Abstract: Apparatus for separating relatively large undesirable particles from a slurry includes an endless movable filter belt mounted for movement along a horizontal path and supply means depositing slurry carrying large particles on the upper surface of the filter means. Pressurized gas jets are positioned beneath the lower surface of the filter means in the area beneath which the slurry and relatively large particles are deposited to agitate same and suction means beneath the filter belt to separate the slurry from the relatively large particles to provide purified slurry. Gas from the slurry is separated by a degasser having a spiral floor partition which slurry comprises drilling mud and said large particles comprise earth cuttings comprises a common wall between gas and slurry outflow conduits in a space-saving manner.

Abstract: Control apparatus for preventing inadvertent operation of the drawworks of a drilling rig upon closure of an associated blowout preventer, the drawworks being at least partially operated by air from an air source connected thereto by an air conduit. The control apparatus may comprise control components for connection to the air conduit and movable from a first mode, in which air is permitted to communicate with the drawworks through the air conduit, and a second mode, in which air is prevented from communicating with the drawworks. Also included are monitor components for connection to the blowout preventer and the control components for sensing whether the blowout preventer is in opened or closed positions and initiating movement of the control components to the second mode upon movement of the blowout preventer to the closed position.