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Hitachi’s ZAXIS Line and the EX270’s Role
The Hitachi EX270 ZAXIS, launched in the early 2000s, was part of Hitachi’s push to modernize its mid-size excavator lineup with electronically controlled hydraulics and improved operator feedback. Hitachi Construction Machinery, founded in 1970, had already built a reputation for precision and durability, especially in mining and civil works. The EX270 ZAXIS, weighing roughly 27 metric tons, was equipped with a high-pressure hydraulic system and a refined control valve bank designed for smooth multi-function operation.
By 2005, the ZAXIS series had gained significant traction in North America and Asia, with thousands of units sold. However, as these machines aged, some operators began reporting unusual hydraulic noise—particularly during stick operation under full relief pressure.
Cavitation Sounds and Stick Function Anomalies
One of the most common complaints involves a cavitation-like sound when the stick is fully extended or retracted under load. Cavitation refers to the formation and collapse of vapor bubbles in hydraulic fluid, typically caused by low pressure or air ingestion. In the EX270, this sound is often isolated to the stick function, though some operators report faint echoes during boom operation.
Key terms:
- Cavitation: A destructive phenomenon where vapor bubbles implode, causing noise and potential damage.
- Relief pressure: The maximum pressure allowed in a hydraulic circuit before a valve opens to protect components.
- Control valve bank: A series of valves that direct hydraulic flow to specific actuators like the boom, stick, or bucket.
The issue tends to worsen over time, especially after 500+ hours of operation, suggesting progressive wear or contamination.
Pump Replacement and Persistent Symptoms
In many cases, operators have already replaced the main hydraulic pump—often with a remanufactured unit from John Deere or Hitachi. Despite this, the noise persists, leading to suspicion that the root cause lies elsewhere. A new pump may restore pressure and flow, but if internal valve components are worn or misaligned, cavitation can still occur.
One technician in Pennsylvania noted that even after a $13,000 pump replacement, the machine continued to vibrate under stick load. The problem was eventually traced to a leaking valve plate and worn shoe faces inside the pump housing—components that weren’t replaced during the remanufacture.
Relief Valve and Filter Considerations
Another potential culprit is the relief valve in the control valve bank. If the valve is sticking or set incorrectly, it may allow pressure to spike or drop unpredictably, triggering cavitation. Additionally, an old or clogged hydraulic filter can restrict flow, especially during high-demand operations like stick extension.
Recommendations:
Temperature Sensitivity and Oil Viscosity
Interestingly, the cavitation sound often disappears during cold starts and returns as the machine warms up. This suggests that oil viscosity plays a role. Thicker oil at lower temperatures may dampen cavitation, while thinner oil under heat allows vapor bubbles to form more easily.
Operators experimenting with heavier-grade hydraulic oil (e.g., ISO 68 instead of ISO 46) have reported temporary improvements. However, this is not a long-term fix and may affect system responsiveness.
Suggestions:
Inside the hydraulic pump, the valve plate and shoe faces are critical to maintaining seal integrity and pressure balance. Over time, these surfaces can wear unevenly, leading to internal leakage and pressure instability. This wear is often invisible until disassembly.
Options for addressing wear:
Preventive Maintenance and Long-Term Strategy
To extend the life of the EX270’s hydraulic system:
Conclusion
Noisy hydraulics in the Hitachi EX270 ZAXIS—especially during stick operation—are often a symptom of deeper issues like valve wear, cavitation, or pressure instability. While pump replacement may seem like the obvious solution, true resolution requires a holistic approach: inspecting relief valves, cleaning filters, testing flow, and understanding temperature effects. With careful diagnostics and preventive care, this mid-size excavator can continue to deliver reliable performance well beyond its expected service life.
The Hitachi EX270 ZAXIS, launched in the early 2000s, was part of Hitachi’s push to modernize its mid-size excavator lineup with electronically controlled hydraulics and improved operator feedback. Hitachi Construction Machinery, founded in 1970, had already built a reputation for precision and durability, especially in mining and civil works. The EX270 ZAXIS, weighing roughly 27 metric tons, was equipped with a high-pressure hydraulic system and a refined control valve bank designed for smooth multi-function operation.
By 2005, the ZAXIS series had gained significant traction in North America and Asia, with thousands of units sold. However, as these machines aged, some operators began reporting unusual hydraulic noise—particularly during stick operation under full relief pressure.
Cavitation Sounds and Stick Function Anomalies
One of the most common complaints involves a cavitation-like sound when the stick is fully extended or retracted under load. Cavitation refers to the formation and collapse of vapor bubbles in hydraulic fluid, typically caused by low pressure or air ingestion. In the EX270, this sound is often isolated to the stick function, though some operators report faint echoes during boom operation.
Key terms:
- Cavitation: A destructive phenomenon where vapor bubbles implode, causing noise and potential damage.
- Relief pressure: The maximum pressure allowed in a hydraulic circuit before a valve opens to protect components.
- Control valve bank: A series of valves that direct hydraulic flow to specific actuators like the boom, stick, or bucket.
The issue tends to worsen over time, especially after 500+ hours of operation, suggesting progressive wear or contamination.
Pump Replacement and Persistent Symptoms
In many cases, operators have already replaced the main hydraulic pump—often with a remanufactured unit from John Deere or Hitachi. Despite this, the noise persists, leading to suspicion that the root cause lies elsewhere. A new pump may restore pressure and flow, but if internal valve components are worn or misaligned, cavitation can still occur.
One technician in Pennsylvania noted that even after a $13,000 pump replacement, the machine continued to vibrate under stick load. The problem was eventually traced to a leaking valve plate and worn shoe faces inside the pump housing—components that weren’t replaced during the remanufacture.
Relief Valve and Filter Considerations
Another potential culprit is the relief valve in the control valve bank. If the valve is sticking or set incorrectly, it may allow pressure to spike or drop unpredictably, triggering cavitation. Additionally, an old or clogged hydraulic filter can restrict flow, especially during high-demand operations like stick extension.
Recommendations:
- Inspect and clean the strainer at the bottom of the hydraulic tank
- Replace hydraulic filters every 500 hours or sooner in dusty environments
- Test relief valve pressure settings against factory specs
- Use a flow meter to verify pump output under load
Temperature Sensitivity and Oil Viscosity
Interestingly, the cavitation sound often disappears during cold starts and returns as the machine warms up. This suggests that oil viscosity plays a role. Thicker oil at lower temperatures may dampen cavitation, while thinner oil under heat allows vapor bubbles to form more easily.
Operators experimenting with heavier-grade hydraulic oil (e.g., ISO 68 instead of ISO 46) have reported temporary improvements. However, this is not a long-term fix and may affect system responsiveness.
Suggestions:
- Use OEM-recommended hydraulic oil unless operating in extreme climates
- Monitor oil temperature during operation using infrared sensors
- Consider installing an auxiliary cooler if operating in high ambient temperatures
Inside the hydraulic pump, the valve plate and shoe faces are critical to maintaining seal integrity and pressure balance. Over time, these surfaces can wear unevenly, leading to internal leakage and pressure instability. This wear is often invisible until disassembly.
Options for addressing wear:
- Lap the valve plate and shoe faces to restore flatness
- Replace worn components with OEM or high-quality aftermarket parts
- Pressure test the pump housing before reinstallation
- Avoid running the machine under full relief for extended periods
Preventive Maintenance and Long-Term Strategy
To extend the life of the EX270’s hydraulic system:
- Avoid sudden stick movements under full load
- Keep fluid clean and change filters on schedule
- Inspect hoses and fittings for leaks or air ingress
- Monitor system pressure and flow regularly
- Train operators to recognize early signs of cavitation
Conclusion
Noisy hydraulics in the Hitachi EX270 ZAXIS—especially during stick operation—are often a symptom of deeper issues like valve wear, cavitation, or pressure instability. While pump replacement may seem like the obvious solution, true resolution requires a holistic approach: inspecting relief valves, cleaning filters, testing flow, and understanding temperature effects. With careful diagnostics and preventive care, this mid-size excavator can continue to deliver reliable performance well beyond its expected service life.
