A2FO28/61R-VBB05 Rexroth Axial Piston Motor 28cc 400 bar

Product Overview

The A2FO28/61R-VBB05 (Material No. R902075308) is a core model within the 28 frame size of Bosch Rexroth’s A2FO Series of bent axis axial piston fixed displacement pumps/motors, built on the Series 61 (high-pressure version) platform. The A2FO Series features a 40° bent-axis axial tapered piston rotary group design, developed for hydrostatic drives in open circuit hydraulic systems, suitable for both mobile and stationary applications.

The A2FO28/61R-VBB05 has a nominal displacement of 28.1 cm³/rev, with a nominal working pressure of up to 400 bar (5800 psi) and maximum pressure of 450 bar (6527 psi), making it an ideal power component for high-pressure heavy-duty hydraulic drives. The unit employs a 40° bent-axis design with tapered pistons sealed by piston rings, delivering output flow strictly proportional to drive speed and displacement. At 400 bar working pressure, theoretical output torque is approximately 179 N·m.

Model code breakdown: A2FO = bent axis axial piston fixed displacement pump/motor (open circuit); 28 = nominal displacement 28 cm³/rev; 61 = Series 61 (high-pressure version); R = clockwise rotation (viewed on drive shaft); V = FKM (fluoroelastomer) seals; B = DIN 6885 parallel keyed shaft; B = ISO 3019-2 4-hole mounting flange; 05 = SAE flange port A/B at side, SAE flange port S at rear.

The unit features one-piece tapered pistons with piston rings, substantially reducing internal leakage and ensuring superior volumetric efficiency. Drive shaft bearings are designed for the long-life requirements of mobile and industrial applications, capable of withstanding substantial radial and axial loads. As a drop-in replacement, the unit is fully compatible with the OEM Rexroth specification in mounting interface, shaft end configuration, and performance characteristics, enabling direct replacement without hydraulic circuit or mounting bracket modification. Every unit undergoes 100% simulation-based testing prior to shipment, covering displacement calibration, pressure holding performance, and internal leakage.

Technical Specifications

All parameters below are based on Bosch Rexroth official technical documentation, verified supplier technical pages, and industry-standard specifications:

• Complete Model: A2FO28/61R-VBB05

• Material Number (MNR): R902075308

• Brand: Bosch Rexroth

• Product Series: A2FO series, Series 61 (high-pressure version), component series 6X

• Product Type: Bent axis axial piston fixed displacement pump/motor (open circuit)

• Nominal Displacement: 28.1 cm³/rev

• Nominal Working Pressure: 400 bar (5800 psi)

• Maximum Pressure: 450 bar (6527 psi)

• Maximum Flow: 70 L/min (at 2500 rpm)

• Maximum Speed: 2500 – 3200 rpm (depending on specific operating conditions)

• Theoretical Torque (@ Δp = 400 bar): Approx. 179 N·m

• Drive Type: 40° bent-axis design, tapered pistons acting directly on drive shaft flange

• Piston Design: One-piece tapered pistons with piston rings

• Mounting: ISO 3019-2 standard 4-hole mounting flange

• Drive Shaft: DIN 6885 parallel keyed shaft

• Port Connection: SAE flange port A/B (side), SAE flange port S (rear)

• Direction of Rotation: Clockwise (R, viewed on drive shaft)

• Seal Material: FKM (fluoroelastomer)

• Hydraulic Fluid: Mineral oil per DIN 51524 / ISO 11158

• Operating Temperature Range: -30°C to +80°C

• Case Drain: Must be routed via the highest available drain port T1/T2 to a separate reservoir; return back pressure must not exceed 0.5 bar

• Weight: Approx. 9.5 kg

• Mounting Position: Any position; horizontal installation preferred with drain port facing downward

A2FO Series Other Model Specifications Reference (Series 61):

• A2FO10: Displacement 10.3 cm³/rev, weight approx. 6 kg

• A2FO12: Displacement 12.0 cm³/rev, weight approx. 6 kg

• A2FO16: Displacement 16.0 cm³/rev, weight approx. 6 kg

• A2FO23: Displacement 22.9 cm³/rev, weight approx. 9.5 kg

• A2FO28: Displacement 28.1 cm³/rev, weight approx. 9.5 kg

• A2FO32: Displacement 32.0 cm³/rev, weight approx. 11 kg

• A2FO45: Displacement 45.6 cm³/rev, weight approx. 13.5 kg

• A2FO56: Displacement 56.1 cm³/rev, weight approx. 18 kg

• A2FO63: Displacement 63.0 cm³/rev, weight approx. 18 kg

• A2FO80: Displacement 80.4 cm³/rev, weight approx. 23 kg

• A2FO107: Displacement 106.7 cm³/rev

• A2FO125: Displacement 125.0 cm³/rev

• A2FO160: Displacement 160.4 cm³/rev

• A2FO200: Displacement 200.0 cm³/rev

• A2FO250: Displacement 250.0 cm³/rev

Note: Specifications are based on Bosch Rexroth official technical documentation, verified supplier technical pages (importtehsnab.ru, Asendorf Hydraulik, Field Instruments, Lishi Hydraulic, etc.), and industry-standard specifications. The A2FO Series covers a complete product matrix with displacements from 5 to 1000 cm³/rev, with mid-range sizes (10 to 200 cm³/rev) achieving 400 bar nominal pressure. Always verify against the complete model code and consult the latest Rexroth official technical documentation during selection.

Key Technical Advantages

1. 40° Bent-Axis Design for High Power Density and Shock Resistance

The A2FO28 employs a proven 40° bent-axis design, where tapered pistons act directly on the drive shaft flange. Compared with swashplate designs, the bent-axis architecture provides greater resistance to shock and contamination, superior mechanical and volumetric efficiency, and the ability to withstand higher radial loads and angular acceleration, adapting to a wider range of mobile equipment and heavy-duty industrial scenarios. The unit achieves high power density within a compact size, offering greater design flexibility for system integration.

2. One-Piece Tapered Pistons with Piston Rings for High Volumetric Efficiency

The unit’s pistons employ a one-piece tapered structure combined with dedicated piston rings for high-pressure sealing, substantially reducing internal leakage and ensuring superior volumetric efficiency. Meanwhile, wear between pistons and cylinder bores is minimized, maintaining long-term stable performance under high-pressure, high-speed conditions and significantly extending service life. The one-piece construction reduces the number of moving parts, lowering wear risk.

3. High-Load Drive Shaft Bearings with Long-Life Design

Drive shaft bearings are designed for the long-life requirements of mobile and industrial applications, capable of withstanding substantial radial and axial loads, adapting to direct drive, belt drive, and other mounting configurations, reducing system integration constraints. The design satisfies continuous operation requirements of 20,000+ hours under rated conditions.

4. High Overall Efficiency with Economical Design

The A2FO Series features high overall efficiency, with output flow strictly proportional to drive speed and displacement, ensuring stable and controllable performance. The series offers finely graduated displacement sizes (from 5 to 1000 cm³/rev), allowing users to precisely select the most suitable specification for specific drive conditions, achieving system efficiency optimization. The economical design philosophy runs throughout the product series, reducing total cost of ownership while maintaining performance.

5. Complete Specification Coverage with 100% Simulation-Based Testing

The A2FO Series covers a complete displacement range from A2FO5 to A2FO1000, satisfying all requirements from precision industrial transmission micro-flow to high-power heavy-duty drive applications. Every A2FO28/61R-VBB05 undergoes 100% simulation-based testing prior to shipment, covering displacement calibration, pressure holding performance, and internal leakage detection. As a drop-in replacement, the unit is fully compatible with the OEM Rexroth specification in mounting dimensions (ISO 3019-2 4-hole flange), shaft end configuration (DIN 6885 parallel keyed shaft), and performance characteristics, enabling direct replacement of the original unit.

Application Areas

• Construction Machinery: Excavator main hydraulic supply, boom/bucket control; loader lift/tilt hydraulic systems; compactor travel drives

• Concrete Pump Trucks: Boom cylinder and outrigger drive systems

• Cranes & Material Handling: Mobile crane telescopic boom and stabilizer leg hydraulics

• Mining & Tunneling Equipment: Hydraulic drive systems for roadheaders, roof bolters, and related equipment

• Marine & Offshore: Deck machinery, winches, and propulsion system hydraulic transmission

• Industrial Hydraulic Systems: Hydraulic power units, metallurgical equipment, presses requiring high-pressure fixed displacement drives

• Agricultural Machinery: Steering hydraulic pumps for large harvesters, lifting hydraulic pumps for agricultural implements

• Small Stationary Hydraulic Stations: Machine tool clamping pump stations, auxiliary oil sources for small die-casting machines

Expert Maintenance Tips

Pre-Installation Checks:

• Verify mounting flange (ISO 3019-2 4-hole) alignment with equipment mounting surface; ensure surface is clean and free of burrs, flatness deviation not exceeding 0.01 mm/100 mm

• Inspect DIN 6885 parallel keyed shaft mating surface for wear or corrosion; apply appropriate grease

• The unit must be fully filled with clean hydraulic oil via the case drain port prior to installation to prevent dry friction damage to piston/cylinder and bearings during startup

• Confirm SAE flange port seals are intact; tighten diagonally to specified torque

Operational Maintenance:

• Maintain hydraulic oil cleanliness to ISO 4406 18/16/13 or better; use pressure filters with ≤ 10 μm filtration accuracy

• Recommended fluid: mineral oil-based anti-wear hydraulic oil, viscosity range 10 – 600 mm²/s

• Maintain operating temperature within -30°C to +80°C; avoid overheating

• The case drain line must run independently and directly to the hydraulic reservoir; return back pressure must not exceed 0.5 bar; connecting in series with the system main return line is strictly prohibited

• Suction line should be short and large-diameter; suction filter flow ≥ 2 times rated flow; strictly prevent air ingestion causing cavitation

• Use flexible coupling connection; pump shaft must not bear radial and axial external force loads

Troubleshooting Guide:

• No flow output or abnormal flow: Check hydraulic system supply pressure; verify rotation direction is correct (R = clockwise); check suction line for blockage or air leakage

• Insufficient output pressure: Confirm system pressure reaches rated value (400 bar continuous / 450 bar peak); inspect piston rings and cylinder bores for wear

• Abnormal noise or vibration: Check case oil fill level; verify suction line is unobstructed; check mounting bolt tightness

• External leakage: Inspect shaft seal for aging or damage; verify case drain line back pressure is within 0.5 bar

• Excessive oil temperature: Check system for excessive internal leakage; verify cooling system operation; confirm case drain line is unobstructed