# Foam in stilling well



## mpetro (Jan 6, 2016)

Hey guys and gals,

Anyone have any tips on keeping foaming to a minimum in a stilling well? Currently using an Endress+Hauser FMU ultrasonic unit in a fish bypass at a hydro station, and it works great except that every couple days, a foam deposit builds up and leaves a ring around the wall of the stilling well. This causes an artificially high reading, which causes our controls to go out of whack. We tried moving the stilling well down very close to the bottom of the chamber, and the guys in the field are going to put a cap with a hole drilled in it over the end, but I don't have high hopes for that solution. I was thinking something the lines of strapping on a screen (or even a cloth?) over the end to work almost like a filter but I'm not sure if that would work either.

I would have gone with a guided wave sensor if I'd known the foaming would be an issue, but was told that it would be installed out of the way of any turbulence. It is indeed mounted in a corner away from the inlet, and it seems like there shouldn't be any foam making its way in, but it is finding a way.

Any insight would be greatly appreciated!


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## scotch (Oct 17, 2013)

how is the foam getting in the stilling well...we usually used a piece of 12" pvc pipe as the well to stop that...in the olden days we used a bubbler to measure the level so foaming wasn't an issue ever.


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## mpetro (Jan 6, 2016)

scotch said:


> how is the foam getting in the stilling well...we usually used a piece of 12" pvc pipe as the well to stop that...in the olden days we used a bubbler to measure the level so foaming wasn't an issue ever.


I'm not sure exactly how it's getting in, we have the stilling well installed so there's less than a 1/2" gap between the opening of the pipe and the floor of the chamber, and the chamber never drains below about 2". Despite this, we still get foam in it. The actual foam itself doesn't pose a problem, but since it's from a river, it must have a decent amount of biological matter, so it dries in a ring around the inside of the well.

Pic below. Note that the corner doesn't see much turbulence, the foam from the inlet tends to spread outwards and away, behind the POV of the picture. The water level in the pic is *EDIT: below* standard operating level, so the water is almost always about 1/3 of the way up the pipe. We've tried setting the output of the PID controller to maintain that approximate level, but the level of the canal that feeds into the bypass chamber changes based on the draw of the hydro station that the bypass services.


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## scotch (Oct 17, 2013)

Maybe you are having back eddys into the corners ...maybe add an over sleeve.. a larger pvc pipe with slots cut in the base . We used to have lots of fun in the chemical plants ;with the flumes discharging to the treatment plant in Scotland years ago. Good luck


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## mpetro (Jan 6, 2016)

scotch said:


> Maybe you are having back eddys into the corners ...maybe add an over sleeve.. a larger pvc pipe with slots cut in the base . We used to have lots of fun in the chemical plants ;with the flumes discharging to the treatment plant in Scotland years ago. Good luck


That's a good idea, I'll look into that. Thanks!


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## DIRT27 (Aug 25, 2010)

I like scotch's idea of a bubbler. Sounds like you might not be using the right device for the application. I can tell you if you have instrument air available a bubbler would be the best for the application in the pictures.


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## mpetro (Jan 6, 2016)

DIRT27 said:


> I like scotch's idea of a bubbler. Sounds like you might not be using the right device for the application. I can tell you if you have instrument air available a bubbler would be the best for the application in the pictures.


Unfortunately we don't have instrument air available. I also agree that it's likely not the ideal instrument, and would have gone with guided wave radar if I had the opportunity.


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## MechanicalDVR (Dec 29, 2007)

I think the quickest thing to try would be a ring of slotted larger diameter pipe at the bottom of the current pipe with a mesh sleeve around it.


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## mpetro (Jan 6, 2016)

MechanicalDVR said:


> I think the quickest thing to try would be a ring of slotted larger diameter pipe at the bottom of the current pipe with a mesh sleeve around it.


That's another good idea. I'll see if we can give this or scotch's idea a try, they seem to be similar. Thanks again guys!


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## cmdr_suds (Jul 29, 2016)

Hang a submersible level transmitter and your problems will go away. I have had no end of problems using ultrasonics for level control. Foam, vapors, noise ect. 

Sent from my LG-AS330 using Tapatalk


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## MechanicalDVR (Dec 29, 2007)

cmdr_suds said:


> Hang a submersible level transmitter and your problems will go away. I have had no end of problems using ultrasonics for level control. Foam, vapors, noise ect.
> 
> Sent from my LG-AS330 using Tapatalk


If you read all his posts it sounds like he is trying to use the equipment they already have.


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## cmdr_suds (Jul 29, 2016)

True. But I bet if you figure in all of the hours he will burn trying to make an ultrasonic work in what is a bad application, he could more than justify a submersible level transmitter. 

My bet is the foaming is a biological formation and will never go away. Sometimes you just have to drop back and punt.

Sent from my LG-AS330 using Tapatalk


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## MechanicalDVR (Dec 29, 2007)

cmdr_suds said:


> True. But I bet if you figure in all of the hours he will burn trying to make an ultrasonic work in what is a bad application, he could more than justify a submersible level transmitter.
> 
> My bet is the foaming is a biological formation and will never go away. Sometimes you just have to drop back and punt.
> 
> Sent from my LG-AS330 using Tapatalk


Oh I'm not going to disagree with any of that, just stating the facts.


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