Displacer Gland Material

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Displacer Gland Material

Postby therightnee » Sun Jan 10, 2010 12:34 am

Hey all,
I am building a replica of Dr. Senft's N92 engine and would like
to know what foam to use for the displacer gland. I have purchased a
closed cell, low density, PVC foam but it seems like its not working.
Any sugestions?
Also, for the regnerator material what am I looking for? I have
no idea what he means by filter foam discs. thanks!
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Displacer Gland Material - Sneft's LTD Stirling

Postby stan.hornbaker » Sun Jan 10, 2010 12:09 pm

A copy of James Sneft's book is indispensable to replicating his N92 engine. He provides comprehensive information on how-to's, what to use, and why in most cases.

Any LTD engine must have minimum friction and be completely air tight EXCEPT for a tiny bit of "breathing" at the displacer rod.
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Response to Displacer Gland Material

Postby johnemack » Sun Jan 10, 2010 3:39 pm


The displacer (rod) bearing is not a conventional gland, because that would cause too much friction. There is no foam involved. It is a close-fitting brass tube, fairly long to minimize the leakage. The rod must run absolutely freely in it.

The regenerators can be of almost any OPEN-cell foam or weave. Rigid foam is best but not essential. Air filters are often of suitable material - try an air-conditioning supplier. However, I have used flexible foams and even a plastic pan scrubber quite successfully.

Remember, you are using minute power, so cannot afford much leakage or any friction. The engine will run for an hour on an insulated mug of hot water, so the heat flow is very small. Worse, because this is an LTD engine, especially if to run on your hand, very little of the heat flow is converted into mechanical work.

An exhibitor once remarked "Don't ask how long it took to make it, ask how long it took to make it GO!" Good luck with minimizing friction, leakage and in getting the balance right!

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