A4VG90-F02 Rexroth Charge Pump 24/13T

Product Overview

The A4VG Charge Pump / Boost Pump is an integrated auxiliary pump used with Bosch Rexroth A4VG closed-loop axial piston variable pumps.

Its primary function is to provide make-up oil and auxiliary flow for the closed hydraulic circuit, supporting functions associated with charge pressure, internal leakage compensation, cooling and control requirements. It is not a replacement for the main high-pressure axial piston pump.

Bosch Rexroth’s official A4VG Series 32 documentation covers nominal sizes 28, 40, 56, 71, 90, 125 and 180, with an integrated boost pump available as a configured option. The same documentation publishes the corresponding boost-pump geometric displacement values.

For the sizes specified in the original product title:

• A4VG56: 11.6 cm³/rev
• A4VG71: 19.6 cm³/rev
• A4VG90: 19.6 cm³/rev
• A4VG125: 28.3 cm³/rev

These values are published by Bosch Rexroth for the boost pump at p = 20 bar.

The Bosch Rexroth repair documentation identifies the auxiliary unit as an internal gear pump, mechanically driven by the A4VG pump assembly.

For aftermarket replacement, correct matching requires more than pump size or tooth count. We recommend verifying the complete A4VG model, nominal size, drive interface, mounting geometry, shaft/coupling configuration and original charge-pump identification. Replacement units can be subjected to 100% simulated operating-condition testing before shipment.

Technical Specifications

A4VG90 Charge / Boost Pump

• Brand: Bosch Rexroth
• Compatible Main Pump: A4VG Series 32
• Typical Main Pump Size: A4VG90
• Component Type: Integrated Charge Pump / Boost Pump
• Pump Design: Internal Gear Pump
• Primary Function: Charge-oil supply, make-up flow and auxiliary hydraulic supply
• Main Pump Size: A4VG90
• A4VG90 Boost Pump Displacement: 19.6 cm³/rev
• Published Displacement Condition: p = 20 bar
• Main Pump Control Principle: Variable displacement swashplate-type axial piston pump
• Charge Pump Drive: Mechanically driven from the main pump shaft
• 24T / 13T: Tooth/coupling description taken from the supplied product designation; Bosch Rexroth’s current Series 32 technical data located for this review does not establish 24T/13T as a universal charge-pump specification, so the actual configuration must be confirmed from the complete part number.
• A4VG90 Main-Pump Displacement: 90 cm³/rev
• A4VG90 Nominal Pressure: 400 bar
• A4VG90 Maximum Pressure: 450 bar
• A4VG90 Maximum Rotational Speed nmax1: 3300 r/min
• A4VG90 Intermittent Maximum Speed nmax2: 3800 r/min under the manufacturer’s specified conditions.
• Independent Charge-Pump Pressure Rating: No single universal charge-pump pressure value is stated in the Bosch Rexroth Series 32 data located for this review; therefore no unsupported value is provided.
• Peak Pressure: Not independently fabricated. Bosch Rexroth specifies the A4VG main pump using 400 bar nominal / 450 bar maximum pressure rather than assigning that value directly to the internal charge pump.
• Weight: A dedicated universal charge-pump mass was not identified in the official Bosch Rexroth data reviewed and is therefore not stated as fact.

Other A4VG Sizes

• A4VG56 Boost Pump: 11.6 cm³/rev
• A4VG71 Boost Pump: 19.6 cm³/rev
• A4VG90 Boost Pump: 19.6 cm³/rev
• A4VG125 Boost Pump: 28.3 cm³/rev

A4VG Series 32 Main-Pump Reference Data

• Nominal Sizes: 28 / 40 / 56 / 71 / 90 / 125 / 180 cm³/rev
• Nominal Pressure: 400 bar
• Maximum Pressure: 450 bar
• Control Options: HD, HW, DA, DG, EP, EZ and other configurations depending on the complete order code
• Closed Circuit: Yes
• Integrated Boost Pump: Available
• No Boost Pump: Available
• Standard / Large Internal Gear Pump: Available according to the configuration and order code.

Key Technical Advantages

1. Stable Charge-Oil Supply for Closed Circuits

The A4VG charge/boost pump supplies make-up oil to the closed circuit to compensate for leakage and support auxiliary hydraulic functions.

Bosch Rexroth describes the A4VG as an integrated closed-loop power unit with an integrated boost pump and pressure-management functions, reducing the need for additional external components.

2. Integrated Internal Gear Pump

Bosch Rexroth’s A4VG repair documentation directly identifies the auxiliary unit as an internal gear pump. It is mechanically driven by the main pump, creating a compact and highly integrated pump architecture.

3. Size-Matched Boost Pump Displacement

The boost-pump displacement differs according to the A4VG nominal size:

11.6 → 19.6 → 19.6 → 28.3 cm³/rev

for A4VG56, A4VG71, A4VG90 and A4VG125 respectively. This confirms that charge-pump selection should be matched to the main-pump frame size rather than treated as a universal component.

4. High Integration with the A4VG Rotary Group

The A4VG assembly incorporates the internal gear pump together with the main rotary group and control architecture. Bosch Rexroth repair documentation identifies components including the internal gear pump, control plate, cylinder, piston, swashplate and controller.

This makes the charge pump a dedicated component engineered around the geometry and drive interface of the A4VG system.

5. Broad A4VG56 / 71 / 90 / 125 Service Coverage

The official A4VG Series 32 documentation covers all four nominal sizes referenced in the supplied product description. This allows aftermarket replacement solutions to be engineered according to the correct main-pump frame size rather than using one generic gear pump across the complete product family.

6. Suitable for Precision Retrofit Engineering

For a true replacement, interchangeability depends on:

Pump size + mounting geometry + drive interface + gear/coupling configuration + axial dimensions + sealing arrangement.

Our replacement process therefore focuses on complete model verification rather than tooth count alone, followed by 100% simulated operating-condition testing.

Application Areas

A4VG closed-loop pumps with integrated charge pumps are used in applications such as:

• Excavators and mobile construction equipment
• Wheel loaders
• Mining machinery
• Agricultural machinery
• Harvesting equipment
• Hydrostatic transmissions
• Concrete machinery
• Road construction machinery
• Winch and vehicle drive systems
• Specialized mobile machinery

Bosch Rexroth identifies A4VG as a closed-circuit mobile hydraulic product and lists it among its hydraulic solutions for demanding mobile and mining applications.

Expert Maintenance Tips

1. Do Not Purchase by Tooth Count Alone

The 24T / 13T description in the supplied title may identify a particular tandem-drive or coupling arrangement. Because the Bosch Rexroth Series 32 documentation reviewed here does not define 24T/13T as a universal charge-pump specification, ordering should be based on:

Complete A4VG model + charge-pump identification + nameplate + nominal size + drive-interface photographs.

2. Inspect the Mechanical Drive Interface

Because the boost pump is mechanically driven, check:

• Gear engagement
• Axial clearance
• End-face fit
• Mounting surface condition
• O-ring and seal condition

Incorrect axial positioning can produce abnormal gear contact, localized heating and premature wear.

3. Do Not Apply the 450-Bar Main-Pump Rating Directly to the Charge Pump

The 400 bar nominal / 450 bar maximum specification belongs to the A4VG Series 32 main variable pump. It should not be represented as the independent pressure rating of the internal charge pump.

4. Prime the Pump Before High-Speed Operation

After pump replacement or long-term shutdown, make sure the hydraulic circuit and pump housing have adequate fluid before high-speed operation. Avoid operating the mechanically driven gear pump under severe dry-running conditions.

5. Maintain Hydraulic Cleanliness

The internal gear pump depends on controlled internal clearances. Inspect:

• Filter condition
• Metallic contamination
• Hydraulic-fluid cleanliness
• Oil viscosity
• Abnormal oil temperature

Contamination and unsuitable viscosity can accelerate gear and housing wear.

6. Verify Charge Pressure During Commissioning

Do not immediately place a newly installed A4VG system under full load.

A controlled startup should verify the progression of:

Charge Pressure → Control Pressure → Closed-Loop Pressure

while checking noise, vibration and leakage.

7. Inspect the Complete Internal Gear-Pump Assembly During Service

Bosch Rexroth maintenance documentation treats the internal gear pump as a dedicated service area and specifies inspection of the pump cover, O-rings and sealing surfaces.

Therefore, a low-charge-pressure problem should not automatically be attributed only to the gear set. The complete assembly should be inspected:

Gear Set → Pump Cover → Sealing Surfaces → O-Rings → Drive Interface