Troubleshooting Screw-Type Air Compressor Problems: In-Depth and Practical

[MikePhua]

Understanding How Screw Compressors Work
A rotary screw compressor uses two intermeshing rotors—usually male and female—to compress air continuously. Oil is often injected for lubrication, sealing, and cooling, then separated out via an oil-gas separator and recirculated. This design enables smooth, consistent air delivery under high demand.
Key Terminology

• Inlet (unloader) valve: Controls whether air is inducted and compressed or whether the compressor idles without producing air.
  
• Oil-gas separator: Component that separates lubricating oil from compressed air.
  
• Relief valve: Protects the compressor by releasing excess pressure.
  
• Solenoid valve: Electrically actuated valve that manages air or control circuits.
  
• Overload relay: Electrical protection device that trips when excessive current is drawn.
  
• Thermostatic valve: Regulates oil temperature and keeps flow optimal.
  

Common Fault Types, Causes & Solutions
Starting Issues or No Air Output

• Causes:
  • Power supply failure, tripped breaker, or an engaged emergency stop .
    
  • Inlet valve (unloader) incorrectly positioned or malfunctioning .
    
  • Slide valve not at zero setting, causing high resistance at startup .
    
• Solutions:
  • Verify power supply, reset breakers, and ensure safety switches are disengaged.
    
  • Manually rotate compressor to drain oil accumulation.
    
  • Check and reset inlet/unloader valve position or solenoid control .
    
  • Position the slide valve correctly before startup.
    

Insufficient Airflow or Low Pressure

• Causes:
  • Air leaks in piping or fittings reduce effective pressure.
    
  • Clogged intake filters or clogged air/gas separator .
    
  • Compressor not loading due to solenoid control failure .
    
• Solutions:
  • Listen for hissing or test connections with soapy water to locate leaks.
    
  • Inspect and clean or replace intake filters and oil separator elements.
    
  • Check solenoid operation and ensure correct control-air supply to inlet valve.
    

Compressor Overheating or High Operating Temperature

• Causes:
  • Blocked or dirty oil cooler or after-cooler.
    
  • Insufficient lubrication due to low oil levels or wrong oil grade .
    
  • Thermostatic valve failure preventing proper mixing of hot and cool oil.
    
• Solutions:
  • Clean cooling fins, ensure good ventilation around the unit.
    
  • Maintain proper oil levels with correct grade.
    
  • Replace or repair clogged thermostatic valves and clean or replace oil filters and coolers.
    

Motor Overloads or Frequent Tripping

• Causes:
  • Excessive starting current from inadequate voltage or repeated cycling.
    
  • Relief valve set improperly or controller misconfiguration leading to continuous high pressure.
    
  • High back-pressure in systems with multiple compressors.
    
• Solutions:
  • Monitor current draw using a clamp meter; inspect the power supply for voltage dips .
    
  • Adjust or replace relief valve if motor is undersized.
    
  • Confirm proper staging of parallel compressors and equalize discharge pressures .
    

Vibration, Noise, or Unusual Sounds

• Causes:
  • Loose mounting bolts or misalignment between motor and compressor.
    
  • Worn internal components such as bearings or rotor clearance issues .
    
• Solutions:
  • Tighten mounting and align drive systems precisely.
    
  • Inspect internal components if noise persists—disassemble and replace bearings or rotors if clearance has increased beyond specification.
    

Oil in Discharge Air or Excessive Oil Consumption

• Causes:
  • Saturated or failing oil separator.
    
  • Blocked scavenge lines or excessive oil level leading to carryover .
    
• Solutions:
  • Replace oil separator and filters.
    
  • Clear or replace blocked scavenge lines.
    
  • Adjust oil level to within manufacturer’s recommended range.
    

Real-World Mini-Story: Downtime Avoided
A small fabrication shop noticed its screw compressor was cycling unusually fast but not responding when isolated. Following advice from industrial diagnostics, the operator closed the line after the compressor; it continued building pressure until unloading—indicating demand, not fault. Only after closing the larger facility load was the root cause traced—uneven inlet valve actuation and a worn solenoid. A quick valve replacement restored proper load-unload cycling, saving hundreds in downtime and avoiding unnecessary repair.

Practical Maintenance and Troubleshooting Checklist

• Daily checks:
  • Oil level, visible leaks, and listening for unusual noise.
    
• Weekly tasks:
  • Inspect filters, solenoids, and valve functioning.
    
• Monthly tasks:
  • Clean coolers and heat exchangers; test safety devices.
    
• Quarterly or as-needed:
  • Perform vibration analysis and use thermal imaging to detect hotspots .
    
  • Check current draw patterns and electrical connection integrity.
    

Key Parameter Snapshot

• Startup condition: Slide valve at zero, inlet valve ready.
  
• Air output: Full pressure only when loading.
  
• Temperature: Monitor oil and air temps; aim within spec.
  
• Electrical current: Should stay within motor rating except startup.
  
• Oil quality & level: Always maintained per manufacturer’s intervals.
  

Closing Thoughts
A screw-type compressor is robust and efficient—but thermal, filtering, control, or electrical faults can cause subtle or drastic breakdowns. By methodically diagnosing each subsystem—power, valves, filters, lubrication, cooling—you can often prevent unplanned downtime and expensive repairs. A logical, condition-based approach ensures the compressor stays productive, safe, and long-lived.