(A Practical Guide for Water Well Drilling Contractors)
Choosing the right diesel screw air compressor for DTH drilling is not guesswork.
It is calculation.
Many contractors only check pressure (bar) and ignore air flow (m³/min).
That is why drilling becomes slow at deeper levels.
In this guide, we explain how to calculate the air requirement for your DTH hammer step by step.
If you are new to DTH systems, you may first read:
👉 How DTH Drilling Actually Works
Every DTH hammer requires:
Working Pressure (bar or psi)
Air Consumption (m³/min or CFM)
Pressure determines impact force.
Air flow determines impact frequency and flushing efficiency.
Both must be sufficient.
Each hammer model has a technical data sheet showing:
Recommended pressure range
Air consumption at different pressures
Example (typical 4 inch hammer):
| Working Pressure | Air Consumption |
|---|---|
| 14 bar | 9–10 m³/min |
| 17 bar | 11–12 m³/min |
Important:
Air consumption increases when pressure increases.
The deeper the hole, the higher the air loss due to:
Pipe friction
Pressure drop
Leakage
General rule:
Add 10–15% extra air capacity for every 100 meters of depth beyond 100m.
Example:
Target depth: 200m
Base requirement: 12 m³/min
Recommended compressor capacity:
12 × 1.15 = 13.8 m³/min minimum
For safety margin → choose 14–15 m³/min
Harder formations require:
Higher working pressure
More stable air flow
If drilling in:
Granite
Basalt
Hard limestone
You should select a compressor operating near the upper pressure range of the hammer.
Low pressure in hard rock = weak impact + slow penetration.
(If drilling speed is already slow, see:
👉 Why Your DTH Drilling Is Slow - 90% of the Time, the Diesel Screw Air Compressor Is Wrong)
| Hammer Size | Recommended Pressure | Air Flow Range |
|---|---|---|
| 3 inch | 14–15 bar | 6–8 m³/min |
| 4 inch | 15–17 bar | 10–13 m³/min |
| 5 inch | 17–20 bar | 14–18 m³/min |
| 6 inch | 20–25 bar | 18–25 m³/min |
These are general field values.
Always confirm with actual hammer specs.
Many contractors choose a compressor that matches the minimum requirement.
That is risky.
You need extra capacity for:
Depth increase
Air leakage
High temperature conditions
Wear over time
Undersized compressors cause:
Reduced penetration rate
High fuel consumption per meter
Hammer instability
Step 1: Check hammer air consumption at working pressure
Step 2: Add 10–20% safety margin
Step 3: Add depth correction factor
Step 4: Confirm compressor can deliver rated flow at rated pressure continuously
Final rule:
Compressor rated flow at working pressure ≥ 120% of hammer air consumption
That ensures stable drilling.
Hammer: 5 inch
Recommended: 17 bar
Air consumption: 15 m³/min
Depth: 250m
Step 1: Base air = 15 m³/min
Step 2: Add 15% depth factor → 17.25
Step 3: Add 10% safety margin → ~19 m³/min
Recommended compressor:
17–18 bar
19–20 m³/min
That ensures efficient drilling.
Correct air calculation directly affects:
Drilling speed
Fuel cost
Bit life
Hammer reliability
In DTH water well drilling, the diesel screw air compressor is not just equipment.
It is the power system of your hammer.
If you are unsure how to calculate the requirement for your project, you can send:
Hammer size
Target depth
Rock type
Current compressor model
We can help you verify whether your air capacity is sufficient.
