CPCS A47 A48 Piling Rig - Bored Practice Questions - CPCS A47 A48 Piling Rig - Bored (NOCN CPCS, UK) Exam

How does a mechanical locking Kelly bar differ from a friction Kelly bar during drilling operations?

Mechanical locking Kelly bars feature drive pocket locks to transfer maximum crowd force in hard rock, whereas friction Kelly bars rely on friction between sections Friction Kelly bars can only be used for drilling in hard granite, while mechanical locking Kelly bars are limited to soft clay Mechanical locking Kelly bars do not retract telescopically and must be removed in one piece Friction Kelly bars automatically clean the auger flights during extraction without operator input

Correct Answer:

Mechanical locking Kelly bars feature drive pocket locks to transfer maximum crowd force in hard rock, whereas friction Kelly bars rely on friction between sections

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