Troubleshooting High Hydraulic Pressure Issues on the John Deere 790E

[MikePhua]

The John Deere 790E is a versatile and reliable tractor that relies on its hydraulic system to power attachments, lift arms, and other essential functions. However, like all machinery, the 790E’s hydraulic system can encounter issues over time, one of the most common being hydraulic pressure staying too high. This problem can lead to inefficient operation, overheating, and even damage to the hydraulic components.
In this article, we will explore why your John Deere 790E hydraulic system may be staying on high pressure, potential causes for this issue, and how to fix it. Whether you’re a professional operator or a DIY enthusiast, understanding these issues will help ensure your equipment continues running smoothly.
Understanding Hydraulic Pressure in Heavy Equipment
Hydraulic systems use pressurized fluid to transfer power within the equipment. In the John Deere 790E, the hydraulic pump generates this pressure, which is then distributed throughout the system to power various components like the loader arms or attachments.
The hydraulic pressure should be maintained within a specific range to ensure the proper functioning of the system. If the system’s pressure remains too high for extended periods, it can cause wear and tear, decreased efficiency, and potential overheating of components. Over time, this can lead to costly repairs and downtime.
Why Hydraulic Pressure Stays High on the John Deere 790E
There are several potential causes for high hydraulic pressure in the system. Let’s take a look at the most common issues:

1. Faulty Pressure Relief Valve
   The pressure relief valve is a crucial component in regulating the hydraulic pressure. If the valve becomes stuck or malfunctions, it may not release pressure when needed, causing the system to remain at high pressure. This is often the most common cause of high pressure in hydraulic systems.
   How to Fix:
   • Inspect the pressure relief valve for any signs of wear or debris.
     
   • Clean or replace the valve if necessary.
     
   • Test the valve by checking the system pressure with a gauge to ensure it is functioning correctly.
     
2. Clogged or Dirty Hydraulic Filters
   A clogged hydraulic filter can restrict the flow of hydraulic fluid, causing the pump to work harder and maintain higher pressure than normal. If the filter is not replaced regularly, dirt and debris can accumulate, leading to performance issues and even pump failure.
   How to Fix:
   • Replace the hydraulic filters as per the manufacturer’s recommended intervals.
     
   • Inspect the filter for any visible blockages and clean the area around it before installing a new one.
     
3. Sticking or Faulty Hydraulic Valve
   The hydraulic control valve manages the direction and flow of fluid in the system. If a valve becomes stuck in the closed position or develops internal leaks, it can cause excessive pressure buildup. This can occur if the valve is damaged or not properly maintained.
   How to Fix:
   • Inspect the hydraulic control valve for any signs of wear or damage.
     
   • If necessary, disassemble and clean the valve, or replace it entirely if it’s beyond repair.
     
4. Incorrect Fluid Levels or Viscosity
   Low hydraulic fluid levels can cause the pump to work harder, trying to compensate for the reduced fluid volume. On the other hand, if the fluid is too thick (high viscosity), it may not flow properly through the system, resulting in higher pressure. It’s essential to ensure the hydraulic fluid is at the correct level and has the appropriate viscosity for your climate and operating conditions.
   How to Fix:
   • Check the fluid levels and top up as necessary using the recommended fluid type.
     
   • Test the fluid’s viscosity, and if it appears thick or contaminated, replace it with fresh hydraulic fluid.
     
5. Pump Issues
   The hydraulic pump could be another culprit when dealing with high pressure. A failing pump may cause excessive pressure to build up in the system. In some cases, an internal fault in the pump could cause it to pump more fluid than the system can handle, leading to high pressure.
   How to Fix:
   • Inspect the pump for signs of wear or damage.
     
   • If the pump is faulty, consider replacing it with a new or refurbished pump.
     
6. Hydraulic Hose Blockages
   Blockages or restrictions in the hydraulic hoses can also cause high pressure. If a hose is pinched, kinked, or internally damaged, it can restrict fluid flow, leading to pressure buildup in the system.
   How to Fix:
   • Inspect all hydraulic hoses for signs of damage or blockages.
     
   • Replace any damaged hoses, and ensure there are no kinks or twists that could impede fluid flow.
     

How to Diagnose High Hydraulic Pressure Issues
Diagnosing high hydraulic pressure issues on the John Deere 790E is relatively straightforward with the right tools and a systematic approach. Here are a few steps you can follow:

1. Check Pressure Readings
   The first step in diagnosing high pressure is to check the system’s pressure using a pressure gauge. This will give you a direct reading of the hydraulic system's pressure, allowing you to determine if it’s above normal operating levels.
   
2. Inspect the Pressure Relief Valve
   If the system is showing consistently high pressure, the next step is to check the pressure relief valve. Using a manual or automatic tester, you can check if the valve is operating at the correct pressure.
   
3. Check for Leaks or Clogs
   Check for any leaks, particularly around the pump, hoses, or control valves. Leaks may indicate worn seals or fittings that could be contributing to the issue. Additionally, ensure that the hydraulic filter is clean and free from blockages.
   
4. Monitor System Behavior
   Run the equipment under normal operating conditions and observe how the hydraulic system behaves. Look for signs of overheating, unusual noises, or a reduction in hydraulic power, which may indicate that the system is under excessive pressure.
   

Real-World Example: Hydraulic Pressure Issues on the Job
A contractor working with a fleet of John Deere 790E dozers shared a story where high hydraulic pressure caused a significant delay on the job site. The issue was traced back to a faulty pressure relief valve that failed to release excess pressure, causing the system to overheat and reduce efficiency. Once the valve was replaced, the dozer was back to full performance, and the contractor emphasized the importance of regular maintenance on hydraulic systems to avoid unexpected breakdowns.
This experience highlights how simple issues, such as a malfunctioning pressure relief valve, can lead to significant downtime and costly repairs if not caught early.
Preventing High Hydraulic Pressure in the Future
To avoid high hydraulic pressure issues in the future, consider the following preventative measures:

1. Regular Maintenance
   Perform routine checks on your hydraulic system, including fluid levels, filters, and the condition of the pressure relief valve. Following the manufacturer’s maintenance schedule can help prevent issues before they arise.
   
2. Proper Fluid Management
   Ensure the hydraulic fluid is kept at the proper levels and replaced regularly. Use the right fluid type for your operating conditions, and avoid mixing different types of fluid, which can affect performance.
   
3. Regular Inspections
   Regularly inspect hydraulic hoses, pumps, and control valves for signs of wear, damage, or leaks. Catching small issues early can prevent them from escalating into larger, more costly problems.
   
4. Operator Training
   Educate operators on the importance of maintaining hydraulic pressure and avoiding operating the machine under extreme conditions that could cause excessive strain on the hydraulic system.
   

Conclusion
High hydraulic pressure on the John Deere 790E is a common issue that can cause a variety of operational problems, from overheating to equipment damage. By understanding the potential causes of this issue—such as faulty relief valves, clogged filters, or incorrect fluid levels—you can troubleshoot and fix the problem effectively. Regular maintenance, proper fluid management, and routine inspections will go a long way in preventing high hydraulic pressure issues and keeping your equipment running smoothly.