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Old 04-15-2011, 02:54 AM   #11
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I don't use a RIMS system, but it would appear to me that you should leave your heater off until you get enough flow. Maybe wait 5 minutes and gradually get flow through the mash before you turn it on?

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Old 04-15-2011, 03:45 AM   #12
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Here is a graph of the temp inside my RIMs tube when I shut off the flow completely (several times). This was an experiment to see how quickly the system would stop an over shoot in case of a stuck mash.

I'm using a BCS in PID mode, but you can see the wort never came close to boiling temps.
If I may, what kind of heating element are you using? We're using a 1500W, 120V, low density element.

I think I'd see a similar graph during our mash if we took data from the thermocouple, but it's obvious upon visual inspection that boiling is taking place. The temp on our PID reads anywhere between 148 and 165, but if you watch the clear tubing on the outlet, you can see a lot of air escaping where none came in on the inlet. I think the wort gets mixed quickly enough to bring the temp down before it hits the thermocouple, but there is definitely boiling taking place directly on the heating element surface. I've seen the problem while testing with water, as well, at max flow rate (about 16 gpm).

Maybe I'm just overthinking this - it just seems that my efficiency would suffer if I was killing off enzymes that are in contact with the heating element when it fires, and I'd prefer not to (the last mash/first batch on this guy was messed up in other ways, so we didn't take an efficiency reading this time around).

What would you guys estimate is your max flow rate?
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Old 04-15-2011, 06:03 AM   #13
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I have no idea what flow I'm getting, but I can tell you without a doubt that I can set the PID to 100% on manual with a 5500 W element and not boil pure water when I'm recirculating at full speed. I do this when I'm heating up my clean up water. On the other hand, if I recirculate too slowly during a mash I also get bubbles coming out the return tube while my PID reads 150ish. That's what's making me think that you're recirculating too slowly.

As far as flow rates, I would propose that there is a flaw in your overall design that is limiting your flow. At full speed you shouldn't be able to boil water with a 1500 W element if your PID is reading below 180 I wouldn't think. Look for obvious restrictionsin your connections, like places where teflon tape might have slipped out during assembly.

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Old 06-15-2011, 03:29 PM   #14
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Just wanted to post an update to this thread:

We actually found out we were getting a slow flow rate due to some issues with our pump inlet. We increased the flow to the pump, and are actually getting a very smooth operation going now with no boiling whatsoever! The PID and RIMS tube are maintaining temperature very well throughout the mash, and it clears the wort very well.

The only issue I have (and it may be a non-issue) is that the flow rate is pretty fast, and the mash tends to foam with the spray from our diffuser/sprinkler-head type thing. I'm under the impression we should be more gentle with the grain bed, but I can't imagine disturbing the top is really affecting the bottom any, given that the whole grain bed is about 10-15" tall (13 lbs of grain in a 10gal cooler).

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Old 06-15-2011, 04:18 PM   #15
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Quote:
Originally Posted by Dimerizer View Post
We actually found out we were getting a slow flow rate due to some issues with our pump inlet. We increased the flow to the pump

<snip>

The only issue I have (and it may be a non-issue) is that the flow rate is pretty fast, and the mash tends to foam with the spray from our diffuser/sprinkler-head type thing.
Maybe I am reading too much into this, but do you NOT have a ball valve on the output of your pump?

Your comments lead me to believe that you might have been trying to control flow by adjusting the ball valve on the MLT output and then just letting the pump go free.... and now you have changed things so that you are opening the MLT ball valve all the way.

You should have a valve on the output of the pump to control flow. This would allow you to have a more gently return of wort to the MLT during circulation.
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Old 06-15-2011, 04:25 PM   #16
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We do have a ball valve on the output & we've been running it fast. I'm worried about slowing it down and getting the boil problem again. We'll test that soon, but the group I brew with and I are generally around 4-5 beers in by that time, so our focus is not great.

We always had the ball valve open on the MLT out, we just had the pump positioned too low and had too small an inlet hose for our setup. Raising the pump and putting a larger ID hose on the inlet helped a lot. One of the others is the pump expert, so I'm not super-clear on the details, but apparently the flow rate was severely depressed earlier because of the head pressure the pump was generating, based on its location and inlet.

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Old 06-17-2011, 01:15 AM   #17
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As long as wort is moving at more than a trickle, it won't boil. I preheat to say 164, then adjust my set temp to 152, close the valve to stop flow and dough in. During this time the RIMS tube is still in the low 160's so it won't turn on. Once doughed in, I slowly open the valve. After 2 or 3 minutes I have the pump wide open but I don't think I am using a pump as powerful as yours. It takes about 6 or 7 minutes after dough in for the mash to settle at 152 and then the BCS starts to fire the element.

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Old 06-17-2011, 01:24 AM   #18
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Yeah, I'll give it a try slowing it down next time. Though, other than disturbing the top of the grain bed, we haven't had any issues with stuck mashes at that flow rate or anything, so that's good.

I'll work on seeing how slow we can get it, but as of now I'm not really seeing any problems, so I'm happy.

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Old 06-17-2011, 01:35 AM   #19
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Quote:
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...I've set up an electric brewery using RIMS, with a 1" stainless tube containing a 1500W/120V, low density heating element under PID control with the thermocouple in the same tube on the output side...
I am probably way off mark with this but; Most RIMS tubes I have seen are at least 1.5" if not 2", maybe there is something in the smaller pipe diameter that makes the boiling problem worse.
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Old 06-17-2011, 02:05 AM   #20
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I am probably way off mark with this but; Most RIMS tubes I have seen are at least 1.5" if not 2", maybe there is something in the smaller pipe diameter that makes the boiling problem worse.
I think you are probably correct.
Below is an experiment I did with a 2" RIMs tube and a BCS control.
Where the temperature spikes in the graph, I closed the valve on the output of my pump to simulate a stuck mash. You can see that the temp spiked before it leveled back out to the setpoint temp (157f) but got no where near boiling. I did the same test several times as the input temp raised to see how it would respond.

A PID does not constantly monitor the temp. It measures the temp, calculates and executes a correction, then measures again. If there is not enough "buffer", the wort "could" boil during the "correction" before the next measurement.

In my experiment, I think the volume of the RIMs tube provided the buffer needed for the controller to respond before the temp got to far above set temp.

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