Herms-loop makes system cavitate

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Smellyglove

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I have spent almost nine hours trying to figure out why I get cavitation in my system. I've narrowed it down to the herms-loop, but that's it.

It restrics flow quite a lot. I've changed every bit and piece when it comes to QDs and barbs. When troublehooting every component works good, when looping through the herms, I get bubbles.

I've turned my brain inside out and I'm about to take up on knitting as a new hobby.

Anyone?
 
Are you sure it's cavitation? Cavitation usually sounds like gravel rattling in a pump. The sound is made by bubbles imploding on the impeller. If you have bubbles coming out the top of your coil, that's just air in your system somewhere.

I don't have a HERMS, I'm building up to one. But there are two main causes of cavitation: not enough net positive suction head and too much restriction on the inlet to the pump.

You can create more head for your pump by simply lowering the pump in relation to the BK.

Otherwise, focus on reducing headless on the auction side of the pump: larger pipe diameter, gentler elbows, make sure your valve is open all the way. And if you use a false bottom, make sure it isn't too restrictive of flow.
 
If your pump doesn't cavitate with the HERMS coil out of the loop, the coil shouldn't cause it. Just to be sure, you're going kettle, pump, HERMS in that order right? Do you see bubbles between the pump and coil?
 
I primed the **** out of that pump yesterday.

No bubbles are left in the hoses whatsoever. I dont see any bubbles when running the pump. I've been sitting like a monk looking for bubbles. My girlfriend was wondering if I'm alright..

I prime the pump, even shake it to release air inside it, turn it on. And after 30 seconds-one minute I can hear air inside it, and it's slowly getting worse the longer I run the pump intil the pump will sqeal and lock up.

Yes I'm running hlt-pump-coil-hlt.

The coil ia 10m x 6mm ID. It's restricting flow a lot.
 
I primed the **** out of that pump yesterday.

No bubbles are left in the hoses whatsoever. I dont see any bubbles when running the pump. I've been sitting like a monk looking for bubbles. My girlfriend was wondering if I'm alright..

I prime the pump, even shake it to release air inside it, turn it on. And after 30 seconds-one minute I can hear air inside it, and it's slowly getting worse the longer I run the pump intil the pump will sqeal and lock up.

Yes I'm running hlt-pump-coil-hlt.

The coil ia 10m x 6mm ID. It's restricting flow a lot.


6mm does seem tight, but if it gets worse over time then your pulling air in somewhere. If you fill the HLT to completely cover the coil, does it still do it?

Can you post a pic?
 
I guess i misunderstood the meaning of the word cavitation.

I guess im sucking air. Does this point have to be before the pump, or can it be after also?
 
My pump seems like it "throws the magnet" kinda like a stir plate does when I open the ball valves fully. Might be worthwhile to try restricting the valve on the output to closer match the tubing ID.

That almost seems like it would be tough to prime with the coil being the same height as the pump. Do you get a good prime on the pump? Maybe try putting the pump on the floor.
 
Cavitation and air bound will both cause your pump to run crappy.

Cavitation is caused by restricted flow on the low pressure side which causes a large pressure drop and the liquid phase changes to a gas. When it passes through the pump to the high pressure side, the gas bubble phase changes back causing the bubble to implode. The impeller is usually the preferred place for it to implode and will eventually destroy the impeller.

Air bound means you have air in the pump. Air bound will cause the pump to run very hot.

I'd disconnect the HEX coil and run MT -> pump -> MT or to a bucket. You should still have the same problem. If you do, it proves the problem is on the suction side and narrows it down for you.
 
If what I'm about to say is correct, its unbelievable. Although I shouldn't say it becaus I'll be jinxing it.

I think it works. Five minutes and no sound of air.

The umbelievable part is that I had the sparge arm submerged in the hlt water all these 12 hours of cursing. The air couldnt escape the coil.

Another culprit might be the way to thin teflon tape I used. I ran out of proper teflon tape last night and only had thin tape left. The last part I changed tape on was the PID-NPT-probe so I didnt think that was it. Today I got out and bought som proper tape and changed the tape on the pid I put on yesterday. That one part has for some reason always had the thin tape, swapped it several times but I always for the thin tape since I've been running out of proper tape once in a while and used the crappy thin tape as backup.
 
Air being pulled in comes only on the inlet side of the pump. I notice that you have quite a few fittings between the MLT output and the pump inlet. Any one of them might be allowing air into the system. You might try to put a drop of concentrated food coloring on each joint in sequence and look for it in the hose at the pump outlet.

I found that my RIMS system sucked air through a bad washer in a cam lock disconnect when I had a thick mash and almost got a stuck sparge. That was difficult to troubleshoot because of the geometry of a cam lock.
 
I primed the **** out of that pump yesterday.


I prime the pump, even shake it to release air inside it, turn it on. And after 30 seconds-one minute I can hear air inside it, and it's slowly getting worse the longer I run the pump intil the pump will sqeal and lock up.

I get the same thing when whirlpooling at the end of the boil. It starts fine, and in 30 seconds or so it starts to make a little noise. If I don't correct it, the squealing starts soon after. I assume its due to the near boiling temps making phase change much easier. As long as I throttle back on the pump a little bit with the output ball valve its not a problem, probably due to the increase pressure inside the pump cavity. Keeps the water in liquid form.

Doesn't sound like the same as your problem though, so I'm glad you got it all worked out
 
Well.. I jinxed it. After about ten minutes its back, and I see small airbubbles out of the spargearm.

Then it must be the comp fittings, or still maybe a QD.. Anyway, im gonna brew today.
 
Double check your suction side, a straight length of pipe on the suction side of the pump head may help settle down any turbulence induced issues. Also make sure your not sucking air at the kettle.
 
I had a straight one before, same thing happened. It works like a charm if i go straight hlt-pump-hlt. Leaving the coil out.

But. I bet it's the comp fitting in the coil. I remember i tried to remove it long time ago, but that didn't work so maybe it got a bit roughed up in the process.

Anyhow. A new ss coil and new comp fittings are already a week in transit, so this is anyhow the current coils last brew.

Edit. I ment mlt.
 
It can be facing the way mine is. The output is slightly higher then the input due to its design.

Now that im running wort through the system its way easier to see bubbles. Theres a solid stream from the mlt, or the priming valve. So now I knoe where to look. A theory is that connecting the herms does something to the pressure and reaistance in the system.
 
From your picture you have a 90 degree fitting going into the pump. You need 10X the Diameter of straight pipe before the pump. If you're running 1/2" hose then you need 5" of straight pipe before the pump.
 
Hmm. Didn't know about that, although I understand why. But. I've been running the elbow for at least 30 brews without problems.

My mlt is my problem afaik.
 
Fixed it.

Thanks for all your input. Learnt a bunch of new stuff when it comes to design of flow with a pump in the system.


Edit; I cant believe it. Ive been sous vide-ing the whole day and its been working fine. The second I post here it starts to crap out again.
 
I'm still having issues. Every time I fire up the herms it happens.

Anyone know why this wold happen? It happens when the temperature rises.
 
I'm still having issues. Every time I fire up the herms it happens.

Anyone know why this wold happen? It happens when the temperature rises.


If it's temp related, maybe your sucking air through a hose, maybe the HERMS bulkhead fittings are sucking air?
 
Maybe your pump is gutless. I would try swapping the pump with a friend's pump just to see if that fixes it.

Also maybe you have some crap stuck in the herms coil blocking flow.

I would also try taking the tee off the pump discharge and try it with just the valve there.
 
It works unless I'm ramping temps. Sometimes it just works fine when ramping temps, but 9/10 times it sucks air when I ramp temp.

I'm pretty sure it's between MLT and pump, because if start the pump, leave it, check what's going on, I can see tiny air bubbles stuck on the edge of the barb at the MLT, the ones that didn't make it down into the pump.

It works with cold water. I've tried everything. The only randomness is whenever it does NOT happen if I ramp the temp. If I bypass the herms it works 100% of the time. If I go through the herms it works with cold water, and 1/10 times with temp ramps. It's starting do drive me nuts.
'
 
My thought too, but I've changed every QD, barb and added different teflon tape on every connection in the brewery, added hose clamps and what not.

My last resort is to try another O-ring inside the march-pump, I'm still waiting for it. I don't know if the air comes from the MLT, or rises from the pump.
 
When liquid is hot, it undergoes phase change faster. So, gas just sort of forms inside the liquid. Combine that with the weird pressure highs and lows that exist inside of the pump cavity, enough gas could form that it causes some nasty behavior. This problem is exacerbated when you have some restrictions on the pump inlet. On one side of the impeller blades, there can be a near vacuum created, which will definitely cause some gas to form.

Throttling back on the pump outlet ball valve keeps the pressure inside the cavity a little higher so the phase change isn't as rapid, so it could help your pump run a little smoother.

It happens on mine when whirlpooling. I have chugger center inlets and 1/2" line. No elbows or anything on the input. However, its boiling liquid, so it doesn't take a lot to get the liquid to go to gas. Throttling back on the output ball valve makes the problem go away. Doesn't even take a lot of throttle. I'd guess if I used 3/4" tubing on the input like I'm supposed to there wouldn't be a problem in the first place.

Just a thought.
 
November BYO has a good article on pump configuration (which side should point up). The pump output is always higher than input or you will get an air bubble that cannot get out.

Edit: your photo looks corrrect - so perhaps you are pulling in air after all.
 
Sorry I keep beating this horse, but it isn't dead until the sound of air is gone..

I've tried restricting the output, but that didn't seem to help much. Although it was a logical thing to do.

I just discovered something new.

I tilted the mt just to drain it, it's a 10g boilermaker. And as I tilted it huge amounts of air escaped from under the FB. I have NO idea what that amount of air was doing down there. This is a mystery to me. So I'm guessing I'm sucking that air into my pump. Now the question is if that air builds up over time, and if it does, why does it happen.

Idk if this has anything to say, but when I open up the priming valve, which is located on the pump exit, it immediately sucks tonnes of air.

Could it be that the FB is to tight for how I'm running the system? There's way more restriction after the pump (herms and sparge arm) than before the pump.

Thanks for your patience guys. Everything helps.

Btw, I'm 100% sure its not a leak in threads, I've swapped everything, but I haven't run the system without the FB.

Edit: even clogged the sight glass, no difference. The water which i start out with is very cold. Its winter here in Norway.
 
What is the inside diameter of the herms coil? How long is it?
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I know the OD. Which is 1/2" and its SS. about 6-7 feet long. I'm restricting it when I recirc, or else I'm getting a brick grainbed.
 
Sorry I keep beating this horse, but it isn't dead until the sound of air is gone..

I've tried restricting the output, but that didn't seem to help much. Although it was a logical thing to do.

I just discovered something new.

I tilted the mt just to drain it, it's a 10g boilermaker. And as I tilted it huge amounts of air escaped from under the FB. I have NO idea what that amount of air was doing down there. This is a mystery to me. So I'm guessing I'm sucking that air into my pump. Now the question is if that air builds up over time, and if it does, why does it happen.

Idk if this has anything to say, but when I open up the priming valve, which is located on the pump exit, it immediately sucks tonnes of air.

Could it be that the FB is to tight for how I'm running the system? There's way more restriction after the pump (herms and sparge arm) than before the pump.

Thanks for your patience guys. Everything helps.

Btw, I'm 100% sure its not a leak in threads, I've swapped everything, but I haven't run the system without the FB.

Edit: even clogged the sight glass, no difference. The water which i start out with is very cold. Its winter here in Norway.

Back to the photo - if I understand correctly that ball valve on the output of the pump is your priming valve. If so then you are missing a second ball valve on the output of the pump - that is the only place you can throttle the flow in this setup without cavitation/compacting the mash/pulling air.

pump.jpg
 
I have a ball valve on the sparge arm, after pump and herms. Its on the far end on the loop. Do Ineed one just after the pump?

Edit: added a valve just after the priming valve, restricted A LOT, same thing happens but slower than before.
 
Cavitation and air bound will both cause your pump to run crappy.

Cavitation is caused by restricted flow on the low pressure side which causes a large pressure drop and the liquid phase changes to a gas. When it passes through the pump to the high pressure side, the gas bubble phase changes back causing the bubble to implode. The impeller is usually the preferred place for it to implode and will eventually destroy the impeller.

Air bound means you have air in the pump. Air bound will cause the pump to run very hot.

I'd disconnect the HEX coil and run MT -> pump -> MT or to a bucket. You should still have the same problem. If you do, it proves the problem is on the suction side and narrows it down for you.

I just started to re-read the thread and I think I missed this post. Great reply, wish I saw it sooner :)
 
I have a ball valve on the sparge arm, after pump and herms. Its on the far end on the loop. Do Ineed one just after the pump?

I don't think you can safely shut that valve off without some risk of bursting the hose, and you will be shutting it way down. Move that valve to the pump (right after the tee where your bleeder is).

You can only pump wort as fast as it will gravity drain through the mash without becoming stuck, or pulling air. Some folks have crushed false bottoms with these pumps by running the flow wide open.
 
I don't think you can safely shut that valve off without some risk of bursting the hose, and you will be shutting it way down. Move that valve to the pump (right after the tee where your bleeder is).

You can only pump wort as fast as it will gravity drain through the mash without becoming stuck, or pulling air. Some folks have crushed false bottoms with these pumps.

Check my edit just before my last pic.
 
I don't think you can safely shut that valve off without some risk of bursting the hose, and you will be shutting it way down. Move that valve to the pump (right after the tee where your bleeder is).

You can only pump wort as fast as it will gravity drain through the mash without becoming stuck, or pulling air. Some folks have crushed false bottoms with these pumps.

Check my edit just before my last pic.
 
Even if i close the new restricting valve on the output of the pump it happens..
 
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