Water glass erratic level

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dnevil
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Water glass erratic level

Post by dnevil » Thu Apr 27, 2017 10:49 am

The "old-timers" seem to have all the answers on live steam construction. Take a look at this one.

Jim Jackson wrote in the Houston Area Live Steamers Stack Talk, October 1991:
From Southern Oregon Live Steamer, Gerry Bowden, who is visiting David Hannah this week, comes a way to reduce erratic water level bounce often seen in the boiler sight glass. Run the lowest backhead pipe connection a full quarter inch past the inside of the backhead. This buffers the unrestricted water movement in the boiler keeping the sight gauge level steadier.
More advice on water glass placement can be had by visiting this page:

http://ibls.org/mediawiki/index.php?title=Water_gauge

Happy steaming
Daris
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Bill Shields
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Re: Water glass erratic level

Post by Bill Shields » Thu Apr 27, 2017 5:16 pm

Mr. Jackson really does not understand what is going on because there is no 'buffering' involved...(not really sure how you buffer water...)

Making the pipe longer by 1/4" can have a good - or a very different affect. You need to understand the dynamics of what is going on and why.

If the extra 1/4" gets the pipe UP CLOSE to the firebox wrapper, you can end up with a false reading caused by high circulation flow past the end of the pipe causing reduced pressure in the tap -> hence an apparent LOWER water level than you would see when the boiler is cold (which is not necessarily a bad thing).

Extending the pipe a LITTLE BIT past the inner wall of the outer shell can help with erratic levels caused by circulation past the end of the fitting -> but to make a blanket statement of 1/4" is dangerous and should be considered VERY CAREFULLY before accepting at 'gospel'.

The idea is to get the end of the pipe AWAY from any 'high circulation' areas.

Try pipe IN / OUT / JUST PLAIN MOVE the fitting to another area.

Sometimes putting a 90 degree ell on the end of the fitting (inside the boiler) fixes the problem....sometimes it makes it worse.

Experimentation is often necessary because what works for one design of boiler / fitting location will not work for another.

One of my first BIG BOILER experiences with my father was a case where there were 3 water glasses, all with separate taps, but all within 12" of each other - all giving different readings...one of which was showing darn near NO WATER in the glass at all...all caused by random circulation around the lower tap point that was causing pressure differential (see Bernoulli...)
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dnevil
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Re: Water glass erratic level

Post by dnevil » Fri Apr 28, 2017 3:27 pm

Just curious, how do you add or remove a 90 degree ell inside the boiler?

Daris
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Bill Shields
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Re: Water glass erratic level

Post by Bill Shields » Fri Apr 28, 2017 3:30 pm

you have a large fitting in the wall of the boiler and a neck-down pipe with a 90 bent on it inserted...

or use a blind pipe with a hole drilled at 90 degrees on the end.

it's tricky but doable once you see it.
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Re: Water glass erratic level

Post by dnevil » Mon May 01, 2017 8:57 am

And does it matter which direction the ell points (up, down, left, right), or is that part of the experimentation as well?

Thanks,
Daris
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Re: Water glass erratic level

Post by Bill Shields » Mon May 01, 2017 9:00 am

Experimentation
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John Hasler
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Re: Water glass erratic level

Post by John Hasler » Mon May 01, 2017 11:27 am

If the pipe protrudes into the boiler you could get flow parallel to the pipe. This could cause it to act like a pitot tube and read high.

A thin plate on spacers centered over a flush opening should straighten the flow near the opening and thereby reduce fluctuations due to turbulence.

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Re: Water glass erratic level

Post by Bill Shields » Mon May 01, 2017 12:10 pm

you are correct...

Note also that ANY flow across the end of the tube (straight or not) can also cause a LOW pressure and make it read LOW....

I had one boiler where I had to put the bottom tap FORWARD of the firebox to get out of flow conditions.
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Re: Water glass erratic level

Post by John Hasler » Mon May 01, 2017 1:08 pm

Bill Shields writes:
> Note also that ANY flow across the end of the tube (straight or not) can also cause a LOW pressure and make it read LOW....

But straight flow across a flush opening (with a flat surface for at least ten diameters up and downstream) will not affect the reading. This is how pressure taps are done in industrial piping systems. Sometimes flow straighteners are installed upstream of a tap. Of course, in a boiler which way is upstream could vary unpredictably, which is why I suggested a plate.

Here is a set of lecture notes (ignore the supersonic parts): http://ocw.metu.edu.tr/pluginfile.php/1 ... ements.pdf

Another problem I read about somewhere (perhaps here) is that if there is too small a restriction in the lower port surface tension can keep the glass from draining.

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Bill Shields
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Re: Water glass erratic level

Post by Bill Shields » Mon May 01, 2017 1:14 pm

you are correct, but in many cases you don't have a flat surface for 10 diameters in any direction in our small boilers
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Re: Water glass erratic level

Post by John Hasler » Mon May 01, 2017 1:59 pm

Hire the guy who wrote those lecture notes as a consultant? (joke)

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Re: Water glass erratic level

Post by Bill Shields » Mon May 01, 2017 2:49 pm

no...the notes are very applicable to BIG BOILERS..

however many BIG BOILER standard practices just don't 'quite' work in small boilers...nucleate / sub-nucleate boiling looks the same in 1/16" scale as full scale...

consider the space between the outer shell and the firebox wall...it is VERY EASY to get high (turbulent) flows everywhere between the sheets and have no placed to put a pressure tap that is really static...

Sticking the tap in to get away from the outer sheet and running smack in to the inner sheet is not something you have to worry about with a boiler the size of an apartment building..

It's been a while but I seem to remember that if you have a pressure tap that is directly opposite a sheet that is generating bubbles and the bubble is forming directly over the end of the tap, then collapsing....you get some pretty weird pressure readings and the water level will jump up and down like crazy (hence don't just stick the tap in 1/4" and assume you are OK).
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