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sight glass float

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dave greenham20/09/2014 22:11:36
100 forum posts

Hi guys.

I'm building a 1. 1/2" single cylinder traction engine. The problem I've come up against is the sight glass. The glass is 5mm O/D and the I/D is 3mm. The length of the tube is around 1.1/2" long. With my eyesight seeing the level of the water is going to be somewhat of a problem. I've seen larger engines which have a floating ball inside the tube, but what is the ball made off ? I can't see this just being a normal plastic ball like those used by fishermen as I think it wouldn't stand the heat. I did think it could be Delrin. But doing a search a supplier said at the bottom off the page that Delrin doesn't float. So I'm now stuck as to what they are made off and hope one off you may be able to tell me and point me in the right direction to a supplier.

Many thanks in advance.


John Alexander Stewart20/09/2014 23:42:55
798 forum posts
53 photos

Dave - another approach is to put a diagonally lined bit of metal behind the glass, you'll find that (depending on distance of the metal to glass) the lines will go horizontal.

You can also get "red line" or "blue line" glass, where the size of the line grows where the glass is - on a locomotive I'm currently steaming, the line goes from thin red line above the water level to solid red below.

Just an alternative thought.


julian atkins20/09/2014 23:43:25
1238 forum posts
353 photos

hi dave,

there are various ways of getting round the problem you describe. although im not a miniature traction engine builder (miniature locos being my thing) ive driven and steered a few fullsize traction engines.

the easiest way to solve your problem is to place a white painted strip of brass behind the water gauge with diagonal lines marked on it in black. in fact most of my locos have nothing more than a strip of white card behind the water gauge with black lines added with black biro.

schellbach gauge glas is another option, but is more brittle than ordinary gauge glass.

i dont approve of balls bobbing up and down in gauge glasses and they dont give a clear reading in the event of bubbles forming and arent acceptable in miniature loco practice.

there is a flourescent dye you can add to the boiler feed water/boiler. this was used in power stations (and still might be). i had a great friend in the SMLS who used this on his miniature locos.



dave greenham22/09/2014 23:12:59
100 forum posts

Hi John & Julian.

thanks both for you're suggestions.

i think I'll do some tests with a dye first as it seems the easier option. Failing that. I shall make the plate you suggest with the stripes. Speaking off the plate, should the stripes be 45 degrees, or steeper ?

thanks again for the replies.


John Alexander Stewart23/09/2014 01:00:48
798 forum posts
53 photos

Nick - take a bit of card, and try it! About 45 is fine, maybe 30 degrees.

Depending on the distance of the card from the rear of the gauge glass, the lines will bend more/less, so experiment a bit.

As Julian says, try it with a bit of card. One of mine has paper on aluminium, and was cheap and cheerful to make, but it got replaced this past spring with a bit of red-line gauge glass.


Edited By JasonB on 23/09/2014 07:29:30

Paul Lousick23/09/2014 01:37:19
1707 forum posts
627 photos

Hi Dave,

Water gauge glass can be purchased with a red stripe down the back which makes the level of water visible. Much like that on a thermometer. (do an internes search for a supplier)

The other option is to add a backing plate with lines at 45 degrees. The water in the glass refracts the light and makes the lines appear in the opposite direction. (see image below)

I would not use a float in the glass, it may block the flow of water and give an inaccurate reading. Also take care adding anything to the water as it may cause foaming.


water gauge.jpg

CLEAR COLUMN                    CHEVRON BACKING                 RED STRIPE


Edited By Paul Lousick on 23/09/2014 01:38:48

julian atkins23/09/2014 02:10:43
1238 forum posts
353 photos

hi dave,

paul's advice is excellent with the caveat that schellbach glass (with the coloured vertical stripe) is more brittle.

the angle of the stripes is dependant on the distance from the glass.

the dye used in fullsize power stations doesnt cause foaming.

i woud always fit a strip behind the glass painted white with black stripes whether dye is used or not - i dont use dye on my locos but it was very common on the SMLS years ago when ray parsons worked at shoreham power station plus night running coz the dye was flourescent!

some traction engines had spots instead of stripes though most traction engines in fullsize have klinger type gauges.



Gary Wooding23/09/2014 09:19:56
822 forum posts
211 photos

It's not unusual to add some tannin to the water in steel boilers - it helps to protect the steel from corrosion. A side effect is that it makes the water a pale brown which makes it more visible in the sight-glass. I don't know if it's suitable for copper boilers.


Bazyle23/09/2014 13:25:14
5834 forum posts
217 photos

My loco has a tiny 3v bulb next to the galss. Makes a huge difference having proper light.

Michael Gilligan06/10/2014 15:35:25
17667 forum posts
811 photos


Here are a couple of photos of the real thing.p1180801_s.jpg




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