Bosch Rexroth A4VTG071 closed circuit axial piston variable hydraulic pump

The A4VTG071 is a closed-circuit, variable-displacement axial piston pump built on a swashplate design. It belongs to Bosch Rexroth's A4VTG series (Series 32), a product line purpose-built for hydrostatic drum drives — most notably the rotating drums on truck-mounted concrete mixers.

Key Characteristics

Design type: Axial piston, swashplate, variable displacement

Circuit type: Closed circuit (fluid recirculates between pump and motor rather than returning to an open reservoir loop)

Size designation: 071 refers to the nominal displacement class (roughly 71 cm³/rev), consistent with Rexroth's sizing convention

Nominal pressure: Typically rated around 400 bar (5,800 psi), with peak pressures higher depending on control configuration

Primary application: Drum drive systems in mobile concrete mixers, though the broader A4VTG/A4VG platform also serves other mobile hydrostatic transmission needs

How the A4VTG071 Works

Swashplate Mechanics

At the core of the pump is a rotating group of pistons arranged axially around a shaft, riding against an adjustable swashplate. As the shaft turns, the pistons reciprocate in their bores. The angle of the swashplate determines the stroke length of each piston — and therefore how much fluid is displaced per revolution.

Zero angle: No fluid displacement, even while the shaft is turning

Positive angle: Flow in one direction

Negative angle: Flow reverses direction, without needing to reverse shaft rotation

This is what allows a single pump to drive a mixer drum forward (mixing/loading) and backward (discharging) without additional valving to reverse flow.

Closed-Circuit Operation

Unlike open-circuit pumps that draw fluid from and return it to a reservoir, closed-circuit pumps like the A4VTG071 keep fluid circulating in a loop between the pump and its matched hydraulic motor. A boost (charge) pump, usually integrated or mounted as an auxiliary unit, maintains a minimum pressure in the low-pressure side of the loop, replenishes internal leakage, and helps prevent cavitation.

This closed-loop design has real advantages for mobile equipment:

Smaller reservoir requirements

Faster response to directional changes

Reduced aeration risk in a compact package

Control Options

Rexroth typically offers the A4VTG071 with multiple control types, including:

HW (hydraulic proportional control): A mechanical servo actuated via a hexagon shaft and lever, often used for manual drum-speed control from the cab or a mounted lever.

EP (electric proportional control): Solenoid-actuated with spring return and emergency actuation, allowing electronic or automated control of drum speed — useful for telematics-integrated fleets or automated batching sequences.

Installation and Maintenance Considerations

Fluid Cleanliness

Axial piston pumps operate with tight internal clearances between pistons and bores. Contaminated hydraulic fluid is the single most common cause of premature wear. Rexroth's technical documentation consistently emphasizes strict filtration targets (commonly ISO 4406 cleanliness codes in the 19/17/14 to 20/18/15 range) for long service life.

Charge Pressure Verification

Because the A4VTG071 relies on a charge (boost) circuit to keep the closed loop pressurized, low charge pressure is a frequent root cause of noise, cavitation damage, or sluggish drum response. Verifying charge pressure with a calibrated gauge should be the first diagnostic step on any complaint of pump noise or inconsistent drum speed.

Shaft Seal and Temperature Range

Standard shaft seals are typically FKM (fluoroelastomer), rated for a wide housing temperature range, with NBR seals specified for colder climates. Matching seal material to the operating environment matters for trucks that see extreme seasonal temperature swings.

Control Linkage Wear

On HW (hydraulic/mechanical) control versions, the lever linkage and servo components are exposed to vibration and road grime. Periodic inspection of linkage wear, and free movement of the control lever helps avoid erratic drum speed control — a common field complaint that's mechanical, not hydraulic, in origin.

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Specifications

Selection Table

Q1: Is the A4VTG071 the same as the A4VG071?

A1: No. Both are closed-circuit variable axial piston pumps and share core swashplate technology, but A4VG is built primarily for hydrostatic travel/propulsion drives (like excavator travel motors), while A4VTG is engineered specifically for rotary drum-drive duty, such as mixer trucks. Mounting flanges, control options, and porting differ between the two.

Q2:What causes an A4VTG071 to lose drum speed or respond sluggishly?

A2: Common causes include low charge (boost) pressure, worn control linkage on HW control versions, contaminated hydraulic fluid affecting internal leakage, or a failing solenoid on EP control versions. Charge pressure should typically be checked first.

Q3:How to purchase an A4TVG071 hydraulic pump?

A3:You can click on the right sidebar or the contact information in the top bar to contact us to purchase. You can do so via email, form, WeChat, WhatsApp, or other methods.

Q4:What is the price and delivery time of the A4VTG071 hydraulic pump?

A4:The specific price and delivery time will be provided based on the specific model you provide.