Causes of Pressure Drop in Oil-Injected Screw Compressors and Effective Solutions
Pressure drop in oil-injected screw compressors is one of the most common operational challenges in compressed air systems. A sustained or sudden pressure loss can significantly reduce system efficiency, increase energy consumption, and negatively affect downstream equipment performance. Understanding the root causes of pressure drop and implementing appropriate corrective actions is essential for maintaining optimal compressor operation.
This article provides a comprehensive and academic analysis of the main causes of pressure drop in screw compressors, along with practical engineering solutions.
What Is Pressure Drop in a Screw Compressor?
Pressure drop refers to the reduction of actual discharge pressure below the designed or required operating pressure of the compressed air system. This phenomenon may occur internally within the compressor or externally in the compressed air distribution network and is often an indicator of mechanical, operational, or design-related issues.
Major Causes of Pressure Drop in Oil-Injected Screw Compressors
1. Clogged or Restricted Inlet Air Filter
The inlet air filter supplies clean atmospheric air to the airend. When the filter becomes clogged:
Solution:
✔ Periodic inspection and replacement of inlet air filters
✔ Use of high-quality filters with low pressure resistance
✔ Monitoring differential pressure across the filter
2. Airend Wear and Internal Leakage
The airend is the core component of a screw compressor. Over time, rotor wear or increased internal clearances lead to internal air leakage, resulting in reduced volumetric efficiency.
Symptoms:
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Gradual pressure reduction
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Elevated discharge temperature
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Reduced air delivery (CFM or m³/min)
Solution:
✔ Routine airend condition monitoring
✔ Timely overhaul or replacement of worn airends
✔ Use of manufacturer-approved compressor oil
3. Air Leaks in the Compressed Air System
Leaks in hoses, fittings, flanges, valves, and joints are among the most frequent causes of pressure loss.
Consequences:
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Reduced pressure at points of use
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Increased compressor runtime
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Higher electricity consumption
Solution:
✔ Regular leak detection using ultrasonic or soap-bubble methods
✔ Replacement of damaged or aged fittings
✔ Proper installation and tightening of all connections
4. Blocked Oil Filter or Oil Separator Element
In oil-injected screw compressors, clogged oil filters or saturated separator elements increase internal resistance and cause pressure losses.
Solution:
✔ Scheduled replacement of oil filters
✔ Replacement of oil separator elements based on operating hours
✔ Use of OEM or high-efficiency separator elements
5. Malfunctioning Minimum Pressure Valve (MPV)
The minimum pressure valve maintains sufficient internal pressure for effective oil separation. If the valve sticks or fails, system pressure may drop significantly.
Solution:
✔ Inspection and functional testing of the MPV
✔ Cleaning or replacement of faulty valves during maintenance
6. Incorrect Pressure Switch Settings or Failure
A faulty or improperly calibrated pressure switch can cause premature unloading of the compressor, resulting in inadequate system pressure.
Solution:
✔ Calibration of pressure switches according to system requirements
✔ Replacement of defective pressure control components
7. Poor Compressed Air Piping Design
Even with a properly functioning compressor, an inefficient piping network can lead to excessive pressure losses.
Common design issues include:
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Undersized pipe diameters
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Excessive pipe length
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Too many bends, elbows, and restrictions
Solution:
✔ Engineering-based compressed air piping design
✔ Selection of appropriate pipe diameters
✔ Minimization of unnecessary fittings and pressure losses
Preventing Pressure Drop in Screw Compressors
✔ Implementation of a preventive maintenance (PM) program
✔ Continuous monitoring of pressure and temperature parameters
✔ Routine inspection of filters, valves, and separators
✔ Regular leak audits in the compressed air system
✔ Optimized compressed air distribution design
Conclusion
Pressure drop in oil-injected screw compressors is a critical issue that directly affects energy efficiency, system reliability, and operational costs. By identifying the underlying causes and applying structured maintenance and design practices, pressure losses can be minimized or completely avoided.
A comprehensive approach that includes compressor health monitoring, proper maintenance, and optimized compressed air system design is essential for achieving long-term operational stability and efficiency.