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Old 09-23-2011, 02:44 AM   #1
MG1602
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Have a 10 gallon polarware kettle with false bottom. Past two brews, my false bottoms have collapsed while recirculating and I don't know why. Can anyone help me figure this out why this happened?



 
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Old 09-23-2011, 02:57 AM   #2
day_trippr
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Ok, what exactly are your "false bottoms" made from??

I've tried flexing my FB, and it takes a lot of force to get my FB to bend, way more than the pressure that 20-odd pounds of grain in 60-odd pounds of water could ever provide...

Cheers!



 
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Old 09-23-2011, 03:09 AM   #3
Hang Glider
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Switch to a metal false bottom

 
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Old 09-23-2011, 03:26 AM   #4
MG1602
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They are metal.

 
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Old 09-23-2011, 03:39 AM   #5
two_hearted
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Quote:
Originally Posted by MG1602 View Post
They are metal.
Can you describe them in more detail? Or post a pic?

 
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Old 09-23-2011, 03:39 AM   #6
Catt22
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I have a 10 gallon Polarware with the matching full width false bottom. More than a few times I have had a stuck mash and pulled down on the FB with a pump at full throttle and the FB did not collapse or show any sign of stress. It's not only the weight of the grain and water. It's mostly the atmospheric pressure pushing down on the FB that can cause it to collapse when sucking on it with a pump. Atmospheric pressure is about 14.7 psi. Assuming the pump cannot be 100% efficient, the force would probably be more on the order of maybe 10 psi or so. The Polarware FB has a surface area of about 160 square inches (This is a rough estimate). The total force pushing down on the FB at the assumed 10 psi would be 1,600 lbs. Even if we assume that my calcs are off to the high side by 1/3rd, it would be a half ton of total force on the FB. That's a hell of a load no matter how you look at it. I'm actually quite surprised that I haven't collapsed my FB yet, but it's well built with very substantial supports.

What kind of FB are you using? That should reveal a lot.

 
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Old 09-23-2011, 04:01 AM   #7
day_trippr
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Umm...1600 pounds of force?

I have to believe there's something fatally flawed with that calculation, and my first guess is you're multiplying the pump draw (which, fwiw, unless you're using a positive displacement pump, is probably closer to zero than 10 psi) by the area of the FB, when you probably should be dividing the draw by the area.

Or maybe I'm wrong...but I have an excuse, I lost count how many drafts I've drawn tonight, and the buzz is fairly intense...

Cheers!

 
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Old 09-23-2011, 04:02 AM   #8
MG1602
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I have the same false bottom as you Cat. One of the three legs just basically gave out.
I can't load the pic right now. Is this a faulty FB?

 
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Old 09-23-2011, 04:04 AM   #9
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https://mail.google.com/mail/u/0/s/?...attd&safe=1&zw

 
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Old 09-23-2011, 04:05 AM   #10
MG1602
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Sorry. Paste did not work.



 
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