Author Topic: How hot ?  (Read 7520 times)

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Offline Ian

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How hot ?
« on: 19 Dec 2006 at 23:52 »
I have been trying to work out the best material to use for the inlet manifold gasket on my OC. Anyone know roughly how hot the material would need to be able to cope with ? I have found some stuff which handles 260 degrees C - that should be plenty I would have thought ? Its having its first run tomorrow but it will have to be short as I only have rubber O rings in place till I can sort things out !!

Offline Doug

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Re: How hot ?
« Reply #1 on: 20 Dec 2006 at 02:51 »
Ian,

Normal Buna-N o-rings are only good for 230 F. They do make silicon o-rings, but they are pricy. Some catalogs say they are good for 500 F, but that must be an intermittent maximum, as most give the max as 400 F. The latter max is the same as Viton o-rings, and they are cheaper than silicon, but more than Buna-N. The problem with o-rings is they really do not suit the gland space right. When I looked at doing the glands on my F28, one was not enough to fill the available conical space, and two was really one too many. Plus the pair did not want to 'pack' properly when squashed. So I used gland packing cord.

You could try Teflon cord used in old style water pump and valve glands; it will take the heat of the intake gland. But Teflon cord is a bit soft, done up too tight and it would tend to just extrude into the gland or the port, or both, if it has anywhere where it can escape. If you have the original tin washers in place, that should keep it from extruding up into the gland nut. It tends to cold flow under persistent pressure, and with the thermal cycling in use; the glands would probably always need tightening up after every run. I think the reliable maximum for Teflon is 500 F, before it starts to break down.

However you can still get graphite packing gland cord, as used on steam valves. It is available in the US 1/8 square cross section, perhaps smaller if one were to look harder. Indeed it is available in quite a variety, but most variations are due to different lubricity and wear properties that do not apply to a static packing gland. There is even one with food-safe lubricant! The cheapest to consider are graphite impregnated Aramid, good for 600 F, US$6 for10'. Next is graphite impregnated graphite, good up to 800 F, US$17 for 10'. You may see higher temperature quoted for this packing, up to 1200 F, but that is temperature in steam, dry heat values are much less.

A bit smaller in cross section is PTFE cord, 3/32 diameter Goretex is US$20 for 10', and Value Seal is a bargain (sic) at US$14 for the same size, both good to 500 F.

But I wonder if you could not get away with some inexpensive cotton cord or manila twine? Probably the original material was just some paper or plant fiber based material. Later flange mount manifolds just use a paper base gasket on the intake ports, so how hot can it get? Worse it can do is char and need replacing with something better. Just make sure you do not use any string with any polyester in it or you will have a snotty mess to pick out of your gland threads!

-Doug




[fix corrupt text symbols. -Doug  17Feb14]
« Last Edit: 18 Feb 2014 at 00:27 by Doug »

Offline Ian

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Re: How hot ?
« Reply #2 on: 20 Dec 2006 at 04:13 »
Doug, the way the inlet manifold joins is similar to the fixed end on a TS - and I would think used the squashable copper washers - but can't get the right size now. There is no groove or flange to hold cord in place. I am going to try cutting up some teflon sheet that a gasket guy here suggested but it has a heat limit of 260 C - I am not sure if that is enough.

Offline Doug

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Re: How hot ?
« Reply #3 on: 21 Dec 2006 at 04:02 »
Ian,

I am not terrible familiar with the inlet ports on the TS, though I did rebuild a gearbox for one. I have a set of late 2-3/4hp barrels though, and they have the end bored tapered for what looks like packing material, but the taper is much shallower than what I see on my 350 EW, A31, or F28. The 2-3/4hp spare list just calls them 'washers' and 'Hallite washers'. Hallite is a firm that has been in business for about a century making seals.

The F28 uses an arrangement like this:


Larger view

The packing material is listed as 'asbestos washer' leaving no doubt as to the material of choice! As mentioned, the conical taper is much steeper than seen on the 2-3/4hp barrels. I would have thought the OC used a similar arrangement to this shown, and as used on the other Douglas models of the era.

The smaller twins like the EW and A28, also have mention of a flanged collar in the spares lists. The packing material is now called a 'double cone asbestos washer.' Why double cone I do not know, the gland nut does not have a corresponding taper to suit. I can only guess they made it idiot proof, no matter which way the owner installed it, it would compress adequately and seal.

The copper-asbestos joint washers are meant for applications like the valve caps, where the copper is indented to prevent the asbestos material from expulsed from the joint area when crushed by the valve cap. In the packing gland, a copper sheath would just inhibit the packing material from conforming to the gland space and making a good seal without excessive pressure. After all you do need to allow some movement between the inlet manifold and the cylinders due to expansion and contraction.

-Doug

Offline Ian

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Re: How hot ?
« Reply #4 on: 21 Dec 2006 at 04:08 »
On the OC there is no taper - just flat to flat !! Makes it difficult. I ran the bike today - found some old copper gaskets that fitted and used a jointing compound. Will see how it goes.

Offline Doug

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Re: How hot ?
« Reply #5 on: 21 Dec 2006 at 04:15 »
Just found some pictures of a bare OC that I took several years back, and yes, no conical taper. Oh well, so much for that idea...

-Doug

Offline trevorp

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Re: How hot ?
« Reply #6 on: 22 Dec 2006 at 11:59 »
Also i would be very carefull using teflon it starts to give off toxic fumes at the tempratures we are talking about and i believe the fumes causes birds lungs to hammaorage and causes a plume fever in humans