When I talked to the BalSeal rep, he thought the McMaster parts might be
from their company. But since McMaster doesn't list the brand (unlike
Grainger), it may be whoever has the lowest bid. I got a quote from
BalSeal from some custom seals that had a heel you could grip to keep
the OD attached and a different material/seal lip but it was way out of
my price range ($600 NRE plus $100/seal I think). I've had such good
luck with the larger McMaster seals as static seals for my injector so I
figured they might work for a dynamic application. I can say that when I
tested them with LN2, they sealed initially then leaked upon turning so
hopefully if I can keep the shaft from wobbling around I'll have better
luck. Do you have any price quotes for small quantities (20x) of the
other brands?
I had planned on testing with water prior and then drying it out without
disassembly prior to the LN2 testing. What does the water do to the
Molykote Z? I soaked the bearings in acetone for a few hours, rotating
them occasionally to get the existing lubricant out of them but I didn't
re-lubricate them. Since the motion is just intermittent, I thought I
would just run them dry. I cleaned the bearings in my LOX flowmeter the
same way and ran them dry.
-Bob
On 05/23/2016 09:46 PM, Lloyd Droppers wrote:
Looks nice Bob, and the bearing arrangement should work out. I think the Belleville washer that other people suggested might be nice, but if everything in the load path (shaft, bearings, nut and spacers) have the same CTE the belleville washer shouldn't be necessary.
My main concern about the valve, if I were building it, would be the PTFE spring energized seals. I have never been able to get the cheap mcmaster versions (the used to be Coors-Tek brand) to work without leaking even with good surface finishes. So if they end up leaking on you, I would recommend spending a bit more on something from BAL or Trelleborg before you throw the design out as not working as I have had much more luck with the higher quality shaft seals.
For the lubrication you shouldn't certainly shouldn't use krytox, it will freeze at cryo temperatures. The Molykote Z works fine if you keep it dry. Speaking of dry make sure to purge the cavity with dry gas as ball bearings really do not like ice buildup, but you have done this before and probably knew that already.
Lloyd