Home > PB21B-3R Spider Concrete Placing Boom — 21 m

PB21B-3R Spider Concrete Placing Boom — 21 m

The PB21B-3R is a mobile spider concrete placing boom designed for horizontal concrete distribution across expansive slabs and decks. It operates from a free-standing, inclined-outrigger base without requiring structural anchorage. The unit provides a 21 m placement radius through a 3-section R-fold articulating boom. Operating on a 380V/50Hz electrical supply with a 7.5 kW motor, the system is fully hydraulic and utilizes a 28 MPa hydraulic circuit. The total operational weight is 9,150 kg, with the maximum single lifting unit restricted to 5,850 kg, requiring an adequately sized tower or mobile crane for relocation.

The boom features a continuous 360° slewing range driven by a gear-slewing mechanism, ensuring angular stability for the 21 m boom during placement operations. Functioning as the terminal distribution unit, it integrates with a separate stationary or truck-mounted line pump via a delivery pipeline to distribute concrete at the designated pour location.

1. Inclined-outrigger base — Deploys on a splayed-leg structure to maintain stability on flat surfaces without requiring structural anchoring.

2. 21 m extended radius — Provides wider horizontal coverage per setup, reducing the frequency of relocations on expansive floor plates.

3. 3-Section R-Fold articulation — Fully hydraulic articulation provides a 21 m placement radius and folds compactly for crane handling.

4. Continuous 360° slewing — Provides full-circle rotational coverage from a single setup position.

5. Gear-slewing drive — Utilizes a gear-driven slewing mechanism to manage the increased rotational mass and maintain stability under load.

6. Dual remote control systems — Operations are managed via wireless radio remote or cable remote control to maintain direct visual contact with the pour.

7. Crane relocation capability — Designed to be lifted between pouring zones, utilizing a maximum single lifting unit weight of 5,850 kg.

8. Standardized components — The hydraulic and electrical systems incorporate components from established suppliers to ensure operational stability.

Get a Quick Quote

Technial Parameters

Item	Unit	PB21B-3R
Performance
Max. Radius of Placing Boom	m	21
Free-Standing Height (to boom root joint)	m	3
Slewing Range	/	360°
Mode of Slewing	/	Gear Slewing
Application Scenario	/	Mobile (Spider)
Circumstance Temperature	℃	-20 ~ 55
Power Supply (customisable)	/	380V / 50Hz
Boom (3-Section R-Fold)
1st Section — Length	m	8.4
1st Section — Articulation	°	0 ~ 90
2nd Section — Length	m	6.9
2nd Section — Articulation	°	0 ~ 180
3rd Section — Length	m	5.7
3rd Section — Articulation	°	0 ~ 180
Delivery Line
Delivery Pipeline Diameter	mm	Φ125 × 4.5
Delivery Hose Diameter	in × mm	5" × 3000
Power & Hydraulics
Motor Power	kW	7.5
Hydraulic Pressure	MPa	28
Hydraulic Oil (5℃–55℃)	/	HM46 anti-wear
Hydraulic Oil (-20℃–5℃)	/	HM32 anti-wear
Weight
Total Weight	kg	9150
Max. Lifting Unit	kg	5850

Dimensions & Working Range

The working-range diagram maps the operational envelope of the PB21B-3R, detailing the 21 m horizontal radius across a 360° sweep and the vertical reach of the 3-section folding boom. The free-standing height of 3 m indicates the maximum vertical elevation above the support without external bracing. This data should be cross-referenced with structural layouts and outrigger footprint dimensions to plan optimal placement zones.

Applications

The PB21B-3R is engineered for applications requiring extensive horizontal concrete distribution where the placement equipment must be frequently relocated across the site.

Large floor slabs and decks

Facilitates concrete placement across suspended slabs and decks by completing sequential 21 m radius pours and relocating via crane without fixed installations.

Podiums and transfer slabs

Supports the construction of broad podium decks and transfer slabs requiring phased concrete distribution across distinct pour zones.

Raft foundations and ground slabs

Applies to raft foundations and ground slabs, providing uniform concrete spread while eliminating manual hose handling.

Projects with capable crane support

Integrates with site tower or mobile cranes capable of managing the 5,850 kg maximum lift unit weight, enabling repositioning across large floor plates.

FAQs

PB21B-3R or PB17B-3R-II — which spider boom should I choose?

Reach versus portability dictates the selection. The PB21B-3R provides a 21 m radius, covering a larger area per setup, but operates at a total weight of 9,150 kg with a 5,850 kg maximum lifting unit and utilizes gear slewing. The PB17B-3R-II provides a 17 m radius, weighs 6,500 kg with a 1,520 kg lifting unit, and utilizes turbo-worm slewing. The PB21B-3R is specified for expansive floor plates where reducing setup frequency is prioritized and adequate crane capacity is available.

How is it moved around the site?

The unit is relocated using a site tower crane or mobile crane. The total weight is 9,150 kg, and the modular design restricts the maximum single lifting unit to 5,850 kg, requiring a crane rated for this capacity.

Why does it use gear slewing instead of worm drive?

The 21 m boom generates a higher slewing load due to its extended reach and greater mass. A gear-slewing drive accommodates these elevated loads, providing stable, powered 360° rotation. The smaller 17 m model utilizes a turbo-worm drive suitable for its lower mass.

How is a spider boom different from a climbing boom?

A climbing boom attaches directly to the building structure or formwork and ascends vertically as construction progresses. A spider boom, such as the PB21B-3R, operates on a single horizontal plane, distributes concrete across a specific area, and is lifted laterally to subsequent pour zones. Spider booms are deployed for horizontal slab coverage, whereas climbing configurations are utilized for vertical core construction.

Is the placing boom a concrete pump?

No. The placing boom functions strictly as a concrete distributor. It requires a separate stationary or line concrete pump to drive material through a delivery pipeline to the boom's inlet.

Is it electric, and what is supplied?

The unit is electrically driven, operating on a 380V/50Hz supply with a 7.5 kW motor. It does not feature an onboard diesel engine. The standard configuration includes the boom, outrigger base, hydraulic and control systems, and remote controls. The delivery pipeline, hoses, and spare parts are specified according to project requirements.

Spider boom selection parameters

The mobile spider placing boom series includes two primary models optimizing reach versus portability: the 17 m PB17B-3R-II and the 21 m PB21B-3R. The PB21B-3R maximizes coverage area per setup, reducing the frequency of relocations on large floor plates. This extended reach necessitates a heavier 5,850 kg maximum lifting unit and a gear-slewing drive. The PB17B-3R-II prioritizes portability with a 1,520 kg lifting unit. Selection depends on the required coverage area per setup versus available crane capacity.

System integration in concrete placement

In a standard placement sequence, concrete is pumped from ground level via a stationary or truck-mounted line pump through a delivery pipeline. The spider boom functions as the terminal distribution equipment. Operating from a fixed outrigger base, the PB21B-3R maneuvers its articulating arms to deposit concrete precisely, eliminating manual hose handling. Once the designated area is completed, the crane relocates the unit, and the pipeline is adjusted accordingly.

Mounting configurations

Concrete placing booms utilize different mounting and mobility mechanisms based on structural requirements. Spider booms, such as the PB21B-3R, are free-standing units designed for horizontal slab distribution and rely on site cranes for relocation. Wheeled mobile booms roll between positions without crane assistance. Climbing booms mount to structural cores or formwork, utilizing hydraulic cylinders to ascend synchronously with vertical construction.