Hydraulic Issues in Hitachi ZX120-5: Troubleshooting and Solutions

[MikePhua]

Hydraulic systems are at the heart of most modern heavy machinery, particularly in excavators like the Hitachi ZX120-5. They control a range of essential functions such as the boom, arm, and bucket movements. Hydraulic malfunctions can severely impact the performance of the equipment, leading to reduced productivity, increased downtime, and potential damage to the machine’s components. One common issue faced by operators is the hydraulic system's failure to function unless the system is "deadheaded." This can point to a variety of underlying causes that need to be addressed.
This article will explore the possible reasons behind hydraulic failures in the Hitachi ZX120-5, examine how to troubleshoot these issues, and provide recommendations for repair and maintenance to avoid similar problems in the future.

Understanding the Hydraulic System in the Hitachi ZX120-5
The Hitachi ZX120-5 is a mid-sized hydraulic excavator that relies on a sophisticated hydraulic system to perform heavy-duty tasks in construction, demolition, and material handling. The hydraulic system uses pressurized fluid to transfer power to various moving parts of the machine. When there is a problem with the hydraulic system, the efficiency and functionality of the machine can be significantly compromised.
Key components of the hydraulic system include:

1. Hydraulic Pumps: These convert mechanical energy from the engine into hydraulic energy, driving the movement of the excavator’s arms, boom, and bucket.
   
2. Hydraulic Valves: These control the flow of hydraulic fluid to different parts of the system, enabling precise movement of the excavator’s arms and attachment tools.
   
3. Hydraulic Cylinders: These provide the force necessary to move the arms and bucket.
   
4. Hydraulic Hoses and Lines: These carry hydraulic fluid under pressure to various parts of the system.
   

The system's reliability depends on the proper function of these components. When any one part malfunctions, it can disrupt the entire hydraulic process.

Symptoms and Initial Diagnosis: Hydraulic Deadheading
One of the most common symptoms of a hydraulic issue in the Hitachi ZX120-5 is when the hydraulic system fails to operate unless "deadheaded." Deadheading refers to the condition where the hydraulic system is blocked at the pump, causing the fluid to stop circulating to the actuators and cylinders. This can happen when the hydraulic fluid flow is restricted or when there is an issue with the hydraulic pump, valve, or other parts of the system.
The symptoms include:

• Inability to Operate Hydraulic Functions: The boom, arm, or bucket may not respond to control inputs unless deadheading occurs. This means that the machine’s hydraulics only work when the fluid is forced to recirculate in a loop, essentially bypassing the system’s normal operation.
  
• Slow or Inconsistent Movements: Even when the machine's hydraulics function, there may be sluggish or jerky movements in the arms, boom, or bucket.
  
• Unusual Noise or Vibration: In some cases, a failing hydraulic system may produce grinding, whining, or high-pitched noise, which can indicate air in the system or an issue with the hydraulic pump.
  

Possible Causes of Hydraulic Malfunctions
There are several potential causes for a hydraulic system in the Hitachi ZX120-5 to fail unless deadheaded. These include:

1. Air in the Hydraulic System
   Air contamination can cause erratic or inconsistent operation of the hydraulics. If air enters the hydraulic lines, it can create bubbles in the fluid, reducing its ability to transmit pressure effectively. This could be due to a leaking hydraulic seal, improperly installed fittings, or a damaged hose.
   
2. Low Hydraulic Fluid Levels
   Low hydraulic fluid levels can result in inadequate pressure being generated, leading to the malfunctioning of the hydraulic functions. This may be caused by fluid leakage from seals, hoses, or connections. Inadequate fluid levels can also cause overheating of the hydraulic fluid, further compromising the system’s efficiency.
   
3. Faulty Hydraulic Pump
   The hydraulic pump is responsible for creating the necessary pressure in the system. If the pump is worn or damaged, it may not be able to generate enough pressure for the hydraulic functions to operate. This could result in slow or non-functioning hydraulics unless deadheading forces the system to work in a bypassed mode.
   
4. Clogged Hydraulic Filters
   Over time, debris and contaminants can build up in the hydraulic fluid, clogging the filters. A clogged filter restricts the flow of fluid, preventing it from circulating properly through the system. This can lead to erratic or inconsistent hydraulic operation, particularly in high-demand conditions.
   
5. Malfunctioning Hydraulic Valves
   The hydraulic valves control the direction and flow of the hydraulic fluid. A malfunctioning valve could cause the system to lose pressure or restrict fluid flow to certain parts of the machine. This may cause the machine to only operate under certain conditions, such as when the system is deadheaded.
   
6. Internal Leakage in Hydraulic Cylinders
   Internal leakage in the hydraulic cylinders can result in reduced force and slow movement. The seals inside the cylinders may wear over time, allowing fluid to leak past and causing a loss of pressure in the system.
   

Troubleshooting Steps
To resolve the hydraulic malfunction in the Hitachi ZX120-5, operators can follow a step-by-step troubleshooting process:

1. Check Hydraulic Fluid Levels
   • Inspect the hydraulic fluid levels and ensure they are at the recommended level. Low fluid levels should be topped off with the appropriate type of hydraulic fluid.
     
   • Check for signs of leaks in hoses, connections, or seals. If any fluid leakage is observed, it should be repaired immediately.
     
2. Inspect for Air in the System
   • If air is suspected in the system, bleed the system to remove any trapped air. This may involve operating the machine’s hydraulic functions in a specific sequence to allow air to escape.
     
   • Inspect all hydraulic lines for any visible signs of damage or leakage that could allow air to enter the system.
     
3. Test the Hydraulic Pump
   • If there are no issues with fluid levels or air in the system, the next step is to test the hydraulic pump. Use a pressure gauge to check the output pressure from the pump. If the pump is not generating sufficient pressure, it may need to be repaired or replaced.
     
4. Examine Hydraulic Filters
   • Inspect the hydraulic filters for any blockages or buildup of contaminants. If the filter is clogged, it should be replaced with a new one to ensure proper fluid flow.
     
5. Inspect Hydraulic Valves
   • Inspect the hydraulic valves for proper operation. Check for any signs of damage or malfunction that could be restricting fluid flow or causing inconsistent operation.
     
6. Inspect Hydraulic Cylinders
   • If the problem persists, inspect the hydraulic cylinders for signs of internal leakage. This may require removing the cylinders and checking the seals and components for wear. Replacing worn seals or components will restore proper functionality.
     

Preventive Maintenance Tips
To avoid hydraulic issues in the future and extend the life of the Hitachi ZX120-5’s hydraulic system, consider these preventive maintenance practices:

1. Regular Fluid Checks
   • Regularly check the hydraulic fluid levels and condition. Replace the fluid according to the manufacturer’s recommendations to avoid contamination and wear.
     
2. Scheduled Filter Replacements
   • Change hydraulic filters at regular intervals to prevent clogging and ensure optimal fluid flow. Clogged filters can lead to poor system performance and long-term damage to components.
     
3. Seal Inspections
   • Inspect hydraulic seals regularly for wear and tear. Replacing damaged seals early can prevent leaks and loss of pressure, ensuring that the system functions properly.
     
4. Hydraulic System Bleeding
   • Periodically bleed the hydraulic system to remove air pockets and ensure smooth fluid circulation. This is especially important after servicing the system or replacing hydraulic components.
     
5. Monitor Operating Conditions
   • Be mindful of the operating conditions in which the machine is used. Extreme temperatures, heavy-duty operations, or high-stress tasks can strain the hydraulic system and lead to premature wear.
     

Conclusion
Hydraulic issues in the Hitachi ZX120-5, such as malfunctioning hydraulics unless deadheaded, can stem from a variety of causes, including air in the system, low fluid levels, faulty pumps, or clogged filters. By following a systematic troubleshooting process and performing regular maintenance, operators can ensure the hydraulic system remains in good working order, minimizing downtime and preventing costly repairs. Through proactive care and attention to detail, the hydraulic system of the ZX120-5 can provide reliable service for years to come.