Abstract: A mobile tank for transporting liquids has a vent valve with a safety device to assure that the vent valve is always open during draining, to relieve vacuum build-up. The vent valve is coupled to a vent port in the top of the tank, and operates on air pressure. The air pressure is controlled by a control valve mounted near the discharge valve. The control arm on the control valve is mounted in an interfering position with the discharge valve, requiring the air control valve to be opened before the tank discharge valve can be opened.

Abstract: An apparatus for retrieving drill collars in an earth boring drill string when stuck. A sub is connected between two drill collars at various points. Each sub is a cylindrical member with a reduced annular or notched area at one point that is no greater in wall thickness than the drill pipe. A locator is secured to a wire line and lowered into the drill string to the vicinity of one of the subs located above the stuck point. The locator carries an explosive charge of capacity sufficient to cut drill pipe. The locator has a pivotal dog that engages a landing in the sub. The landing is spaced above the annular area a distance selected to position the explosive charge adjacent the annular area when the dog engages the landing.