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Gauge Glass Valve

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Alan Worland05/01/2010 21:24:36
247 forum posts
21 photos
Having trouble with the tapered valve on the water gauge.
I took it apart while silver soldering on a new threaded part which screws into the boiler as I thought it might not do it any good getting that hot.
Anyway, put it together after a very light gring with T Cut (didn't know what else to use) and it leaked, I have now tried various grinding media from very fine carbourundum paste, Auto Solvo chrome polish and a couple of grades of T cut type products - and it still leaks!
Looking at the mating surfaces they look good and even and I must be removing material as the tapered male part is now further through the body!
I always give both parts a good clean to remove all media and give it a light application of graphited grease on assembly but no matter how tight I make the operating handle it leaks.
It leaks through the valve and also from the small diameter end of the taper (both sides of the 'loading' washer!
It's obviousely not being ground in correctly, but I don't know what to do! (apart from chucking it over the fence and buying a new one)
Help!
Steve White23/03/2010 23:33:38
11 forum posts
2 photos
Hi there Alan,just spotted your post.
sorry, I have no experience of tapered valves but could you fit an "O" ring or ptfe washer either side of the valve? Just a thought. It seems you are grinding in correctly.
 
I seem to remember some tiny water gauge fittings made by Roy Amsbury? and described in ME many years ago. I think they were parallel but fitted with  "O" rings internally.
I have read that to make small tapered cocks is difficult and once they are steam/watertight, they are too tight to turn!
 
I am sure others in the forum will have some good ideas -good luck.
regards
Steve
 
 
Circlip24/03/2010 10:59:17
1723 forum posts
Unless you've clearance between the small end of the tapered "Plug" and the valve body it won't seal. Only way to ensure a good seal is to recut the tapers at one machining setting, re-lapping seldom (as you already know) works.
 
  Regards  Ian.
Ian S C24/03/2010 11:14:01
avatar
7468 forum posts
230 photos
Toothpaste is good for lapping in valves and tapers, its much finer than brasso. The smell can be a wee bit strong after a while. I use some that was a freeby on an airline, or was it a hotel, it tastes awful. Ian S C
chris stephens25/03/2010 13:03:09
1049 forum posts
1 photos
Hi Alan ,
Your post also passed me by till now.
Tapered taps are a real PITA (I hope our editor does not need to edit THAT)
As stated above when they are tight enough to seal they are too tight to turn easily, regrettably that seems to be the nature of the beast.
When restoring some petrol cocks from a pre-war car recently, I even resorted to making PTFE sleeves  to overcome friction, they worked but did not look right. In the end I cut "O" ring grooves into the male member, one each side of the central hole. and sealed it that way, so far so good. 
christephens 
 
Alan Worland25/03/2010 13:45:25
247 forum posts
21 photos
Thanks for your replie(s)!
I eventually got round the problem by making a D bit to cut the body true, then made a new male part (if you pardon the phrase!) A light lap in with toothpaste and heh prest a result, works fine and doesn't leak.
I ground the original in so much that the valve was unservicable - the annoying part was the discovery that the complete valve unscrewed from the water gauge any way! so I needn't have mucked it up in the first place!

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