Bosch Rexroth A4VG closed circuit hydraulic pump for the Schaeffer Telescopic boom forklift 070-390-019 070-390-313U 550-018-101U

The Bosch Rexroth A4VG is a variable displacement axial piston pump built specifically for closed circuit hydrostatic drive systems. Unlike a standard open circuit pump that pulls fluid from a reservoir and returns it after every cycle, the A4VG operates in a closed loop: hydraulic fluid flows continuously between the pump and the hydraulic motor, with only a small portion diverted for cooling, filtration, and case drain.

Role in Schaeffer Telescopic Boom Forklifts

Schaeffer telehandlers are compact, articulated, and built for tight-space maneuverability on farms, in yards, and on construction sites. This design philosophy demands a drivetrain that's responsive, smooth, and capable of instant directional changes — exactly the strengths of a closed circuit hydrostatic system.

In a Schaeffer telescopic boom forklift, the A4VG pump typically works as part of a hydrostatic drive train paired with an A6VM or similar variable displacement motor. The pump is usually mounted directly to the diesel engine's power take-off (PTO), spinning continuously whenever the engine runs.

What this setup delivers to the operator:

Stepless acceleration and deceleration, similar to a CVT

Excellent low-speed control for precision loading and stacking

Strong hydraulic braking effect (dynamic braking) when the operator releases the drive pedal

Reduced mechanical wear compared to traditional clutch-and-gearbox drivetrains

How the Closed Circuit Design Works

Fluid Flow Path

In a closed circuit system, oil discharged from the pump flows directly to the hydraulic motor and returns to the pump's intake side — it never passes back through the main reservoir during normal operation. A small charge pump, integrated into the A4VG housing, tops off the circuit continuously to compensate for internal leakage and to purge a portion of hot oil through a flushing valve for cooling.

This design is efficient because it minimizes energy loss associated with constantly refilling and pressurizing a full reservoir volume, which matters a great deal in a compact telehandler where engine power is limited and needs to be used wisely.

Swashplate and Variable Displacement

The A4VG uses a swashplate that can tilt in both directions from center. As the swashplate angle increases, piston stroke length increases, which increases both flow output and drive speed. Tilting the swashplate past center reverses the flow direction, which is how the pump achieves forward and reverse travel without any mechanical reversing gear.

This is a major reason Schaeffer telehandlers can smoothly transition from forward to reverse — the operator simply commands a directional change, and the pump's swashplate does the rest hydraulically.

Charge Pressure and Control Systems

Every A4VG unit includes a charge pressure circuit that maintains a minimum pressure in the low-pressure side of the loop, preventing cavitation and pump damage. Control of the swashplate angle is typically achieved through one of several methods:

HW (hydraulic, manual lever actuation)

EP (electric proportional control)

DA (hydraulic remote control, dual direction)

Most modern Schaeffer models use electrohydraulic (EP) control, allowing the pump's displacement to be managed by the machine's electronic control unit (ECU) in coordination with engine speed, travel direction switches, and inching/braking pedals.

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Q1: How do I know what size A4VG pump my Schaeffer telehandler uses?

A1: Check the pump's nameplate for its full Bosch Rexroth part and type code, or consult the Schaeffer parts manual for your specific model and serial number range, since displacement varies by machine size and model year.

Q2: Why is my Schaeffer forklift losing drive power on inclines?

A2: This is often linked to low charge pressure, worn pistons reducing volumetric efficiency, or a swashplate control fault — all of which reduce the pump's ability to deliver full flow to the drive motor under load.

Q3:What is the price and delivery time of the A4VG hydraulic pump for the Schaeffer Telescopic boom forklift?

A3: The specific price and delivery time will depend on the equipment model or specific product model you provide.

Q4:How to purchase an A4VG hydraulic pump for the Schaeffer Telescopic boom forklift?

A4:You can visit https://www.baolilaihydraulic.com/contact/ to contact us and purchase our products through various methods.