Single Pass VS Multiple Passes

How I Run My Centrifuge
This is a question I get asked fairly often so I figured I'd make it easy and answer it here.  Why do I run multiple passes through my direct drive centrifuge and would one slower pass be just as good?

I'll answer the second part of the question first.  So time in the bowl is the goal no matter how you look at it.  The longer the oil is in the bowl of the centrifuge, the more time the forces are acting on that oil, pulling out contaminates.  It doesn't really matter if you run 50 gallons through twice at 5gph, or once at 2.5gph, the oil will spend the same amount of time in the bowl.

So why would I waste time and effort by running multiple passes?

Running more than one pass gives me the chance to open the unit up and see how things are progressing.  On many occasions, I've opened the lid on my unit and found the bowl completely full of a black pudding like substance.  This is a mixture of moisture and particulate.  This all comes from oil that has been settling for months, and in some cases, a year plus.  When that happens, I can give the bowl a quick cleaning and be back up and running for pass #2.  Pass #2 TYPICALLY ends with a light layer on walls of the bowl that has a crayon like texture instead of a bowl full of pudding.  This means the oil is dry and relatively clean.

So let's say you went the route of one slow pass.  20 hours after starting, you open the lid and find the centrifuge bowl is completely full of sludge.  How long has the bowl been full?  Is the oil in your "clean" container actually clean?  As the bowl on the unit fills with solids/sludge, it's efficiency drops off.  How much of that pudding like substance was flung from the bowl and made it to your clean drum?  Now you get to decide to either call it good, or re-run the batch and dealing with that if your setup isn't capable of easily returning the clean oil drum contents to the feed drum.

I've found it easier and faster overall to run multiple passes at a higher flow rate compared to a single slower pass.  No matter which direction you choose to go, I'd still shoot for no more than 5gph through the unit.  TIME is important.
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