Mash Tun Suction Gauge

[Charlie]

... an open tube (like a sight glass) is put inline with the drain valve (but before the pump). He said you can use this to gauge how much suction you are putting on the grainbed...
Mylo

That is a cool idea!

This could be something as simple as a sight gauge mounted on the MT. The lower connection would be below the false bottom and the upper connection would be above the liquid level. You could mark the water level in the tube (your zero) after mash in and then note how far it dropped when you turned the pump on. The drop in inches would be indicative of the suction you're putting on the grain bed at the false bottom.

As far as calibrating it, you really don't need to, but...

1 psi = 27.7 inches of water or;

1 inch of water = 0.036 psi

This also means your 10 to 12 inch grain bed is going to cavitate (suck air through the sight tube) if you exceed -0.36 to -0.43 PSI.

Somebody needs to do the experiment to see if that's enough negative pressure to work with.

Charlie

[Quin]

The level would initially be as high as the liquid in the mash. As soon as you started the flow through the pump, it would drop lower than the liquid - because there would be less resistance than through the mash. Too far, and you will obviously loose prime. I'm not saying it would be an exact measure of the pressure on the bottom of the grainbed or anything. But just a visual indicator of how hard your driving the recirc or run off.

Maybe one of our propeller head brothas would have some sort of formula to determine actual pressure with this method - but I think it might be more of a subjective thing. For example, you are mashing a pale ale - and you just did a mashout. Chances are you can run that thing pretty fast. On the other had, you doing a Roggenbier with a shit load of Rye - you might want to go real slow.... you get the point.
Mylo

Initially the level in the sight glass would drop as you mentioned, but it would return to essentially the same level assuming flow into the MT equaled flow out of MT. The difference in elevation would be the friction the liquid had to overcome between the MT and sight glass. Not very much.

On one of the Dan Gordon shows, he mentioned they use a flow controlled pump to speed up the sparge. They go slow until the grain bed is set and then full blast.

The grain bed is a filter. You have to go slow enough so that you are not pulling alot of fines through the grain bed. You also have to make sure there is enough husks to act as a filter. The depth of the grain bed is the primary issue. That's probably why some have no problems using as much as 60% wheat and others get stuck mashes with less than 50% wheat.

[Mylo]

Initially the level in the sight glass would drop as you mentioned, but it would return to essentially the same level assuming flow into the MT equaled flow out of MT. The difference in elevation would be the friction the liquid had to overcome between the MT and sight glass. Not very much.

Maybe you are not understanding it properly. There is a T after the false bottom, but before the pump. The suction from the pump is going to pull on both the mash and the liquid in the site gauge simultaneously. The mash liquid has to be pulled through the grain, while the site gauge does not have that resistance. It will go down and stay down as long as the pump is on. It has nothing to do with how much water you are adding on top (assuming you didn't just dump five gallons of sparge water on top of your grain).


Mylo

[Quin]

Maybe you are not understanding it properly. There is a T after the false bottom, but before the pump. The suction from the pump is going to pull on both the mash and the liquid in the site gauge simultaneously. The mash liquid has to be pulled through the grain, while the site gauge does not have that resistance. It will go down and stay down as long as the pump is on. It has nothing to do with how much water you are adding on top (assuming you didn't just dump five gallons of sparge water on top of your grain).
Mylo

I understand it perfectly. THe pump does not suck on the grain bed. The March pumps are not self-priming pumps. You have to prime the pump (it has to be below the level in the MT). Gravity pushes the fluid through the grain bed.

I guarantee if you try it, it will be as I described above. Trust me.

[Charlie]

There is a T after the false bottom, but before the pump. The suction from the pump is going to pull on both the mash and the liquid in the site gauge simultaneously. The mash liquid has to be pulled through the grain, while the site gauge does not have that resistance. It will go down and stay down as long as the pump is on.

Yes, but that is the definition of a venturi! You will get reduced pressure at the right angle joint of the "T" in proportion to the velocity of the liquid in the main tube even without any restriction due to the false bottom.

The joint with the sight glass gauge has to come off the MT below the false bottom. It can't come off the line to the pump, otherwise the pressure drop will be a reflection of both the resistance of the grain bed _*AND*_ the velocity of the flow. It will not be accurate.

This is a cool thing Mylo. Let's write it up and submit it. You're first author and I'm contributing along with the guy that thought it up. This is better than the "widget of the month" things I've seen. We ought to be able to get 3 or 4 pages.

Let's do it!

Charlie (UPS just graced my front door with 4 lbs of hops!)

[Mylo]

Ok, I'm with you on the venturi effect. You lost me on the following statements.

The joint with the sight glass gauge has to come off the MT below the false bottom. It can't come off the line to the pump, otherwise the pressure drop will be a reflection of both the resistance of the grain bed _*AND*_ the velocity of the flow. It will not be accurate.

Here is what I envisioned:



Note: the small curved section of hose on top is to avoid the inevitable mess when you shut the pump off.

I thought the whole point was to measure the resistance of the grain bed, no? But if you are only measuring flow rate -here's another thought - you could use another one on the HLT - so you have a visual indication of the flow rates. It would be a snap to sync them.


Mylo

[Charlie]

Ok, I'm with you on the venturi effect. You lost me on the following statements.

The joint with the sight glass gauge has to come off the MT below the false bottom. It can't come off the line to the pump, otherwise the pressure drop will be a reflection of both the resistance of the grain bed _*AND*_ the velocity of the flow. It will not be accurate.

OK. In a pipe with fluid flowing through it there will be a pressure drop at any point where there is a right angle "T". That's your venturi effect. Hey! I looked it up.

http://en.wikipedia.org/wiki/Venturi_effect

If we put the T in the MT out-flow line we measure not only the negative pressure on the grain bed, but also the flow rate through the out-flow line.

Charlie

[Mylo]

Sorry, man. I'm still not getting your statement that the T has to be below the grainbed, and not in the line to the pump. What are you suggesting? to put an actual T right at the end of the pickup tube in the center of the false bottom - and run one lead to the sight gauge, and one to the pump?

Intuitively, I would think that you would need to put the T as close as reasonably possible to the end of the pick up tube (ie. you obviously wouldn't want to put it right before the pump). It's seems very convenient to put it right before the ball valve outside the MT. Would that skew the reading to be too much of a combination between flow rate and amount of vacuum? or worst - just an indicator of flow rate?

Sorry to grill you brotha, but I just want to make sure that we are one the same page. Either way, we should do a little proof of concept. Unfortunately (or fortunately) I am in "drink all my homebrew mode". Broken arm, gravity sculpture going to my buddy, going away for a week in two weeks. Hopefully the new single tier will be close to being done by the time I get back. Then it's "get it on" mode, in all aspects of the term.


Mylo