thomas. Excavator. May 21st , 2018.
Hydraulic excavators usually couple engine power to (commonly) three hydraulic pumps rather than to mechanical drivetrains. The two main pumps supply oil at high pressure (up to 5000 psi) for the arms swing motor track motors and accessories while the third is a lower pressure (~700 psi) pump for pilot control of the spool valves; this third circuit allows for reduced physical effort when operating the controls. Generally the 3 pumps used in excavators consist of 2 variable displacement piston pumps and a gear pump. The arrangement of the pumps in the excavator unit changes with different manufacturers using different formats.
Attached to the end of the boom is the stick (or dipper arm). The stick provides the digging force needed to pull the bucket through the ground. The stick length is optional depending whether reach (longer stick) or break-out power (shorter stick) is required.
In the 1950s Louis and Cyril Keller operated Keller Welding and Repair near Rothsay Minnesota. In 1956 Eddie Velo a turkey farmer in the area described to the Kellers a need for a machine small enough to maneuver inside a pole barn and light enough to operate on its upper level. The brothers developed a small three-wheeled design with a belt-driven transmission and delivered it to Velo on February 4 1957.3 Velo allowed the Kellers full access to his operations and after the Kellers learned of drawbacks with the belt-driven transmission they developed and patented a more robust clutch-based transmission system in 1958. The new transmission became the basis of the Melroe M60 loader.
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