How to Deal with Excessive Oil Carryover from Screw Air Compressors

Certain special production industries impose strict quality requirements on compressed air discharged by screw air compressors. Textile and food industries, in particular, 

demand extremely low oil content, ideally achieving nearly oil-free compressed air. When oil carryover occurs at the compressor discharge, how should we resolve this fault? Below is an analysis of the main causes:

1. Damaged Oil Separator Element

During operation of the screw air compressor, if the oil separator element suffers damage such as rupture or perforation, it will lose the oil-gas separation function. In other words, 

the oil-air mixture forms a direct passage to the compressor discharge pipeline. A large quantity of oil fails to be separated and is carried out of the machine together with airflow, resulting in oil carryover at the discharge outlet.

2. Faulty Oil Return Pipeline

The oil return pipeline undertakes a critical task during compressor operation. A pressure difference is formed between the interior of the oil separator element and the compressor inlet. 

Driven by this pressure difference, the oil return pipeline transports oil collected at the bottom of the separator element back into the compressor for reuse in the next cycle.

If the oil return line is blocked, fractured or incorrectly installed, accumulated oil at the bottom of the separator cannot be recirculated. Excess oil builds up and gets entrained in the airflow, leading to oil carryover.
3. Excessively Low System Operating Pressure

When system pressure is controlled too low, airflow velocity inside the separator becomes excessively high. This prevents the separator from functioning effectively. 

The air entering the separator element carries excessive oil beyond its separation capacity, causing incomplete oil-gas separation and oil carryover during discharge.

4. Failed Minimum Pressure Valve

The minimum pressure valve ensures that internal system pressure stays above the preset minimum value during operation. If the minimum pressure valve malfunctions, 

the required minimum system pressure cannot be maintained, which triggers oil carryover at the discharge.

5. Overfilled Compressor Lubricating Oil

Before startup, if non-compliant lubricating oil is added, or the oil has exceeded its service life and loses cooling performance, it cannot achieve effective cooling and oil-gas separation during compressor operation. 

Oil carryover at discharge will inevitably occur.

6. Substandard Lubricating Oil Quality

Using unqualified lubricating oil or oil beyond its service life impairs its cooling and separation performance. During screw compressor operation, 

poor-quality oil cannot realize proper oil-gas separation and will lead to oil carryover at the discharge.

Only after identifying the root causes of oil contamination in compressed air can targeted troubleshooting be implemented. Common solutions are listed below:
01. Fault of Damaged Oil Separator Element

Oil separator element damage is a common failure. Equipment inspection must be carried out before startup; operating procedures shall be strictly followed during operation, 

and regular maintenance shall be performed after shutdown.

Replace the separator element immediately once rupture or perforation is found to guarantee stable equipment operation.
02. Malfunction of Oil Return Line

If oil return blockage occurs during operation, first check the pressure differential across the separator. If the pressure differential is normal, 

clean the oil separator element. Replace the element promptly if fracture is detected.

03. System Pressure Too Low
Operators shall be familiar with the rated operating pressure of the unit. Once the fault occurs, reduce system load to bring pressure up to the rated working range.
04. Failure of Minimum Pressure Valve
If the minimum pressure valve fails in service, it must be replaced. Do not resume operation until replacement is completed.
05. Overfilling of Compressor Lubricating Oil
Operators shall confirm the rated oil filling volume before refilling. Dedicated personnel should be assigned for oil addition. Normally, the oil level shall be kept below the middle mark of the sight glass.