Keggle false bottom collapse! - Page 3

MacBruver · 03-19-2010, 06:41 PM

Quote:

Originally Posted by shortyjacobs

While your math is good, 1 PSI of vacuum is on a 113 in^2 surface. Your pump hose is, what, 1/2" ID? that's an area of 0.2 in^2. To get 1 PSI of vacuum on the false bottom requires (113/0.2) 565 PSI vacuum inside the hose. I sincerely doubt the March pump can pull 565 PSI.

Edit: In fact, March's site (PDF) lists the 809HS can pull 5.26 PSI max. 5.26 PSI over 0.2 in^2 is 0.0093 PSI over 113 in^2, giving a max vacuum total pressure of ~1 lb on the false bottom.

Double edit: My thinking may be quite wrong here...feel free to flame...need more coffee.

one PSI is one PSI... if it could really pull 5psi at the orifice there, across 113sq in it could pull 500+lbs of force. You can basically think of a hydraulic system with two different sized pistons as gears or pulleys. You trade stroke on a narrow piston for force on a large piston... it's a multiplier. Since the pump in this case would be a piston with infinite stroke, it could just keep on pullin'. Well, until it sealed off completely.

At any rate- I didn't take into account the hose collapsing though. The only way that would work is if it was all using hard lines.

Fin-lander · 03-19-2010, 07:17 PM

Great info guys - thanks a tun!

I will def. try the screw / spring thing on the FB. As I said earlier the FB kind of folded on one of the outer edges - not the middle where you'd expect if weight were the only factor. Didn't snap any pics as I was trying to save the batch. I'll prob just put a few screws on the perimeter as well for added stability. Part of me still thinks that if this happens though like it did to me, it'd still crumple around the supports, as you saw what it did to Beerthirty in the other post. An ounce of prevention though ...

Call me a hardhead, but I'm subscribing to the vacuum theory. Hopefully backing down the pump/a less agressive crush/and an occasional stir will remedy that.

**Walker** · 03-19-2010, 07:20 PM

Quote:

Originally Posted by Fin-lander

As I said earlier the FB kind of folded on one of the outer edges - not the middle where you'd expect if weight were the only factor.

If it is going to have a structural failure, it will do so at the weakest point, not necessarily at the center.

Fin-lander · 03-19-2010, 07:48 PM

Quote:

Originally Posted by Walker

If it is going to have a structural failure, it will do so at the weakest point, not necessarily at the center.

Perhaps a moot point, but I'd expect a cave in towards the middle (if we're talking a weight induced failure) as the support would be on the outer edge of the FB. The middle is not supported, and is the farthest from the support, thus the weakest point. I immagine if I started shoveling gravel onto the FB, it would eventually cave in towards the middle, as this would be a sheer weight caused failure. Just thinking aloud ...

**Walker** · 03-19-2010, 08:14 PM

I understand your point, but imaging a bridge, parallel to the ground and running between two cliffs. If it was structurally sound all the way across, but you simply loaded it with ore weight that it could handle, it would fail in the center where the support was the weakest.

But, now imagine that the bridge was secured to one the cliffs with poorly manufactured materials. The other cliff is fine, and the rest of the bridge is sound. If you load the bridge up with weight now, and it will fail at the weak point attached to the cliff and not in the center because the one cliff attachment was weakest.

edit: maybe there was a crack or something in one edge of your FB or maybe some of the holes were closer together there, or something.... whatever. If that spot was weakest (maybe because of concentrated heat) that's where it could fail. and not at the center.

klyph · 03-19-2010, 08:15 PM

Quote:

Originally Posted by Walker

I understand your point, but imaging a bridge, parallel to the ground and running between two cliffs. If it was structurally sound all the way across, but you simply loaded it with ore weight that it could handle, it would fail in the center where the support was the weakest.

But, now imagine that the bridge was secured to one the cliffs with poorly manufactured materials. The other cliff is fine, and the rest of the bridge is sound. If you load the bridge up with weight now, and it will fail at the weak point attached to the cliff and not in the center because the one cliff attachment was weakest.

Maybe he shouldn't have loaded his mash tun with raw ore...

**Walker** · 03-19-2010, 08:17 PM

LOL. At least you are a typo cop with a sense of humor!

Fin-lander · 03-19-2010, 08:30 PM

The FB is made from a perforated commercial sheet of SS. I see your point though, and it's valid. Guess it's impossible to know either way what happened. I did get some great suggestions, so thanks again.