Keggle false bottom collapse!

[Fin-lander]

I am posting this to see if anyone has gone through this and can shed some light as to why this happened: (sorry for the length)

I have a brutus 10 system using keggles. My mash tun has a full diameter false bottom made out of approx. 1/8" thick perforated stainless sheet. It has no hinges as I cut slots in the top of the keggle to get it in and out. It is supported at the bottom of the keg by the sides as the keg narrows at the bottom. It's fairly strong stuff. Last night I brewed my first 10 gal. batch on the system (24 lbs grain). I have done numerous 5 gal. batches with no problems. Half way through the mash, with the pump recirculating, I noticed the mash was getting pretty thick on the bottom 1/3 or so of the keg when i went to stir it. I mashed at 1.75 qts/lb of grain. I stirred it and mixed things up a bit, but about 10 mins after that I noticed grain in my lines. I knew something was very wrong and tried to clear the lines numerous times, but every time, more grain in the line. I finally had to physically move the mash into another keg and remedy the problem. The problem was that the false bottom collapsed on itself. It was crinkled in one corner, and I have a feeling the failure was due to a vacuum being created rather than sheer weight. As it is a direct fire mash tun, I had the pump on almost full blast to recirculate. After hammering the false bottom back to shape the best I could, I reassembled everything, and actually saved the brew. I was sure to stir the mash several times during the remainder, and knocked the pump down to about 1/2 or less.

Has this happened to any of you? Do you think if I keep the pump at a lower level I should be fine next time? I was afraid of scorching the wort, and trying to keep a uniform mash temp, so I had the pump on wide open. I really don't want to go through this again! I've seen others use a false bottom like this without issue. I also don't want to worry about constantly stirring the mash every couple of minutes.

Thanks.

 

[Walker]

I really doubt that a wort pump could create enough suction to collapse 1/8" steel, if that is what you are suggesting.

 

[Fin-lander]

I really doubt that a wort pump could create enough suction to collapse 1/8" steel, if that is what you are suggesting.

I guess that is what I'm suggesting. The power of a vacuum is a powerful thing. My guess is that a vacuum was created when the sparge compacted, and the pump kept on. The weight from the grain/wort on top added some force as well. Perhaps someone who's a bit more up on their fluid dynamics / physics than myself will shed light.

The way the thing crumpled in one small place was strange, not a total uniform failure around the edges, or the center caving in, it's like the thing quickly snapped in on one small place - like an accordian fold. Didn't seem like something that happened from too much weight.

 

[MacBruver]

I really doubt that a wort pump could create enough suction to collapse 1/8" steel, if that is what you are suggesting.

A 12" dia. circle is 113 sq in of area. Even one PSI of vacuum would be 113 lbs of force, plus another 24lbs of grain sitting on top of it. I don't think it's outside the realm of possibility- especially if the mash was so sticky that it was not flowing well. If it was basically sealing off the false bottom, I think it would be possible to create enough vacuum to do some damage.

 

[shortyjacobs]

A 12" dia. circle is 113 sq in of area. Even one PSI of vacuum would be 113 lbs of force, plus another 24lbs of grain sitting on top of it. I don't think it's outside the realm of possibility- especially if the mash was so sticky that it was not flowing well. If it was basically sealing off the false bottom, I think it would be possible to create enough vacuum to do some damage.

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.

 

[Synovia]

Edit: In fact, March's site (PDF) lists the 809HS can pull 5.26 PSI max.

No, it doesn't.


It says it can PUSH 5.26 PSI max. The way these pumps are designed, they handle head pressure a lot better than they handle intake restriction. I'd be surprised if they can pull more than 2 psi.

 

[Mischief_Brewing]

I'm wondering if a couple of stainless nuts and bolts near the middle could keep this from happening again? Think tiny little legs

 

[Walker]

This is an interesting problem. Clearly something happened that should not have happened.

Don't forget that he mentioned that the false bottom was 1/8" thick steel. That is some REALLY thick stuff, which is why I doubted that the pump would have been able to crumple it.

You mentioned that the MLT is direct fired and the false bottom rests against the curved bottom of the keg, right? I wonder how much of a factor heat played in this?

 

[Fin-lander]

The false bottom is just a smidge under 1/8" thick, still, it is quite strong considering all of the holes. I put all the force I could with my hand, and couldn't get it to budge. I don't know the math involved, but I still gotta think the vaccum idea holds some weight here (no pun intended).

In searching the web, I came across a brewery mash tun manufacturer website that said something like their mash tun being a closed system that eliminates the possibility for mash tun vacuum collapse. I'm sure that system has one hell of a pump, but that tun is several times as large as well. If you scale everything down, maybe these march pumps can pull enough do do what happened to me?

I guess I'll just make sure to stir the mash more often, and scale the pump down during the mash. I thought for sure someone had come across this before...

 

[EvilGnome6]

I think beerthirty had the same thing happen to him once.

EDIT: Here's a post about it: https://www.homebrewtalk.com/f36/brewing-sucks-74941/#post784415

 

[brewagentjay]

Need some pictures next time to really get an idea on what happened.....

Just a suggestion

 

[Synovia]

If you scale everything down, maybe these march pumps can pull enough do do what happened to me?
.

Your pump would burn out before it pulled enough vacuum. I'd worry more about the heat or something.

 

[Fin-lander]

Evilgnome6 - thanks for that post about Beerthirty. That seems to be just about the same thing that happened. As you can see in his post with pictures, his FB looks like it was run over by a truck - I gotta think there was some other physics involved besides just weight on the FB. My FB doesn't have the support legs, but it is supported around the whole keg edge, and is maybe a bit thicker material. In the brew he did, he had pumpkin in the mash leading to a stuck sparge. Mine probably had the pump on too high, leading to a stuck sparge as well. Perhaps the weight on the FB combined with the heat combined with a vacuum from the pump? I dunno.

All I know is when I reassembled everything and slowed down the pump and kept up the stirring I had no problems. I also had a "fixed" FB in action, and a lot more heat as I had to get the mash up from about 140 to 153.

I'll try to post back here when I do my next 10 gal batch. I appreciate the ideas / suggestions - keep 'em coming!

 

[EvilGnome6]

My only suggestion would be to try malt conditioning. I use a 10 gallon cooler with a false bottom and constant recirculation for my HERMS. I've found that the wort flows much better since I started conditioning the malt.

 

[smee44]

Remember a gallon for water weighs approx. 8 lbs.

I don't think a "vacuum" was pulled but what i think happened was your pump was pumping wort quicker than it was drain through the false bottom. So now the false bottom is supporting all the weight of water and grain.

When you slowed down the pump the wort could drain through the false bottom quicker than the pump was taking it away so the area under the false bottom is full of wort and that wort is supporting some of the weight.

Not sure this post is very clear but what i am trying to say is it is a simple balance of forces on the false bottom.

 

[Fin-lander]

Smee,

Good point - you very well could have solved the mystery. If all of the liquid was pumped from below, there would be nothing there to help support the weight.

I guess at the end of the day, it really doesn't matter why it happened (other than me not replicating the scenario) I just want to learn what not to do. Thanks for all the help - I think I may check into the malt conditioning on larger batches, and perhaps some sort of support below the FB. That and watching my pump flow.

 

[OLDBREW]

I am posting this to see if anyone has gone through this and can shed some light as to why this happened: (sorry for the length)

I have a brutus 10 system using keggles. My mash tun has a full diameter false bottom made out of approx. 1/8" thick perforated stainless sheet. It has no hinges as I cut slots in the top of the keggle to get it in and out. It is supported at the bottom of the keg by the sides as the keg narrows at the bottom. It's fairly strong stuff. Last night I brewed my first 10 gal. batch on the system (24 lbs grain). I have done numerous 5 gal. batches with no problems. Half way through the mash, with the pump recirculating, I noticed the mash was getting pretty thick on the bottom 1/3 or so of the keg when i went to stir it. I mashed at 1.75 qts/lb of grain. I stirred it and mixed things up a bit, but about 10 mins after that I noticed grain in my lines. I knew something was very wrong and tried to clear the lines numerous times, but every time, more grain in the line. I finally had to physically move the mash into another keg and remedy the problem. The problem was that the false bottom collapsed on itself. It was crinkled in one corner, and I have a feeling the failure was due to a vacuum being created rather than sheer weight. As it is a direct fire mash tun, I had the pump on almost full blast to recirculate. After hammering the false bottom back to shape the best I could, I reassembled everything, and actually saved the brew. I was sure to stir the mash several times during the remainder, and knocked the pump down to about 1/2 or less.

Has this happened to any of you? Do you think if I keep the pump at a lower level I should be fine next time? I was afraid of scorching the wort, and trying to keep a uniform mash temp, so I had the pump on wide open. I really don't want to go through this again! I've seen others use a false bottom like this without issue. I also don't want to worry about constantly stirring the mash every couple of minutes.

Thanks.

Probably answered already, but I haven't read the thread.

It happens often with a perforated full false bottom.
The best solution is to buy a four stainless steel machine screws and eight nuts, either 2" x #8-32 or #10-20 size.
Drill four holes in a square pattern toward the center of the full false bottom for stabilizer legs. Use two nuts for each machine screw. The screw head faces down and rests on the bottom of the keggle, then one nut under, and one nut over the drilled holes in the false bottom. Adjust the height so the screw heads touch the bottom, then tighten the nuts up. Cut the extra threads sticking up past the top nut and you wont have the problem again.

 

[Walker]

something like this (but longer screws)?

(this is the underside of my false bottom)

I had to do this to keep the false bottom from creating a seal against the slightly warped bottom of my MLT a long time ago.

 

[Bobby_M]

I support mine with a stiff spring shoved over the siphon tube from underneath but the stainless machine screw thing is a fine way to go.

 

[klyph]

Even if the March pump can't "pull" suction, as long as the in-tube is full of liquid, it will pump it, pulling a vacuum until it runs the supply hose dry. Not saying this was the cause of the collapse, but I do think it's possible for a mag-drive pump to pull a vacuum, given a long enough supply line.

 

[MacBruver]

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]

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]

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]

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]

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]

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]

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

 

[Fin-lander]

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.

 

[newtobrew1981]

I guess that is what I'm suggesting. The power of a vacuum is a powerful thing. My guess is that a vacuum was created when the sparge compacted, and the pump kept on. The weight from the grain/wort on top added some force as well. Perhaps someone who's a bit more up on their fluid dynamics / physics than myself will shed light.

The way the thing crumpled in one small place was strange, not a total uniform failure around the edges, or the center caving in, it's like the thing quickly snapped in on one small place - like an accordian fold. Didn't seem like something that happened from too much weight.

Heat will also add to the vacuum as well

 

[LarMoeCur]

There are pictures posted on this forum of actual false bottoms made from perforated stainless steel ripping, steel legs being mashed flat, hinged bottoms separated at the welds. All from pump vacuum.

I haven't done physics math in 20 years but I'll bet the point closest to the intake will be generating the most force. Think of it as a black hole and the intake tube is the center. There would have been a fluid vortex pulling the grains and weight inward before the fluid runs out. Right at that point when the fluid and air pumping action starts the vacuum. That's where the most force will be. Same way a 1/4 hp Jacuzzi pump can hold a man under water with just a 2" pipe at the point of contact.