Cleaning Q&A: Oil and Water Separation

How do we choose the capacity of our coalescer?


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Q. We are planning to install a coalescer as the first stage of filtration in our parts washing system. How do we choose the capacity of the coalescer? Does the capacity have to be the same as the discharge of the jet pump flow rate?

A. I am glad to see you considering coalescers as an option for oil removal from an aqueous parts washer system. Alone or combined with an oil skimmer, this technology can greatly extend the life of the cleaning stage. They are also generally cost effective when accounting for the extension of the cleaner life, improved quality due to a more consistent cleaning bath and a reduction in waste disposal.

I can only give you general guidance regarding system design based on experience. I know you would not need to size a coalescing system to handle 100 percent of your tank turnover if using a recirculation system for turbulence and agitation. The coalescer needs residence time to enable the lubricant feed through the coalescing media, split from the cleaner and float. A lamellar flow is needed for this to occur. If a highly turbulent flow is sent through a coalescer, it would be too disruptive to enable the system to separate and split any of the oil. As a result, the system will typically be designed to turn over a tank a specific number of times in an hour (maybe 2–10 times per hour depending on the chemistry of the cleaner and oil along with the effectiveness of the coalescing media). I recommend you contact some coalescer manufacturers to give you a better idea of system engineering requirements at pfonline.com.

Originally published in the November 2015 issue.