Patent Number: 6,293,359

Title: Pressure control of a drilling apparatus

Abstract: Apparatus for blast hole drilling includes a hammer and drill bit driven by a hydraulic drive motor outside the hole through a drill string extending along the drilled hole to the drill bit. The drive motor is carried on a mast with a telescopic hydraulic cylinder driving the motor along the mast in a forward direction for forwarding the drill bit along the hole to the rock face and for applying a feed force on the drill bit at the rock face and in a rearward direction for reducing the feed force and for withdrawing the drill bit from the hole. The cylinder assembly has a pulldown pressure side fed at a constant supply rate and a holdback pressure side controlled to discharge the fluid when moving downwards and to supply the fluid at a constant rate when pulling up. The control system includes a first valve for controlling a rate of supply of fluid to the motor for controlling the rate of rotation of the drill bit, a drilling valve operable to supply fluid to the pulldown side or to the holdback side, a second valve for controlling the rate of supply of fluid to the pulldown side, a third valve for controlling the rate of discharge of fluid from the holdback side, a hydraulic feedback line for communicating an increase in pressure of the fluid at the motor, caused by an increase in resistance to the rotation of the drill bit, to the holdback side of the so that the rate of forward movement of the drill bit is varied in proportion to changes in the pressure at the motor and a pressure switch responsive to pressure of the fluid at the hydraulic drive assembly exceeding a predetermined pressure limit to repeatedly cycle an upward and downward movement of the drill bit until the overpressure condition clears or until a number of cycles is completed.

Inventors: Dobran; Mauro F. (Winnipeg, CA), Desrosiers; Georges J. (Winnipeg, CA), McIvor; James Wilfred (Winnipeg, CA)

Assignee: Cubex Limited

International Classification: E21B 19/086 (20060101); E21B 19/00 (20060101); E21B 15/00 (20060101); E21B 15/04 (20060101); E21B 015/00 ()

Expiration Date: 09/25/2018