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Author Topic: cracked sight glass 3/16 dia by 2 inch long  (Read 417 times)

DBS88

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cracked sight glass 3/16 dia by 2 inch long
« on: October 01, 2020, 08:36:45 PM »

Have unfortunately cracked the sight glass on my boiler. The union cock valves that were installed to isolate the sight glass have seized solid so decided to sort them out, they are being extremely stubborn so have have to resort to some more persuasive techniques - tips or suggestions are welcome.


Its just as well I have started to sort it out because it has revealed other issues with dubious sealant that further down the line would be likely to cause a problem so its now a complete boiler strip down and put it back together before getting it tested.



Any way the sight glass that is broken is an old size together with its fittings, the glass is 3/16 inch od 0.187", the replacements I have found are 5mm just under 0.200" so if you know where to get 3/16 od sight glass please let me know, I am looking for 3/16 od glass by 2 inches long - thank you
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Jerry C

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #1 on: October 01, 2020, 11:21:35 PM »

If it’s any help, Blackgates Engineering do 4mm gauge glass. 70p for 6”
Jerry C.

DBS88

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #2 on: October 02, 2020, 06:05:32 PM »

Ok it’s proving difficult to get 3/16 od sight gauge glass, it turns out that where it’s advertised as 3/16 the glass offered is actually metric and 5mm. So options appear to be;
1) Go with a smaller dia and use 4mm glass 0.159” or
2) go with 5mm glass which means drilling out the fittings and nuts by 0.020” to achieve 5mm holes.


What are the advantages of 4 or 5mm glasses?
Has anyone else replaced a 3/16 glass with 4 or 5mm glass?


I am tempted to go the 4mm route which leaves the options to fit either a 3/16 glass if I find one or to fit 5mm
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rhavrane

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #3 on: October 02, 2020, 08:46:45 PM »

Bonjour,
Based on my calculations, 3/16" means 4,76 mm so I would quindly suggest you to chooze a 5mm glass tube.
I have already broken several tubes and, based on my experience, I suggest a procedure to refit one :
https://www.youtube.com/watch?v=CSaQvMN7ok4
To sum up, there should never be any effort to install the tube, it should be loose even when the nuts are tight and it is the slightly tight joints that will make the seal.
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Raphaël
Raphaëlopoulos Steam Lines UnLimited
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southsteyne2

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #4 on: October 03, 2020, 04:28:07 AM »

Some very accurately cut silicon tubing slipped over the glass each end makes a perfect seal and also shock resistant I use 5mm glass with red stripe
and 1'4x40 fitting
Cheers
John
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tghsmith

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #5 on: October 03, 2020, 03:24:43 PM »

PM research (USA) handles 3/16th tube, so it is available,, I would email suppliers near you and see if it can be found..
https://www.pmmodelengines.com/shop/steam/steam-accessories/water-gauge/
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DBS88

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #6 on: October 03, 2020, 08:21:16 PM »

Thank you for the replies so far, they are appreciated. Have now contacted a few suppliers in the UK but have only found metric 4 or 5 mm glass. Have contacted a company in the US to confirm that 3/16 is 3/16 and whether or not they will post to the UK - Have also found 4mm glass with a red vertical stripe so that may also be an option
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KNO3

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #7 on: October 04, 2020, 10:23:08 AM »

Drill out for 5 mm glass tube, if the fittings allow this. A wider diameter tube is always preferable because it usually shoots for a more reliable water level reading.  In a narrow tube, capillary forces are stronger and air bubbles are also a problem.
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DBS88

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #8 on: October 08, 2020, 09:36:24 PM »

Thank you for the help and advice, as an update I have failed to find 3/16 od glass, apparently its not been made for 30 years!!! Any way thought I would give the 4mm with a stripe a go, if that behaves poorly it still leaves me the option of drilling out to 5mm. Heres a photo of the red stripe in action, it certainly works and looks effective - what do you think?
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rhavrane

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #9 on: October 09, 2020, 06:54:55 AM »

Bonjour Derek,
On this picture, it looks effective  :-))  To be validated after a real test  ok2
Personally, I slip a copper wire into the glass tube to avoid bubbles in the water level :
https://www.youtube.com/watch?v=RkK82YE44XI
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Raphaël
Raphaëlopoulos Steam Lines UnLimited
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southsteyne2

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #10 on: October 09, 2020, 07:41:38 AM »

Yet to be validated ?,I don't want to sound like a know all but the red line glass has been used by just about every model steam engineering society on the planet at least I thought so.
Cheers
John
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SteamboatPhil

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #11 on: October 09, 2020, 09:06:53 AM »

I have some 3 1/6 Dave, will put it in the post for you (then its down to French snail mail)  :-))
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DBS88

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #12 on: October 09, 2020, 10:11:10 AM »

Phil Thankyou it is appreciated, I definitely owe you a beer or three!!! My preference is for the 3/16 since it keeps things original, so you have once again helped me out with a problem, stay safe
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ooyah/2

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Re: cracked sight glass 3/16 dia by 2 inch long
« Reply #13 on: October 09, 2020, 03:20:17 PM »

Yet to be validated ?,I don't want to sound like a know all but the red line glass has been used by just about every model steam engineering society on the planet at least I thought so.
Cheers
John


John ,
It was at least 40 years ago when I first used it with a blue line and then about 2 years ago it disappeared.
It's available from Polly Model engineering but very expensive at £4 per 6"inches.+ postage  4mm with red line.and  £4.20 per 6inches for blue line.+ postage.


George.
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