# O-Rings in steam engines



## cfellows (Jul 28, 2011)

Does anyone have experience using an o-ring instead of packing around the connecting rod where it enters the cylinder? Connecting rod will be 1/8" diameter, o-ring would be 1/8" ID, 1/4" OD. The engine will be run on live steam at some point.

Thx... Chuck


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## tel (Jul 28, 2011)

Yo Chuck, I've only ever used 'em once - on a Duplex steam pump I built years ago, and I can't say that I was very impressed with 'em at all.

I know lots of people use 'em, and have success, but as far as I'm concerned I'll stick with my trusty teflon (PTFE) tape, twisted into a string and used in the usual manner.


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## Blogwitch (Jul 28, 2011)

Chuck,

You should have no trouble at all, it is now becoming a fairly standard practice.

Instead of having the cone shaped areas to form the packing gland out of normal material, you sit the o-ring on a flat face and have a flat faced tightening gland screw.

As you tighten up the screw, it deforms the o-ring section into an oval and so seals against the shaft.

I always preferred viton rather than silicone. Silicone seemed to have more friction, plus it will self destroy if you get WD40 anywhere near it.

Hope this helps


John


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## Ken I (Jul 29, 2011)

Tel,
   Twisted PTFE tape ? thanks for the tip - I've been faffing around with all sorts of stuff - must give it a try.

As Bog's says - stick to Viton - I've used it on industrial compressor valves at 240°C where everything else fails.

Dynamic sealing is generally not an "O" ring's forté but there are Viton formulations including filler materials such as carbon fibre (and now discontinued - Asbestos) specifically for dynamic applications but can be hard to find in small quantities.

Monotube gas shockasbsorbers use such "O" rings between oil and gas reservoirs - a high duty / dynamic / temperature / life application with no problems - and this seal must absolutely not leak during the life of the shock.

Ken


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## steamer (Jul 29, 2011)

+1 for Viton for steam applications. I use it in several places both static and dynamic

Get the joint geometry right....you can get that online at the Parker site with they're oring manual

Dave


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## Ken I (Jul 29, 2011)

Chuck, A further pointer - get the surface finish right as per manufacturers recomentdation.

Too highly polished and you burn the seal, too rough and it abrades the seal - you need a very fine cross hatch pattern with good "plateau" ie a superfinished surface (the external equivalent of honing).

Polish with emery but at relatively slow speed using rapid longitudinal motion.

Ken


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## cfellows (Jul 29, 2011)

Thanks, all, for the good input. 

One of the main reasons I had considered an o-ring is because they don't typically require any adjustment mechanism. You just create a fixed groove or gland and pressure takes care of the rest. Perhaps the pressure in a small steam engine is too small to create a proper seal?

This is the assembly I had in mind:







The o-ring is 1/8" ID x 1/4" OD. The application is a 7/16" bore, 7/8" stroke, 2 cylinder, double acting, oscillating steam engine.

Chuck


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## Ken I (Jul 29, 2011)

Chuck, I have one designed (but not yet built) more or less identical to your proposal.

Pressure is not the issue - whatever preload pressure is created in the "O" ring it is always added to by the applied pressure - so it will seal from nothing to almost anything (it eventually extrudes through any clearance) - I have used an "O" ring dynamically for burst testing of tubing up to 16000 psi.

I would suggest going light on the intererence to cut down on friction.

Ken


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## picclock (Jul 29, 2011)

Hi Chuck

You may have issues with the oring tightening at high temperatures with that configuration. They tend to have a fairly high coefficient of expansion and on dynamic seals that can be an issue. A way round this is to ensure that there is plenty of room for the outside to expand and to compress the oring until the centre contracts to form an effective seal.

http://www.rlhudson.com/O-Ring Book/Gland Dimensions/table48.html

This outfit has a lot of info on dynamic oring seals.

Best Regards

picclock


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## shred (Jul 31, 2011)

Kozo uses them for packing on his steam locos. There's a section in the back of one of his books on it. IIRC he uses a much smaller than 'normal' crush value-- 5-10% or so. I think he just squeezes on the OD as well.


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## steamer (Jul 31, 2011)

Yes..Kozo runs very little "squeeze" on his O-rings.  I think 5-10% is about what he stated.

Dave


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