Cavitation when pumping boiling liquid

[fusa]

Whenever I try to pump water or wort when it is boiling there is cavitation. I have tried pumping the liquid well before it reaches boiling, but as soon as it is boiling the problem starts. I have tried reducing the flow after the pump but this hasn't helped. Is there any way to prevent this?

 

[govner1]

What type of pump?



Sent from my iPhone using Home Brew

 

[fusa]

March 809HS-PL Pump

 

[Foosier]

Where is your pickup tube located? I was watching a buddy brew and his pickup was drawing from right in the middle of his keggle. With the water boiling, the pickup tube was drwaing in bubbles from the boil. Once they got in the pump they would catch and build up until the pump lost all suction. The problem did not occur if the water was not actively boiling.

I'd recommend checking for your pickup tube drawing bubbles into your pump.

 

[fusa]

For the boil kettle the pickup tube draws from the side of the keg's bottom. This is the one where I am having most problems since I am trying to recirculate to sanitize the tubing, plate chiller and pump. The HLT draws from the bottom center. It also has some problems when transfer boiling water for mash-out.

 

[Foosier]

You might try a boil with just water and see if you are getting bubles coming up around the pickup tube. If they come up near the pickup tube, they are likely getting drawn in. This could build up in your pump. This what I saw happening to my buddy's pump. No matter how he tried to throttle the inlet, the bubbles we already getting sucked in and then slowly he'd lose suction till we had to re-prime the pump.

 

[TopherM]

Better question: why do you need to transfer boiling liquid?

 

[baulz]

Better question: why do you need to transfer boiling liquid?

I re-circulate boiling wort through my chiller to sanitize it in the last 10-15 minutes of my boil.

 

[TopherM]

Gotcha. Any temp above 160F will sanitize your chiller. You could just wait until after flameout to start your recirculation. It's an option!

 

[thefost]

Check out later in this thread for the details on why this happens https://www.homebrewtalk.com/f11/why-my-pump-losing-prime-484890/

Basically the vapor pressure of boiling wort is too high for the pump. These pumps just can't handle boiling liquid without significantly throttling back the flow.

With a very low flow you might be able to recirculate through the chiller at boiling. Really though you don't need to recirculate boiling liquid at all. At the end of the boil you can kill the heat and pump the hot wort slowly for a minute or two - that will more than sanitize it.

 

[Bobby_M]

Right, 10-15 minutes is very much not needed. Recirculate for 1 minute at flame out and you're good.

 

[fusa]

Thanks for the info. I had been relying on the near boiling liquid to sanitize the hoses, pump and plate chiller after the boil. For my last batch I wanted to be try recirculating during the boil, to be more on the safe side that everything is sanitized. Next time I'll recirculate after I kill the propane for a couple of minutes, then turn the cool water on for the chiller.

 

[Owly055]

Consider running cold water on the pump body......not the motor obviously. The closer you are to the pot, and the less restriction there is on the intake, the less of a problem you are going to have. If the pump is "vapor locking" which is obviously what is happening, cooling it down is going to make a big difference.


H.W.