Understanding Charge Pressure in Bobcat 732 Skid Steer Loaders

[MikePhua]

Introduction
The Bobcat 732 Skid Steer Loader, produced between 1978 and 1981, is a compact and versatile machine widely used in construction and landscaping. One critical aspect of its hydraulic system is the charge pressure, which ensures the proper functioning of the hydrostatic transmission (HST) and other hydraulic components. Maintaining the correct charge pressure is essential for optimal performance and longevity of the machine.
What is Charge Pressure?
Charge pressure refers to the hydraulic pressure supplied by the charge pump to the hydrostatic transmission system. This pressure is vital for lubricating the hydrostatic pump and motor, as well as for releasing the brakes in the drive motors. Insufficient charge pressure can lead to erratic machine behavior, reduced performance, and potential damage to the hydraulic components.
Charge Pressure Specifications for Bobcat 732
For the Bobcat 732, the charge pressure relief valve is set to operate between 85 to 115 PSI, depending on the type of pump used (vane or gear). The charge pressure switch is designed to activate the warning light when the pressure drops below 40 PSI. Operators should monitor the charge pressure regularly to ensure it remains within the specified range.
Symptoms of Low Charge Pressure
Operators may notice several symptoms indicating low charge pressure:

• Activation of the hydraulic warning light shortly after starting the machine.
  
• Erratic or unresponsive movement of the loader arms or drive motors.
  
• Increased engine RPM without corresponding hydraulic response.
  
• Unusual noises from the hydraulic system.
  

Troubleshooting Low Charge Pressure
If low charge pressure is suspected, consider the following steps:

1. Check Hydraulic Fluid Levels and Quality: Ensure the hydraulic reservoir is filled to the recommended level with clean, high-quality fluid. Contaminated or degraded fluid can impair system performance.
   
2. Inspect the Charge Pressure Switch: The charge pressure switch may be faulty or inaccurate. Testing the system with a calibrated gauge can help determine if the switch is providing correct readings.
   
3. Examine the Charge Pump: A worn or damaged charge pump can fail to generate adequate pressure. Inspecting and replacing the pump, if necessary, can restore proper function.
   
4. Check for Hydraulic Leaks: Leaks in the hydraulic lines or components can cause a drop in pressure. Inspecting the system for leaks and repairing them promptly is crucial.
   
5. Verify the Relief Valve Setting: The relief valve should be set to the manufacturer's specifications. An improperly set valve can lead to incorrect pressure levels.
   

Maintenance Tips
To maintain optimal charge pressure:

• Regularly Change Hydraulic Filters: Clogged filters can restrict fluid flow and reduce pressure. Replace filters at intervals recommended by the manufacturer.
  
• Use the Correct Hydraulic Fluid: Always use the hydraulic fluid specified in the operator's manual to ensure compatibility and performance.
  
• Monitor System Performance: Regularly check for any signs of hydraulic issues and address them promptly to prevent further damage.
  

Conclusion
Maintaining the correct charge pressure in the Bobcat 732 Skid Steer Loader is essential for its performance and longevity. By understanding the importance of charge pressure and following proper maintenance and troubleshooting procedures, operators can ensure their machines operate efficiently and reliably.