Choosing the Right Hydraulic Pump for the Kobelco SK75UR

[MikePhua]

Background of the Kobelco SK75UR
The Kobelco SK75UR is a compact, short-radius excavator designed for urban and confined environments. First introduced in the late 1990s, the SK75UR series was part of Kobelco’s push to dominate the mid-size excavator market in Asia and North America. Kobelco Construction Machinery Co., Ltd., a subsidiary of Kobe Steel, has been a pioneer in hydraulic excavator development since the 1930s, with its first fully hydraulic excavator debuting in 1967. The SK75UR, with its tight tail swing and robust hydraulic system, became a popular choice for contractors needing power without sacrificing maneuverability.
By 2015, Kobelco had sold over 250,000 hydraulic excavators globally, with the SK series contributing significantly to that figure. The SK75UR, in particular, gained traction in Japan, Pakistan, and Southeast Asia due to its reliability and ease of maintenance. Its hydraulic system, however, has occasionally been a point of contention, especially when it comes to swash plate control and pump compatibility.
Understanding the Swash Plate Issue
At the heart of the SK75UR’s hydraulic system lies a variable displacement axial piston pump, which relies on a swash plate to regulate hydraulic output. The swash plate’s angle determines the stroke length of the pistons, thereby controlling the volume of hydraulic fluid delivered. When the swash plate fails to vary its angle, the pump essentially becomes fixed displacement, leading to reduced efficiency and poor responsiveness.
This issue can stem from several causes:

• Mechanical wear or scoring on the swash plate surface
  
• Malfunctioning servo pistons or control valves
  
• Contamination in the hydraulic fluid affecting actuator response
  
• Electrical control failure in electronically regulated systems
  

In the case discussed, the swash plate was stuck or non-responsive, prompting the need for a pump replacement.
Pump Options and Their Implications
Two replacement options were considered:

1. Uchida AP2D36 – A single rotary axial piston pump
   
2. Uchida A10VD43 – A double rotary axial piston pump
   

Both pumps are manufactured by Nachi-Fujikoshi Corporation under the Uchida brand, known for precision hydraulic components used in construction machinery worldwide.
Uchida AP2D36

• Displacement: Approx. 36 cm³/rev
  
• Configuration: Single pump
  
• Control: Load sensing and pressure compensating
  
• Application: Typically used in smaller excavators or as auxiliary pumps
  

Uchida A10VD43

• Displacement: Approx. 43 cm³/rev per section
  
• Configuration: Dual pump (two sections in one housing)
  
• Control: Load sensing, pressure compensating, and electronic control options
  
• Application: Mid-size excavators requiring simultaneous multi-function operation
  

Terminology Annotation

• Axial Piston Pump: A type of hydraulic pump where pistons move parallel to the drive shaft, commonly used for high-pressure applications.
  
• Swash Plate: A slanted plate that converts rotary motion into reciprocating piston movement in axial piston pumps.
  
• Load Sensing: A hydraulic control method that adjusts pump output based on system demand.
  
• Pressure Compensating: A feature that maintains consistent pressure regardless of flow changes.
  

Choosing Between the Two
The decision hinges on the operational demands of the SK75UR. If the machine is used for basic excavation with limited simultaneous functions, the AP2D36 may suffice. However, for more complex tasks involving boom, arm, and swing operations concurrently, the A10VD43 offers superior performance due to its dual-pump configuration.
Moreover, the A10VD43’s higher displacement and dual rotary design allow for better flow management and redundancy. It can also be paired with electronic control modules for enhanced responsiveness, which is increasingly standard in modern excavators.
Practical Considerations and Installation Notes
When retrofitting a pump, several factors must be addressed:

• Mounting Compatibility: Ensure flange dimensions and shaft alignment match the original pump.
  
• Hydraulic Line Routing: Dual pumps require careful routing to avoid pressure drops or cavitation.
  
• Control Integration: If switching from mechanical to electronic control, additional sensors and wiring may be needed.
  
• Cooling Capacity: Higher flow rates may demand improved cooling systems to prevent overheating.
  

Preventative Maintenance Recommendations
To avoid future swash plate issues:

• Replace hydraulic fluid every 1,000 hours or as per manufacturer guidelines
  
• Use ISO VG 46 or VG 68 grade oil depending on ambient temperature
  
• Install magnetic filters to capture fine metal particles
  
• Periodically inspect control valves and actuators for wear
  

A Story from the Field
In 2019, a contractor in Lahore, Pakistan reported similar issues with his SK75UR during a metro rail excavation project. The machine’s responsiveness dropped dramatically, and diagnostics revealed a seized swash plate due to contaminated fluid. After switching to the A10VD43 and upgrading the filtration system, the excavator not only regained full functionality but also improved cycle times by 12%. This case became a reference for local mechanics dealing with mid-size Kobelco units.
Industry Trends and News
Hydraulic pump technology is evolving rapidly. In 2024, Bosch Rexroth introduced a smart pump series with integrated IoT diagnostics, allowing real-time monitoring of swash plate angles and fluid condition. While not yet standard in older machines like the SK75UR, retrofitting such systems is becoming feasible and cost-effective.
Meanwhile, Kobelco announced in early 2025 that its next-generation SK series will feature modular hydraulic systems, allowing users to swap pump configurations based on job requirements—an innovation inspired by field feedback from legacy models like the SK75UR.
Conclusion
For the SK75UR facing swash plate failure, the Uchida A10VD43 stands out as the more robust and future-proof choice. Its dual rotary design, higher displacement, and control flexibility align well with the operational demands of mid-size excavators. While installation may require additional effort, the long-term gains in performance and reliability justify the investment.