Recently, EPSEA service engineers handled a hidden fault at a packaging materials plant. A 150HP-5 screw air compressor had been experiencing continuous oil level loss for a long time. However, key parameters such as operating pressure and discharge temperature remained normal. The oil return line was clear, there was no obvious oil accumulation inside the oil separator, and no differential pressure alarm had been triggered. The customer initially suspected the oil separator and replaced it with different brands several times, but the problem remained. The real cause, however, was not the oil separator.

1. On-Site Inspection: An Unusual Heat Source Reveals the Clue

2. Root Cause: A Failed Seal Created a Hidden Bypass

The differential pressure switch is designed to monitor the pressure difference across the oil separator filter element and does not normally carry the main airflow. However, when its internal seal deteriorates or fails, the switch can become a hidden bypass path. High-temperature oil-laden air can pass directly through the switch, bypassing the oil separator and entering the clean-air side. As a result, lubricating oil is continuously carried away by the high-speed airflow, effectively bypassing the oil separation process. This explains why the oil level kept dropping even though conventional inspection items appeared normal.

3. Solution: Eliminate the Bypass Path

After identifying the fault, the engineer removed the failed differential pressure switch and securely plugged the two interfaces on the oil drum.This completely eliminated the hidden bypass path. The compressor was then monitored for 30 days. The oil level remained stable, the condensate from the air receiver returned to a clear condition, and no further oil contamination occurred in the customer's downstream equipment. The problem was completely resolved.

4. Technical Takeaway: Hidden Faults Require a Systematic Approach

This case shows that normal parameters do not always mean a healthy system. Any pipe, valve, or component connecting the upstream and downstream sides of an oil separator should be considered during troubleshooting. A differential pressure alarm not being triggered does not necessarily mean the switch seal is intact, and abnormal oil consumption does not always indicate an oil separator quality issue. Effective maintenance requires a systematic approach and thorough troubleshooting. EPSEA air compressor filters are rigorously tested for filtration accuracy, sealing performance, and real-world operating conditions. With 45 branches worldwide, our professional service teams provide efficient support before, during, and after sales, helping customers identify and eliminate hidden risks in their compressed air systems. Proper selection and systematic maintenance are essential to keeping compressed air systems stable and reliable over the long term.