O- rings

[miken]

I wish to incorporate some O-rings into  the pipework that connects the superheaters to the cylinders on my loco.
What is the most suitable material to use?
Silicon ,nitrile, viton or something else?
I need ID/OD  8X10 and 12x14.
Can anyone suggest a supplier please (In UK).
Thanks
Mike

[millman]

Not sure what material would be best but for suppliers I just googled o ring suppliers uk and got dozens of results.

[uuu]

I use Simply Bearings for this kind of thing. They have a free postage on orders over £5. Here's their 8/10mm ring in Viton, which they show as suitable for 200 degrees. Link to Simply Bearings - and the 12/14mm: Link2

Wilf

[miken]

Thanks for the replies. I'll get on to them in the morning
Slightly weird that they proudly announce that o-rings are "found everywhere from plumbing to the space shuttle" when you remember what caused the Challenger disaster!

[chris vine]

Yes, but the large o rings on the solid boosters were a highly unusual design.
When there were problems (before the disaster), NASA asked the makers of the o rings for some confidence that the system was ok. The makers replied that the use of the o rings in that situation was quite abnormal and that they were just making the rings to the specification...

Superheated steam can be much hotter than the saturated steam temperature for your pressure. So, I am wondering if you are making a possible problem for yourself. Most times, metal to metal joints work perfectly well. Brass cones etc, or you could use soft copper washers. At least if they do leak it will be more or less undetectable. If an o ring which you are relying on fails, you might have a major steam leak which spoils a day's running..

Chris.

[springcrocus]

Hello Mike,

Like Chris, I would question the need for "O" rings in this situation. Surely, either metal-to-metal or maybe a red fibre washer or compressable copper ring would be preferable here?

"O" rings normally need a pocket to sit in to achieve a seal whereas fibre washers just sit between two flat faces and, generally, behave very well.

Regards, Steve

[miken]

I agree, metal to metal and other conventional methods work fine.
However, this is for my Webb compound Dreadnought loco which I am finally in the process of painting after several years sitting under my bench gathering dust after I ran it a couple of times.
It's a very unconventional design.
The HP and LP pipes are both in two parts each.
The HP pipes are approximately 180 mm long and 8mm diameter.
They snake tortuously between the narrow double frames where there is a telescoping joint that allows for expansion and assembly.
The original 1895 drawings show a joint containing circular asbestos glands.
I have simplified this arrangement somewhat and incorporated a stack of 5 of ptfe rings in each joint which worked ok but I now want to substitute some of the ptfe rings for o-rings.

[92220]

It would be very easy to make up a simple press tool that produces circular rings/ridges in a shim-copper washer, which would seal well, between 2 flat faces.

Bob.

[rrmrd66]

Morning Bob and everyone else

I do love these discussions about a topic I was involved in for 40+ years.

Sorry to say Bob, someone beat you to it with your idea of ridges in flat shim washers. See:

www.nicholsons.co.uk/products/corruplus/

They were the only seal that would work in Concorde's Olympus engines back in the '60's

Cheers

Malcolm

[miken]

Jul 18, 2022 7:54:19 GMT 92220 said:

It would be very easy to make up a simple press tool that produces circular rings/ridges in a shim-copper washer, which would seal well, between 2 flat faces.

Bob.

Sent

I agree,
However I'm not sealing 2 flat faces I'm sealing 2 concentric tubes that have to be able to slide.
In this case I'm sealing a 8mm outside diameter tube that goes into a 10mm bore tube.
And 12mm od inside a 14mm bore.

[Gary L]

Jul 18, 2022 6:39:28 GMT miken said:

I agree, metal to metal and other conventional methods work fine.
However, this is for my Webb compound Dreadnought loco which I am finally in the process of painting after several years sitting under my bench gathering dust after I ran it a couple of times.
It's a very unconventional design.
The HP and LP pipes are both in two parts each.
The HP pipes are approximately 180 mm long and 8mm diameter.
They snake tortuously between the narrow double frames where there is a telescoping joint that allows for expansion and assembly.
According to the original 1896 drawings,Mr Webb used a series of round asbestos gland rings in this very inaccessible location clamped with notched nuts and tightened with a hook spanner. I have simplified this arrangement somewhat and incorporated a stack of 5 of ptfe rings in each joint which worked ok but I now want to substitute some of the ptfe rings for o-rings.

FWIW, the outside steam pipe extensions on Paddington (or at least on my Paddington, I can’t remember what the drawings say!) have flanges top and bottom, which also support the steam pipe cleading. I couldn’t rely on a perfectly parallel fit, nor did I expect to be able to tighten the flange bolts sufficiently to make a reliable flat steam joint. Thus O-rings were the obvious, and possibly the only solution. I couldn’t decide between Viton and Silicon; from memory I think I used Silicon, because abrasion is not an issue. It is too early to say if they will last, but they seal OK at the moment. I think the issue with Viton and Nitrile is they gradually harden with exposure to high temperatures.

I think this is legitimate from the temperature POV, because (1) superheat is modest (coaxial pattern) (2) the outside steam pipes are exposed to atmosphere, more or less. [The cleading (thin brass tube) is as likely to act as a heat radiator as an insulator] (3) the considerable mass of the cylinders themselves will act as a heat sink/radiator and reduce the superheat still further. But I realise this won’t apply so much to your inside cylinder on a Compound.

Nonetheless, there is undoubtedly an issue with all the commonly available O-ring compositions, because if you read the specs none of them really suit the temperatures involved. I rather think Roger might have something more useful to say…

Gary

[miken]

Thanks for the replies.
For interest and to clarify, Here is what Im doing.
Due to the enormous central LP cylinder on this locomotive the pipework has to be shoehorned down between the narrow gap either side, between frames.
There is no room to swing a cat, let alone a spanner.
The black stuff around the pipes is insulation.

[miken]

Here are some better pics.

[John Baguley]

Hi Mike,

If you have any reasonable superheat then ordinary Silicone or Viton O rings will probably not stand the temperature. I found this with my Helen Long which has fully radiant superheaters. I tried using O rings in the joints between the steam manifold and the cylinders and they failed very quickly, turning into something resembling chewing gum!

If you really want to use O rings in this situation then they need to be made of a material such as Kalrez which has a much higher temperature rating than Silicone or Viton. They are hard to get hold of - probably special order - and VERY expensive.

I use Polymax Ltd for my O rings. They do list Kalrez O rings but not the prices! I did make enquiries at the time and had to sit down after hearing the price! I ended up using compression joints with copper olives and that has worked perfectly for years now.

John

[andyhigham]

I would try viton O rings.
If they work - great
If they need replacing every year or two - not a big problem
If they fail miserably - you've only lost a few pence

[miken]

I've ordered some viton rings from simply bearings.

[Roger]

I'm a huge fan of 'O' rings, but I've only used them on the Wet Header of the Superheater. The outputs from the Superheaters use flat copper washers. I don't think 'O' rings are suitable anywhere near the output of a Superheater.

[rrmrd66]

Jul 18, 2022 14:19:13 GMT Roger said:

I'm a huge fan of 'O' rings, but I've only used them on the Wet Header of the Superheater. The outputs from the Superheaters use flat copper washers. I don't think 'O' rings are suitable anywhere near the output of a Superheater.

It may be of interest, and apologies for thread wander, but steel continuous casting machines basically pour molten steel (1550-1650°C) into water cooled copper mould boxes on the "second or third floor" and gently lower the semi molten steel to ground level. The moulds are mounted in a large radius. Water supply copious.

The cover plates of the mould boxes were sealed with, guess what?

!0 - 12mm cord diameter Silicone O rings. British Steel were happy to change them regularly as it was the only material that would give something like acceptable service life. Weeks not months.

Most elastomers, including Viton, are particularly poor in steam service.

Cheers

Malcolm

[GWR 101]

Hi Mike, apologies for the slight diversion. I notice that your super heaters appear to be stainless and are silver soldered into the header.

I am intending to use the same approach on my Jubilee build, I already have the radiant end welded.

Can I please ask what type of solder and flux you used at the header end.
The people who welded the spears recommend Tenacity 5 flux powder. Regards Paul.

[springcrocus]

Hello Mike,

Now that I've seen what you're doing, I think you may better sticking with your original choice - PTFE rings. They should handle the heat and will expand to close the joint at the right time. I don't see any advantage looking for an alternative, you already (probably) have the best solution.

Regards, Steve