Troubleshooting Komatsu PC55 Hydraulic Pump Staying Stroked at Start-Up

[MikePhua]

The Komatsu PC55 is a versatile and reliable mini-excavator that is widely used in construction, landscaping, and other industries requiring compact and powerful machinery. However, like any complex hydraulic system, issues can arise over time, and one common problem that operators may face is a hydraulic pump that stays stroked at start-up.
This issue, if left unresolved, can lead to poor performance, excessive wear, or even severe damage to the hydraulic system. In this article, we’ll explore the possible causes of this issue, solutions to address it, and some important considerations for preventing future hydraulic pump problems in the Komatsu PC55.
Understanding the Hydraulic Pump and System
The hydraulic pump in the Komatsu PC55 plays a crucial role in powering the hydraulic system. It draws fluid from the reservoir and sends it under high pressure to the hydraulic components, such as cylinders and motors, that drive the machine’s various functions—boom, arm, bucket, and swing. The pump must operate smoothly and efficiently to ensure precise and responsive control.
When a hydraulic pump "stays stroked" at start-up, it means that the pump’s internal components are not returning to their neutral position as expected. This can cause several issues, including:

• Loss of hydraulic pressure and function
  
• Erratic movement of hydraulic components
  
• Increased wear and risk of further damage to the system
  

What Does "Staying Stroked" Mean?
"Staying stroked" refers to the hydraulic pump failing to return to its neutral position after being engaged. Typically, a hydraulic pump has a stroke control mechanism that ensures the internal components return to neutral when not in operation. If the pump fails to return to its neutral stroke position, the pump continues to circulate hydraulic fluid even when the machine is not in use, which can lead to several operational and mechanical problems.
Common Causes of Hydraulic Pump Staying Stroked
Several factors could be causing the Komatsu PC55 hydraulic pump to stay stroked at start-up, even after installing a new pump. Let’s explore the most common causes and potential solutions:
1. Faulty or Improperly Adjusted Pump Relief Valve
The relief valve plays an essential role in regulating the pressure within the hydraulic system. If the relief valve is faulty, improperly adjusted, or clogged, it may cause excessive pressure in the system, leading to the pump being unable to return to its neutral position.

• Symptoms:
  • Hydraulic pump stays stroked after start-up.
    
  • High pressure readings or erratic movement in hydraulic functions.
    
• Solution:
  • Check the relief valve settings and ensure they are correctly calibrated.
    
  • Replace a worn-out or faulty relief valve.
    
  • Clean or replace any clogged valves to allow for proper flow regulation.
    

2. Air in the Hydraulic System
Air trapped within the hydraulic system can cause cavitation and irregular behavior in hydraulic components. If air is present in the lines or the pump, it can result in the pump staying stroked and causing performance issues.

• Symptoms:
  • Unstable hydraulic pressure.
    
  • Jerky or inconsistent movements in the machine’s functions.
    
  • Difficulty in building up pressure.
    
• Solution:
  • Bleed the hydraulic system to remove any trapped air.
    
  • Ensure that all hydraulic lines and connections are airtight to prevent further air intake.
    

3. Contaminated Hydraulic Fluid
Contaminants such as dirt, debris, or water in the hydraulic fluid can severely affect the performance of the pump and other hydraulic components. Contaminated fluid can cause pump failure, internal damage, or cause the pump to stay stroked due to improper lubrication.

• Symptoms:
  • Hydraulic fluid looks cloudy or contains visible particles.
    
  • Increased pump noise or vibrations.
    
  • Sluggish or inconsistent hydraulic performance.
    
• Solution:
  • Perform a hydraulic fluid flush and replace the contaminated fluid with clean, high-quality hydraulic oil that meets Komatsu’s specifications.
    
  • Check and replace the hydraulic filter if it’s clogged or worn.
    

4. Hydraulic Pump Inlet Blockage
A blockage in the pump inlet can prevent the pump from receiving adequate fluid flow, causing it to stay stroked. This could be due to a clogged suction filter or debris in the lines.

• Symptoms:
  • Slow or weak hydraulic function.
    
  • Hydraulic pump noise or vibration at start-up.
    
• Solution:
  • Inspect the pump inlet for blockages and clean or replace the suction filter if necessary.
    
  • Ensure the hydraulic lines leading to the pump are free from obstructions.
    

5. Faulty Pressure Sensors or Valves
The pressure sensors in the Komatsu PC55 relay information to the control system regarding the hydraulic pressure. If these sensors are malfunctioning, they may not properly control the pump’s behavior, causing the pump to stay stroked.

• Symptoms:
  • Erratic hydraulic pressure readings.
    
  • Faulty or inaccurate performance readings from the machine.
    
• Solution:
  • Inspect the pressure sensors and valves for damage or malfunction.
    
  • Replace any faulty sensors and recalibrate the system if necessary.
    

6. Incorrect Pump Installation or Incompatible Parts
If the new pump is not installed correctly or is not compatible with the Komatsu PC55, it may continue to operate incorrectly, even after installation. Issues can include improper pump mounting or incorrect connections.

• Symptoms:
  • The new pump operates similarly to the old one, failing to fix the issue.
    
  • The hydraulic system still struggles with the same performance issues.
    
• Solution:
  • Double-check the installation of the new pump to ensure all connections are secure and compatible with the existing hydraulic system.
    
  • Refer to the Komatsu service manual for the correct pump installation procedure.
    

Step-by-Step Troubleshooting
To address the issue of the hydraulic pump staying stroked, it’s important to follow a systematic troubleshooting approach. Here’s a step-by-step guide to help diagnose the root cause:

1. Inspect Fluid Levels:
   • Ensure that the hydraulic fluid levels are within the recommended range. Low fluid levels can lead to air entering the system, causing irregularities.
     
2. Check Hydraulic Fluid Quality:
   • Examine the condition of the hydraulic fluid. If it appears dirty, cloudy, or contaminated, perform a fluid flush and replace the fluid with the correct type.
     
3. Test the Relief Valve:
   • Check the relief valve for proper operation. If it’s faulty or improperly adjusted, it can cause excessive pressure, preventing the pump from returning to its neutral position.
     
4. Bleed the System:
   • If air is suspected to be in the system, bleed the hydraulic system thoroughly to remove any trapped air.
     
5. Inspect the Pump Inlet:
   • Ensure that the pump inlet is free from debris and that the suction filter is clean and functioning.
     
6. Check Pressure Sensors and Valves:
   • Test the pressure sensors and valves for accuracy and proper function. Replace any faulty components.
     
7. Verify Pump Installation:
   • Confirm that the newly installed pump is correctly fitted and compatible with the Komatsu PC55. Ensure all connections are secure.
     

Conclusion
Hydraulic pump issues in the Komatsu PC55 can lead to significant operational disruptions if not addressed promptly. A pump that stays stroked at start-up is typically a sign of underlying issues such as faulty relief valves, air in the system, or contaminated fluid. By following a detailed troubleshooting process, operators can identify the root cause of the problem and implement the necessary solutions.
Regular maintenance, including monitoring fluid levels, inspecting filters, and performing hydraulic system flushes, can go a long way in preventing these issues from occurring in the first place. If the issue persists despite troubleshooting, it may be necessary to consult with a certified Komatsu technician for further assistance.
By taking care of your hydraulic system, you ensure the longevity and reliable performance of your Komatsu PC55, reducing downtime and maximizing productivity on the job site.