Rexroth A4VG90 axial piston variable hydraulic pump

The A4VG90 is an axial piston variable displacement pump designed for closed circuits (hydrostatic drives). The "90" refers to its nominal displacement—90 cm³/rev. It’s commonly used as the prime mover in the hydrostatic transmission of medium-to-large vehicles.

Key Entities & Naming Breakdown

A4VG = Series identifier (A4 = high-pressure axial piston, V = variable displacement, G = large bearings for high loads)

90 = Displacement in cc/rev

DA/HD/EP control variants-e.g., DA (hydrostatic speed-related), EP (electric proportional)

Unlike open-circuit pumps, the A4VG90 works in a loop with a charge pump to replenish fluid, cool the system, and provide control pressure.

How the A4VG90 Works-Inside the Closed Circuit

The Swashplate Principle

Inside the housing, a rotating group of nine pistons bears against a movable swashplate. As the swashplate angle increases, piston stroke lengthens, and displacement rises-from zero up to 90 cc/rev. Change the angle the other way, and flow reverses direction (forward/neutral/reverse).

The Closed-Loop Advantage

In an open circuit, the pump draws from a tank and returns fluid to the tank. In a closed circuit (like the A4VG90):

Pump outlet goes directly to a hydraulic motor.

Motor return goes directly to pump inlet.

A smaller charge pump (integrated) makes up for leakage and maintains ~20-25 bar of supercharge pressure.

Real-world example: On a tandem vibratory roller, the A4VG90 drives the traction motor. When the operator pushes the joystick forward, the swashplate tilts, sending flow to the motor. To brake, the swashplate crosses zero, reversing flow—no service brakes needed.

Common Applications

Because of its robust bearings and high-pressure capability (up to 450 bar peak), the A4VG90 appears in:

Wheel loaders (small to mid-size)-hydrostatic fan drives or traction.

Tracked excavators-one pump per track for skid steering.

Agricultural tractors-CVT transmission applications.

Paving equipment-pavers and compactors.

Marine winch drives-closed-loop winch control.

Control Options-DA, EP, HD Explained

DA Control (hydrostatic, speed-related)

Uses engine RPM to control swashplate.

Common in mobile machines where engine speed lever doubles as drive speed control.

EP Control (electric proportional)

A proportional solenoid directly moves the swashplate.

Used in joystick-controlled vehicles (telehandlers, AGVs).

HD Control (hydraulic, manually remote)

Hydraulic pilot pressure from a separate valve.

Best for simple, low-cost applications where electronics aren’t wanted.

For more information on the A4VG90 hydraulic pump, please visit https://www.baolilaihydraulic.com/product/.

Specifications

Selection Table