Views: 230 Author: Site Editor Publish Time: 2026-11-11 Origin: Site
A knuckle boom crane is a hydraulic crane whose boom is made of two or more sections joined by a hinge, the “knuckle”, so it can fold and unfold like a finger. Most are mounted on a truck just behind the cab, where they fold into a compact package for driving and unfold to load and unload the truck and deliver goods over walls, fences and onto roofs.
This guide explains what a knuckle boom crane is, the parts it is made of, how its hydraulics work, what it is used for, and its advantages and disadvantages. The figures come from the technical drawings of our own knuckle boom truck mounted cranes, seven models from 0.8 t to 25 t, compiled in November 2026.
A knuckle boom crane is a type of articulated hydraulic crane designed to lift, move and position loads through a series of connected boom sections.
Its defining feature is the hinged connection between the boom sections. This arrangement gives the crane greater freedom of movement than a conventional straight boom design.
The main boom is attached to the crane base and provides the primary lifting movement. A secondary boom, also known as the outer boom, connects to the main boom through a knuckle joint. Depending on the crane design, additional boom sections or hydraulic extensions may be fitted to increase its working reach.
When the crane is not in use, the boom sections fold together. During operation, hydraulic cylinders push the sections outward, allowing the operator to unfold the crane and position the lifting attachment.
The same machine goes by several names. “Articulating crane” and “folding boom crane” describe the jointed boom. “Loader crane” describes its usual job, loading and unloading the truck it is mounted on. A truck fitted with one is often called a knuckle boom truck. In each case it is the same type of crane. In Europe, loader cranes are covered by the standard EN 12999; in the US, ASME B30.22 covers articulating boom cranes.
Most knuckle boom cranes are mounted on trucks, between the cab and the load bed. They are also fitted on ships, workboats and docks, and as fixed cranes in yards. This guide focuses on the truck mounted type.
Although both machines use hydraulic power to lift heavy loads, their boom structures and working methods are different.A straight boom crane generally uses a telescopic boom that extends and retracts in a straight line. A knuckle boom crane uses articulated sections that bend at one or more joints.
This difference affects how each crane performs on the job.A straight boom crane is often a suitable choice when the operator needs considerable horizontal reach and a relatively direct lifting path. A knuckle boom crane is particularly useful when materials must be placed in confined spaces, moved around obstacles or delivered to locations that are difficult to access from directly above.
For example, a building material delivery truck may need to place roof tiles behind a wall or lower equipment into a restricted area. The articulated boom allows the operator to adjust the boom angle and work around obstacles without moving the truck repeatedly.Neither design is universally better. The right choice depends on the load, working radius, available space and type of lifting operation.
Our knuckle boom models from 1 t to 25 t sit in the same truck mounted crane line as our 2 t to 20 t telescopic boom models.
Taking our F105K-03 hydraulic knuckle boom crane as an example, its main structure consists of the boom assembly, knuckle joints, hydraulic cylinders, telescopic sections, slewing mechanism, mounting base, outriggers and hydraulic power system.
Understanding these components helps explain how the crane operates and what to look for when selecting or maintaining one.
The main boom is the primary lifting arm of a knuckle boom crane. It connects to the crane base and supports the outer boom assembly.
Its main function is to raise and lower the working arm, allowing the crane to move loads between different heights and positions.
On the F105K-03 model, the main boom is operated by a hydraulic cylinder. When pressurized oil enters the cylinder, the piston extends or retracts, changing the angle of the boom.
The main boom is manufactured from high-strength steel to withstand the bending forces generated during lifting operations.
The outer boom is connected to the main boom through an articulated joint, commonly known as the knuckle.
This component gives the crane its distinctive folding movement. Rather than moving only in a straight line, the outer boom can change its angle relative to the main boom.
During operation, this flexibility allows the operator to position materials around obstacles, reach restricted spaces and place loads more accurately.
When the crane is not in use, the outer boom folds towards the main boom, reducing the space required for transportation.
The telescopic boom sections are designed to extend the crane's horizontal working reach.
Unlike a fixed-length boom, a telescopic section can slide outward from the main boom assembly through hydraulic operation.
The F105K-03 drawing shows an extendable boom arrangement, with a maximum reach dimension indicated from approximately 4,450 mm to 8,050 mm, depending on the boom configuration.
This extension capability allows the crane to handle loads at different distances from the mounting column.
It is important to remember that lifting capacity decreases as the working radius increases. The maximum reach should therefore not be confused with the maximum lifting capacity.
Knuckle joints connect the individual boom sections and allow them to rotate relative to one another.
They are essential to the folding and unfolding movement of the crane.
Heavy-duty connecting pins and bushings are used at these joints to support mechanical loads while allowing controlled rotation.
Because these connections experience repeated movement and stress during operation, regular lubrication and inspection are necessary to reduce friction and prevent excessive wear.
Hydraulic cylinders provide the force needed to move the boom sections and operate the crane.
The F105K-03 uses hydraulic cylinders to control its articulated boom movements and telescopic extension.
The main functions include:
Main boom cylinder: Raises and lowers the main boom.
Knuckle cylinder: Controls the folding angle between the main boom and outer boom.
Extension cylinder: Drives the telescopic boom section outward and inward.
Outrigger cylinders: Extend and retract the stabilizing supports.
Each cylinder converts hydraulic pressure into mechanical force. Their dimensions and arrangement are designed to meet the crane's required lifting and movement performance.
The slewing mechanism allows the entire crane assembly to rotate around its vertical mounting axis.
This movement enables the operator to move loads between different working positions without having to reposition the truck.
The F105K-03 has a specified slewing angle of 400°, providing a wide working range for material handling operations.
The slewing system works together with the crane's hydraulic system to provide controlled rotational movement.
The crane base is the supporting structure that connects the lifting assembly to the truck chassis.
It carries the weight of the crane and transfers the forces generated during lifting to the vehicle's mounting structure.
For the F105K-03, the specified installation space is 1,050 mm.
The mounting structure must be properly matched to the truck chassis, taking into account structural strength, axle loading and vehicle stability.
Correct installation is essential for safe and reliable crane operation.
Outriggers are extendable support legs installed on both sides of the crane mounting structure.
Before lifting, they are deployed to increase the supporting footprint of the vehicle and improve stability.
The F105K-03 drawing shows a stabilizer arrangement with an adjustable support span of approximately 2,260–5,120 mm.
The vertical stabilizer cylinders lower the support feet onto the ground, helping distribute the load and reduce the risk of vehicle tipping.
Outriggers must be deployed according to the manufacturer's operating instructions and ground conditions. They should never be treated as a substitute for checking the crane's rated load chart.
The hydraulic pump supplies pressurized oil to the crane's hydraulic circuit.
The control valve directs the oil to the appropriate cylinder or hydraulic actuator, allowing the operator to control boom lifting, folding, extension and slewing movements.
The F105K-03 has the following hydraulic specifications:
Recommended power: 22 kW
Hydraulic system flow: 35 L/min
Hydraulic system pressure: 28 MPa
Oil tank capacity: 100 L
These specifications determine the hydraulic system's operating conditions and provide important reference information for matching the crane with a suitable power source.
The lifting attachment is fitted at the end of the boom and provides the connection between the crane and the load.
A lifting hook is commonly used for general material handling, together with suitable slings, shackles or other approved rigging equipment.
Depending on the intended application, compatible attachments such as hydraulic grabs or other material-handling tools may also be available.
The attachment must be suitable for the load and the crane's design. Its weight must be included when determining the permissible lifting load.
All the components described above work as one integrated lifting system.
The hydraulic pump supplies pressurized oil, while the control valves direct the flow to different hydraulic cylinders and actuators. These cylinders move the main boom, outer boom and telescopic sections. The slewing mechanism changes the crane's working direction, while the outriggers provide the necessary support during lifting.
When the operation is complete, the boom sections fold back into their transport position, making the crane more compact for road travel.
For the F105K-03, the maximum rated lifting capacity is 5,000 kg, with a maximum lifting moment of 10.5 ton·m. Its self-weight is approximately 1,850 kg.
These specifications provide a useful overview of the crane's structure and performance. However, actual lifting capacity depends on the working radius, boom configuration and operating conditions. Always refer to the manufacturer's load chart before carrying out a lifting operation.
A knuckle boom crane is used wherever a truck has to load or deliver its own cargo without a separate crane or forklift on site. Typical jobs include:
Building materials delivery: bricks, blocks, roof tiles, cement and timber on pallets, set down over a fence or onto a scaffold.
Steel and precast concrete: rebar bundles, beams, pipes, kerbs and small precast units.
Equipment and containers: generators, compressors, small machines, tanks and site cabins.
Stone and landscaping: stone slabs, blocks and bulk bags.
Utilities and municipal work: poles, cable drums, manhole parts and road furniture.
Marine work: on ships, workboats and docks, where the folded crane takes little deck space.
The articulated boom gives a knuckle boom crane several practical advantages, particularly when working space is limited. Our F042K-03 2-tonne model combines a compact structure with a 6.5 m maximum reach, making it suitable for light-duty lifting and material handling.
Compact design. The F042K-03 has a self-weight of just 620 kg and requires only 680 mm of installation space. Its folded boom structure helps keep the crane compact when not in use, making it suitable for smaller truck installations.
Good reach for its size. The boom extends from 3.76 m to 6.5 m, allowing operators to handle loads at different working distances without moving the truck for every lifting operation.
Flexible positioning. The articulated boom can fold and unfold at its joints, making it easier to position materials around walls, fences and other obstacles. This is useful for construction material delivery and general loading and unloading work.
Wide slewing range. The F042K-03 offers a 370° slewing angle, allowing the operator to move loads between different working positions around the truck without repositioning the vehicle.
Stable support. Its adjustable outrigger span ranges from 1,870 mm to 3,020 mm, providing a wider supporting footprint during lifting operations. Proper outrigger deployment helps improve vehicle stability.
Moderate hydraulic requirements. The crane operates with a recommended power of 9.0 kW, a hydraulic flow rate of 20 L/min and a system pressure of 20 MPa. Its 25 L hydraulic oil tank provides the required oil supply for the system.
Limited lifting capacity at longer reach. The maximum rated lifting capacity is 2,000 kg, with a maximum lifting moment of 4.2 ton·m. Actual lifting capacity decreases as the working radius increases. Always check the load chart before lifting at the maximum 6.5 m reach.
Limited reach compared with larger models. With a maximum reach of 6.5 m, the F042K-03 is better suited to light-duty material handling than applications requiring long-distance lifting or heavy industrial operations.
Requires regular maintenance. The articulated boom contains multiple joints, connecting pins, hydraulic cylinders and hoses. These components need regular lubrication, inspection and maintenance to maintain reliable operation.
Takes up installation space. Although compact, the crane still requires 680 mm of installation space behind the cab. Buyers need to check the truck chassis, available mounting area and remaining cargo body length before installation.
Requires proper stabilization. The outriggers need sufficient ground space to extend, with a support span of up to 3,020 mm. Narrow roads or restricted working areas may limit where the crane can operate safely.
Requires trained operation. Coordinating the main boom, knuckle joint, telescopic extension and slewing movements takes practice. Operators must understand the load chart, working radius and stabilizer requirements before lifting.
Tell us your heaviest load, the reach you need and your truck, and we will suggest models from our range with the technical drawing and load chart for each. Contact us to start.
