[modeleng] Re: Is piston rings : Was Lack of mail - just testing

Hi,

You would not have to knot the string or hemp, just lay it around the piston 
groves and overlap the ends.

Depending on the size of piston ,PTFE rings in grooves might be ideal. Make 
a seal, yet very slippery and dry.

Regards

Clif

----- Original Message ----- 
From: "Tony Wells" <oaksfield@xxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Friday, September 05, 2008 4:49 PM
Subject: [modeleng] Is piston rings : Was Lack of mail - just testing


> Partly so that Mike doesn't feel too lonely ... ;-)
>
> As I am finally back on line (curtesy of a new modem!) a question for all 
> of
> you steam engine experts ... I have been asked to make a model steam 
> engine
> out of wood, for demonstrating their operation with. Whilst there is to be 
> a
> "boiler", propulsion will be via compressed air, most likely an electric 
> car
> tyre pump, by the way, so there definitely and deliberately won't be any
> temperature problems to burn any fingers, let alone set fire to it all!
>
> As it will be all wooden construction, there will be some small movement 
> due
> to humidit and temperature fluctuations, more than likely, and so I am
> worried about how to ensure a permanent seal between the piston and the
> cylinder walls, as metal piston rings would only move with temperature
> changes, and then not to any noticeable amount. I had thought about using
> neoprene O-rings, tight fitting enough to still form a seal if it all
> slackens up a bit, but can anyone recommend anything better please? I had
> also thought about greased hemp or even string, but would I need to knot 
> it,
> with the knot then causing an obstruction, for instance.
>
> With thanks in anticpation,
>
> TonyW.
>
> MODEL ENGINEERING DISCUSSION LIST.
>
> To UNSUBSCRIBE from this list, send a blank email to,
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> line.


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