thomas. Excavator. May 23rd , 2018.
Excavators (hydraulic) are heavy construction equipment consisting of a boom dipper (or stick) bucket and cab on a rotating platform known as the "house".1 The house sits atop an undercarriage with tracks or wheels. They are a natural progression from the steam shovels and often mistakenly called power shovels. All movement and functions of a hydraulic excavator are accomplished through the use of hydraulic fluid with hydraulic cylinders and hydraulic motors.2 Due to the linear actuation of hydraulic cylinders their mode of operation is fundamentally different from cable-operated excavators which use winches and steel ropes to accomplish the movements.
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.
The two main sections of an excavator are the undercarriage and the house. The undercarriage includes the blade (if fitted) tracks track frame and final drives which have a hydraulic motor and gearing providing the drive to the individual tracks and the house includes the operator cab counterweight engine fuel and hydraulic oil tanks. The house attaches to the undercarriage by way of a center pin. High pressure oil is supplied to the tracks hydraulic motors through a hydraulic swivel at the axis of the pin allowing the machine to slew 360° unhindered.
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