Presentations from the 12th Equipment Management Workshop
Installing a counterweight to aerial equipment is another means of stabilizing the unit. The location of the counterweight is dictated by the weight and configuration of the boom(s).
Booms are an important feature of aerial equipment. The boom(s) are generally operated by hydraulic cylinders located at the pivot areas of the device. On units designed for high-voltage power line maintenance, a portion of the boom(s) will be made with fiberglass. When certain manufacturing processes are applied, fiberglass will take on an insulating quality, termed dielectric within the industry.
Most aerial devices have at least one turntable, which is usually operated by a hydraulic orbit motor mounted on a gearbox.
The platform is generally mounted on the outermost portion of the boom system. Personnel operate the boom(s) by means of electrical controls such as joysticks or valve handles mounted on the platform. Platforms are usually made of fiberglass or aluminum. A manufacturer's decal located on the platform notes the maximum rated platform capacity that should not be exceeded.
The hydraulic system usually consists of a hydraulic pump, which is mounted to a power take off system on the truck transmission or directly coupled to a drive shaft connected to the truck engine. In some cases, a hydraulic pump is directly coupled to an auxiliary engine. There are several variations on this system, to provide fluid hydraulic pressure for the operation of the booms. The main valve is generally located at the base control station, usually at or near the main turntable. This valve controls the hydraulic pressure and flow to the hydraulic cylinders and orbit motors, which move the boom(s) and turntable(s). The main hydraulic valve is usually considered to be the primary control point. Another feature of the hydraulic system is the override device, which allows operation of the boom(s) should the electrical system fail. Aerial equipment that allows the booms to travel overhead may incorporate a manual let down system (valve), which allows the booms to be lowered if the hydraulic system fails.
Stability of some aerial equipment is controlled through a combination of electrical limit switches and the hydraulic system. If the booms are being moved near a position that could create an unstable condition, a limit switch is tripped and the hydraulic flow is shut