Abstract: A quick changeover hydraulic circuit for use in an auger drive mode or percussion hammer mode, controllable in each mode by the same flow regulator. The circuit comprises a first branch circuit which powers a first auxiliary hydraulic powered device and a hydraulic motor for drill steel rotation. A second branch circuit powers a hydraulic percussion motor for a drill steel hammer or a rotary hydraulic motor for an auger, only one of which is in the circuit at one time. An interbranch circuit comprises a priority flow divider which distributes flow. In a first mode with the percussion motor for the drill steel hammer connected into the second branch the flow is delivered to the steel rotation motor and the first auxiliary device. In a second mode with the auger motor connected into the second branch, combined flow from both branches is delivered to the auger motor.

Abstract: A temporary roof support comprising a boom pivotally mounted and positioned on the front of the mining vehicle. A temporary roof support jack is pivotally mounted to the front of said boom. The jack comprises a base structure secured to the boom and extending laterally thereof. The base structure has four pivot pins including an inside pair of pivot pins symmetrically spaced on each side of the base structure and an outside pair of pivot pins symmetrically spaced on each side of the base structure. Two pairs of swing arms are pivoted to said inside pivot pins. Two linkage extensions are pivotally joined to each other and at opposite ends to the free ends of the swing arms. Two extensible hydraulic means are pivotally secured at one end to the outside pivot pins and pivoted at the opposite ends to the swing arms such that the axes of the swing arms and extensible hydraulic means are always crossed. A beam is attached to the pivot joint of the linkage arms for supporting the roof.