Why Screw Compressor Oil Consumption Rises — and How to Fix It

In industrial compressed-air systems, one of the most common issues affecting oil-injected screw compressors is rising oil consumption. This problem can lead to increased operating costs and potential damage to the compressor if not addressed promptly. Understanding the causes and implementing appropriate maintenance practices can help mitigate these issues.

Separator Element Condition

The separator element is a critical component in oil-injected screw compressors, responsible for separating the oil from the compressed air. Over time, the separator element can degrade due to wear, contamination, or improper maintenance. When the separator element is compromised, it allows more oil to pass through into the compressed air, leading to higher oil consumption. To check the condition of the separator element, follow these steps:

• Inspect the separator element for signs of wear or damage.
• Measure the oil carry-over rate by collecting samples from the air outlet and analysing the oil content.
• Replace the separator element if the carry-over rate exceeds the manufacturer’s recommended threshold.

Oil Return Line

The oil return line is another critical component that can affect oil consumption in screw compressors. If the oil return line is clogged or improperly installed, it can impede the flow of oil back to the sump, causing the oil level to rise and leading to higher oil consumption. To ensure the oil return line is functioning properly, perform the following checks:

• Inspect the oil return line for blockages or debris.
• Verify that the oil return line is properly connected and not kinked or bent.
• Clean or replace the oil return line if it is found to be clogged or improperly installed.

Temperature

Temperature plays a significant role in oil consumption in screw compressors. When the compressor operates at higher temperatures, the oil becomes less viscous and more likely to be carried over into the compressed air. This can lead to higher oil consumption rates. To manage temperature-related issues, consider the following:

• Monitor the compressor’s operating temperature using temperature sensors.
• Ensure proper cooling of the compressor through adequate ventilation or cooling systems.
• Adjust the cooling system if the compressor is operating at temperatures above the manufacturer’s recommended range.

Oil Type and Level

Using the wrong type of oil or maintaining an incorrect oil level can also contribute to higher oil consumption in screw compressors. The type of oil used should be compatible with the compressor’s requirements, and the oil level should be maintained within the manufacturer’s recommended range. To address oil type and level issues, take these steps:

• Verify that the correct type of oil is being used in the compressor.
• Check the oil level regularly and top up as necessary.
• Adjust the oil level if it is found to be too high or too low.

Over-Pressure

Over-pressure conditions can cause higher oil consumption in screw compressors. When the compressor operates at pressures above the recommended range, it can lead to increased oil carry-over. To prevent over-pressure conditions, consider the following:

• Monitor the compressor’s discharge pressure using pressure sensors.
• Ensure that the compressor is not overloaded by adjusting the load or adding additional capacity as needed.
• Adjust the pressure settings if the compressor is operating at pressures above the manufacturer’s recommended range.

Short Cycling

Short cycling, or frequent start-stop cycles, can also contribute to higher oil consumption in screw compressors. When the compressor is frequently started and stopped, it can cause the oil to become agitated and more likely to be carried over into the compressed air. To reduce short cycling, consider the following:

• Optimise the control system to minimise frequent start-stop cycles.
• Use a variable speed drive (VSD) to control the compressor’s output more efficiently.
• Adjust the control settings if the compressor is found to be cycling frequently.

Diagnostic Sequence and Preventive Maintenance

To effectively diagnose and address rising oil consumption in screw compressors, follow a systematic approach. Start by checking the separator element, oil return line, and temperature. If these components are functioning correctly, then investigate the oil type and level, over-pressure conditions, and short cycling. Regular preventive maintenance, including routine inspections and timely replacements of worn components, can help prevent rising oil consumption and extend the life of the compressor.

By understanding the causes of rising oil consumption and implementing appropriate maintenance practices, plant engineers, maintenance managers, and energy managers can ensure the efficient and cost-effective operation of their compressed-air systems. Regular monitoring and proactive maintenance can help identify and address issues before they become more serious.

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