Bobcat 722 Skid Steer with Low Charge Pressure: Causes, Diagnosis, and Repair

[MikePhua]

Introduction to Low Charge Pressure Issues
The Bobcat 722 skid steer loader, a popular machine for versatile construction tasks, relies on its hydraulic system to deliver reliable power for lifting, digging, and maneuvering. Low charge pressure within the hydraulic system is a critical problem that can result in poor machine performance, sluggish operation, and potential damage to components if left unresolved.
Understanding Hydraulic Charge Pressure

• Definition: Charge pressure refers to the hydraulic pressure supplied to the pump inlet, ensuring adequate fluid flow and preventing cavitation (formation of vapor bubbles) in the hydraulic pump.
  
• Importance: Proper charge pressure maintains hydraulic fluid volume and pressure, which are vital for smooth operation of hydraulic functions.
  
• Symptoms of Low Charge Pressure: Reduced lift speed, sluggish controls, overheating, abnormal noises, and sometimes error codes or warning lights.
  

Common Causes of Low Charge Pressure in Bobcat 722

• Worn or Damaged Charge Pump: The small pump supplying charge pressure can wear out, reducing output pressure.
  
• Leaking or Blocked Charge Lines: Damaged hoses, fittings, or clogged filters restrict fluid flow.
  
• Faulty Charge Relief Valve: A malfunctioning relief valve can vent pressure prematurely, lowering system charge pressure.
  
• Air Intrusion in Hydraulic System: Air bubbles cause pressure fluctuations and reduce effective fluid delivery.
  
• Low Hydraulic Fluid Level: Insufficient fluid compromises charge pressure and overall hydraulic performance.
  
• Contaminated Hydraulic Fluid: Dirt or water contamination affects pump and valve function.
  

Diagnostic Procedures for Low Charge Pressure

• Visual Inspection: Check hydraulic fluid levels, hoses, fittings, and filters for leaks or damage.
  
• Pressure Testing: Use hydraulic gauges to measure charge pressure at pump inlet and compare against specifications.
  
• Pump Testing: Evaluate charge pump operation by monitoring output flow and pressure under load.
  
• Valve Inspection: Test relief valve for correct opening pressure and function.
  
• Air Bleeding: Inspect and purge air from hydraulic system to ensure proper fluid flow.
  
• Fluid Analysis: Test fluid condition for contamination or degradation.
  

Effective Repair and Maintenance Actions

• Replace worn or faulty charge pumps with genuine Bobcat parts for reliability.
  
• Repair or replace leaking hoses, fittings, and clogged filters to restore fluid flow.
  
• Adjust, repair, or replace malfunctioning relief valves to maintain correct pressure.
  
• Conduct thorough air bleeding procedures after repairs to prevent cavitation.
  
• Maintain hydraulic fluid levels and perform scheduled fluid changes using manufacturer-approved fluids.
  
• Regularly inspect the hydraulic system for early signs of wear or contamination.
  

Case Example: Restoring Charge Pressure in a Bobcat 722
An owner experienced sluggish hydraulic response and unusual whining noises from the Bobcat 722 hydraulic pump. Upon inspection, the charge pump showed significant wear and the charge relief valve was sticking intermittently. Replacement of the charge pump and servicing the relief valve restored normal charge pressure, improving machine responsiveness and reducing noise.
Industry Insights and Preventive Practices
Low charge pressure issues are common in aging skid steers or machines with heavy usage. Preventive maintenance focusing on hydraulic fluid cleanliness, timely filter replacement, and routine system inspections extends component life and prevents performance losses. Operator awareness of early symptoms allows prompt intervention, minimizing downtime.
Summary of Key Points

• Charge pressure is critical for hydraulic pump health and machine performance.
  
• Common causes include worn pumps, leaks, faulty valves, air intrusion, and low fluid levels.
  
• Diagnosis involves visual checks, pressure testing, and system bleeding.
  
• Repairs focus on replacing worn components and maintaining fluid integrity.
  
• Preventive maintenance is key to avoiding charge pressure-related failures.
  

Conclusion: Ensuring Optimal Hydraulic Performance in Bobcat 722
Understanding the causes and solutions for low charge pressure empowers operators and technicians to maintain the Bobcat 722’s hydraulic system effectively. With proper diagnostics, repairs, and proactive maintenance, this skid steer can deliver reliable power and precision for diverse applications, minimizing costly repairs and maximizing operational uptime.