Product Overview
The AA4VG28HW1/30R-PSC60F001 is the 28 cc-class core model within the Bosch Rexroth A4VG series 30 of swashplate axial piston variable displacement pumps. The A4VG series is Rexroth’s flagship platform for closed-circuit hydrostatic transmissions, spanning displacements from 28 to 250 cm³/rev with a nominal pressure of 400 bar and peak pressure of 450 bar, widely deployed in construction machinery travel drives, concrete mixer drum drives, and industrial hydraulic systems.
The A4VG series features a swashplate design where flow is proportional to drive speed and displacement and is infinitely variable. The pump is equipped with two pressure-relief valves on the high pressure ports to protect the hydrostatic transmission (pump and motor) from overload, with the high-pressure relief valves also functioning as boost valves. The integrated boost pump acts as a feed and control oil pump, with maximum boost pressure limited by a built-in boost pressure relief valve. The integral pressure cut-off is standard across the range.
Model Code Breakdown (for procurement and engineering reference):
Using AA4VG28HW1/30R-PSC60F001 as example:
A (prefix): Indicates SAE version (US market configuration), or complete pump unit assembly version
A4VG: Rexroth closed-circuit swashplate axial piston variable pump
28: Nominal size (NG), geometric displacement 28 cm³/rev
HW1: Hydraulic Control, Mechanical Servo. Pump displacement is infinitely varied by rotating the control lever between 0° and ±29°. A feedback lever connected to the stroking piston maintains constant pump flow for any given lever position. Spring centering automatically returns the pump to neutral (zero displacement) when lever torque is released
/30R: Series 30 (Baureihe 3, Index 0), clockwise rotation (viewed from shaft end)
PSC60F001: P = NBR seals (nitrile rubber); S = ANSI B92.1a standard splined shaft; C = port configuration code; 60 = design variant; F001 = factory calibration code
Drop-in Replacement Advantage: Manufactured to exact Rexroth OEM specifications, this pump achieves complete drop-in interchangeability with the original A4VG series 30 for SAE J744 mounting flange, splined shaft, SAE main port layout, and HW1 control module interface. Every pump undergoes 100% simulated load testing prior to shipment, validating 400 bar pressure loading, HW1 control response, and volumetric efficiency under conditions replicating real-world duty cycles.
Technical Specifications
Model AA4VG28HW1/30R-PSC60F001:
Model Code: AA4VG28HW1/30R-PSC60F001
Series: Rexroth A4VG Series 30 (Closed Circuit, Swashplate Design)
Nominal Size: NG 28
Geometric Displacement (Variable Pump): 28 cm³/rev
Auxiliary Pump Displacement (p = 20 bar): 6.1 cm³/rev
Nominal Pressure: 400 bar (continuous)
Peak Pressure: 450 bar (intermittent)
Continuous Maximum Speed (nnom): 4250 rpm
Limited Maximum Speed (nmax1): 4500 rpm
Intermittent Maximum Speed (nmax2): 5000 rpm
Minimum Speed: 500 rpm
Maximum Flow (nnom, Vg max): 119 L/min
Maximum Power (Δp = 400 bar, nnom): 79 kW
Maximum Torque (Vg max, Δp = 400 bar): 178 N·m
Torque (Vg max, Δp = 100 bar): 45 N·m
Control Type: HW1 — Hydraulic Control, Mechanical Servo
Control Lever Angle Range: 0° to ±29° (spring-centered zero flow position)
Start of Control: β = 3°
End of Control: β = 29° (max displacement Vg max)
Mechanical Stop: Sizes 28 corresponding to ±40°
Maximum Required Lever Torque: 170 N·cm (15 lb-in)
Rotation: Clockwise (viewed from shaft end, R code)
Mounting Flange: SAE J744 two-bolt flange
Shaft: ANSI B92.1a standard splined shaft (S code)
Main Ports: SAE flange connections
Housing Material: High-strength cast iron
Seal Material: NBR (nitrile rubber), suitable for mineral oil-based hydraulic fluid
Fluid Cleanliness: ISO 4406 20/18/15 or better
Operating Temperature Range: -40°C to +90°C
Weight: Approx. 29 kg (without through drive)
Through Drive Capability: Supports mounting of subsequent pumps of same or smaller size
A4VG Series Displacement Size Reference:
A4VG28: 28 cm³/rev, nnom 4250 rpm, flow 119 L/min, power 79 kW
A4VG40: 40 cm³/rev, nnom 4000 rpm, flow 160 L/min, power 107 kW
A4VG56: 56 cm³/rev, nnom 3600 rpm, flow 202 L/min, power 134 kW
A4VG71: 71 cm³/rev, nnom 3300 rpm, flow 234 L/min, power 156 kW
A4VG90: 90 cm³/rev, nnom 3050 rpm, flow 275 L/min, power 183 kW
A4VG125: 125 cm³/rev, nnom 2850 rpm, flow 356 L/min, power 238 kW
A4VG180: 180 cm³/rev, nnom 2500 rpm, flow 450 L/min, power 300 kW
A4VG250: 250 cm³/rev, nnom 2400 rpm, flow 600 L/min, power 400 kW
Key Technical Advantages
1. HW1 Mechanical Servo Control with Precise Flow Regulation
The AA4VG28HW1/30R-PSC60F001 is equipped with the HW1 hydraulic control, mechanical servo module. Pump output flow is infinitely varied in the range of 0 to 100%, proportional to the rotation of the control lever between 0° and ±29° from the spring-centered zero flow position. A feedback lever, connected to the stroking piston, maintains the pump flow for any given position of the control lever. The spring centering function ensures the pump automatically moves into neutral position (zero displacement) as soon as there is no longer any torque on the control lever, providing fail-safe protection for travel drive systems. The start of control is at β = 3°, with the end of control at β = 29° (max displacement). The maximum required torque at the lever is only 170 N·cm. The HW control module features relatively simple construction with superior contamination resistance and reliability compared to electro-hydraulic proportional control.
2. Closed-Circuit Design with High Power Density
The A4VG series is specifically designed for closed-circuit hydrostatic transmissions. Compared to open-circuit systems, closed-circuit designs offer compact structure, higher efficiency, and smaller reservoir volume. The 28 cc size delivers maximum power of 79 kW, maximum flow of 119 L/min, and maximum torque of 178 N·m at 400 bar nominal pressure. Output flow increases smoothly with the swivel angle of the swashplate from 0 to maximum value, and flow direction changes smoothly when the swashplate is moved through the neutral position.
3. Integrated Boost Pump with Closed-Circuit Protection System
The A4VG series incorporates an integrated boost pump with a displacement of 6.1 cm³/rev (at p = 20 bar), serving as both feed pump and control oil pump. The pump is equipped with two pressure-relief valves on the high pressure ports to protect the hydrostatic transmission (pump and motor) from overload. The high-pressure relief valves also function as boost valves. Maximum boost pressure is limited by a built-in boost pressure relief valve. The integral pressure cut-off is standard, automatically reducing pump displacement to zero when system pressure reaches the setpoint.
4. High-Strength Cast-Iron Housing with Wide Temperature Adaptability
The pump body is precision-cast from high-strength cast iron, with the material’s damping characteristics effectively suppressing structural vibration and fluid-borne noise. The wide operating temperature range accommodates extreme ambient temperatures from -40°C to +90°C, particularly suitable for mobile hydraulic equipment operating outdoors and in harsh conditions. The series is designed for operation with HLP mineral oil (per DIN 51524), with system cleanliness maintained at ISO 4406 20/18/15 or better in closed circuits.
5. Through Drive and Modular System Expansion
The A4VG series supports through drive, allowing direct mounting of subsequent pumps of same or smaller size on the rear of the main pump for single-motor multi-pump compound hydraulic systems. Modular control designs enable field conversion and upgrade. Standardized SAE J744 mounting flange and shaft require no adaptation for replacement, significantly reducing equipment downtime.
6. Compact Lightweight Design with High Power Density
The A4VG28 achieves a displacement of 28 cm³/rev with a weight of only approximately 29 kg (without through drive), achieving a power density of approximately 2.7 kW/kg, leading its displacement class. The compact axial dimensions make the A4VG28 particularly suitable for small compactors, small farm utility vehicles, and other mobile hydraulic applications with strict installation space requirements.
Application Areas
Small Compactors: Travel drive hydraulic systems for small vibratory rollers (A4VG28 is widely used in compact compaction equipment)
Small Farm Vehicles: Small tractor travel drives, agricultural transport vehicle hydraulic systems
Concrete Mixer Trucks: Drum drive closed-circuit hydraulic systems for small mixers
Construction Equipment: Mini excavator travel drives, compact wheel loader travel hydraulic systems
Sweepers & Municipal Vehicles: Sweeper travel drives, municipal utility vehicle hydraulic systems
Industrial Hydraulic Power Units: Closed-circuit hydraulic power units, test bench hydraulic systems
Marine & Offshore: Small deck machinery hydraulic drives, marine winch closed-circuit systems
Expert Maintenance Tips
1. Hydraulic Fluid Cleanliness
The A4VG series HW1 control servo spool operates with extremely tight clearances and is highly sensitive to particulate contamination. System fluid cleanliness must meet ISO 4406 20/18/15 or better. Recommended fluids are HLP mineral oils (per DIN 51524) with viscosity grades VG46 or VG68. Install a 10 μm absolute-rated filter element at the pump inlet. Replace elements at 500 hours after first commissioning, then every 1,000 operating hours or 6 months, whichever comes first. Finer filtration improves hydraulic fluid cleanliness, which directly extends the service life of the axial piston unit.
2. HW1 Control Lever Operating Procedure
HW1 control adjusts displacement via mechanical servo lever, with pump displacement proportional to the control lever angle. Operate the lever smoothly, avoiding rapid large-angle movements that cause system pressure spikes. With the lever at neutral (0°), pump displacement is zero. The spring centering function automatically returns the pump to neutral when lever torque is released, providing fail-safe protection for travel drive systems. To prevent damage to the HW control module, a positive mechanical stop must be provided for the HW control linkage. The mechanical stop for size 28 is ±40°.
3. Case Drain Line Requirements
The case drain line must return directly to the reservoir. Maximum permissible back pressure is 2 bar (0.2 MPa). The drain outlet must terminate below oil level at all times to prevent air ingestion. The drain line diameter must not be smaller than the pump case drain port size. Case drain temperature (influenced by pressure and speed) may be higher than the control temperature or circuit temperature, but the temperature at any part must not exceed 115°C.
4. Pre-Start Priming and Air Bleeding
Before first start, fill the pump housing with clean hydraulic fluid through the case drain port. After installation, turn the drive shaft by hand several revolutions to confirm free rotation without binding. Position the HW control lever at neutral (zero displacement) and run at low speed for 5–10 minutes. Verify continuous bubble-free flow from the case drain. Only after confirming adequate lubrication and boost pressure should the pump be loaded.
5. High-Pressure Relief Valve and Pressure Cut-Off Inspection
The pump’s built-in two high-pressure relief valves protect the hydrostatic transmission from overload and also function as boost valves. Inspect the relief valve setting pressure every 2,000 operating hours to confirm it remains below the 450 bar peak pressure and that the bypass function operates correctly. The integral pressure cut-off is standard; during commissioning, verify that its cut-off pressure setting is approximately 3 MPa lower than the main relief valve setting to ensure proper system protection.
