Subject: Re: Live Steam: Water Gauge how-to

From: [email-masked] (David William Jenkins)
Date: Sun, 26 Feb 1995 21:34:19 GMT

>Andy Dingley                             [email-masked]
>
>In no way should the content of this message be taken to condone the
>use of perfectly useful machine tools for the building of steam engines,
>particularly pointless little ones.
>

How about particularly pointless BIG steam engines, e.g. 5" gauge?

;-)

David Jenkins              -- aka --             Lathyrus Computers Ltd
***********************************************************************
* All incorrect spelling and grammar is intentional.  Corrections are *
* superfluous and will be ignored.  So there.                         *

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From: [email-masked] (Roger Mitchell)
Date: 28 Feb 1995 15:49:37 GMT

Miniature water gauges for boilers are available from Coles Power Models in
Ventura, California. If you desire to build your own I would recommend using
"O" rings for sealing the fittings to glass. I use them on all of my scale
model locomotives and also used them on the water column of the 6 inch to
the foot scale 2-6-2 prairie that Alex Schneider and I built for our
Timnath Northwestern Railway. The water column on this locomotive was made 
from a piece of 1.25 inch hex brass stock about 8 inches long. The middle
was bored out to 1/2 inch with "O" ring grooves cut into the top and bottom
and openings milled along the flats to view the glass. We end up replacing
"O"rings on this engine about once every 3 years.
				
				Roger Mitchell
				Vice President and Master Mechanic
				Fort Collins Municipal Railway
				Co-builder: Timnath Northwestern Railway

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From: [email-masked] (David William Jenkins)
Date: Tue, 28 Feb 1995 20:25:39 GMT

In article <[email-masked]>, Charles Lamont ([email-masked]) writes:
...
>  However (although I have seen at least a couple of 
>gauge glasses fail on models under steam without causing the slightest 
>injury in any case) I would advise caution here because, as has been 
>said, these things are potentially quite dangerous if not designed and 
>used with due care.
>

I've seen a few fail, all in the same manner - the glass splits in
several places but holds together reasonably well.  Usually
there's just a whisp of steam showing.

The great peril is that it is now very fragile, and will give way
at the slightest touch.  It will usually hang together long enough
to allow the user to dump the fire and get the pressure down fast
as long as it's left alone.

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From: [email-masked] (Charles Lamont)
Date: Mon, 27 Feb 1995 18:19:10 +0000

If an o-ring is too bulky a seal you could cut a ring from a piece of 
rubber tube.  To get a square cut, mount the tube on a rod held in  
the lathe chuck and part off washers with a razor blade (using soapy 
water as a lubricant, as I remember it). 

Yes, capillary attraction is a potential problem, and 1/8 inch is about 
the smallest acceptable bore for any scale.

You also need to ensure that all water and steam passages through the
gauge are no smaller than the bore of the glass, and that the glass is
an easy fit in the metal parts it passes through, so that it is really
held only by the rubber.

On the other hand, one good authority has it that differental expansion
is not actually relevant in this case, and goes on to cite several
examples of designs that have been successful in practice while totaly
ignoring this issue.  (Or may be the designers actually did some sums 
and found that they would not expect any untowardstresses in this case, 
I don't know).  However (although I have seen at least a couple of 
gauge glasses fail on models under steam without causing the slightest 
injury in any case) I would advise caution here because, as has been 
said, these things are potentially quite dangerous if not designed and 
used with due care.

BTW, does surface tension vary significantly with temperature and 
pressure? 

-- 
Charles Lamont

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From: [email-masked] (Greg Dermer)
Date: 28 Feb 1995 20:41:47 GMT

Gore sells a new product called Glide that is (of all things) a
teflon impregnated tooth floss.  Has anyone tried using it as
packing in place of small diameter asbestos yarn?  (by the way, its
really good tooth floss)

Greg

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From: [email-masked] (Ian Kirby)
Date: Wed, 01 Mar 1995 08:32:12 +1100

In article <[email-masked]>,
[email-masked] (Mark Horridge) wrote:

> I hope to make a water gauge for a small steam engine (boiler diameter
> 2 1/2 "). I have seen various plans which all use a gland (sealed with an O-
> ring or graphited yarn) to attach the glass tube to brass fittings. Trouble 
> is, I can see that the gland is going to be disproportionally large, 
> compared to the glass and to other fittings.
> 
> I'd like to glue the tube into a close fitting brass socket. Can anyone 
> suggest a cement that withstands 100 psi steam pressure ? The tube is .25" 
> diameter.
  I would strongly advise *against* gluing the glass tube in.  Glass and
metal expand/contract at different rates, and in a gauge glass situation,
reliance on the relative flexibility of the packing material is needed to
accommodate this.  Even with packing, if the gland nut is done up too
tight, the glass will snap, almost every time, because of the
inflexibility.
  On a small boiler, I think you will just have to put up with a slightly
oversize gauge glass - too small a glass tube, and the capillary action
will lead to incorrect indication of water level, which will lead to....
I forget who first stated it, but it bears repeating; "Nature cannot be
scaled".
Regards, Ian.
-- 
Ian Kirby.                          Ph: +61 42 213353
Dept of Mechanical Engineering,     Fax:+61 42 213101
University of Wollongong.           Email: [email-masked]
Northfields Avenue,
Wollongong. 2522.
NSW Australia

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From: [email-masked] (Steve Rayner)
Date: Thu, 2 Mar 1995 10:56:33 GMT

>suggest a cement that withstands 100 psi steam pressure ? The tube is .25" 
I make most of my own fittings, they must be a bit out of scale to work. 
Some of the commercial designs are a bit clumsy, so why not design your own?
I did.  Even at room temperature epoxy will shear away from glass, and
most metals, in a water gauge it will fail for sure. "O" rings should be
sillicon, the black ones can break down at high temperatures, and some of
the black ones can release hydroflouric acid if they break down.

-- 
                                Steve Rayner.