I considered a gear motor (a smaller one) but the two standard ball valves I
tried leaked with LN2. Also, most valves have stainless bodies and they weigh
about a pound each. My semi-custom valve with servo and bracket is only 0.27
lb. I'm not trying to go crazy with weight savings but my vehicle empty weight
is 45 lb. Since there are 4 valves onboard, that's quite a bit of savings. I
ordered one of the aluminum Petersen ball valves but after inspection, I don't
think it will work well at cryo temps either.
-Bob
On May 23, 2016, at 11:44, Paul Mueller <paul.mueller.iii@xxxxxxxxx> wrote:
Just in case you haven't considered it (and it may be too heavy and/or
power-hungry for you): we've used an automotive power window motor to drive a
nitrous ball valve (which can also be kind of stiff when under pressure).
That way you just brute-force it and not have to "reinvent the ball valve"
(though I can see that is fun in its own right). I can't find the one we
used (the hazards of buying stuff surplus), but here's something similar:
http://www.surpluscenter.com/Electric-Motors/DC-Gearmotors/DC-Gearmotors/62-RPM-12-VDC-BOSCH-GEARMOTOR-5-1832.axd
You have to adapt the mounting and drive to your valve, but it's doable.
On Mon, May 23, 2016 at 5:56 AM, Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
wrote:
I should have added a note about the ball not being visible in the drawing.
You're right - I could have deleted the inner sleeve but I wanted a check
against overtorquing the nut and damaging the bearings. The better way to
go is to use the Belleville washer as you and Ben suggested and then the
inner sleeve isn't needed. And then a nut clip or lockwire could be used to
keep the nut in place.
The next thing I need to consider is the forces on the bearings. The
bearings are rated to 90 lb of axial force but I'm sure I can go higher than
that for a static, low-life application like this. The 500 psi pressure load
will push the 3/8 bottom portion of the stem up about 55 lb while the seal
will push against the washer and outer race with about 43 lb. The outer
sleeve will keep both outer races in place. It seems I can (and should) put
up to 45 lb of preload using the nut and a spring washer. I'll have to
think about that a bit more though.
-Bob
On 05/23/2016 01:25 AM, Norman Yarvin wrote:
On Sun, May 22, 2016 at 10:12:16PM -0500, Robert Watzlavick wrote:
I'm not sure I understand your last paragraph.It was premised on the idea that the ball was rigidly attached to the
stem, so doesn't apply.
Anyway, okay, the idea here is to preload the one bearing against the
other, not any of the other possibilities I was contemplating. For
that you could leave out the inner sleeve; it's resisting that preload
rather than contributing to it. (Though it does make it so that you
tighten the preload nut harder, which lessens the chance of it getting
loose.)