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(Post Link) post #1 of 8 Old 26-08-12 Thread Starter
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One for the precision engineers?

As I was only a very rough and ready mechanic in years past, my knowledge on such matters is virtually zilch.

So my question is: Two machined surfaces, both pretty parallel, not quite to slip gauge 'rub and stick' quality, but two finely machined faces.

These two faces when screwed together are required to be an airtight seal under pressure with 'some' sort of compound between them?

Is it feasible that an effective seal could be achieved? I hasten to add, no heat present, no liquids present, just highly compressed air? Any views welcomed.:
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Are you saying some sort of sealing compound will be between the plates? If this is a yes then providing the plates don't deform when tightened together then I can't see why not. Are we talking a lot of pressure being held back?
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Max 230 bar.The reason why I ask is: On this particular appliance, when I disturbed this face to face joint, it appeared to have some sort of sealant of a clear type, and I cleaned this off with no problem, so what it was was is mystery to me. :

This particular joint had not leaked previously at all, but on reassembly it did, albeit quite slowly. So I thought maybe a Dowty, bonded steel washer was required, after fitting one, success it holds the 230 bar pressure.

Now I know for sure that when I first dismantled this appliance there was definitely no bonded steel washer at the face to face joint. So whatever it was assembled with plain face to face to effect a seal, I'd love to know? :
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Ah I see. Well if the faces are pretty damn flat then you would only need the thinnest of seals just to ensure a seal. Could have been a light smear of a sealing compound. Maybe even a smear of grease? Who knows. So long as its holding now
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Thanks Hobson very much, as on the technical drawing it refers to an 'O' ring seal, but as it was face to face as you will no doubt know that would of been totally ineffective.

I reckon you are correct, it was perhaps some sort of grease used. Possibly knowing that an interfering old bore like me would assemble it and end up with a leak? Service charge would of been quite costly, but I guess I missed out initially by assuming face to face was ok just dry. Still it's as you say fine now but well you can guess the rest.:
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There are products in the range of loctite etc called (don't laugh) Flange Sealants and it's used for this very purpose. Most common in use on camshaft housing to cylinder head joints, inlet manifolds etc where no gasket is used.
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Quote:
Originally Posted by Alfafamily View Post
There are products in the range of loctite etc called (don't laugh) Flange Sealants and it's used for this very purpose. Most common in use on camshaft housing to cylinder head joints, inlet manifolds etc where no gasket is used.
Yup, used some myself when messing with Pug 306 xsi heads etc in the past. Some sealants stay semi liquid so as to provide a flexible enough seal, especially when things such as heat expansion/contraction are an issue.
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(Post Link) post #8 of 8 Old 26-08-12 Thread Starter
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Points received with thanks on my part AF and H204. So I wonder why the bonded steel washer was physically left out? To deter DIY O/H of the unit?
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