A4VG125EP4D1 A4VG125EP4DM1 Rexroth Piston Pump 400 bar

Product Overview

The A4VG125EP4D1/32R-NZF02F021SH (Material No. R902123171) and A4VG125EP4DM1/32R-NZF02N00XEH-S (Material No. R902123413) are the 125 cc-class core models within the Bosch Rexroth A4VG series 32 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):

A4VG125EP4D1/32R-NZF02F021SH:

• A4VG: Rexroth closed-circuit swashplate axial piston variable pump

• 125: Nominal size (NG), geometric displacement 125 cm³/rev

• EP4: Electric Proportional control with proportional solenoids, pump displacement proportional to solenoid current signal

• D1: Control variant code, D1 = standard electric control configuration

• /32R: Series 32, clockwise rotation (viewed from shaft end)

• NZF02F021SH: N = mounting flange and port code; ZF = shaft configuration; 02 = design variant; F021 = factory calibration code; SH = additional configuration identifier

A4VG125EP4DM1/32R-NZF02N00XEH-S:

• A4VG: Rexroth closed-circuit swashplate axial piston variable pump

• 125: Nominal size (NG), geometric displacement 125 cm³/rev

• EP4DM1: EP4 electric proportional control, DM1 = control variant code (with specific feedback/auxiliary function)

• /32R: Series 32, clockwise rotation (viewed from shaft end)

• NZF02N00XEH-S: N = mounting flange and port code; ZF = shaft configuration; 02 = design variant; N00 = standard configuration; XEH = additional configuration code; S = seal material designation (NBR)

EP4 Control Function Details:

EP4 is an electro-hydraulic proportional control method. Electrical energy is converted to force acting on the control spool through proportional solenoids. Each solenoid (a and b) controls one flow direction. Pressure directed through a proportional 4/3 directional valve drives the control piston, changing the swashplate inclination angle for precise pump displacement adjustment. EP4 control uses proportional valve direct control of the stroking piston, offering simple structure, low manufacturing cost, and strong contamination resistance. The control current range is typically 200–600 mA (24 VDC configuration) or 400–1200 mA (12 VDC configuration), with displacement steplessly proportional to the current signal across 0–100%.

Drop-in Replacement Advantage: Manufactured to exact Rexroth OEM specifications, these pumps achieve complete drop-in interchangeability with the original A4VG series 32 for SAE J744 mounting flange, shaft dimensions, SAE main port layout, and EP4 control module interface. Every pump undergoes 100% simulated load testing prior to shipment, validating 400 bar pressure loading, EP4 control response, and volumetric efficiency under conditions replicating real-world duty cycles.

Technical Specifications 

A4VG125 Series General Specifications:

• Series: Rexroth A4VG Series 32 (Closed Circuit, Swashplate Design)

• Nominal Size: NG 125

• Geometric Displacement (Variable Pump): 125 cm³/rev

• Auxiliary Pump Displacement (p = 20 bar): 28.3 cm³/rev

• Nominal Pressure: 400 bar (continuous)

• Peak Pressure: 450 bar (intermittent)

• Continuous Maximum Speed (Vg max): 2850 rpm

• Limited Maximum Speed: 3250 rpm

• Intermittent Maximum Speed: 3450 rpm

• Minimum Speed: 500 rpm

• Maximum Flow (nnom, Vg max): 356 L/min

• Maximum Power (Δp = 400 bar): 237 kW

• Maximum Torque (Vg max, Δp = 400 bar): 795 N·m

• Torque (Vg max, Δp = 100 bar): 198.8 N·m

• Moment of Inertia: 0.0232 kgm²

• Maximum Angular Acceleration: 14000 rad/s²

• Housing Material: High-strength cast iron

• Weight: Approx. 80 kg

Model A4VG125EP4D1/32R-NZF02F021SH Configuration:

• Model Code: A4VG125EP4D1/32R-NZF02F021SH

• Material Number: R902123171

• Control Type: EP4 — Electric Proportional Control, proportional solenoid driven

• Rotation: Clockwise (viewed from shaft end)

• Series: 32

• Factory Calibration: NZF02F021SH configuration

Model A4VG125EP4DM1/32R-NZF02N00XEH-S Configuration:

• Model Code: A4VG125EP4DM1/32R-NZF02N00XEH-S

• Material Number: R902123413

• Control Type: EP4 — Electric Proportional Control, DM1 control variant

• Rotation: Clockwise (viewed from shaft end)

• Series: 32

• Factory Calibration: NZF02N00XEH-S configuration

A4VG Series Displacement Size Reference:

• A4VG28: 28 cm³/rev, continuous speed 4250 rpm, flow 119 L/min

• A4VG40: 40 cm³/rev, continuous speed 4000 rpm, flow 160 L/min

• A4VG56: 56 cm³/rev, continuous speed 3600 rpm, flow 202 L/min

• A4VG71: 71 cm³/rev, continuous speed 3300 rpm, flow 234 L/min

• A4VG90: 90 cm³/rev, continuous speed 3050 rpm, flow 275 L/min

• A4VG125: 125 cm³/rev, continuous speed 2850 rpm, flow 356 L/min

• A4VG180: 180 cm³/rev, continuous speed 2500 rpm, flow 450 L/min

• A4VG250: 250 cm³/rev, continuous speed 2400 rpm, flow 600 L/min

Key Technical Advantages

1. EP4 Electric Proportional Control with Precise Displacement Regulation
The A4VG125EP4D1 and A4VG125EP4DM1 are both equipped with the EP4 electric proportional control module. EP4 control receives current signals via proportional solenoids, converting electrical energy into force acting on the control spool. Each solenoid controls one flow direction, with pressure directed through a proportional 4/3 directional valve to drive the control piston, changing the swashplate inclination angle for precise pump displacement adjustment. Pump displacement is proportional to the proportional solenoid current signal, steplessly adjustable across 0–100%. EP4 control uses proportional valve direct control of the stroking piston, offering simple structure and strong contamination resistance, particularly suitable for mobile equipment applications requiring remote pump displacement control from the cab via electrical signals.

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 125 cc size delivers maximum power of 237 kW, maximum torque of 795 N·m, and maximum flow of 356 L/min at 400 bar nominal pressure, achieving a power density of approximately 3.0 kW/kg, leading its displacement class. 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 28.3 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 to protect the system from overpressure damage.

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 +104°C, particularly suitable for mobile hydraulic equipment operating outdoors and in harsh conditions. The low-inertia rotating group (0.0232 kgm²) and high angular acceleration (14000 rad/s²) ensure excellent system dynamic response characteristics.

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. High Volumetric Efficiency with Low Energy Consumption
The A4VG125 employs precision-ground pistons and cylinder bores with micron-level clearances, and a precision port plate design, achieving volumetric efficiency of ≥93%. The EP4 electric proportional control achieves on-demand flow delivery, effectively reducing throttling losses and system heat generation, improving overall energy efficiency.

Application Areas

• Concrete Mixer Trucks: Drum drive closed-circuit hydraulic systems

• Construction Equipment: Excavator travel drives, wheel loader travel hydraulic systems, bulldozer hydraulic drives

• Road Rollers: Vibratory roller travel drive hydraulic systems

• Agricultural Machinery: Combine harvester hydraulic drives, high-horsepower tractor closed-circuit transmissions

• Mining Equipment: Mining truck hydrostatic drives, underground LHD hydraulic systems

• Marine & Offshore: Deck machinery hydraulic drives, marine winch closed-circuit systems

• Industrial Hydraulic Power Units: Closed-circuit hydraulic power units, test bench hydraulic systems

Expert Maintenance Tips

1. EP4 Proportional Solenoid Maintenance
Both EP4DM1 and EP4D1 controls are equipped with proportional solenoids, with pump displacement proportional to the solenoid current signal. Regularly inspect the proportional solenoid electrical connectors for corrosion, moisture ingress, or loose pins. Verify the control current signal waveform with an oscilloscope every 2,000 hours to ensure proper PWM waveform. The control current range is typically 200–600 mA (24 VDC) or 400–1200 mA (12 VDC), with displacement proportional to the current signal across 0–100%. The proportional solenoid supply voltage and current range must conform to Rexroth technical specifications.

2. 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. For 125 cc class pumps, case drain flow is substantial — drain line design must fully account for flow demand to avoid excessive case pressure from pipe resistance.

3. Pressure Cut-Off Valve Setting and Inspection
The A4VG series is equipped with an integral pressure cut-off as standard, automatically reducing pump displacement to zero when system pressure reaches the setpoint. The pressure cut-off setting is typically approximately 3 MPa lower than the main relief valve to ensure proper system protection. Inspect the pressure cut-off setting every 2,000 operating hours to confirm it remains below the 450 bar peak pressure and that the function operates correctly.

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 control 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. Hydraulic Fluid Cleanliness
The A4VG series EP4 control spool and pressure cut-off valve operate with extremely tight clearances and are highly sensitive to particulate contamination. System fluid cleanliness must meet ISO 4406 18/15/12 or better. 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.

6. Through Drive End Maintenance
If equipped with through drive, regularly inspect rear pump mounting bolt tightness and spline connection wear. The through-drive end bearing is lubricated by the pump’s internal case drain circuit — no additional maintenance required. However, the rear pump’s power demand must not exceed the through-drive rated torque capacity. Inspect through-drive end bolt torque at 500 hours after first commissioning, then recheck every 2,000 operating hours.