A mounting apparatus for a rotational drive unit. The rotational drive unit includes a socket portion which receives a truck or carrier. Opposing engagement surfaces of the carrier are separated by a distance greater than the length of the socket. The resulting lost motion connection allows for a range of free movement of the rotational head on the carrier.

A control is disclosed for inhibiting the tilting of an earth drilling machine that is supported on hydraulic jacks. A hydraulic downfeed motor for the drill string is operated by a control that has pressure responsive switches connected to the hydraulic jacks, and in the event the drilling machine starts to rise upwardly during drilling one of the pressure responsive switches will operate to shut off fluid pressure to the downfeed motor and to entrap fluid within the motor. The entrapment of fluid in the motor maintains a drilling pressure that permits drilling to continue with a drilling force that will not allow the machine to rise upwardly on the supporting jacks.

A device for applying an additional downward force to the rotating cutting tool of an earth boring machine. The machine has a mast and a rotating drive member suspended by the mast for vertical movement and for rotating the cutting tool. A rotatable drum is carried by hydraulic cylinders adjacent and below the top of the drive member. The drum has a brake and is connected by a downcrowding cable to the top of the drive member. Downward movement of the hydraulic cylinders while the drum brake is locked creates tension in the cable, applying downward force to the drive member. A take-up cable is wrapped around the drum in the opposite direction. It is reeved over the mast and connected to the top of the drive member by a spring. The spring takes up slack in the cable when the hydraulic cylinder returns for a new stroke and allows the kelly to move downward as the drum is pulled down by the cylinder.

A rotary drill rig includes an elongated mast, a pulldown head disposed for linear traversal along the mast and connected to mechanism for effecting pulldown and hoisting movements on a drill string, and a rotary drive unit adapted to be connected to the pulldown head for unitary movement therewith to form a rotary top drive drilling head. The rotary drive unit may be detached from the pulldown head and disposed at the lower end of the mast for performing joint breakout operations on the sectional drill string members and for performing drilling operations as a rotary table drive. A pair of parallel tracks are disposed on the mast for guiding the pulldown head and the rotary drive unit. The tracks are turned inward into the mast near the top end thereof to provide for parking the pulldown head out of the way of a block and tackle which may be used to raise relatively long drill strings from the drill hole.

Apparatus for manipulating equipment by selectively holding it in a gripping device mounted on a movable closed-loop belt. In the particular embodiment shown, a swivel and elevator combination is mounted on a brace which runs along a track in the derrick of a well workover rig. A belt chain is joined to the brace to form a closed loop, and is motor-driven to raise or lower the swivel and elevator arrangement to move drill pipe or casing into or out of a well.