Cavitation problems

[centralpabrewer]

What do you guys do to control/stop cavitation when pumping from your boil kettle. I have a march pump and CFC chiller. About 20 minutes from the end of the boil, i recirc through the CFC to sanitize it. I have a hard time keeping the pump inlet hose from the BK to the pump full. This only happens when the wort is boiling. I have tried closing the valve on the pump out side, but it doesn't seem to help much.

I have considered just bringing some water to around 180F and pumping that through the CFC for 15 minutes or so instead of the wort, but then how do you get that extra water out of the CFC before chilling your wort? Thoughts on that?

Is there anything else I could do to stop the cavitation? Also, I have keggles and the pickup tube in the BK is almost dead center.

 

[Brulosopher]

Before turning the pump on, open the valves and make sure all the lines are full of wort, then close the out valve on the pump about 75% before turning the pump on. This always worked for me... when I used pumps... I hate pumps.

 

[centralpabrewer]

Thanks for the suggestions. I already tried that. When I prime the inside of the pump while the BK is at full boil, the tube fills very slowly and as soon as I turn on the pump, the inlet hose is emptied, then i just get surges.

 

[IslandLizard]

Are your hops plugging up your diptube? That would prevent a good wort flow and causes the pump to starve.

Since you only have the problem while boiling, the other thing I can think off is that water vapor gets in the diptube and hose, so you lose prime.

My pump inlet is a few inches lower than my kettle, and the hose which is short (18") fills nicely, keeping prime going. I recirculate for 10-15 minutes.

 

[Bsquared]

The problem you are having is because the wort is actually boiling in the pump head. Even though the wort will have cooled to below boiling temps as it enters the pump, the pump lowers the the pressure on one side of the pump head and increasing it on the opposite side. This resulting area of lower pressure will also reduce the boiling temperature of water/wort, causing bubbles to release from the water/wort into the pump head causing the cavitation you see.

If you just open the valve and fill the head with 200+ºF liquid and let it sit for 5-10min, you will sufficiently sanitize the head, assuming it is clean and free of dirt, or other gross contaminants.

 

[centralpabrewer]

But I am recirculating through a CFC to sanitize that. I am contemplating just recirc'ing with some 180F water instead of wort, but then i will have water i the CFC not wort.

 

[grathan]

Your opening the pump output valve too far. Close it all the way then turn the pump on. Open it until the liquid in the feed line starts disappearing then back off some so that it catches up again. This is your max flow.

 

[Pezzonovante11]

Yeah it's pretty hard to pump boiling water through a march pump without it cavitating. After all, your water is turning into a gas at that point. Been there done that.

But to answer your question, what I did when I was using a counterflow was to recirculate through while I was heating from mash-out to boiling temps. As soon as the pump started to cavitate I turned it off. Then I turned it on again after flame out.

If you add it up, the pump and tubing sees ~30-60 minutes of temps between 170 and 208.

There's nothing magic about 212 degrees. What kills bugs is a combination of temp and time. At these temps and times, you're not likely to see any problems with infection. If you do, it's more likely a screw up on the cold side than something that wasn't killed during the boil.

I didn't take scrupulous care of my chillers. In fact, I just sold my counterflow, and I my plate chiller is for sale too. Now days I use a good old immersion chiller (stainless of course) and I'm actually quite happy with the performance