Abstract: In a machine for digging a trench, in which the digging apparatus comprises an elongated boom having a movable chain around its periphery and which is lowered into the ground, the problem of dislodged boulders which heretofore would be excavated into the machine where they often damaged the conveyor belt system or became stuck, is prevented by an elongate bar or drum which is attached to the frame of the machine in close proximity to the operating chain and immediately before the boulder would otherwise enter the machine. The boulder is held there until it either breaks apart or its abraded by further action of the chain to a sufficiently small size that it can safely navigate through the machine and be expelled in the normal course.

Abstract: A vehicular ditching apparatus in which an oil-cooled mechanism having rotating friction discs and plates, and further having a fluid controlled piston for increasing the friction between the discs and plates, is incorporated into the ditcher, aft of the transmission, as a torsional limiting device to protect the components of the drive chain in the event the cutting wheel of the ditcher is subjected to unexpected increased load, such as when it hits an unseen obstruction.

Abstract: An improved torsional limiting device and associated control system are incorporated in a large scale trencher between the power source and the cutting wheel to provide for protection of the equipment components in the event the cutting wheel encounters unforeseen obstructions. The control system provides for prompt and variable adjustment by the operator of the amount of torque transmitted to downstream components and also provides for the prompt and easy resumption of the trenching operation after an obstruction has been encountered.