I never though to ask McMaster but they responded quickly:
The vendor for the PTFE seal is Bal Seal Engineering Co Inc and their
part number is 100MB-012-T or X124209.
I can't find that part number in their catalogs but the MB describes the
spring. The 012 is probably the series and T corresponds to Virgin
PTFE. Attached is the datasheet I received from them.
I recall our conversation about leakage a couple of years ago and my
quick fix was to use two of them and a pressurized cavity with both
U-cups facing toward the pressurization port. That did wonders for the
leakage and almost completely eliminated it. Now that I've improved the
bearing situation, maybe it will be better. I could add a 2nd seal in
this design but it would shrink the distance between the bearings down.
I could always make the valve body longer if needed but that means
redesigning a few other things on the vehicle.
I'm using these shafts:
https://www.servocity.com/html/3_8__precision_shafting.html
and it says they are 303 SS with a 10 RMS micron finish. There are
better shafts out there but the 303 makes it easy to cut for threads for
the nut. They tend to have some very small nicks in them from rattling
around in the bag so I used graduated sanding pads to polish them up:
http://micro-surface.com/index.php/products-by-type/soft-touch-pads/micro-mesh-soft-touch-pad-variety-packs.html#
These go all the way up to 12000 grit so I hopefully I am improving the
surface finish - it looks almost chrome plated when I'm done with them.
I suspect though that due to shrinkage, the seal locks itself around the
shaft and it is the OD of the seal turning against the bore that becomes
the new sliding surface. The bore looks pretty smooth, mainly because I
ran the last pass by hand instead of using the mill power feed but I
would like to polish it up some more if anybody has a good suggestion.
I thought of making my own 0.500 sanding pad but I don't want to oval
the bore or take too much off since it is 6061-T6. I've seen rotary
grinding stones - maybe those would work without taking too much off. I
did find these although 140 grit seems pretty low:
http://www.artcotools.com/precision-diamond-pin-gx-141c.html
-Bob
On 05/24/2016 10:20 PM, David Gregory wrote:
Another note: some amount of leakage for spring energized seals in dynamic
aoolications is quite common in my experience. Often the leakage will subside
after the motion stops. Also, I think I've mentioned before I've seen higher
leakage with lower pressures due to insufficient preload (at higher pressures
the seal is assisted by the fluid pressure). What surface finish do you have
on the shaft? 16 or better is typically called for.
David
Attachment:
Cut Sheet for 13125K66.pdf
Description: Adobe PDF document