The A2F series axial piston unit operates on the bent-axis principle, providing a fixed displacement characteristic suitable for both hydrostatic transmission pump and motor applications. Designed for high-pressure operation in open and closed circuits, the unit utilizes a rotating group consisting of a cylinder block and piston-connecting rod assembly. The angular orientation of the cylinder block relative to the drive shaft axis determines the stroke of the pistons; in the A2F configuration, this angle is fixed, ensuring a constant displacement per revolution. The design minimizes internal leakage through precise spherical valve plate-to-cylinder block interface geometry, facilitating high volumetric efficiency even under elevated differential pressures.
Operational Characteristics and Mechanical Integration
The A2F unit is engineered for high power density, utilizing a robust bearing arrangement to accommodate significant radial and axial shaft loads. In motor applications, the unit provides high starting torque, making it suitable for winch drives, swing drives, and heavy-duty industrial machinery. The interface geometry adheres to DIN 24340 and ISO 4401 mounting standards, ensuring interchangeability within existing hydraulic manifolds. When utilized in closed-loop circuits, the A2F requires an auxiliary charge pump to maintain minimum suction pressure, preventing cavitation and ensuring the piston slippers remain in contact with the valve plate.
Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Displacement Range | 5 cc/rev to 1000 cc/rev |
| Max. Operating Pressure | Up to 400 bar (continuous) / 450 bar (peak) |
| Mounting Standard | ISO 3019-1 / SAE J744 |
| Fluid Compatibility | HLP Mineral Oil (DIN 51524) |
| Max. Case Drain Pressure | 2 bar (static) / 6 bar (dynamic) |
Fluid Cleanliness and Filtration Requirements
The longevity of the A2F rotating group is strictly dependent on the fluid cleanliness level. Due to the tight tolerances between the piston-bore interface and the valve plate, particulate contamination can induce accelerated wear, leading to increased internal leakage and eventual catastrophic failure. Adherence to ISO 4406:1999 cleanliness class 20/18/15 is the minimum requirement for standard operation. In high-pressure or high-duty-cycle applications, a cleanliness level of 18/16/13 is recommended to mitigate the risk of spool silting and valve plate scoring. Filtration should be implemented on the pressure line or return line, with a beta ratio of $\beta_{x(c)} \geq 75$ to ensure effective particle capture.
Seal Elastomer Compatibility and Thermal Management
The selection of seal materials is critical for maintaining system integrity under varying thermal loads. The A2F is typically supplied with NBR (Nitrile Butadiene Rubber) seals for standard mineral oil applications, providing adequate performance within a temperature range of -20°C to +80°C. For applications involving synthetic fire-resistant fluids or elevated operating temperatures exceeding 90°C, FKM (Viton) seals are mandatory. FKM offers superior chemical resistance and thermal stability, preventing premature hardening and leakage at the shaft seal interface. Operators must verify fluid compatibility with the chosen elastomer per ISO 1219 standards to prevent seal degradation, which can lead to air ingress and subsequent cavitation within the piston chambers.