Series CA (Clearance Arm) Dumpmaster

An early example of the revised Dumpmaster, which now featured a Dempster-built packer body with 58,000 pounds of force delivered by a telescopic cylinder.
"Over-the-cab" (OTC) lift arms improved safety and maneuverability. Note the small extensions over the lift forks which were quickly discontinued.

    "The nearest thing to automation in the rubbish collection field" is how Dempster described their new 1957 Dumpmaster front loader. Though similar in principle to the original 1955 version, this machine was so new and so advanced that it is somewhat astonishing how quickly the firm developed it. The new Dumpmaster was the result of a collaboration between George R. Dempster and an engineer by the name of William R. Herpich. Herpich was responsible for the Hydro E-Z Pack side loader built by Hercules-Galion, which was one of the first heavy-duty, all hydraulic side loaders on the market. Accordingly, the 1957 Dumpmaster packer body is based on a very similar concept with a top-loading bay and full-travel packer panel powered by a double-acting telescopic hydraulic cylinder. In fact, the use of this type body on a front loader is arguably a more practical application, since manual loading height was not a factor. The heavily reinforced body supported packing pressures of up to 58,000 pounds, more than twice that of the old mechanical Pak-Mor body. The result was a claimed 3:1 packed volume reduction, giving the Dumpmaster an unprecedented range of operation before unloading was necessary.

    If this were not impressive enough, Dempster and Herpich completely redesigned the lift mechanism and container coupling, creating a new industry standard. Like previous front loaders, the lift arm pivot axis was near the lower front section of the body, just behind the cab. But instead of straight, horizontally inclined arms as before, the new arm rose vertically to a point above the vehicle cab and then curved forward and dropped again just ahead of the font bumper. This "over-the-cab" (OTC) arm completely cleared the vehicle cab door area and rear view mirrors during all phases of the loading cycle, eliminating a major safety hazard to the driver, as well as doing away with the need for retractible mirrors. As a side benefit, the vehicle could be safely maneuvered and even driven with the arms in the lowered position.

    Dempster called it the "Clearance Arm", and bodies equipped with it became known as the "CA" series. Solidly patented by Dempster, the OTC lift arms touched off legal battles with other manufacturers that Dempster would ultimately lose within a few years. By the end of the 1960s, they would become near-universal within the entire industry, and undoubtedly the single greatest advance in front loader technology of all time.

Approach and coupling was simple with new side fork system. Forks were welded to a hydraulically pivoted rock shaft, which allowed
operator to maintain container in upright position until over the hopper opening, and then invert it to empty the contents into the body.
Lift arm cylinders were mounted under the body.

    The third major change on the new Dumpmaster was in the container coupling and dumping method. Instead of the claw and stud method, coupling was now achieved with a set of forks. Fork coupling had already become the standard of west coast front loaders, which predominantly used a set of flat forks engaging slots in the bottom of the container. Dempster's new models set the forks on edge and moved them to the outboard ends of the loading arm assembly to engage shallow pockets welded to the sides of each container. These "side forks" gave the driver a much better view of the coupling during hook-up. The side pocket slots were also far less hazardous to pedestrians than the studs of the 1955 Dumpmaster container, which protruded from the containers at eye-level. The forks were affixed to a rock shaft connecting the ends of each lift arm, which was pivotable by a pair of cylinders allowing pitch control of the container and full inversion once over the loading hopper. This pivoting shaft method was first used on the short-lived Cook Brothers front loaders, and soon became standard on virtually every front loader design.

Dumpmaster lift and dump cycle illustrated

Dumpmaster with containers up to 8-cubic yards

Left: dock-loading wheeled containers using optional outside controls.
Right: load ejection showing how rear door is pushed open by refuse

Dumpmaster with container inverted over hopper opening


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