Re: Back to O rings

[Royce Woodbury]

THANK YOU MIKE !

Now am I to assume that when you say the depth of the groove must allow 
for an interference fit of .004-.006, does that mean that the OD of the 
Oring as stretched by the groove diameter should result in an OD of 
.004-.006 larger than the bore ?  Or .008-.012 ?

And thanks to all the other folks who gave me research sites on Oring 
design, I've learned that in "traditional" Oring design, there IS an 
interference fit between the groove diameter and bore.  NOT, as I was 
assuming, that the groove diameter is LESS than the ID of the Oring in 
it's free state.  It would seem that this condition would provide the 
LEAST amount of friction while still contacting the bore with sufficient 
interference to seal against 40 psi.  But I guess I'm wrong.

Mike Chaney wrote:

For the last 15 years, I've been fitting O rings as follows:-

1.  The groove must be one and a half times wider than the O ring to allow it to
roll.
2.  The depth of the groove must allow an interference fit of about 0.004" to
0.006" to provide a good seal at the pressures we use for our small locos.
This works!

Note that the actual diameters of the piston or cylinder are not critical - it
is the difference between them that needs to be spot on.  The O ring will expand
or be compressed to fit (within reason.)
Mike
 

Thanks to all.

royce in SB - who's gettin close to having an actual steam loco.