How to Solve Oil Carry‑over in Air Compressor Discharge Gas?

In certain special production industries, there are stringent requirements for gas discharged by compressors. Textile and food industries in particular generally demand extremely low oil content in compressed air, ideally achieving oil‑free compressed air. So how should we troubleshoot when oil carry‑over occurs in the discharge of an oil‑free air compressor? Below is an analysis of the main causes for this fault:

1. Damaged oil‑gas separator element During air compressor operation, if the oil‑gas separator element is damaged, such as torn or perforated, it will lose its oil‑gas separation function. That is to say, mixed gas is directly communicated with the compressor exhaust pipeline. A large quantity of cooling oil fails to be separated and is discharged out of the unit together with gas, resulting in oil carry‑over during exhaust.

2. Fault in oil‑return pipeline During equipment operation, the oil‑return pipeline undertakes critical duties. A pressure difference forms between the interior of the oil‑gas separator element and the compressor inlet. Driven by this pressure difference, the oil‑return pipeline transports oil accumulated at the bottom of the oil‑gas separator element back to the compressor for reuse in the next cycle. If the oil‑return circuit suffers blockage, fracture, incorrect installation or other faults, oil collected at the bottom of the separator element cannot be fed back to the compressor. Excessive oil accumulates at the bottom and is discharged along with gas, giving rise to oil carry‑over during exhaust.

3. Excessively low system pressure setting When the compressor is running, if system pressure is controlled too low, the centrifugal force inside the separator will fall below the required operating value. Consequently, the separator cannot perform its full function. The gas entering the separator element at the subsequent stage carries excessive oil beyond its separation capacity, which leads to incomplete oil‑gas separation and oil carry‑over in compressor exhaust.

4. Failure of minimum pressure valve The minimum pressure valve functions to keep system operating pressure above the minimum set pressure. If the minimum pressure valve fails, the minimum system pressure cannot be maintained. As air‑consuming equipment consumes large volumes of air, system pressure drops too low and oil cannot flow back through the oil‑return pipeline. Oil collected at the bottom of the oil‑gas separator element fails to return to the compressor and is discharged together with compressed gas, causing oil carry‑over during exhaust.

5. Excessive cooling oil filled into the compressor If too much cooling oil is added before compressor startup and exceeds the specified range, the oil level will be too high during operation. Even though the separation system separates oil from gas, cooling oil will still be entrained by the gas flow during discharge. This leads to high oil content in outlet gas and oil carry‑over fault.

6. Sub‑standard cooling oil If unqualified cooling oil is filled, or the cooling oil has exceeded its service life and loses cooling performance during compressor operation, effective cooling and separation of oil and gas cannot be realized. Oil carry‑over will inevitably occur in exhaust gas.

Only after identifying the root causes of oil contamination in compressed air can proper troubleshooting be performed. Common solutions are listed below:

1. For damaged oil‑gas separator element Damage to oil‑gas separator elements is a common fault. Inspect equipment before startup, strictly follow operating procedures during operation, and conduct regular maintenance after shutdown. Replace torn or perforated separator elements promptly to guarantee normal unit operation.

2. For oil‑return circuit faults If oil‑return circuit blockage occurs during equipment operation, first check the pressure drop across the separator. If the pressure drop reading is normal, clean the oil‑gas separator element. Replace the element immediately in case of fracture.

3. For excessively low system pressure setting Operators shall be familiar with the equipment rated pressure. When a fault occurs, reduce system load so that the system pressure rises to the rated working pressure.

4. For failed minimum pressure valve Replace the minimum pressure valve once failure is confirmed; resume operation only after replacement is completed.

5. For over‑filled cooling oil Learn the theoretical filling volume of cooling oil for the compressor before refilling. Assign dedicated personnel for oil filling. Normally keep the oil level below the mid‑point of the sight glass.

6. For poor‑quality cooling oil Fill cooling oil strictly in accordance with equipment specifications, as requirements vary for different compressors. Record the filling date, and replace oil upon expiry of service life. Strictly verify cooling oil quality and prohibit the use of non‑conforming cooling oil.