Which conditions would typically call for an increase in air volume when hard rock drilling?

• A. Deeper holes
• B. All of the above
• C. Increased cuttings in hard or fractured rock
• D. Larger hole diameter

Answer: (B)

Air helps both cool the bit and carry cuttings up and out of the hole. When conditions increase the amount of material to remove or the difficulty of removal, you need more air to keep the cuttings moving and prevent clogging.

Deeper holes mean a longer air column and more friction losses along the borehole. To maintain the necessary air velocity to lift cuttings to surface, you raise the air volume.

More cuttings, especially from hard or fractured rock, produce more chips and can be heavier or more likely to pack in the hole. Increasing air volume helps keep these cuttings suspended and flowing.

Larger hole diameter provides more space for air to move, so at the same flow you’d have a lower velocity. Increasing air volume restores the required velocity to clean the bit and carry cuttings out of the hole.

Taken together, these are conditions that typically call for increasing air volume.