The boom is the primary load-bearing arm on hydraulic excavators, mobile cranes, crawler cranes and telehandlers. It connects the machine's upper structure (or chassis, in the case of telehandlers) to the working end—bucket, hook, or fork carriage—and dictates the reach, maximum lift height and, on excavators, the maximum digging depth achievable. The boom transmits all working loads from the attachment back into the machine's structure and counterweight system, making its design, material and actuation method central to a machine's rated capacity.
Boom Types
On hydraulic excavators, two configurations dominate: the monoboom (a single curved section) and the two-piece boom, which adds a separate stick or dipper arm for extended reach and depth. Monobooms are typically used on compact and short-swing machines where a tighter working envelope is required; two-piece booms are standard on mid-size and large excavators performing trenching or mass excavation.
Mobile and crawler cranes use either lattice booms or telescopic booms. Lattice booms are built from bolted or pinned steel truss sections and are assembled on site for very high capacities and long reach, common on crawler cranes above 300 t. Telescopic booms consist of nested steel sections extended hydraulically; they allow fast setup and are standard on all-terrain and truck-mounted cranes, with lengths reaching into the 80–90 m range on large all-terrain units.
Telehandlers use a single telescopic boom mounted low on the chassis, extending forward and upward to lift pallets, buckets or work platforms. Rotating telehandlers add a 360° turret beneath the boom, allowing the boom to slew independently of the chassis.
Key Parameters
Boom performance is described through a defined set of parameters: boom length (fully retracted and fully extended), maximum working radius, maximum lift height, boom angle range (typically from below horizontal up to 70–80° on telescopic units), and the load capacity at each extension and angle combination. On excavators, boom and stick length together determine the digging envelope, expressed as maximum digging depth and maximum digging reach at ground level.
Standards and Load Charts
Dimensional and capacity ratings for hydraulic excavator booms are determined according to ISO 10567 (Earth-moving machinery — Hydraulic excavators — Determination of ratings and dimensions). Mobile crane boom capacities and stability requirements fall under EN 13000 in the European market. For any boom-equipped lifting machine, the applicable load chart defines permissible loads per boom length, angle and radius; operating outside these values is a primary cause of structural overload and tip-over incidents.
Maintenance and Wear
Boom wear concentrates at pin and bushing connections, telescoping slide pads, and hydraulic cylinder mounts. Regular inspection focuses on pin bore elongation, weld seam cracking near the boom foot, and hydraulic cylinder seal condition, since leakage at the lift or telescope cylinder directly affects load holding and boom stability.
Coverage of Booms in This Magazine
Boom design and its practical consequences for site operation recur across several machine categories covered here. The rotating telehandler feature examines how a full 360° turret lets the operator swing the boom through a complete circle without repositioning the chassis. Capacity limits tied to boom extension and angle are addressed in the telehandler load chart guide. A large-scale telescopic boom application is described in the report on Centro Oeste's Liebherr LTM 1300-6.4, fitted with a 90-metre telescopic boom. The structural role of boom and counterweight positioning in confined sites is discussed in the article on short-swing excavators.