The A11VLO series axial piston variable displacement pump utilizes a swashplate design for hydrostatic transmissions in open-circuit configurations. Engineered for high-pressure applications up to 350 bar nominal and 400 bar peak, the unit features a rotating group consisting of a cylinder block with piston-slipper assemblies, a valve plate, and a swashplate with integrated hydrostatic bearing support. Flow rate is proportional to the drive speed and the swashplate angle, which is modulated by a hydraulic control system to match load requirements, thereby minimizing throttling losses across the control valve.
Hydraulic Control Architectures and Performance
The A11VLO series supports various control interfaces, including pressure-compensated (DR), load-sensing (LR), and power-limiting (LRD) configurations. The control spool geometry is critical to the dynamic response of the pump; precise tolerances are maintained to prevent spool silting, which can lead to hysteresis or unstable pressure regulation. The swashplate angle is adjusted via a servo-piston, with the feedback loop governed by the selected control module. When operating in load-sensing mode, the pump maintains a constant pressure differential ($\Delta p$) across the external metering orifice, adhering to the principles defined in ISO 1219-1 for fluid power symbols and circuit diagrams.
Technical Specifications
The following table outlines the standard performance parameters for the A11VLO series across common frame sizes.
| Parameter | Unit | Value Range |
|---|---|---|
| Displacement (max) | cm³/rev | 40 – 260 |
| Nominal Pressure | bar | 350 |
| Peak Pressure | bar | 400 |
| Max Speed (at suction pressure 1 bar) | rpm | 1800 – 3000 |
| Mounting Flange | – | ISO 3019-1 (SAE) |
Fluid Contamination and Filtration Standards
The service life of the A11VLO is highly dependent on the cleanliness of the hydraulic medium. Particulate contamination can induce accelerated wear on the cylinder block-to-valve plate interface and the piston-slipper bearing surfaces. System designers must maintain a fluid cleanliness level of at least 20/18/15 according to ISO 4406. To mitigate the risk of premature failure, full-flow filtration is recommended on the pressure line, with a minimum beta ratio of $\beta_{20} \ge 75$ per ISO 16889. Monitoring for metallic debris via magnetic plugs or oil analysis is advised to detect early-stage fatigue in the rotating group.
Elastomer Compatibility and Seal Selection
Seal integrity is contingent upon the chemical compatibility between the hydraulic fluid and the elastomer compound. Standard units are typically equipped with NBR (Nitrile Butadiene Rubber) seals, which are suitable for mineral oil-based fluids (HLP/HLPD) within a temperature range of -25°C to +90°C. For applications involving synthetic esters or phosphate esters, or where operating temperatures exceed 90°C, FKM (Viton) seals are required. It is imperative to verify that the fluid’s viscosity index remains within the 10 to 1000 mm²/s range during operation to ensure adequate lubrication of the hydrostatic bearings and to prevent cavitation-induced erosion of the valve plate.