As I make a list of all the tasks a pump will make possible I am pondering this question I only vaguely considered in the past. Do the whirlpool/immersion chiller setups cause oxidation of the wort? Since you are pumping boiling hot wort through this system isn’t there some oxygen pickup along the way? I know the return is supposed to be below the wort surface in the kettle, but it just seems like air is going to be pulled in somewhere in the process.
It can’t be much - does it really matter?
From where?
Yeah. If you pull out deoxygenated boiled wort and put it back in under the surface, how can oxygen get in? Unless I missed something…
I have been doing this for over a year. No problems that I can detect.
you could pull in air if you did not have your draw tube tightly fastened to your out spigot - pretty easy to spot that.
you could also introduce (thought it should be immediately boiled out) some if you have the return arm above the surface of the wort, causing splashing.
I would not worry about it. Aren’t you going to oxygenate your wort for your yeast anyway?
I think the concern here is the reputed evils of hot side aeration.
the air maybe? 
3 psi of oxygen just sitting there?
Air will get into the wort just from surface agitation. So yes, it will introduce some oxygen but the real question is: Is it enough to cause HSA problems? My guess is that if it did, Jamil (or one of the many good brewer friends and judges that have tasted his beers) would have detected it. Also, some breweries and homebrewers do hot whirlpools and if done right I don’t hear of HSA problems there either. I’ve heard/read that unless your really splashing around and making a lot of foam you should be fine.
alrighty then. I thought it was a legitimate concern… guess not. :-[
Having never seen one in action I was curious. When I first read about them I thought the wort was being splashed back into the kettle. I learned that was not the case later. I guess my next suspicion was that if you had a rather vigorous whirlpool going it was going to suck air from the surface. Personally I have never been overly concerned about HSA but I do like to learn what I can about potential risks so I can choose for myself what I will do personally.
Thanks folks. Now back to daydreaming about my brewery…
Just to keep the topic open a bit, wouldn’t a vigorous whirlpool increase the absorbtion of air into the wort? This is how a mix-stir works, right?
Mine does not create a vortex like a mix-stir. More of gentle rotation of the wort. The hops end up in the chiller coil for the most part, so it is working as a whirlpool.
+1 Gentle rotation with hops in the middle for the most part.
The one area of surface turbulence is where the chiller and whirlpool tubing enter the wort. It has never been strong enough to warrant backing down the pump output in my experience.