A2FK5R4P4 Rexroth Bent Axis Motor 4.93cc 400bar

Product Overview

The A2FK5R4P4 is a miniature bent-axis axial piston fixed motor from the Bosch Rexroth A2FK series, NG5 frame size. The motor employs a bent-axis design with an axial tapered piston rotary group, suitable for hydrostatic drives in both open and closed circuits. It offers a geometric displacement of 4.93 cm³/rev, rated pressure of 350 bar (35 MPa), peak pressure of 400 bar (40 MPa), maximum speed up to 8000 rpm (short-term peak), continuous speed of 5600 rpm, and weight of only approximately 2.5 kg. This motor is the smallest displacement size in the A2FK series, specifically engineered for low-flow, high-precision polyurethane foam injection metering pump applications, widely used in refrigerator, cold storage, wall panel, automotive seat, and insulation pipe industries.

The A2FK series is a dedicated fixed displacement pump/motor product line developed by Rexroth for the polyurethane (PU) foaming industry, covering NG5, NG6, NG10, NG12, NG23, NG28, NG45, and NG55 frame sizes, with displacements from 4.93 cm³/rev to 107 cm³/rev. The series employs a bent-axis design with a spherical control area, featuring self-centering, low peripheral speed, and high efficiency. The robust rolling bearing endures long service life, and the drive shaft is capable of adopting radial loading. Working pressure can reach 25 MPa, enabling efficient pumping of polyurethane components.

The model code decodes as: “A2FK” = A2F series fixed pump/motor PU foaming version, “5” = 4.93 cm³/rev displacement frame, “R” = clockwise rotation (viewed from shaft end), “4” = series number, “P4” = shaft end and rear cover configuration code. The A2FK12R4P4 in the original title belongs to the same series at a mid-range displacement, offering 11.6 cm³/rev, rated pressure of 350 bar, peak pressure of 400 bar, maximum speed of 6000 rpm, and weight of approximately 6 kg — also widely used as a core component in high-pressure foaming machines.

The motor offers complete interchangeability: mounting flange, drive shaft, and port configuration are identical to the original Rexroth specification, enabling drop-in replacement without hose or bracket modification. Every unit undergoes 100% simulated duty-cycle testing before shipment, covering full-load pressure cycling, volumetric efficiency calibration, and sealing performance verification.

Technical Specifications 

A2FK5R4P4 (Primary Model)

• Model: A2FK5R4P4

• Brand Series: Bosch Rexroth A2FK Series / NG5

• Motor Type: Bent-axis axial piston fixed motor, axial tapered piston rotary group

• Geometric Displacement Vg: 4.93 cm³/rev

• Rated Pressure: 350 bar (35 MPa)

• Peak Pressure: 400 bar (40 MPa)

• Continuous Speed nnom: 5600 rpm

• Maximum Speed nmax: 8000 rpm

• Rated Flow (@nnom): 27.6 L/min

• Output Power (Δp = 350 bar): 14.5 kW

• Output Torque (Δp = 350 bar): 24.7 N·m

• Rotary Stiffness: 0.63 kNm/rad

• Rotary Group Inertia: 0.00006 kg·m²

• Maximum Angular Acceleration: 5000 rad/s²

• Case Volume: 0.17 L

• Weight: Approximately 2.5 kg

• Rotation: Clockwise (R configuration)

• Series: 4

• Configuration Code: P4

• Fluid Compatibility: Mineral oil (reference RE 90220)

Note: Parameters are compiled from Xeriwell publicly available technical data tables (theoretical values, without efficiency and tolerances).

A2FK Series Other Displacement Sizes (Series Reference)

• NG5: Displacement 4.93 cm³/rev, continuous speed 5600 rpm, max speed 8000 rpm, rated flow 27.6 L/min, power 14.5 kW (@350 bar), torque 24.7 N·m (@350 bar), weight 2.5 kg

• NG10: Displacement 10.3 cm³/rev, continuous speed 3150 rpm, max speed 6000 rpm, rated flow 32 L/min, power 19 kW (@350 bar), torque 57 N·m (@350 bar), weight 6 kg

• NG12: Displacement 12 cm³/rev, continuous speed 3150 rpm, max speed 6000 rpm, rated flow 38 L/min, power 22 kW (@350 bar), torque 67 N·m (@350 bar), weight 6 kg

• NG16: Displacement 16 cm³/rev, continuous speed 3150 rpm, max speed 6000 rpm, rated flow 50 L/min, power 29 kW (@350 bar), torque 89 N·m (@350 bar), weight 6 kg

• NG23: Displacement 22.9 cm³/rev, continuous speed 2500 rpm, max speed 4750 rpm, rated flow 57 L/min, power 33 kW (@350 bar), torque 128 N·m (@350 bar), weight 9.5 kg

• NG28: Displacement 28.1 cm³/rev, continuous speed 2500 rpm, max speed 4750 rpm, rated flow 70 L/min, power 41 kW (@350 bar), torque 157 N·m (@350 bar), weight 9.5 kg

• NG45: Displacement 45.6 cm³/rev, continuous speed 2240 rpm, max speed 4250 rpm, rated flow 102 L/min, power 60 kW (@350 bar), torque 254 N·m (@350 bar), weight 13.5 kg

• NG55: Displacement 54.8 cm³/rev, continuous speed 2000 rpm, max speed 3750 rpm, rated flow 112 L/min, power 65 kW (@350 bar), torque 313 N·m (@350 bar)

• NG63: Displacement 63.0 cm³/rev, continuous speed 2000 rpm, max speed 3750 rpm, rated flow 126 L/min, power 74 kW (@350 bar), torque 351 N·m (@350 bar)

• NG80: Displacement 80.4 cm³/rev, continuous speed 1800 rpm, max speed 3350 rpm, rated flow 145 L/min, power 84 kW (@350 bar), torque 448 N·m (@350 bar)

Note: Series parameters are compiled from Xeriwell publicly available technical data tables.

A2FK12R4P4 (Series Reference)

• Model: A2FK12R4P4

• Displacement: 11.6 cm³/rev

• Rated Pressure: 350 bar (35 MPa)

• Peak Pressure: 400 bar (40 MPa)

• Maximum Speed: 6000 rpm

• Weight: Approximately 6 kg

• Typical Applications: Core component in high-pressure foaming machines for refrigerator, cold storage, wall panel, automotive seat, and insulation pipe industries

• OEM Reference: A2F12R4P4

Key Technical Advantages

① Bent-Axis Spherical Control Area Design — High Efficiency and Self-Centering

The A2FK5R4P4 utilizes Rexroth‘s signature bent-axis design, in which pistons are arranged at an angle to the drive shaft and contact the drive plate through spherical ends, directly converting pressure into torque. The spherical control area design features self-centering characteristics, with pistons automatically aligning during operation to reduce lateral forces and eccentric wear. The low peripheral speed design further reduces friction losses and heat generation, maintaining high volumetric and mechanical efficiency even under high-pressure conditions. For polyurethane foam injection metering pump applications requiring continuous precise metering over extended periods, this efficiency advantage translates directly into stable flow output and precise ratio control.

② Robust Rolling Bearing and Long Service Life Design

The A2FK series is equipped with a robust rolling bearing capable of withstanding combined loads under high-speed and high-pressure conditions, ensuring long service life. The drive shaft is designed to adopt radial loading, offering significant advantages in belt or gear drive applications with radial forces. For the continuous, uninterrupted operation characteristics of foaming machine metering pumps, this bearing configuration effectively prevents premature failure and reduces maintenance frequency.

③ Miniature High Power Density — Compact NG5 Frame Design

The A2FK5R4P4 belongs to the smallest NG5 frame size in the A2FK series, with an overall weight of only approximately 2.5 kg and a case volume of just 0.17 L. Within this exceptionally compact housing, the motor still delivers 14.5 kW of power (@350 bar) and 24.7 N·m of torque, achieving outstanding power density. The miniature structural design enables convenient integration into the compact installation spaces of foaming machine equipment, meeting the requirements for low-flow precision metering.

④ High-Speed Capability — Meeting Precision Metering Requirements

The A2FK5R4P4 achieves a continuous speed of up to 5600 rpm and a maximum speed of 8000 rpm — significantly higher than the typical speed range of equivalent axial piston motors. The high-speed capability enables the motor to provide sufficient flow output at small displacement, working in conjunction with the precision metering system of polyurethane foaming machines to achieve precise component ratio control. The high angular acceleration (5000 rad/s²) ensures the motor can rapidly respond to flow adjustment commands, meeting the dynamic response requirements of the foaming process.

⑤ Broad Series Selection and Interchange Compatibility

The A2FK series offers complete displacement coverage from NG5 (4.93 cm³/rev) to NG80 (80.4 cm³/rev), enabling users to precisely select displacement size based on the flow and pressure requirements of their foaming equipment. Standardized mounting interfaces and drive shaft configurations maintain mounting compatibility across different displacement sizes within the same series, facilitating equipment upgrades or displacement adjustments. The A2FK5R4P4‘s mounting flange, drive shaft, and port configuration are identical to the original Rexroth specification, enabling drop-in replacement of OEM components.

Application Areas

• Polyurethane Foaming Equipment (Primary Application): High-pressure foaming machine metering pumps for precise metering and proportioning of polyurethane components (Polyol and Isocyanate) in refrigerator, cold storage, wall panel, automotive seat, and insulation pipe industries

• Miniature Mobile Machinery: Travel drive motors for 1–3 ton mini excavators, vibration motors for compact road rollers, auxiliary/charge pumps, fan drive motors

• Industrial Precision Metering: Chemical metering systems requiring low-flow, high-precision, high-pressure metering

• Others: Compact hydraulic transmission systems not requiring high shaft side-loading

Expert Maintenance Tips

Pre-Installation Inspection: Verify flatness and cleanliness of the mounting flange mating surface; check thread condition of mounting bolt holes. The drive shaft-to-coupling fit must conform to standards, avoiding interference fits that could damage the shaft. The A2FK series drive shaft is capable of adopting radial loading, but the direction and magnitude of radial forces must remain within allowable limits when installing pulleys or gears. Use bolts of strength class 8.8 or higher, tightened in diagonal sequence to specified torque.

First Commissioning: The motor casing must be filled with clean hydraulic oil before initial start-up. Fill through the highest casing port until oil overflows from the level port. Dry starting causes metal-to-metal contact between piston-to-bore surfaces and the valve plate without lubrication, resulting in irreversible damage. For polyurethane foaming machine applications, also confirm proper sealing of the metering pump suction lines and complete air bleeding before startup.

Fluid Cleanliness and Temperature Control: Maintain system oil cleanliness at NAS 8 (ISO 4406 18/16/13) or better. The bent-axis piston motor’s valve plate and piston pairs are sensitive to particulate contamination. The A2FK series is unsuitable for operation with HFA hydraulic fluid; if HFB, HFC, HFD, or environmentally acceptable hydraulic fluids are being used, the limitations regarding technical data and seals must be observed. Oil temperature must not exceed 115°C (sizes 5–200). VG46 or VG68 viscosity grade hydraulic oil is recommended, with VG68 selected for higher operating temperatures. Inspect return filter elements regularly and replace per the machine manufacturer‘s recommended interval.

Scheduled Inspection: Check casing drain flow and output shaft seal condition every 500 operating hours. Under normal conditions, drain flow should remain stable; a sustained increase or decreased output flow indicates accelerated wear of piston pairs or valve plate surfaces, and preventive maintenance should be scheduled. Also verify ratio accuracy for drift; in polyurethane foaming applications, changes in flow precision may originate from internal motor wear or other components of the metering system.

Long-Term Storage Protection: If the motor will be idle for more than 3 months, fill the casing with rust-preventive hydraulic oil and manually rotate the shaft several turns monthly to prevent corrosion or adhesion on piston pairs and valve plate surfaces. Perform a no-load run-in before returning to service, confirming stable output flow and pressure before applying load.