08-20-2025, 09:26 PM
Machine Background
The Hitachi EX120-2 is a mid-size hydraulic excavator widely used in construction, mining, and general earthmoving projects. Known for its robust build and reliable performance, the EX120-2 is powered by an Isuzu 4BG1T turbocharged diesel engine delivering about 81 horsepower at 2,100 RPM. The excavator features Hitachi’s proprietary hydraulic system, optimized for smooth and efficient digging and material handling operations.
Hydraulic Pump Details
The EX120-2 uses a dual variable-displacement axial piston pump setup (model HPV091), capable of delivering approximately 50.2 gallons per minute (189 liters per minute) of hydraulic flow. This arrangement powers the main hydraulic circuits including boom lift, arm, bucket, and swing functions as well as travel motors.
Converting or rebuilding the hydraulic pump on the EX120-2 involves replacing key components such as rotor groups, valve plates, shafts, bearings, and seals. During conversion or repair, attention must be paid to:
Technical and Operational Specifications
A contractor replaced a failing HPV091 hydraulic pump in their Hitachi EX120-2 with a professionally rebuilt unit. Post-installation, the excavator regained full hydraulic responsiveness with improved lifting speed and smoother operation. The contractor emphasized picking high-quality rebuild kits and pre-testing units to avoid repeated breakdowns — critical for minimizing costly project delays.
Conclusion
The Hitachi EX120-2’s hydraulic system centers on high-capacity HPV091 variable displacement pumps delivering the power required for consistent performance. Pump conversion or rebuilds involve precise replacement of internal components, requiring careful adherence to specifications and professional assembly. Properly maintained and serviced, the EX120-2’s hydraulic system ensures efficient and reliable excavator operation across demanding jobsite conditions.
The Hitachi EX120-2 is a mid-size hydraulic excavator widely used in construction, mining, and general earthmoving projects. Known for its robust build and reliable performance, the EX120-2 is powered by an Isuzu 4BG1T turbocharged diesel engine delivering about 81 horsepower at 2,100 RPM. The excavator features Hitachi’s proprietary hydraulic system, optimized for smooth and efficient digging and material handling operations.
Hydraulic Pump Details
The EX120-2 uses a dual variable-displacement axial piston pump setup (model HPV091), capable of delivering approximately 50.2 gallons per minute (189 liters per minute) of hydraulic flow. This arrangement powers the main hydraulic circuits including boom lift, arm, bucket, and swing functions as well as travel motors.
- Main pump capacity: 50.2 GPM (two pumps combined)
- Pressure relief valve settings near 4,980 psi (34.3 MPa)
- Pilot pump: fixed displacement gear pump delivering approximately 8.1 GPM for control circuits
- Hydraulic reservoir capacity: approximately 35.4 gallons (132 liters) ensuring sufficient fluid volume for cooling and lubrication
Converting or rebuilding the hydraulic pump on the EX120-2 involves replacing key components such as rotor groups, valve plates, shafts, bearings, and seals. During conversion or repair, attention must be paid to:
- Matching replacement parts to OEM specifications ensuring pressure and flow rates remain within operational parameters
- Proper assembly to avoid leaks or wear that could cause operational inefficiencies or failure
- Testing the rebuilt pump under simulated conditions to verify hydraulic capacity and pressure output before reinstallation
Technical and Operational Specifications
- Operating weight: about 11,800 kilograms (26,000 lbs)
- Maximum digging depth: approximately 5.4 meters (17.7 feet)
- Maximum reach: approximately 8.5 meters (28 feet)
- Engine power: 63 kW (85 hp)–up to 66.2 kW (90 hp) in HP mode
- Swing speed: approximately 12.7 RPM
- Travel speed: ranges between 3.42 mph (5.5 km/h) depending on terrain and setup
- Regularly monitor hydraulic fluid quality and levels; change per manufacturer schedule using genuine fluids
- Inspect pump seals and connections to prevent leaks and pressure loss
- Use qualified technicians for pump repairs or conversion to ensure proper assembly and testing
- Maintain cleanliness during hydraulic component disassembly and reassembly to avoid contamination-related failures
- Employ pressure gauges and system diagnostics after conversion to check for optimal performance
- Variable Displacement Pump: A hydraulic pump whose output can adjust to system demand, improving efficiency
- Axial Piston Pump: A type of pump where pistons move parallel to the pump shaft, common in heavy machinery hydraulics
- Pressure Relief Valve: Device that limits maximum hydraulic pressure to protect components
- Pilot Pump: Small auxiliary pump supplying low-pressure control oil for valve operation
- Rotating Group: The internal rotating assembly including pistons in the pump
A contractor replaced a failing HPV091 hydraulic pump in their Hitachi EX120-2 with a professionally rebuilt unit. Post-installation, the excavator regained full hydraulic responsiveness with improved lifting speed and smoother operation. The contractor emphasized picking high-quality rebuild kits and pre-testing units to avoid repeated breakdowns — critical for minimizing costly project delays.
Conclusion
The Hitachi EX120-2’s hydraulic system centers on high-capacity HPV091 variable displacement pumps delivering the power required for consistent performance. Pump conversion or rebuilds involve precise replacement of internal components, requiring careful adherence to specifications and professional assembly. Properly maintained and serviced, the EX120-2’s hydraulic system ensures efficient and reliable excavator operation across demanding jobsite conditions.
