NOTE: A common rule of thumb is to never swingor perform work with a revolving unit over the cab orfront of the truck.Some truck-mounted units are equipped withoutriggers mounted on the rear that increase the stabilityof the truck. These outriggers are normally hydraulicallyactuated and controlled from the cab of the truck andprovide a much larger and more rigid base than tires.The advantage of truck mounting over trackmounting is its capacity for rapid movement from onejob to another. The boom can be placed easily in theboom rest for traveling and then driven down the roadat 25 to 35 miles per hour. This is better than the slowlaborious job of trailer loading, securing, hauling, andunloading a track-mounted excavator.The truck-mounted excavator suffers from a lack ofmaneuverability compared to the track mounting,because it requires a large area to turn around or tosidestep. Additionally, an important weakness is the easewith which it can get stuck. Constant care must beexercised to keep away from soft ground during or afterit rains. Also, tire damage can occur when working ingarbage dumps or a rock quarry.Self-Propelled Wheel MountedThe self-propelled single-engine unit has a two-range transmission, enabling it to travel between 3 and28 miles per hour. Maneuverability on the job is subjectto the same limitations as the truck mounted, except theshort wheelbase, and in some models, four-wheelsteering allows it in tighter places.The self-propelled model has front axle oscillationlock levers. These levers are used to lock out the frontaxle from oscillating up or down, holding the axle rigidand level with the main chassis. The lock lever is usedto help stabilize the excavator when working over theside.NOTE: When reading, make sure the oscillationlock levers are up in the oscillate position, allowing theaxle freedom to oscillate up or down.The self-propelled model has a set of outriggersused to increase the stability of the unit. These outriggersare hydraulically actuated and are controlled from thecab and provide a much larger and more rigid base whenthe revolving unit is placed in the working position.When traveling, always check the travel route forweight, height, and width limits, make sure the boomand steering selector are placed in the travel position,and the swing brake is engaged. Do not travel with the9-24boom over the side of the excavator, and if traveling offof the road, do not travel faster than 5 miles per hour.NOTE: After 2 hours of highway travel or every 50miles, whichever occurs first, stop the machine to let thetires cool for 1/2 hour. Heat damages the tires and cancause tire failure.ATTACHMENTSAll hydraulic excavator attachments are made ofthree strong structural members, such as the boom, thedipper stick, and the bucket (fig. 9-58). The structuralmembers are hinged to each other, and the boom ishinged to the revolving unit. Movement at each hinge iscontrolled by two-way hydraulic cylinders.BoomThe boom is normally concave towards the groundthat allows space to pull the bucket closer to theexcavator, permits deeper digging without interferencefrom the travel unit, and enables the operator to see pastit more easily when it is raised. There are two holes forconnecting the boom cylinder rod eye to the boom (fig.9-59). The top hole is for maximum digging depth, andthe bottom hole is for maximum dump height. Be sureto read the operator’s manual for instructions on theboom height-depth adjustment.The outer end of the boom is usually prolonged intoa two-piece bracket, in which the dipper stick is held bya heavy hinge pin or pins.Dipper StickThe dipper stick is usually one-piece, but somemodels may hydraulically extend and retract by atelescoping boom. The dipper stick hydraulic crowdcylinder is either connected on the top or on the bottomof the dipper, and the bucket and bucket dump arms areconnected at the end.If the dipper stick hydraulic crowd cylinder ismounted on the top, extending the cylinder forces thebucket in towards the machine, known as “crowding.”Retracting the cylinder forces the bucket outward,known as “extending.” When the cylinder is mountedunderneath the boom, retracting the cylinder crowds thedipper stick, and extending the cylinder extends thedipper stick.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business