pulled into a second position, closing a set of electrical contacts and enabling a circuit.
Difficulties were experienced with this mechanical apparatus. The tool was subsequently modified to eliminate the trigger mechanism activated by upward pull on the wire line. Well pressure was instead used to close an electrical switch, with well pressure moving a piston longitudinally within the tool. Unfortunately, these modifications led to an incident where debris was trapped on the piston leaving the electrical switch in a closed position. When an operator at the surface reloaded an explosive charge, the switch was closed, activating the explosive and injuring the operator severely.
The American Petroleum Institute developed Recommended Practice 67 for handling oilfield explosives safely. Section 4.3 of Recommended Practice 67 states that detonators and initiators must incorporatediameter and a second larger diameter. A sealing blanket is provided for the drum and is automatically adjusted for different drum diameters to provide proper tension on the film as it passes around the expandable drum.
In that configuration, manual rotation of a hex nut assembly while the machine is stopped increases or decreases the drum's diameter through a series of appropriately mounted mitre gears and ring gears. Once this adjustment is made, the machine begins operation. Readjustment of the drum diameter can only be accomplished by stopping the machine to adjust the hex nut assembly.
Additionally, very small errors in drum diameter size can lead to acute problems, particularly when the film passing through the machine has preprinted material thereon which has to appear at the same relative position