Product Overview
The 51D110-1-RD4N-E2B1NNU1NNN is a mid-frame axial piston fixed displacement motor from Sauer Danfoss’ Series 51, featuring a displacement of 109.9 cm³/rev, rated working pressure of 480 bar, peak pressure of 510 bar, and speed range of 2200–5600 rpm with maximum speed up to 7000 rpm. Series 51 motors employ a bent-axis design with spherical pistons acting against a thrust plate, delivering high starting torque and smooth operation across the full speed range—making them ideal for closed-circuit hydrostatic transmission systems.
The model code breaks down as follows: 51D identifies the Series 51 fixed displacement motor (D = Fixed Displacement); 110 denotes the 109.9 cm³/rev displacement; 1 indicates 51-1 generation design; RD4N is the control and regulator configuration code; E2B1 is the control type code (E2 series control); NNU1NNN is the standard option combination.
Series 51 motors support bidirectional rotation with a 5:1 maximum-to-minimum displacement ratio (109.9 cm³/rev maximum, 22 cm³/rev minimum), and are available with SAE or DIN flanges and splined shaft configurations. The series is widely deployed in hydrostatic travel drives for road rollers, telescopic handlers, compact track loaders and more.
Every 51D110 unit undergoes 100% simulated operating-condition bench testing prior to shipment, covering pressure cycling, speed stepping and thermal shock. Mounting flange, shaft end and port dimensions comply with SAE/DIN standards and are identical to the original Sauer Danfoss 51D110, ensuring true drop-in interchangeability with zero modification required.
Technical Specifications
Series 51 Frame Size Specifications:
51D060: Max displacement 60.0 cm³/rev (3.66 in³/rev), min displacement 12.0 cm³/rev (0.73 in³/rev), rated flow 216 l/min (57 US gal/min), max flow 264 l/min (70 US gal/min), max power 336 kW (450 hp), weight ~28 kg (62 lb), mass moment of inertia 0.0046 kgm²
51D080: Max displacement 80.7 cm³/rev (4.92 in³/rev), min displacement 16.1 cm³/rev (0.98 in³/rev), rated flow 250 l/min (66 US gal/min), max flow 323 l/min (85 US gal/min), max power 403 kW (540 hp), weight ~32 kg (71 lb), mass moment of inertia 0.0071 kgm²
51D110 (This Model): Max displacement 109.9 cm³/rev (6.71 in³/rev), min displacement 22.0 cm³/rev (1.34 in³/rev), rated flow 308 l/min (81 US gal/min), max flow 396 l/min (105 US gal/min), max power 492 kW (660 hp), weight ~44 kg (97 lb), mass moment of inertia 0.0128 kgm²
51D160: Max displacement 160.9 cm³/rev (9.82 in³/rev), min displacement 32.2 cm³/rev (1.96 in³/rev), rated flow 402 l/min (106 US gal/min), max flow 515 l/min (136 US gal/min), max power 644 kW (864 hp), weight ~56 kg (123 lb), mass moment of inertia 0.0234 kgm²
51D250: Max displacement 250.0 cm³/rev (15.26 in³/rev), min displacement 50.0 cm³/rev (3.05 in³/rev), rated flow 550 l/min (145 US gal/min), max flow 675 l/min (178 US gal/min), max power 850 kW (1140 hp), weight ~86 kg (190 lb), mass moment of inertia 0.0480 kgm²
51D110-1-RD4N-E2B1NNU1NNN Additional Specifications:
Model Code: 51D110-1-RD4N-E2B1NNU1NNN
Type: Bent axis axial piston motor, fixed displacement
Displacement: 109.9 cm³/rev (6.71 in³/rev)
Rated Working Pressure: 480 bar (7000 psi)
Peak Pressure (Intermittent): 510 bar (7400 psi)
Minimum Input Pressure: 10 bar (145 psi)
Rated Speed Range: 2200–5600 rpm
Max Speed: 7000 rpm
Specific Torque (at max displacement): ~0.35 N·m/bar (~1067 lbf·in per 1000 psi)
Rotation: Bi-directional (clockwise / counter-clockwise)
Mounting Type: SAE 4-bolt flange (ISO 3019/1) / 2-bolt cartridge
Shaft Configuration: SAE or DIN splined shaft
Port Connections: Main pressure ports SAE flange; remaining ports SAE straight thread O-ring boss
Temperature Range: -40°C to +115°C
Weight: ~44 kg (97 lb)
Circuit Type: Closed circuit
Control Type: E2B1 control configuration, hydraulic servo control
Key Technical Advantages
1. Bent-Axis Spherical Piston Design for High Startup Torque and Smooth Operation
The 51D110 employs Sauer Danfoss Series 51’s signature bent-axis design, with the cylinder block angled relative to the output shaft and pistons acting directly against a thrust plate. This architecture delivers high torque at startup and smooth operation from 0 rpm to maximum rated speed. Spherical pistons with precision-ground cylinder bores minimize internal leakage, maintaining high volumetric efficiency across the full speed and pressure range.
2. High Pressure Capability — 480 Bar Rated
The 51D110 supports 480 bar rated working pressure and 510 bar peak pressure, enabling adaptation to high power-density closed-circuit hydraulic systems. Rated flow reaches 308 l/min with maximum flow of 396 l/min and maximum corner power of 492 kW, offering significant advantages in travel drive and tool drive applications requiring high torque density.
3. Wide Displacement Ratio and Closed-Circuit Compatibility
Series 51 motors achieve a 5:1 maximum-to-minimum displacement ratio (109.9/22.0 cm³/rev), delivering maximum torque at high displacement (grade climbing, heavy compaction) and higher speed at low displacement (flat ground travel). Shifts occur under load without changing pump output. The motor supports bidirectional rotation for closed-circuit hydrostatic transmissions, with optional loop flushing valves to maintain circuit fluid cleanliness and temperature control.
4. SAE/DIN Standard Mounting and Global Interchangeability
The 51D110 features SAE 4-bolt flange or 2-bolt cartridge mounting configurations with SAE or DIN splined shaft options. Main pressure ports are SAE flange, with remaining ports SAE straight thread O-ring boss, compatible with mainstream hydraulic systems worldwide. Mounting dimensions match the original Sauer Danfoss 51D110 exactly, enabling direct replacement without pipework or interface modification.
5. 100% Simulated Load Testing
Each 51D110 unit is bench-tested under simulated operating conditions prior to dispatch, covering pressure cycling, speed stepping and thermal variation. Test data is traceable, ensuring product performance meets original technical specifications.
Application Areas
The 51D110 is deployed across demanding mobile hydraulic applications in closed loop circuits:
Road Rollers: Bomag BW 156 D-3, BW 216 DH, BW 219 DH, BW 226 DH series vibratory roller travel drives
Telescopic Handlers: Merlo P28.7 KT and similar models with hydrostatic travel drives
Compact Track Loaders: Bobcat T2556 and similar models
Agricultural Machinery: combine harvester hydrostatic travel drives
Industrial: closed-circuit hydrostatic transmission systems
Expert Maintenance Tips
1. Oil Cleanliness and Temperature Control: Maintain system oil cleanliness at ISO 4406 18/16/13 or better. Case drain temperature is affected by pressure and speed and is always higher than circuit temperature—system temperature must not exceed 115°C at any point. Replace hydraulic oil and filter after the first 500 hours, then follow a 2000-hour or annual replacement cycle.
2. Loop Flushing Valve Maintenance: If equipped with a loop flushing valve, periodically inspect its operating condition. Insufficient flushing flow causes circuit oil temperature rise and contamination accumulation, affecting motor life. Inspect flushing valve flow and pressure settings every 1000 hours.
3. Displacement Shifting Procedure: The 51D110 allows displacement shifts under load. Under frequent shifting duty, inspect piston ring wear and bent-axis bearing clearance every 500 hours. Abnormal noise or sluggish displacement response requires immediate shutdown and service.
4. Drain Line Management: The drain port must return to the reservoir independently—housing back pressure must not exceed 2 bar. The drain line end must remain submerged to prevent air ingestion. After extended shutdown, fill the housing with clean hydraulic oil before restarting.
5. Splined Shaft and Coupling Inspection: Periodically inspect output splined shaft wear; excessive spline clearance causes abnormal vibration and noise. Coupling alignment deviation must not exceed 0.05 mm to prevent abnormal bearing wear and shaft seal leakage.
