The axial piston variable pump A10VSO (primarily represented in Series 31, 32, and 52) is a swashplate-design displacement unit engineered for hydrostatic drives in open-circuit hydraulic systems. Operating on the principle of variable displacement via swashplate angle adjustment, the pump’s flow rate is directly proportional to its drive speed and displacement volume. By adjusting the swashplate angle, the piston stroke can be continuously varied, allowing for precise volumetric flow control. This component is widely utilized in industrial applications requiring high pressure, long-term duty cycles, and high volumetric efficiency, conforming to mounting standards such as ISO 3019-2 for metric flanges.
Kinematic Architecture and Operating Principle
The internal kinematics of the Axial Piston Variable Pump A10VSO rely on a rotary group consisting of a cylinder barrel, pistons with articulated slippers, a slipper-retaining plate, a swashplate, and a control port plate. The cylinder barrel is splined to the drive shaft. When the prime mover rotates the shaft, the cylinder barrel rotates concurrently. The pistons, guided within the cylinder bores, are held against the inclined surface of the swashplate by the retaining plate.
During rotation, the inclined angle of the swashplate forces the pistons to execute a reciprocating axial stroke relative to the cylinder bores. As the pistons retract, fluid is drawn through the suction port of the port plate (low-pressure phase). As the pistons advance, fluid is discharged through the pressure port (high-pressure phase). The transition between suction and discharge is governed by the high-precision land geometry of the port plate, which is engineered to minimize pressure pulsation and cavitation risks.
The swashplate is supported by cradle bearings, allowing it to pivot. Altering the pivot angle changes the piston stroke length. At a swashplate angle of zero, the pistons execute no stroke, resulting in zero volumetric output (zero-stroke operation), save for internal leakage required for lubrication and cooling.
Control Regulators and Response Characteristics
The dynamic behavior and efficiency of the A10VSO are determined by its control devices. These regulators adjust the swashplate angle via a control piston acting against a bias spring.
DR – Pressure Control
The DR regulator limits the maximum system pressure within the pump’s operating envelope. The regulator compares the downstream system pressure against a pre-tensioned pilot spring. When system pressure reaches the setpoint, the pilot valve opens, directing pressurized fluid to the control piston. This forces the swashplate to pivot toward a smaller angle, reducing displacement to a level that maintains the set pressure. This closed-loop pressure regulation protects the system from overload without the continuous energy loss associated with relief valves.
DFR / DFR1 – Pressure and Flow Control (Load-Sensing)
The DFR and DFR1 controllers operate on a load-sensing (LS) principle. The controller monitors the differential pressure ($\Delta p$) across an external metering orifice (such as a proportional directional valve) placed in the actuator line.
* DFR Control: The pilot line is connected to the spring chamber of the flow control valve. The pump adjusts its displacement to maintain a constant pressure drop (typically 14 to 22 bar) across the metering orifice, ensuring a constant flow rate independent of load pressure fluctuations.
* DFR1 Control: This variant eliminates the bleed hole in the LS port, preventing continuous pilot flow to the reservoir. This is critical in systems where pilot-stage energy dissipation must be minimized, though it requires careful system design to prevent spool silting in the pilot stage due to stagnant fluid.
DFLR – Pressure, Flow, and Power Control
The DFLR controller adds a hyperbolic power override to the pressure and flow control functions. It limits the input torque to the pump to prevent stalling of the electric motor or diesel engine. The controller continuously measures the operating pressure and the swashplate position (displacement). If the product of pressure and displacement ($p \times V_g$) exceeds the set torque limit, the controller overrides the flow and pressure commands, destroke-regulating the pump along a hyperbolic power curve:
$$P = \frac{p \cdot q_v}{600 \cdot \eta_t}$$
Where:
* $P$ is the drive power ($kW$)
* $p$ is the operating pressure ($bar$)
* $q_v$ is the volumetric flow ($l/min$)
* $\eta_t$ is the overall efficiency of the pump
Technical Specifications and Parameter Comparison
The following table outlines the key operational parameters across the standard displacement sizes of the A10VSO series.
| Size (Displacement Class) | Displacement $V_g$ ($cm^3/rev$) | Nominal Pressure $p_N$ ($bar$) | Peak Pressure $p_{max}$ ($bar$) | Max. Speed $n_{max}$ ($rpm$ at 1 bar abs) | Max. Flow $q_{v max}$ ($l/min$ at $n_{max}$) | Max. Power $P_{max}$ ($kW$ at $\Delta p = 280$ bar) |
|---|---|---|---|---|---|---|
| 18 | 18.0 | 280 | 350 | 3300 | 59.4 | 27.7 |
| 28 | 28.0 | 280 | 350 | 3000 | 84.0 | 39.2 |
| 45 | 45.0 | 280 | 350 | 2600 | 117.0 | 54.6 |
| 71 | 71.0 | 280 | 350 | 2200 | 156.2 | 72.9 |
| 100 | 100.0 | 280 | 350 | 2000 | 200.0 | 93.3 |
| 140 | 140.0 | 280 | 350 | 1800 | 252.0 | 117.6 |
Fluid Compatibility, Tribology, and Contamination Control
The tribological interfaces within the A10VSO—specifically the piston-to-cylinder bore clearance, the slipper-to-swashplate sliding face, and the cylinder barrel-to-port plate interface—rely on a hydrodynamic lubricating film. The integrity of this film is highly dependent on fluid viscosity, operating temperature, and cleanliness.
ISO 4406 Cleanliness Guidelines
Solid particle contamination is the primary cause of premature wear and catastrophic failure in axial piston pumps. Abrasive particles entering the high-pressure clearance zones cause three-body abrasive wear, which degrades volumetric efficiency by increasing internal leakage (slip).
To ensure the design life of the A10VSO, the hydraulic fluid must be continuously filtered to meet or exceed the cleanliness levels specified by ISO 4406.
* For standard industrial applications operating up to 280 bar, a minimum cleanliness class of 20/18/15 is mandatory.
* In systems with high dynamic response requirements or those operating near peak pressures, a cleanliness class of 19/17/14 is highly recommended to protect the sensitive pilot valves and control spools from silting and stiction.
Elastomer Selection: NBR vs. FKM
The choice of seal material is critical for chemical compatibility with the hydraulic medium and for thermal stability. The A10VSO is typically offered with either Nitrile Rubber (NBR) or Fluorocarbon Rubber (FKM/Viton) shaft seals and O-rings.
- NBR (Nitrile Butadiene Rubber): Standard seal material suitable for mineral-oil-based hydraulic fluids (HL, HLP) conforming to DIN 51524. It exhibits excellent mechanical properties and wear resistance. The operating temperature range is limited to $-30^\circ\text{C}$ to $+90^\circ\text{C}$.
- FKM (Fluorocarbon Rubber / Viton): Recommended for high-temperature applications (up to $+115^\circ\text{C}$ continuous) and for use with environmentally acceptable hydraulic fluids (HEES, HETG) or fire-resistant fluids (HFDU, HFDR). FKM provides superior chemical resistance to synthetic esters and hydrocarbons, preventing thermal hardening and subsequent case drain leakage.
System Integration and Commissioning Protocols
When integrating the A10VSO into a hydraulic circuit (conforming to ISO 1219 schematic standards), specific installation parameters must be observed to prevent mechanical failure during commissioning.
- Case Drain Piping: The pump housing must be filled with hydraulic fluid prior to commissioning to ensure immediate lubrication of the internal rotary group. The case drain line must be piped directly to the reservoir without any restrictions (no check valves or inline filters) and must terminate below the minimum oil level. The case drain pressure must not exceed 1.2 bar absolute (0.2 bar gauge) under continuous operation to prevent damage to the shaft seal lip.
- Suction Line Design: To prevent cavitation, the inlet pressure at the suction port must not drop below 0.8 bar absolute. The suction line must be as short and straight as possible, with a cross-section sized to keep fluid velocity below $1.5\,\text{m/s}$.
- Alignment: The alignment deviation between the prime mover shaft and the pump shaft must be kept within the limits specified by the coupling manufacturer (typically $< 0.1\,\text{mm}$ radial misalignment) to prevent cyclic bending loads on the front bearing.