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Thread: Grain bed compaction during HERMS

  1. #31
    Gold Member Big_John's Avatar
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    Yes, the silicone tubing gets softer at higher temperatures. I've seen it blow up like a water balloon when tyring to push wort through an immersion chiller. Taz seems to have the solution with the thick walled tubing or better yet, the reinforced stuff. I'm using heavy walled PVC with the polyester reinforcing braid. The hoses I use are large 5/8" ID and 7/8" OD and I don't have any problem at all with them softening or collapsing. Previously I was using the same tubing, but the thinner walled version and I did have trouble with those at times. I'm happy to hear that you seem to have solved the problem. Should be smooth sailing from now on.



  2. #32

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    Quote Originally Posted by Big_John View Post
    There will always be some vacuum or suction under the false bottom unless you vent it to the atmospehere somehow. This is normal. The pressure at the bottom of the MT is caused by the weight of the grain/wort + atmospheric pressure. When you open the ball valve and drain or pump and start the flow, the wort moving through the grain bed is slowed by the grain bed "filter" itself. The wort moves out through the ball valve because the pressure outside is less than the pressure inside the MT. A vacuum or suction will only happen if a siphon is used or a pump. Otherwise it is only gravity flow from the weight of the liquid above the FB. A siphon acts just like a weak pump if the outlet hose is below the valve which is must be to initiate flow. The longer the out fall tube the more suction will be applied. This is due to the weight of the liquid in the tube falling due to graivity and it's just like the weight of the liquid above the FB. The grain bed "filter" causes resistance to the natural flow. When this flow through the grain bed is slowed to a rate less than what is flowing out of the siphon or being pumped, a pressure differential occurs (ie a partial vacuum). You need not eliminate the partial vacuum. Actually, it is beneficial up to a point as it speeds up the draining or circulation. It's only when it becomes excessive that it can cause problems. The tricky part is determining at what point that happens. There's nothing to observe to indicate that a problem is imminent unless you have a riser vent tube or a vacuum gausge. If you add a vent tube anywhere below the FB, it will prevent any pressure differential from happening.

    One thing about the connector tube to the FB. Keep it as short as possible. What I mean is, make it a straight short line directly to the ball valve without any loops or excess. This will help prevent any kinks and such which are more susceptible to collapse. It is a simple problem and the solution is simple. Just make sure that the connecting tube does not and cannot collapse. I mentioned earlier that you can use copper most of the way and make a splice coupling with a short piece of the vinyl tubing. Butt the ends of the copper so that the gap between them is minimal. This close fitting won't give the tubing any room to collapse. It needs at least a few diameters of space to do so. Even a two inch long splice piece would be very unlikely to collapse. You can test my theory on the tube collapse potential. Heat a piece of the tubing in some hot tap water. Put your finger over one end and suck on the other and see if you can make it collapse. I think this would be an enlightening experiment and it will give you an idea of how mushy the hot tubing can get. Not all plastic tubing has the same characteristics, so try it with some non-reinforced racking tubing. That stuff is the softest and will probably easily collapse. I hope this crude explanation helps.
    this vent must be in the mash tun or I can place just outside the tun using a T?

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