can create similar results. Troubleshoot the system rather than changing pressure blindly.

5. What happens when airflow is high but working pressure is too low

A large free-air-delivery number is also not enough if the compressor cannot maintain the hammer's approved working pressure. A DTH hammer is designed around a specific pneumatic operating envelope. If the pressure delivered to the hammer is below that envelope, impact performance can fall even if the compressor brochure advertises a large flow value at a lower pressure.

This is why a compressor quotation should show the available flow at the required working pressure, not merely the machine's largest catalog CFM number. Compressor capacity normally changes across the pressure-flow curve.

6. Air needed to run the hammer is not always the same as air needed to clean the hole

The hammer has a pneumatic operating requirement, but the hole also has a cuttings-transport requirement. Those two demands overlap but are not identical.

Flushing demand changes with factors such as:

• hole diameter and drill-pipe outside diameter;
• annular clearance;
• hole depth;
• penetration rate and cuttings generation;
• cuttings size and density;
• water inflow;
• fractures, cavities and air losses;
• bit flushing configuration.

Mincon, for example, explicitly notes on its HDD hammer-reamer data that additional air can be required to evacuate cuttings in some situations. The same engineering principle applies more broadly: meeting the hammer's minimum pneumatic requirement does not automatically prove that every hole will clean correctly.

Do not use a universal annular-velocity number unless the hammer, rig or drilling-system manufacturer has specified it for the actual application. Deep holes, water, sensitive ground and unusual annuli need application-specific review.

7. How to compare a DTH hammer and compressor correctly

1. Identify the exact hammer. Record make, model, size class, shank and any internal air-control configuration. Do not size from “4-inch hammer” alone.
2. Read the approved pressure range. Use the current OEM manual or data sheet for the exact hammer.
3. Find air consumption at the intended pressure. If the sheet gives several pressure points, use the point closest to the planned operating condition rather than the lowest published consumption.
4. Confirm hole geometry. Record bit diameter, hole diameter, drill-pipe OD/ID and planned depth because these affect flushing demand and pressure loss.
5. Read compressor flow at that pressure. Use the pressure-flow curve or manufacturer rating, not only the headline FAD number.
6. Correct for site conditions. Altitude, ambient temperature, engine or motor derating and duty cycle can change usable compressor output.
7. Check the distribution path. Hose length and diameter, couplings, filters, valves, manifolds, drill-pipe passages and leakage can reduce pressure and flow available at the hammer.
8. Establish a drilling baseline. After commissioning, record compressor load, relevant operating pressure, penetration rate, cuttings return and drilling configuration. Trend changes against the same rock and setup.

For current PerfoMax supply scope, start with the DTH Tools collection. The final compressor match must be confirmed against the exact hammer requirement and the compressor manufacturer's performance data.

8. A practical buyer table: what each number should trigger

9. Common specification mistakes

• Comparing CFM without pressure. A flow number at one pressure is not a guarantee at another.
• Comparing bar without flow. The system can reach pressure but still lack sustainable air volume under load.
• Mixing FAD, SCFM and actual flow without checking reference conditions.
• Using hammer inch class as the air specification. Different designs in the same nominal class can have different consumption.
• Ignoring pressure drop. Compressor outlet pressure is not automatically hammer inlet pressure.
• Ignoring hole-cleaning demand. The hammer may run while the hole still cleans poorly.
• Increasing pressure beyond the approved range. This can raise wear or equipment risk and may not fix the real bottleneck.
• Ignoring altitude and temperature. Available compressor output can change materially from catalog reference conditions.

10. What to send in an RFQ

To avoid a vague “What CFM do I need?” conversation, send the supplier enough information to identify the operating point:

• rig make/model and rotary-head connection;
• exact DTH hammer make/model if already selected;
• bit shank and target bit/hole diameter;
• target hole depth and inclination;
• drill-pipe OD, ID/air passage and connection;
• rock type, hardness/abrasivity and fracture condition;
• water condition and expected flushing difficulty;
• compressor make/model, rated pressure and flow;
• site elevation and ambient-temperature range;
• hose/manifold arrangement and approximate line length;
• current penetration rate or air-supply problem if replacing an existing setup.

PerfoMax can use the drilling-interface and application information to help confirm the tool configuration. For a project review, request a quote and include the compressor and hole data with the hammer/shank details.

Frequently asked questions

Is higher air pressure always better for DTH drilling?

No. The hammer must stay within its approved operating range, and the compressor must still supply the required airflow at that pressure. Higher pressure outside the recommended range can increase wear or risk without solving restrictions, leakage, poor flushing or bit problems.

Can a compressor have enough CFM but not enough pressure?

Yes. Compressor flow normally changes with working pressure. A large CFM rating at a lower pressure does not prove the machine can deliver the same flow at the hammer's required pressure. Compare the pressure-flow operating point.

Which unit is better, CFM or m³/min?

Neither is better; they are different units for volumetric flow. One m³/min is approximately 35.31 CFM. The more important question is the reference condition and the pressure at which the flow is available.

What does “24 m³/min at 24 bar” mean?

It means the specification pairs an airflow quantity with a working pressure. It should not be read as “24 m³/min at any pressure.” Also confirm whether the flow is stated as FAD or by another reference convention.

Why can the pressure gauge look normal while the DTH hammer drills poorly?

The gauge may be upstream of a restriction or leak, or the system may reach pressure without sufficient sustainable flow for the hammer and cuttings transport. Internal hammer wear, bit wear, lubrication and changing rock can create similar symptoms. For a structured diagnostic sequence, see DTH Hammer Excessive Air Consumption: Air Leaks, Wear, and Pressure Checks.

Technical references

1. Atlas Copco — Measuring compressed air quality and Free Air Delivery.
2. Atlas Copco — Compressed-air pressure, volume and flow fundamentals.
3. Sandvik — Leopard DI560 DTH drill-rig specifications.
4. Mincon — HDD pilot-hammer minimum-air specifications.
5. Mincon — DTH hammer range and available-air efficiency guidance.