Here are the weights of the new design (lb):
Body (6061) 0.077
Stem nut (SS) 0.005
Bearings/Sleeves (SS) 0.012
Stem (SS) 0.023
Body bolts/nuts (6061) 0.015
Servo 0.120
Ball/seats (SS/PTFE) 0.027
End caps (-6 male, 6061) 0.066
Servo hub (6061) 0.009
Total: 0.354 lb
Weighing all the items together comes out to 0.324 lb (some scale
resolution issues above). I'm not sure where I got the 0.27 lb number
from before - that may have been without the servo. And I guess the
stem didn't weigh as much as I remembered. Brackets will add another
0.02 or so. Switching from SS to aluminum body bolts saved a lot of weight.
For the main LOX and fuel valves, a pin connects them together since
they are effectively on a common shaft. So I can't drill the pin hole
any deeper or the pin might slip into one or the other stem. I could
use a longer pin but that wouldn't help the weight situation. But for
the vent valves, I could drill out the stem somewhat.
-Bob
On 05/25/2016 11:54 AM, Paul Breed wrote:
Any reason you can't drill out the center of the SS Stem?
The stuff in the middle is adding no real strength...
IE Turn it into a tube....
Leaving 0.075 wall would reduce the weight ~35%..
0.050 wall would save > 50%
On Wed, May 25, 2016 at 9:21 AM, Robert Watzlavick <rocket@xxxxxxxxxxxxxx <mailto:rocket@xxxxxxxxxxxxxx>> wrote:
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
<mailto: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 <mailto: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