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boiler water window

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mick H03/04/2011 18:08:55
795 forum posts
34 photos
I am constructing a steam powered fire engine for my grandson and as a
variation on the glass tube type water gauge I would like to incorporate a water window in the boiler backhead.
 
 
I propose to bed the lens on a silicone "O" ringand sandwich it porthole style between the base which is silver soldered into the backhead and a cover secured by six 6 BA screws. The circular lens has a diameter of 20mm but when the cover is in place the net viewing window will be 10mm. The lens is therefore supported all around by 5mm .
 
The boiler will have a working pressure of 50psi at which pressure the water will be at a temperature around 150 degrees C.
 
I have fashioned an experimental lens from 2mm picture glass and tested it to twice working pressure = 100psi.
 
I have considered using polycarbonate but 150 deg.C is becoming quite close to the deformation temperature of polycarbonate.
 
Can anyone advise me as to whether ordinary glass can be used in this application. What do Beck etc use in their locos fitted with water windows?
 
 
 
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Rob Stevens03/04/2011 20:36:47
12 forum posts
No knowledge or info on your question but the following site may be useful for supplies:
 
 
Rob Stevens
Jeff Dayman04/04/2011 00:34:06
2356 forum posts
47 photos
If you can find a scientific or technical/chemical glassware maker near you, ask them for a high pressure gauge glass of the diameter you need. They will likely have a selection in stock of tempered borosilicate glass disks. I know of one such firm, this side of the pond, but I'm not sure in UK.
 
Do not use polycarbonate in steam service at all. It will not take the temperature and even when cold will only take low pressures.
 
There are a couple of specialty translucent plastics that will take high temperature, but they are not steam service rated and are not to be used for pressure vessels and are VERY expensive. Solvay's 'Topas' is one brand.
 
Glass, tough and thick, will do a good job in steam service at reasonable cost.
 
Just my $0.02. Your mileage may vary.
 
JD
Ian S C04/04/2011 13:19:34
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7468 forum posts
230 photos
Michael, if you can find some one with spare parts for Wilesco, or Jensen toy engines, these one had a water window. Ian S C
mick H24/04/2011 09:12:44
795 forum posts
34 photos
Thank you for your advice Rob, Jeff and Ian. All of it was useful and gave some good leads one of which led to Piper Glass of Watford who were able to supply me with toughened glass lenses and actually sent them to me for free!
 
It is possible to get Wilesco spares but their windows are too big for my application.
 
The watch batteries site mentioned by Rob gives a comprehensive selection of toughened glass lenses which I would have used if I had not come up with Piper.
 
Thanks for your advice on polycarbonate Jeff ........an experiment with live steam could have proved disastrous.
 
From what I can gather toughened glass is cut to size and is then undergoes a toughening process. My enquiries have revealed that pretoughened glass is available as a product called "Borofloat" which can be cut and shaped like ordinary float glass but I have not been able to track any down so far.
Paul Horth25/04/2011 21:24:49
69 forum posts
18 photos
Michael,
 
Are you confident that you will be able to see a water level in the window? It's dark inside the boiler, and there will also be droplets on it. The conventional tubular gauge glass allows light from behind which makes the water level visible. Also, are you sure that 10 mm will give you the range of level that you need to check?
 
Good luck
 
Paul
mick H26/04/2011 07:37:21
795 forum posts
34 photos
Hallo Paul,
 
My only confidence is derived from the fact that several commercial manufacturers use a water window system. I am aiming for simplicity as this model is being made for a seven year old, albeit it will only be used under Dad's supervision. The window is 20mm in diameter and will hopefully show if and when the boiler water level falls to about one third of capacity.......as the boiler is gas fired, I am hoping that this will be an effective failsafe indicator. Only trials will determine how effective it will be in practice. I am reasonable confident that there will be enough light to show water level.
 
Thanks for your interest.
Gordon W26/04/2011 17:21:22
2011 forum posts
This may be relevant:- I.ve just had a new windscreen cut for my car, it's flat toughened glass, about 3 ft x 1ft , I got it cut at a local company who do windows for tractors etc. It came of a sheet 8ft x 4ft ? The chap kindly included the eu logo in the corner as it is needed for MOT. As far as I know now heat treatment was needed, did not see it cut tho.
mick H27/04/2011 07:33:14
795 forum posts
34 photos
Thanks Gordon. I live in tractor country and will make enquiries
mick H28/04/2011 08:19:04
795 forum posts
34 photos
Paul,
Having sown the seeds of doubt by your queries, I carried out a hasty trial of the water window and it performed probably better than I could have wished. The visible window is 12mm in diameter and the meniscus showed as a bright line...about 2.5mm deep....against the darkness of the inside of the boiler. In this sense the darkness of the interior is advantageous. When the boiler is full there is, of course only darkness but as soon as the water level drops within the range of the window the meniscus is quite apparent. No problem with bubbles etc.
 
In my limited experience in the small gauges in which I work, I would suggest that this is a far better water level indication than I have ever had in the quarter inch type gauge glasses in the conventional set up.
 
Once again, thank you for your interest.
Paul Horth29/04/2011 15:30:49
69 forum posts
18 photos
Michael,
OK, I'm glad that your idea worked out. I certainly did not intend to strike a negative or critical note. Good luck and thanks for sharing a clever idea.
Best wishes
Paul
mick H30/04/2011 10:56:08
795 forum posts
34 photos
Paul,
 
Be assured that your comment was not interpreted as negative or critical.......but it
did spur me on to get things tested ! Thanks, again.

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