Rexroth A4VG56 closed circuit Piston Hydraulic Pump

Open circuit systems rely on a central reservoir and directional valves. Closed circuit (hydrostatic) systems, where the pump's outlet connects directly to the motor's inlet, offer superior efficiency and infinitely variable speed control. The A4VG56 excels here for three reasons:

1.Swashplate Design: The through-drive capability allows you to mount a secondary pump (like an A10VO for pilot control) directly onto the back.

2.High Pressure Capacity: Rated for 450 bar (6,500 psi) peak pressure, it handles shock loads without flinching.

3.Compact Power Density: You get 56cc/rev of displacement in a package that fits into tight engine bays.

Decoding the Critical Features

To optimize your system, you need to look past the nameplate. Here is the engineering breakdown.

The "56" and Through-Drive Flexibility

The "56" refers to the geometric displacement per revolution (56 cm³). At 2000 RPM, this translates to roughly 112 L/min (29.6 GPM) of flow.

The most underutilized feature is the through-drive. You can mount a gear pump (for cooling loop) or a smaller piston pump (for pilot control) directly onto the A4VG56's shaft. This eliminates the need for a splitter gearbox, reducing leak points and weight.

Control Systems: From DA to EP

Rexroth offers several control variants. Selecting the wrong one is the 1 cause of poor machine performance.

DA Control (Speed-Related): Ideal for vehicles. The pump automatically increases displacement as the engine speed rises. No electrical sensors required. Best for: Wheel loaders, forklifts.

EP Control (Electrical Proportional): Modern standard. A 0-10V or 4-20mA signal from a joystick moves the swashplate. Best for: Precision applications like aerial lifts or harvesters.

HD Control (Hydraulic Proportional): Manual lever or hydraulic pilot. Best for: Winch drives and basic track drives.

The High-Pressure Relief & Boost Circuit

Do not confuse the A4VG56's internal high-pressure relief valves (typically set between 350–450 bar) with a standard system relief. These are integrated directly into the pump end cap. However, the unsung hero is the boost (charge) pump. It supplies cool, filtered oil to the closed loop, preventing cavitation.

Critical Tip: If your A4VG56 is whining excessively, do not blame the main pump first. Check the charge pump pressure (typically 20–25 bar). If it drops below 12 bar, the main pistons will chatter against the swashplate, leading to catastrophic failure within 40 hours.

For more information on the A4VG56 hydraulic pump, please visit https://www.baolilaihydraulic.com/product/.

Specifications

Selection Table