Mixing Displacements: How to Customize Flow in A11VO Tandem Pumps

The Challenge of Multi-Functional Hydraulic Systems

Modern heavy-duty machinery—such as multi-attachment excavators, large forestry harvesters, and mobile drilling rigs—rarely perform just one task at a time. A rotary drill rig, for instance, requires a massive volume of high-pressure oil to rotate the drill string, while simultaneously needing a smaller, highly precise flow to manage tool handling or cooler fan speeds.

Forcing a single, massive Hydraulic Pump to supply all these distinct functions leads to catastrophic energy waste through throttling. On the flip side, installing multiple separate pumps across a bulky splitter gearbox inflates both mechanical cost and spatial footprint.

The most elegant engineering solution lies in the modularity of a11vo tandem pump configurations, specifically through the strategic mixing of displacements.

The Mechanics of "Mixing and Matching"

The A11VO axial piston variable pump is designed for open-circuit systems and features an exceptionally robust through-drive (PTO) capability. This allows engineers to treat the hydraulic power unit like a set of building blocks. By mounting a second (and sometimes third) pump directly onto the rear of the first unit, a single input shaft can drive multiple independent pumping cores.

"Mixing displacements" means pairing a large-capacity front pump with a smaller-capacity rear pump. For example, an engineer might combine a heavy-hitting A11VO190 as the primary pump with a compact A11VO90 or an A10VO45 as the secondary unit.

Key Benefits of Mixed Displacement Tandem Setups

• Tailored Fluid Allocation: You can allocate raw power exactly where it is needed. The massive front pump handles high-flow, heavy-lifting operations, while the smaller rear pump takes care of high-speed, lower-flow auxiliary tasks.

• Independent Control Strategies: Even though they are locked on the same drive shaft, each pump section retains its own independent control valve. You can run a load-sensing regulator (DFR) on the front pump for precision operation, and a constant pressure-limiting control (DR) on the rear pump to maintain auxiliary clamping pressure.

• Drastic Space Optimization: Because the pumps are mounted sequentially in a single straight line, they bypass the need for a distributor gearbox. This linear footprint easily slides into the narrow chassis channels of modern mobile machinery.

The Golden Rule of Tandem Pumps: Through-Drive Torque Limits

While mixing displacements offers incredible design freedom, engineers must adhere to a critical mechanical boundary: the maximum permissible through-drive torque limit (Tlimit).

When a tandem pump is running, the total torque demanded from the engine is the sum of the torque from both pumps:

More importantly, all the torque required to drive the second pump (T2) must pass entirely through the internal through-drive spline coupling of the front pump. If you pair a massive front pump with an oversized rear pump and run both at a continuous 350 bar peak pressure, you risk shearing the internal drive shaft or stripping the connecting splines.

Common Mixed-Displacement Tandem Combinations

FAQ: Frequently Asked Questions

Q1: Can I tandem-mount a gear pump to the rear of an A11VO Piston Pump instead of another piston pump?

Answer: Yes, absolutely. This is a highly common and cost-effective mixed-displacement configuration. The A11VO’s through-drive rear adapter can be specified with standard SAE A, B, or C flange dimensions and internal splines. This allows you to bolt a low-cost heavy-duty gear pump directly to the rear to handle low-pressure steering, pilot oil supply, or oil-cooling filtration loops, leaving the A11VO to focus entirely on high-pressure work.

Q2: How do I find the specific through-drive torque limit ($T_{limit}$) for my A11VO front pump?

Answer: The torque limits are explicitly defined by the factory based on the frame size of the primary pump and the type of through-drive spline (e.g., splined shaft "S" or "U"). For instance, an A11VO130 has a much higher allowable through-drive torque rating than an A11VO060. Always cross-reference the official ordering code chart (specifically checking codes like K01, K02, K07, or U2) to calculate the maximum permissible input horsepower and pressure for your secondary pump module.

Q3: We noticed oil leaking from the front pump into the rear pump housing during a tear-down. What caused this?

Answer: This indicates a failure of the internal tandem shaft seal arrangement. In a tandem setup, a specialized high-pressure shaft seal resides within the through-drive adapter kit to isolate the case drains of the two pumps. If the case pressure in the front pump spikes excessively (often caused by a clogged case drain line or excessive internal piston wear), it will blow past this intermediate seal, leading to cross-contamination of hydraulic fluid between the two sections. Always replace this seal kit whenever splitting a tandem pump for overhaul.