I'll weigh the components tonight. The heaviest component by far is the SS
stem.
-Bob
On May 25, 2016, at 10:59, Paul Breed <paul@xxxxxxxxxx> wrote:
I'd be interested in the mass break down of your final valve, ie weight of
all the components....
I was looking at building a plug valve with bearings to support it and
a hollow 3D printed plug....
Paul
On Wed, May 25, 2016 at 5:57 AM, Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
wrote:
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