Blow Down Sight Glass

J

John Morgan

Steam Traction
Hi Group,
This winter one job I want to get done is replace the blow down sight glass on my coal fired Shawe Roundhouse "Jack"
Does anyone know the thread size so I can order the correct one ?

Regards.

John.
 
You wanna replace the whole thing??? I've never seen threaded glass! :bigsmile:

Replacement of the glass is a fairly simple job. Replacing the whole thing needs a certain amount of care and knowledge. The important thing is to get the two fitting EXACTLY lined up, that's front to back AND side to side, otherwise the glass may be strained and just break, often when cooling down after a successfull test. Always use a new seal on the glass.
 
Silly me !! I mean I want to replace the whole unit as the blow down valve leaked. I Silver soldered it up, re drilled the water way, to stop it leaking but now wish to replace it complete.

John.
 
Hi John. I would think its probably one of the standard model engineering threads, maybe 1/4" x 40tpi or smaller. You should be able to measure the width and count the tpi if its not too small.

Dave
 
Dave,
This is the problem at the moment. I am sure when I took the fitting off last time it looked smaller than 1/4..... 40. but I am not 100 per cent sure, just wondered if any one knew for sure.

John.

P.S. Off to Specksavers next week for an overdue eye test !
 
M.E. threads go down smaller than 1/4" x 40, but often they change over to B.A. for very small sizes. I wouldn't have expected anything less than 3/16" with a steamway through it, maybe not even that small, especially for a water gauge, as the rule of thumb is 'keep the bores as large as possible'.
 
John, have you measured the gauge glass diameter?. If its 4mm then its probably 3/16 x 40tpi, 5mm then probably 1/4 x 40tpi. I've never seen a M.E. water gauge with a thread smaller then 3/16 x 40tpi.

Dave
 
Dave,

I think you have the answer to the question here. The Shawe loco has a 4mm gauge glass, the Sabre Steam loco a 5mm glass. I believe that it should be 3/16 X 40 , for the Jack. They seem to be freely available on ebay so I shall go ahead and order one. Many thanks.

John
 
John, if you want I can post you a spare 1/4 x 40 nut for you to check the thread before you order just to be sure.

Dave
 
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