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warwickshiresteam
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Joined: 31 Jan 2008
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 Posted: Tue May 06, 2008 2:46 pm Post subject: water level glass |
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| I have trouble with water level sight "glasses" cracking and blowing, particulalry on meths fired locos. What's the most likely cause and best solution? |
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Titan
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Location: Derby
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| Posted: Tue May 06, 2008 2:55 pm Post subject: |
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One solution I have heard of is getting glass microscope slides and trimming to fit. Not sure how easy that is but certainly a bit more heat proof than plastic!
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Graham-Jilly
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Location: Brisbane Qld Australia
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| Posted: Tue May 06, 2008 7:02 pm Post subject: |
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Im haveing the same problem 
so my solution was to buy an uprated boiler 
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warwickshiresteam
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| Posted: Tue May 06, 2008 7:14 pm Post subject: |
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| Titan wrote: | | One solution I have heard of is getting glass microscope slides and trimming to fit. Not sure how easy that is but certainly a bit more heat proof than plastic! |
Thanks, but I have tried that, just once; the glass cracked before running pressure was reached! There may be different grades of slide glass though......
Has anyone tried this succesfully? |
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warwickshiresteam
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| Posted: Tue May 06, 2008 7:28 pm Post subject: |
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| Graham-Jilly wrote: | Im haveing the same problem
so my solution was to buy an uprated boiler |
Glad I'm not the only one ! Your solution sounds a bit drastic (not to mention expensive!) |
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Graham-Jilly
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CCairns
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Location: Glasgow, Scotland
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| Posted: Wed May 07, 2008 2:10 am Post subject: |
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| Quote: | | What's the most likely cause and best solution? |
There would appear to be 3 reasons why sight glass plastics fail on the Mamod/MSS locos, apart from the obvious one of running the boiler water level too low!
1. The supplied 'O' ring is of too small a thickness so that when you tighten up the brass backplate, the sight glass plastic tends to touch the inside of the boiler cutout hole. The extra heat generated by the meths burner (and the same for gas burners) then slowly melts a groove into the glass which will then leak. I have found use of the oval washers as sold for the Mamod SP series sight glass plastics seems to prevent this type of melting.
2. The deflectors fitted to most meths burners are not long enough to reach right up to the boiler underside when fitted, and so there is a possibility of getting the meths flames up into the cab, again melting the plastic.
Illustrated here are two deflectors for this meths burner, which have been shaped to the contour of the boiler underside.
3. It is plastic so it will eventually melt! It has been recommended to use the thicker plastic that is supplied for the Mamod SP series of engines, and this plastic would need shaping to fit the loco sight glass. I've also heard the microscope slide trick as well, but so far my attempt has failed (glass is too thin and cracks easily when fitting brass backplate).
If you've not got a screw fitted backplate, then soldering in 6BA screws to the boiler, where the rivets you've just drilled out go, makes the sight glass plastic changing process much easier (I'll post a photo of this mod later).
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warwickshiresteam
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| Posted: Wed May 07, 2008 7:35 pm Post subject: |
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| CCairns wrote: | | Quote: | | What's the most likely cause and best solution? |
There would appear to be 3 reasons why sight glass plastics fail on the Mamod/MSS locos, apart from the obvious one of running the boiler water level too low!
1. The supplied 'O' ring is of too small a thickness so that when you tighten up the brass backplate, the sight glass plastic tends to touch the inside of the boiler cutout hole. The extra heat generated by the meths burner (and the same for gas burners) then slowly melts a groove into the glass which will then leak. I have found use of the oval washers as sold for the Mamod SP series sight glass plastics seems to prevent this type of melting.
2. The deflectors fitted to most meths burners are not long enough to reach right up to the boiler underside when fitted, and so there is a possibility of getting the meths flames up into the cab, again melting the plastic.
Illustrated here are two deflectors for this meths burner, which have been shaped to the contour of the boiler underside.
3. It is plastic so it will eventually melt! It has been recommended to use the thicker plastic that is supplied for the Mamod SP series of engines, and this plastic would need shaping to fit the loco sight glass. I've also heard the microscope slide trick as well, but so far my attempt has failed (glass is too thin and cracks easily when fitting brass backplate).
If you've not got a screw fitted backplate, then soldering in 6BA screws to the boiler, where the rivets you've just drilled out go, makes the sight glass plastic changing process much easier (I'll post a photo of this mod later). |
Chris,
Thanks for that; looking at the evidence suggests that my particular problem is caused by the 'glass' touching the bolier. I shall try your suggestions and see how it goes.
Neat designs for the deflectors, certainly seems worth doing. |
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CCairns
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Joined: 24 Apr 2007
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Location: Glasgow, Scotland
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