Aerial Devices and Digger Derricks
By Charlie Drummond
Owners of digger derrick and aerial devices are responsible for ensuring their equipment is inspected annually. This responsibility can mean more than just meeting requirements set by OSHA or ANSI. Thorough annual inspections are one of the key components to help ensure the equipment is safe for both the operator and crew members. While safety is the foremost concern, annual inspections can also reveal small operational issues before they cause serious, and possibly expensive, equipment repairs.
Annual inspections are a task to be performed by qualified people, such as Terex Utilities’ factory trained technicians who have access to the right tools to do the job correctly. Organizations with experienced service technicians may choose to perform and document these inspections in-house, or outsource to a third party.
When it’s time to conduct an annual inspection, expect the process to take three to six hours depending on the type of equipment being inspected. It’s a good idea to schedule annual inspections strategically to help minimize downtime of your fleet. Allow extra time for scheduled maintenance and based on the findings from the inspection; you may need to plan for additional required repairs to be performed. For insulated aerial lifts and digger derricks, it is recommended that the annual dielectric testing be done at the same time as the annual inspection.
While user manuals identify the items to be inspected, it takes someone with the proper training, knowledge and experience to ensure a thorough inspection is completed. An aerial lift or digger derrick is often sent to Terex Utilities for repairs after an annual inspection has been performed by another party. In many instances, these repairs can be minimized or eliminated by ensuring a timely and thorough inspection had been completed by a qualified factory trained technician.
According to factory trained technicians at Terex Service Centers, the following are some of the most frequently overlooked inspection items, listed in increasing order of seriousness. Most of them apply to either digger derricks or aerial devices, while the last two are specific to aerials.
Missing Safety or Operational Decals: Operational and Safety decals provide valuable information to the users. Power washing equipment over the course of a year takes a toll on decals. Sometimes it’s not obvious what’s missing from the equipment if you don’t know what decals are supposed to be there. In particular, it’s especially important to make sure hand signal charts aren’t missing from digger derricks. The hand signals provide a means to communicate between the operator and ground personnel when they are in a noisy environment. Failure to communicate clearly could lead to possible injury or equipment damage and could result in an OSHA violation.
Hydraulic Oil Levels Not Maintained and Hydraulic Filters Not Replaced: Oil levels must be checked according to the manufacturer’s recommendations for equipment to operate as designed. More frequent checks based on operating and weather conditions may be necessary. Low levels, if left unattended, could lead to high dollar, unplanned repairs. Burning up one pump is easily a $2,000 repair, not to mention the loss in productivity from the equipment being out of service. Checking the fill level when the outriggers are extended can often lead to over filling. An overfilled system leaves no room for expansion, which can contribute to oil leakage. A dirty oil filter can lead to accelerated wear and damage to pumps, cylinders, hydraulic valves and hoses due to the filter no longer capturing harmful contaminants and particles circulating in the fluid.
Damaged Winch Rope: In addition to the daily visual inspection, the full length of the winch rope should be unspooled and inspected hand-over-hand during the annual inspection. When you feel cuts or a bulge—an indication of internal rope damage that can be caused by shock loading or kinking—the rope should be replaced. Additional inspection and replacement criteria are available from the rope manufacturers.
Rotation Bearing Bolts Not Torqued: While the process is simple, this is one of those items that cannot be overlooked. It may be easier to inspect and re-torque bolts with two people—one to rotate the bearing and the other to check the bolt torque. Information on the proper bolt torque and lubricant is available in the manual and on the Terex Utilities website. Failure to maintain proper torque could lead to bearing bolt failure due to overloading the remaining fasteners. It can also lead to bearing failure representing a $6,000 to $10,000 repair. For more information on how to check the torque on rotation bearing fasteners on Terex equipment, see the sidebar article.
Too Loose Bearing Deflection/Backlash: Checking the amount of allowable play in the rotation bearing takes time and a proper understanding of how to measure it. If there is too much play, this may be an indication that the rotation bearing could be worn and needs replaced. In addition, it could also be an indication the boom has been shock loaded. For more information on how to conduct a Rotation Bearing Deflection Test for Terex equipment, see the sidebar article.
Leveling Chain Has Too Much/Too Little Play: Leveling systems on aerial devices should have specific amounts of preload. Too much or too little tension increases wear and possible damage. Checking leveling tension requires taking the boom cover off. Failure to keep the chain within tolerance could affect the self-leveling of the bucket as the booms move through their range of motion.
Bucket and Liner Damage: Cracks, gouges and damage to the aerial device bucket could affect the structural integrity. Cracks, gouges and wear on the liner contribute to reducing dielectric strength. Often, we find that inspectors fail to remove the liner when looking at the bucket. Tools get dropped, often damaging the liner and the bucket itself, so look underneath, inside and out of the bucket.
Do it Yourself: Pros and Cons
While conducting your own annual inspections may seem the most affordable option, be sure to consider whether your technicians have the expertise required for the specific equipment. The same is true if you choose to outsource the inspection. If hiring someone else to do the inspection, make sure you choose a company that has qualified and trained technicians for the type of equipment being inspected. Someone who is trained and qualified to perform DOT inspections may not be qualified to perform aerial or digger derrick inspections. It is the owner’s/user’s responsibility to have qualified personnel perform the inspections.
To properly conduct the inspections, the technician should be a qualified person who possesses an appropriate technical degree, certificate, professional standing or skill, and who by knowledge, training and experience has demonstrated the ability to deal with problems relating to the subject matter work or project.
For those owners who perform annual inspections in-house, Terex offers several training programs designed to provide technicians with the knowledge to become a qualified inspector to conduct annual inspections.
There are a number of benefits to using the manufacturer’s inspection services. Terex Utilities offers DOT and ANSI annual inspections, five-year inspections, dielectric testing, inspection and maintenance for all makes and models of digger derricks and aerial devices. Terex Utilities will also check to ensure all updates, recalls or bulletin items have been addressed, and if a repair is under warranty, it’s simpler for the OEM to be involved from the start.
Qualified factory trained technicians at Terex Utilities receive on-going training to ensure they are staying current on new technologies and ever-changing equipment. UP
About the author: Charlie Drummond is a Terex Service Center branch manager in Richmond, Va.
The Terex Utilities Service Department provides dozens of Tech Tips, covering the most common questions received from customers.
Here are just two examples. For more information, visit the Support section and choose Tech Tips at www.terex.com/utilities.
Tech Tip #15:
Checking the Torque
on Rotation Bearing Fasteners
• Make sure the torque wrench has a current calibration sticker, typically one year from purchase date or last calibration date.
• Determine the proper torque for the fasteners you are checking.
• When using a socket with an extension, the torque value does not change. When an adapter, such as a “crow’s foot” is used, the torque value of the wrench must be adjusted to account for the change in distance between the center of the square drive and the center of the fastener being checked. Use information supplied with your torque wrench to make this calculation and adjustment.
• Use the correct torque indicated in the manual. Do not jerk the torque wrench as you apply torque; instead apply even pressure.
• Other components may need to be moved to gain access to all fasteners. Do not skip a fastener.
• If you find a loose fastener or one that moves, consult the manual for specific procedures.
• Scribe or stamp the inspection date on the placard that is attached to the unit. The information would be entered under the “Critical Fastener Inspection” column.
• Document this inspection and place the record of inspection in the unit’s maintenance file.
Tech Tip #43:
Rotation Bearing Deflection Test
(TC, TCX, RM, RMX, TM models)
• Read the entire procedure in the manual before starting work.
• Position the truck in a suitable location, checking for overhead obstructions. Set the outriggers and level the machine. There can be no additional tools or materials in the platform with the exception of a platform liner.
• For TC and TCX: Rotate off rear of vehicle. Place lower boom at 0 degrees and upper boom at 50 degrees from horizontal.
• For TM: Place lower boom just out of the lower boom rest and upper at 15 degrees.
• For RM and RMX: Place lower boom at 0 degrees and upper at 50 degrees.
• Attach the dial indicator base to the pedestal, positioning the tip perpendicular to the edge of the turntable bottom plate at the specified indicator radius shown in the manual for specific models.
• Make sure you know which way the dial indicator rotates when it moves to get the correct reading.
• Zero out the dial indicator. Verify that you have at least 0.25 inches of movement on the dial indicator in both directions when zeroing.
• Position boom according to manufacturer instructions.
• Read the number on the dial indicator. This is your rotation bearing deflection. Record the reading and check this against “Maximum Allowable Bearing Deflection.” This value is based on a specific dimension of the reading from the centerline of rotation. This dimension is given with the maximum deflection.
• Measure the deflection at the same boom location and dial indicator radius every time this test is performed to provide consistent measurements that can be compared over the life of the machine.