Rexroth A4VSG closed circuit Variable Displacement Hydraulic Pump

Unlike open circuit pumps that return oil to a tank, closed circuit (hydrostatic) pumps like the A4VSG circulate fluid directly from the pump to the motor and back. This design offers superior efficiency and smoother directional changes.

The A4VSG series is built on three pillars:

1.Size-to-Power Ratio: It packs more displacement into a smaller envelope than most competitors.

2.Control Versatility: From simple hydraulic pilot controls to complex electronic damping.

3.Rugged Longevity: Sintered bronze swashplates and heavy-duty bearings designed for continuous shock loads.

The Swashplate Advantage

Unlike bent-axis pumps, the A4VSG uses a swashplate to tilt a rotating group. This allows for faster response times and simpler case drain configurations. For OEMs designing compact equipment, this is a major win.

Applications: Where You’ll Find the A4VSG

Because of its closed circuit nature, the A4VSG excels in traction and fan drive systems.

Mobile Machinery: Track drives on 20-ton excavators, propel systems on asphalt pavers (e.g., Vögele or Dynapac), and swing drives on telescopic handlers.

Agricultural Equipment: Variable speed combine harvester headers and self-propelled sprayer hydrostatic drives.

Industrial: Extruder drives and test bench dynamometers requiring precise speed holding.

Critical Control Options (The “DA” and “HD” Codes)

HD (Hydraulic, manual proportional): Best for basic hydrostatic transmissions. A lever physically strokes the swashplate.

EP (Electrical, proportional): For modern CAN-bus machines. A 0–10V or 4–20mA signal commands displacement. Ideal for torque limiting.

DA (Dynamic, speed-related): A brilliant design for hydrostatic fan drives. The pump’s displacement is directly proportional to input shaft speed. No sensors. No ECU.

DG (Direct hydraulic control): Used for high-response positioning in industrial presses.

Installation, Maintenance & Common Pitfalls

Even a Rexroth pump will fail prematurely if basic closed circuit rules are broken.

The Charge Pump is Your Lifeline

In a closed loop, the main pump does not suck oil; it is fed by a smaller charge pump (usually a fixed gear pump bolted to the back). If charge pressure drops below the specified 150–250 PSI (depending on size), the A4VSG will immediately de-stroke to neutral to prevent cavitation.

Common failure 1: Operators ignore charge pump filter bypass indicators. Once the bypass opens, debris goes straight into the servo piston control orifices. The result: a pump that refuses to stroke or “runs away” to full displacement.

Flushing and Cooling

Closed circuits trap heat. The A4VSG must be paired with a flushing valve (often integrated into the motor) to bleed hot oil out to the tank for cooling. If your machine runs hot after 30 minutes, the flushing orifice is likely clogged.

For more information on the A4VSG hydraulic pump, please visit https://www.baolilaihydraulic.com/product/.

Specifications

Selection Table