Control Engineering

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Bubblers and DIY instrumentation
June 22, 2007

When we publish articles that are considered "technology roundups," we often receive responses from readers that we left something out. (These are not things we take personally, as long as the response is reasonable.) In most cases we do this deliberately due to space constraints, but sometimes we simply overlook things. Here's a response I received to our June issue article on level sensors from Isaac Corbell, PE, Wilmington, NC:

"I was surprised that the most reliable level sensing and control system was left out of your article: the 'bubbler system.'

Since the 1970’s, when I began my career in controls catering to the then-booming textile industry in NC, I was taught the bubbler method of level control for the water weir in the air washing air handling systems. The volumes of lint and cotton debris in the weir meant that many other types of level controls, mostly floats in those days, would fail. The bubbler would not.

Over the years I always offered the bubbler system to all my customers and was very successful in eliminating level control troubles. Take for example, a large manufacturing plant in Mt Holly NC, that has extensive painting facilities. For over 15 years, bubbler systems have faithfully conquered plant level control needs when very expensive methods that your article discusses failed miserably.

In the painting booths, downdraft air flows rapidly into an under-floor area where a 5 foot deep expansive water tank grabs onto the paint residue and skims it into weirs. Several types of level controls would not work as they constantly got covered in sticky paint residue. We put in a simple bubbler and now, 7 years later, not one problem. The bubbler cleans itself, and can be calibrated to be set off from the bottom to allow for the heaviest sludge and debris there. Similarly, we used them for anti-freeze tanks, paint tanks, fuel tanks, wastewater and sludge tanks, EPA monitoring, etc, etc.

I am now working for a university in Wilmington NC and all of our sewage pump stations, even the ones installed this year, all have bubbler control systems in them.  Easy to maintain, do not clog, and work and work, without problems."

OK, I admit that I left the bubbler out deliberately. Some might take issue with the thought that it is the most reliable method in any application, but it certainly has its advantages. It isn't usable in a situation where there can be no product contact and a tank that isn't at atmospheric pressure will certainly complicate matters. Nevertheless, Isaac's point is well made and it merits consideration with so-called higher-tech methods.

There are commercial units available (Hach is one manufacturer.) but the approach is also suitable for home built installations. All you need is a compressed air supply, a pressure gage or sensor that reads in a low range, and the math skills to make a few volume/pressure calculations.

In olden days when there was less instrumentation available, engineers had to be more creative. You can build your own bubbler device. You can weld your own thermocouples. You can set up your own differential pressure flowmeter. (That sort of brings new meaning to the term, "left to your own devices.") Few engineers at the plant floor level probably have time to build their own anything any more, if a commercial version is available and reasonably priced. I suppose that's a little sad in itself.

Posted by on June 22, 2007 | Comments (0)