DTH Hammer and Drill Bit Selection: Size, Pressure and Matching

DTH Hammer and Drill Bit Selection: Size, Pressure and Matching

The DTH hammer is where the compressed air finally turns into rock work. Everything upstream — the compressor, the rig, the drill string — exists to feed the hammer the pressure and flow it is rated for. Get the hammer wrong and the best rig and compressor combination on site will still drill slowly, burn bits and wander off line.

1. The size ladder: 68 to 311 mm

The DTH hammer line covers hole diameters from 68 mm to 311 mm, with working weights from 12 kg to 304 kg. The ladder is built in families (K, L and M series), each family covering a hole-size band:

The rule of thumb: pick the hammer family from the hole diameter, then confirm the model inside the family against the compressor you can feed it with.

2. Match the hammer to the rig

Each rig class has a natural hammer partner. A KG420B (Φ90-130 mm, 25 m benches) runs a K3/K30C-class hammer at 90-105 mm or a larger hammer when the hole plan moves to 130 mm. A KG520 (Φ105-152 mm) steps up with it. Heavy production rigs like the KT30 (195-254 mm) run the K8/K80 class — the same hammers used on deep water well programs.

If you already own the rig, the rig's hole-diameter range narrows the hammer choice to one or two families. If you are buying the rig and hammers together, size the hole from the blasting or well plan first, then walk both rig and hammer down the ladder together.

3. Match the hammer to the compressor — pressure first, then flow

This is where most field mismatches happen. Two rules:

• Pressure: the compressor's discharge pressure must equal or slightly exceed the hammer's rated working pressure. A hammer that wants 2.0 MPa will not cycle on a 1.2 MPa supply.
• Flow: the compressor must deliver the hammer's rated consumption plus 10-15% margin for leakage, altitude and line losses.

Worked examples from the Kaishan line: the KG420B draws 10-17 m³/min depending on hammer size, so the practical compressor match is a KSCY unit in the 18-21 m³/min class; the KG520 draws 15-22 m³/min and wants the next class up. The KSCY family covers 0.8-2.3 MPa for surface DTH support; deep water well programs pair the bigger hammers with the KSZJ (1.7-2.3 MPa) or LGZJ (2.5-3.5 MPa) families.

4. Bits: button heads, matched per hammer size

Each hammer size has a corresponding bit — the K3 bit drills the 90-105 mm hole of the K3 hammer, the K8 bit the 195-254 mm hole of the K8. Order hammers and bits as a set so the shank and thread always match. For abrasive rock the standard is the hardened button head; confirm the formation hardness when choosing the bit grade, because a harder formation wears a standard button set faster than the drill plan allows.

5. Keep the string running: adapters and sleeves

Drill strings fail first at the connections. Keeping the correct shank adapters and coupling sleeves in stock — sized for the K/L/M hammer range — avoids downtime from worn threads and mismatched connections on production programs. If the rig fleet mixes hammer families, keep one spare set per family, not one spare set total.

6. The selection checklist

• Hole diameter from the blasting or well plan
• Hammer family from the diameter ladder (K3/K5/K8 class)
• Compressor discharge pressure ≥ hammer rated pressure
• Compressor flow ≥ hammer consumption + 10-15%
• Matching bits ordered per hammer size
• Shank adapters and coupling sleeves in stock

Need the hammer, bit and compressor matched as a set? Tell us your hole diameter, rock description and deepest hole — we'll line up the hammer, the bit and the compressor from our DTH K/L/M hammer range and the Kaishan KSCY/KSZJ/LGZJ compressor lines and send a quote. Request a quote here.

---

Data sources

All parameters in this article are verified against the 2026 product catalogue.