Does Oil Reservoir Size Determine Oil Change Intervals?

Ask Atlas Copco is a segment that discusses commonly asked questions about various compressor, vacuum, and blower technologies, processes and best practices. Today’s answer comes from Steve Bruno, product marketing manager for oil-injected screw compressors.

When it comes to compressors, maintenance is vital. This is a factor many people consider during their compressor purchasing process as they calculate capital investment and ongoing costs. However, when considering oil replacement frequency for oil-injected compressors, many people incorrectly assume that the size of the oil reservoir determines how often the oil should be changed. 

What’s the role of oil in screw compressors?

Oil plays a critical role in oil-cooled rotary screw air compressors.  Primarily a coolant, oil removes the heat generated during the compression process. It also lubricates the rotors and seals the compression chamber. Because compressor oil is used for cooling and sealing, it must be special, high-quality oil and cannot be substituted with alternatives such as motor oil.

This higher quality oil comes at a cost. To ease customer’s minds about the price, some compressor manufacturers may use larger oil reservoirs to advertise a longer oil life, but this is misleading.

What determines oil life span?

Heat, not oil reservoir size, determines how long oil lasts. If a compressor is experiencing shortened oil life or requires a larger oil reservoir,, the compressor may be generating more heat during compression. Another possible problem is that excess oil is passing through the rotors because of an unusually wide gap.

Ideally, operators should take into account the total cost of changing oil per running hour and be wary of compressors with oil life expectancy far shorter than the industry average. To find out the average oil life expectancy and oil capacity of an oil-injected screw compressor, refer to compressor’s operator’s manual.

Large oil reservoirs don’t indicate long oil life span

Don’t be fooled by large oil reservoirs. While manufacturers may imply they lead to longer oil life, there isn’t any correlation between the two. Instead, do your research before purchasing a compressor and adhere to an effective maintenance schedule. That way, you can catch potential problems early and avoid wasting money on replacing compressor oil.

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