As the hole deepens in air rotary drilling, how must the air pressure change to maintain effective cuttings removal?

• A. Decrease
• B. Vary randomly
• C. Increase
• D. Stay the same

Answer: (C)

In air rotary drilling, the cuttings are carried to the surface by a column of air. As the hole deepens, the weight of that cuttings column and the friction against the borehole walls increase, creating more back pressure the lifting air must overcome. To keep the same rate of cuttings removal and prevent accumulation or sticking, the air pressure must be increased with depth. Decreasing pressure or keeping it the same would reduce lift and hinder removal, while varying randomly wouldn’t reliably maintain removal efficiency.