Telescopic truck-mounted cranes, also known as boom trucks, are used to lift materials by use of a hydraulic winch and by raising and lowering the boom. Operation is simple enough: rotate, extend, and raise and lower as necessary.
With the entry of knuckle boom cranes to the North American market, and their popularity in foreign markets, it’s important to differentiate between these two types of cranes and understand the advantages a boom truck offers over a knuckle boom crane.
The Winch
Telescopic booms offer a winch that is permanently affixed to the crane and prepared for immediate lifting, whereas an articulated crane primarily uses a hook on the tip of the boom to lift loads. The winch of a telescopic crane, combined with a rotating and telescoping superstructure, moves loads in a linear fashion, making it easier to operate. Therefore, when placing fragile equipment, the winch allows for a gentler placement of loads, regardless of the lifting radius. Wire rope, often used in oil and gas and utilities, also greatly improves the precision of placing or raising loads. Because the winch is the primary lifting mechanism, it features holding valves that make it possible to suspend heavy loads at height for extended periods of time without drift. Knuckle boom cranes are not designed to suspend loads for long periods of time, but for the loading and unloading of materials.
When lifting a load with a telescopic boom, lifting energy goes to the winch first, then to the lift cylinder and crane structure. With a boom truck, moving a load to a different radius is generally done by raising and lowering the boom, not by telescoping the boom itself while the load is suspended. This places significantly less wear and tear on the boom and wear pads than with a knuckle boom crane, which requires the telescoping of loads during most operations. With knuckle boom cranes, the energy goes first into the boom structure and extension cylinders, then to the lift cylinder and crane structure. Over time, this means that knuckle boom cranes face substantially more wear and tear on the boom and extension system, and require more maintenance than a telescopic boom truck crane.
The Controls
Boom truck cranes are controlled either via a lower control station with manual or electric/hydraulic controls, or via remote control. When operating from the fixed controls, the operator is safely off the ground and either standing at the turret or within an enclosed cabin. This provides maximized visibility of the lifting activity. With knuckle boom cranes, the lower control station is typically mounted on the side of the turret and requires standing on the ground next to the crane. This greatly hinders visibility during operation.
The Jib
The availability of a telescopic or fixed jib extension on a telescopic boom is not only easy to attach and use, but it makes it possible to extend the reach of the crane boom by as much as 55 feet. With a jib, boom truck cranes are capable of reaching boom lengths as tall as 201 feet, which is very beneficial when placing loads at height or lifting personnel using a work platform. Articulated cranes are generally limited to around 100 feet of boom length. When using a work platform on a boom truck with a jib extension, working heights can reach as tall as 207 feet (65m). With all boom trucks, the jib itself stores on the side of the boom when not in use and can be removed as necessary.
The Work Platform
Telescopic boom trucks enhance the ease and use of lifting personnel with a work platform, allowing for very smooth and direct movement: just elevate the boom and telescope out. Working heights can reach up to 207’ or more with a boom truck, and the ride is very smooth and stable. With knuckle boom cranes, work platforms attach to the boom tip and the ride itself can be very shaky and unstable due to the non-linear movement of the crane. The work platform on telescopic boom truck cranes offers around the same working height as some of the larger European aerial work platforms, but at a much lower price.
Durability and Climate Protection
Because of the enclosed boom design on boom trucks, sensitive hydraulic cylinders and components are protected from the elements, and are subject to less damage from sun, dust, heat, moisture and other damaging factors. Therefore, telescopic boom trucks will have a longer cylinder life. Knuckle cranes typically have multiple exposed cylinders on the boom, which can be a problem in some environments. Furthermore, most boom trucks over 30 tons are available with enclosed operator cabins with heat and air conditioning, protecting the operator from severe climate conditions. Articulated cranes are normally operated from the ground or via remote control only.
Ease of Service and Training
Telescoping a load with a knuckle boom crane does more wear to the boom than with the telescopic crane because, with a telescopic crane, the boom is lifted and lowered with a load. With less friction on the boom during lifting, the telescopic crane costs less in terms of servicing and owning.
With a knuckle boom crane, because of the complexity of the controls and movement of the boom, training can take several days. This means that owners of telescopic boom truck cranes have a much easier time training and replacing operators throughout the life of the equipment.
It’s clear that telescopic booms pay off in the long run over knuckle boom cranes. If you’re considering purchasing, leasing or renting a boom truck in the coming months, consider downloading our financing guide below.