Adjusting the Relief Valve on a Yanmar 1035-6A Excavator: A Detailed Guide

[MikePhua]

Introduction to the Yanmar 1035-6A Relief Valve Adjustment
The Yanmar 1035-6A is a popular mini excavator model widely used in compact construction and landscaping projects. Key to its hydraulic system's proper function is the relief valve, which protects the hydraulic circuits by limiting maximum pressure, preventing damage to pumps, hoses, and hydraulic components.
Adjusting the relief valve correctly ensures the excavator operates safely within pressure specifications, maximizes efficiency, and prolongs component life. This guide provides a detailed walkthrough on locating, inspecting, and adjusting the relief valve specific to the Yanmar 1035-6A, enriched with practical advice, technical explanations, and maintenance recommendations.

Understanding Hydraulic Relief Valves

• Function: Relief valves act as safety devices in hydraulic systems, designed to open and divert excess hydraulic fluid flow when pressure exceeds preset limits. This prevents overpressure situations that can cause leaks or catastrophic failures.
  
• Location: Typically found on or near the hydraulic pump assembly or integrated within control valve manifolds.
  
• Adjustability: Most relief valves include an adjustable screw and locking nut, allowing technicians to set the pressure limit according to manufacturer specifications or operational needs.
  
• Pressure Setting: Specified in pounds per square inch (PSI) or bar units; keeping the setting precise is critical for system protection and optimal hydraulic performance.
  

Locating and Identifying the Relief Valve on the Yanmar 1035-6A

• The relief valve on the Yanmar 1035-6A is usually part of the main hydraulic control valve or mounted directly on the pump housing.
  
• It appears as a small cylindrical component roughly 3-4 inches long, with an adjustment screw and locknut (jam nut) to secure settings.
  
• Some models may have multiple relief valves for different hydraulic circuits, such as the PTO (Power Take-Off) or auxiliary functions, so confirm the specific valve to adjust.
  

Tools and Safety Precautions

• Tools Needed:
  • A set of wrenches, typically including a 19mm wrench for locknuts.
    
  • A 4mm Allen key (hex wrench) or similar for holding the adjustment screw.
    
  • Pressure gauge capable of reading up to approximately 3,000 PSI connected to the hydraulic system to monitor pressure accurately.
    
  • Safety equipment including gloves and eye protection.
    
• Safety Tips:
  • Perform adjustments on a stable, flat surface with the engine off when installing or loosening components.
    
  • Avoid sudden engine starts or movements during adjustment.
    
  • Never exceed pressure specifications provided by the manufacturer.
    
  • Be cautious as hydraulic fluid under pressure can cause serious injury.
    

Step-by-Step Relief Valve Adjustment Procedure

1. Prepare the Machine:
   • Park the excavator on level ground.
     
   • Turn off the engine and relieve hydraulic pressure by cycling hydraulic functions a few times with the engine off.
     
   • Remove covers or panels needed for clear access to the control valve and relief valve assembly.
     
2. Attach the Pressure Gauge:
   • Connect the pressure gauge to the pressure port or test port on the hydraulic line feeding the circuit serviced by the relief valve.
     
   • Ensure tight, leak-free connections to obtain accurate readings.
     
3. Loosen the Locknut:
   • Using the appropriate wrench, carefully loosen the locknut securing the relief valve adjustment screw.
     
   • Hold the adjustment screw steady with the Allen key to prevent it from turning unintentionally.
     
4. Start the Engine and Engage Hydraulic Function:
   • Start the engine and gently operate the hydraulic function (such as the boom or auxiliary PTO circuit) related to the valve being adjusted.
     
   • Monitor the pressure gauge as you do so.
     
5. Adjust the Relief Pressure:
   • Turn the adjustment screw clockwise to increase relief pressure.
     
   • Turn counterclockwise to decrease pressure.
     
   • Make small incremental turns (e.g., 1/8 turn), waiting briefly between adjustments for pressure to stabilize.
     
   • Reference the Yanmar 1035-6A service manual or attachment specifications for recommended pressure settings, typically around 2,200 to 2,300 PSI for PTO circuits, but verify exact numbers.
     
6. Secure the Setting:
   • Once the desired pressure is reached, hold the adjustment screw in place and tighten the locknut firmly without changing the screw position.
     
   • Recheck pressure to confirm stability.
     
7. Finalize and Test:
   • Turn off the engine.
     
   • Remove pressure gauge and replace any access covers.
     
   • Restart the machine and perform hydraulic function tests to confirm normal operation without unusual noises or leaks.
     
   • Observe system behavior during a full range of movement.
     

Additional Tips and Troubleshooting

• Use a pressure gauge with fine resolution to accurately observe small changes in pressure.
  
• If pressure cannot be adjusted to specification or fluctuates widely, inspect the valve and hydraulic pump for wear or internal damage.
  
• Contaminated or aerated hydraulic fluid can cause inaccurate gauge readings—ensure fluid cleanliness.
  
• Keep detailed records of pressure settings and maintenance performed.
  
• In some cases, consulting or hiring a hydraulic specialist may be advisable when complex issues arise.
  

Terminology Explained

• Relief Valve: A valve that opens to relieve excess pressure in a hydraulic circuit.
  
• Locknut (Jam Nut): A nut used to lock the adjustment screw in place to prevent unintentional movement.
  
• Pressure Gauge/Test Port: Instruments and connections used to measure hydraulic pressure.
  
• PTO (Power Take-Off): A hydraulic circuit or shaft used to power auxiliary equipment.
  
• Hydraulic Circuit: The path and components through which hydraulic fluid flows to operate machinery parts.
  

Real-World Example
A landscaping contractor using a Yanmar 1035-6A with a hydraulic breaker attachment noted inconsistent breaker performance. After pressure measurement revealed a relief valve setting slightly below specifications, an adjustment following the outlined procedure increased hydraulic pressure to the optimum PSI, restoring breaker efficiency and reducing cycle times. This improvement demonstrated the critical nature of relief valve calibration for attachment performance.
In another case, a technician found the relief valve locknut on an excavator had loosened after extended use, causing pressure fluctuations and erratic hydraulic behavior. Tightening the locknut per manufacturer torque specs resolved the problem, emphasizing routine inspection importance.

Summary
Adjusting the relief valve on the Yanmar 1035-6A excavator is a vital maintenance task to ensure proper hydraulic system pressure and machine performance. With the right tools, safety practices, and careful adherence to manufacturer specifications, operators and technicians can fine-tune relief valves to optimize hydraulic functions and prevent undue wear or damage.
Key steps include locating the valve, attaching a pressure gauge, loosening the locknut, adjusting the screw to the correct pressure, securing the setting, and testing the system. Regular checks and clean hydraulic fluid contribute to reliable operation.
This knowledge empowers users to maintain robust hydraulic systems, prolong equipment life, and enhance productivity on-site.

If further detailed procedures, torque specifications, or hydraulic schematics are needed, consulting the Yanmar 1035-6A service manual or authorized dealer resources is recommended for precise model-specific information.