Inner Dome

[smallbrother]

Does the inner dome require a gasket and/or some sealing compound to seal it on the flange?

Thanks,

Pete.

[alanstepney]

Yes.

It is possible to get a seal with perfectly machined faces, but a gasket is much easier and less liable to leak.

[smallbrother]

Thanks for the reply.

When we fired it up a few months ago there was leakage all around the inner dome so it can't be perfectly flat on both faces.

I guess the usual paper gasket would be appropriate. I have some compound too - presumably this would do no harm.

I want to test the boiler is sound prior to stripping it down to sort out the siezed regulator.

[drjohn]

Jul 4, 2010 9:05:28 GMT smallbrother said:

Thanks for the reply.

When we fired it up a few months ago there was leakage all around the inner dome so it can't be perfectly flat on both faces.

I guess the usual paper gasket would be appropriate. I have some compound too - presumably this would do no harm.

I want to test the boiler is sound prior to stripping it down to sort out the siezed regulator.

Concentric grooves in the mating surface of the inner dome and bush plus a gasket are really the only way to seal it satisfactorily

DJ (who also had a leaky inner dome on this latest Simplex)

[smallbrother]

Is there much I can do to the bush without stripping the whole thing down?

[drjohn]

As long as the bush is a good flat surface, I'd leave it alone, but certainly make some light grooves in the dome so that the pressure contact on the bush by the gasket is greater.

DJ

[Deleted]

Hi DJ,

From what you write I infer that you cured your problem by using grooves and a gasket.

I'd be grateful for more gen on that, i.e. number / size of grooves and gasket type / material.

Cheers,

Gareth.

[drjohn]

Hi Gareth, yes I cured my leak - 3 grooves about 1/64" wide and deep and I just used steam gasket the same as on the cylinder covers, but I know others use a thicker more fibrous gasket material.

I have to say that the dome seems a bit like a cylinder head on a car - needs to be tightened down after a few hours steaming - maybe because of the area of contact - dunno.

DJ

[Deleted]

Thanks DJ: I'll give that a try.

I like the sound of mating grooves between dome and bush but the boiler's a bit of a tight fit in the 4 jaw. ;D

Cheers,

Gareth.

[drjohn]

Teach you to buy deckport and bridgel stuff - get a good Chinese one and you'll get the boiler in no probs!! ;D ;D ;D

DJ

[smallbrother]

Slow progress on this I'm afraid.

Checking the "original" screws I find they are a mix of 6 and 7 BA, and also the lengths vary. The drawing shows 6 BA.

The bush seems to be 7/16" depth as per drawing. What is the normal length of thread/depth of hole?

The dome fits evenly on the bush with a gasket in place. Prior to the gasket, the dome rocked slightly from side to side. The dome sits square on the lathe bed, so I assume the problem is with the bush. Fingers crossed, the gasket will relieve this slight uneveness. I will try grooves if not.

Pete.

[Shawki Shlemon]

A thread depth of 1.5 times the diameter of the bolt/screw is what you need . Any extra does no harm or good .

[smallbrother]

I have bought some taps/dies and have tried to re-tap the holes, successfully in most cases. 10 of the 12 holes now take the new 6BA screws of length 3/8".

I am left with 2 adjoining holes that won't take a 6BA tap. Can I drill these out to make them larger, if so, what size bit for a 6BA, and can I use an ordinary hand drill?

Two of the 3/8" screws won't go to their full depth but I guess some washers will be ok to ensure a tight joint. Is this ok or do these holes need to be drilled deeper?

[2tenths]

Sept 2, 2010 20:27:42 GMT smallbrother said:

I am left with 2 adjoining holes that won't take a 6BA tap. Can I drill these out to make them larger, if so, what size bit for a 6BA, and can I use an ordinary hand drill

Hi

2.3 or No 49 tapping size for 6 B A and yes , if you can get a hand drill in then ok

HTH

regards

Tony

[alanstepney]

...but I guess some washers will be ok to ensure a tight joint.

I'm not keen on "some washers". One washer is fine, but if you need more than that, either drill deeper, or file the screws down a little.

[smallbrother]

Thanks for advice gentlemen.

Pete.