Sensor and Solenoid Compatibility for Hitachi EX120 and EX150 Excavators

[MikePhua]

Hitachi’s EX120 and EX150 excavators are among the company’s widely used models, known for their durability and efficiency in construction and heavy-duty operations. Like all advanced machinery, these excavators rely on various sensors and solenoids to maintain smooth operation, control functions, and ensure safety. However, ensuring compatibility between sensors, solenoids, and the excavator’s hydraulic and electrical systems is crucial for optimal performance. In this article, we will delve into the critical aspects of sensor and solenoid compatibility, focusing on the EX120 and EX150, and how to address common issues.
Overview of Hitachi EX120 and EX150 Excavators
The Hitachi EX120 and EX150 are both tracked hydraulic excavators designed for heavy lifting, digging, and grading. These machines are particularly popular in construction, mining, and roadwork projects due to their compact size, strong lifting capabilities, and fuel efficiency. The EX120 model features a 78 kW (105 hp) engine and a 1.2m³ bucket capacity, while the EX150 offers slightly higher power with a 92.5 kW (124 hp) engine and a 1.5m³ bucket capacity.
Like other modern machines, these excavators use an array of sensors and solenoids to control systems such as the hydraulic pump, engine, and transmission. These components play a vital role in ensuring the machine operates at peak efficiency, maintains safety levels, and avoids unnecessary wear on the engine and hydraulic systems.
Role of Sensors and Solenoids in Hitachi Excavators

1. Sensors: Sensors in an excavator monitor a wide range of variables, including temperature, pressure, fuel flow, and hydraulic fluid levels. They provide real-time data to the machine’s control system, allowing it to adjust operations accordingly. For example:
   • Hydraulic Pressure Sensors: Monitor the hydraulic system to prevent over-pressurization, which could cause damage to valves, hoses, or seals.
     
   • Temperature Sensors: Ensure that engine and hydraulic components do not overheat.
     
   • Fuel Flow Sensors: Provide information about fuel usage to optimize engine performance and fuel efficiency.
     
2. Solenoids: Solenoids in an excavator are responsible for controlling the flow of fluid within the hydraulic system. They are electromagnetically actuated, and their role is to open and close valves to direct hydraulic fluid to specific parts of the machine, such as the boom, arm, or bucket. Solenoids are typically used in systems requiring precise fluid control, such as:
   • Hydraulic Control Valves: Control the direction and force of hydraulic fluid used to move parts like the boom or bucket.
     
   • Transmission Control Solenoids: Manage gear shifting in the transmission system.
     

Sensor and Solenoid Compatibility
Ensuring the compatibility of sensors and solenoids with the control systems of the Hitachi EX120 and EX150 excavators is crucial for smooth operation. Here are some essential aspects to consider when selecting and replacing these components:

1. Voltage and Current Requirements: Sensors and solenoids in these excavators typically operate on a specific voltage and current. Most Hitachi excavators use a 24-volt electrical system, meaning components should be compatible with 24V systems. It is essential to check the specifications of replacement sensors and solenoids to ensure they match the electrical system requirements.
   
2. Hydraulic System Pressure Ratings: Solenoids controlling hydraulic fluid must be rated for the pressure in the system. The EX120 and EX150 operate at hydraulic pressures up to 350 bar (5000 psi), so any replacement solenoid must be able to handle this pressure to prevent failure or malfunction. It is vital to select solenoids that match the pressure rating of the excavator's hydraulic system.
   
3. Connector Types: Sensors and solenoids may have different types of connectors, such as weatherproof connectors or specialized fittings designed for specific hydraulic or electrical systems. Ensuring the proper connector type is essential for proper installation and operation.
   
4. Calibration and Software Integration: In modern excavators like the EX120 and EX150, sensors and solenoids are often calibrated and integrated with the machine’s control software. If replacing a sensor or solenoid, it may be necessary to recalibrate or reset the system to ensure the new components are recognized correctly by the machine’s control unit (ECU).
   

Common Issues with Sensors and Solenoids in Hitachi Excavators
Over time, components like sensors and solenoids may experience wear or failure. Recognizing these issues early can prevent costly repairs and downtime. Here are some common sensor and solenoid-related issues in the EX120 and EX150:

1. Sensor Failure: Sensors can fail due to dirt, moisture, or internal component wear. Common signs of sensor failure include:
   • Engine misfires or poor fuel efficiency (fuel flow sensor failure).
     
   • Hydraulic system performance issues (hydraulic pressure sensor failure).
     
   • Warning lights or diagnostic codes on the control panel.
     
   Solution: Replace faulty sensors with OEM (original equipment manufacturer) parts. It’s also important to clean sensor connectors and ensure they are properly sealed to prevent moisture ingress.
   
2. Solenoid Malfunctions: Solenoids may become clogged with dirt or debris, or the internal coil may burn out due to electrical overload. Symptoms of solenoid failure include:
   • Jerky or erratic movements of the boom, arm, or bucket.
     
   • Failure to change gears or operate the hydraulic system smoothly.
     
   • Hydraulic fluid leaks from solenoid valves.
     
   Solution: Clean or replace the solenoid valves. If the solenoid is electrically faulty, it may require replacement. Be sure to use solenoids that are rated for the specific model of excavator and hydraulic pressure.
   
3. Electrical Connector Issues: Corrosion or poor connection in the electrical connectors for sensors and solenoids can lead to intermittent or complete loss of functionality. This can cause inaccurate readings or a failure to control hydraulic movements.
   Solution: Inspect and clean connectors regularly, replacing any damaged wiring or connectors. Use dielectric grease to prevent corrosion and ensure a stable connection.
   

Replacement and Compatibility Tips

1. OEM Parts: Always try to source original parts from the manufacturer. OEM sensors and solenoids are designed to match the specifications of the machine and provide the best performance and longevity.
   
2. Consult the Manual: Refer to the operator's manual for your specific model to identify the correct part numbers for sensors and solenoids. This will ensure compatibility with the excavator’s hydraulic and electrical systems.
   
3. Consider Aftermarket Options: While OEM parts are often the best choice, high-quality aftermarket components can be a viable alternative. However, ensure that aftermarket parts meet the same specifications and performance standards as OEM components.
   

Conclusion
Sensors and solenoids play a crucial role in the operation of Hitachi EX120 and EX150 excavators, and ensuring compatibility is essential for maintaining optimal machine performance. By understanding the electrical and hydraulic specifications, checking connectors, and regularly maintaining these components, operators can avoid costly repairs and ensure that their equipment runs smoothly. Whether replacing a sensor due to failure or upgrading solenoids for better efficiency, proper troubleshooting and correct part selection are key to keeping these powerful machines at peak performance.