Of course the valve mounted outside would be better. But that won't
work because the closer is basically a double acting cylinder. This
means that it needs air pressure to clamp and remain clamped, and air
pressure to unclamp. So the rotary union would need two passages.The
way I use the closer now is with a solenoid operated valve the has one
air inlet, two outlets, and two exhausts.So when one side of the
piston is pressurized the other side is exhausted to the atmosphere.
Since air needs to be sent to both sides of a piston there needs to be
two passages in a rotary union if the valve is outside.
I read that in another of your responses earlier today, and
posted this to which you replied yesterday, otherwise I would not hav
repeated this suggestion.
O.K. Another thought comes to mind. What happens if you use
only one port, and apply either pressure or a vacuum to it? I presume
that you need continuous pressure when it is holding, but do you need
continuous pressure to the other side to open it and hold it, or will it
open and stay pretty much open from a fairly short pulse? If a short
pulse will do, then a valve to feed the pressure to a venturi to get
vacuum will open it. You likely don't want to hold it there for long,
because a venturi is a rather inefficient way to generate a vacuum, lots
of run time on the compressor. But a short burst to open the chuck might
do well. (Check it out with short bursts for open before you mount it,
while it is easy to get to.) If this works, you can use the single
union and no need for valve control in the spindle.
The only air-operated chuck which I have seen had springs to
return to the open state, so only one pressure feed needed. This was
one made for lathe use, so it was designed for single pressure line.
Maybe there is provision inside yours for spring return, if you just
install the springs. (Sorry, that one was sold by a friend on eBay a
couple of years ago.)
I looked at your link last night. I had never heard of sequence valves
before. I would need one that would work with only about 10 PSI
pressure difference. I'm gonna look this weekend to see what's
The max speed for that rotary union is only 250 RPM. I need 4000 RPM.
The single passage ones go that fast while still being affordable. The
dual passage ones that can spin that fast and have air going through
them are about 10 times more expensive.
I alread thought about the solenoid sticking. It will be concentric
with the lathe spindle centerline. I'm not sure but I think the valves
I have are piloted because they use so little current to change the
valve position. And it changes fast. Anyway, I already use these
valves with this closer as well as other air clamping devices. As to
the two passage rotary union you linked to if you read the specs you
will see they cannot be spun anywhere near as fast as I need to spin
it. That's why I'm going through all this falderal (izzat how it's
spelled?). As I have posted I would love a two passage rotary union
that can handle 4000 RPM and 120 PSI air. But they are about 10 times
more than the single passage types with the same air and speed rating.
Like $3000.00. I have even checked eBay. I did find a good deal on a
coolant rotary union and I bought it. But it is for coolant. And is a
single passage union. And it's going into the mill for through spindle
Eric - perhaps just for information, you might try a side access air
coupling. This would comprise the rotating center "tube" you mention
surrounded by a metal piece with 2 "o-ring" seals for each air passage.
You could setup a test on a drill press and use the local hardware store
for "o-rings". Hopefully, the tube's diameter could be reduced.
Probably first testing would be for max pressure with no rotation then
with greater speeds. Next step would likely be searching for teflon "o-rings"
or even higher temp types.
The rotary union I will be using is a side access one but the air
comes out the center. The problem is the high speed, 4000 RPM. O-rings
won't work in that application. It's really interesting to look online
at rotary unions. Lots of single passage 150 PSI 4000 and higher RPM
for air but not two or more. Years ago I had to design and make a
custom rotary union for a gundrill machine where I worked. It had to
seal against 2000 PSI hot oil up to about 1000 RPM. It was actually
pretty easy to do. The design was informed by the Parker Seal folks.
We were going through expensive rotary unions on this machine and my
boss wanted one that would be easy and cheap to repair. The answer was
using the correct rubber compound and letting a little oil leak past
the O-rings. The union was built with a shroud that collected the
slight leakage and drained the oil into the gundrill sump. I have
since seen this type of design on high pressure hydraulic rotating
actuators. It is apparently very common. But since I am using air
special hard seals need to be used, O-rings just won't last.
[ ... ]
Does it *matter* if the air union has some leaks? As long as
you can get enough pressure through. Yes, it will cost more to run the
compressor. Make it a labyrinth style for each part and try it -- first
stationary, then rotating. You can make it with two passages on the
inner part (which goes onto the tube), and two parts which bolt together
around it bolted to the frame of the lathe.
folderol appears to be the most-common spelling, but falderal,
fol de rol, and fol-de-rol are linked as alternatives in
links to a Google Ngrams chart that
compares frequencies-in-books of the four spellings.
I thought about labryrinth sealing but air would leak out pretty fast.
I suppose I could use the labyrinth seal for just the opening cycle so
it would be leaking for the least amount of time. If the tube mounted
solenoid valve doesn't work then maybe I'll give it a try.
No. It was a long time ago. The rubber was not exotic though. I just
looked for rubber compounds that could handle the temperature and oil
composition. It mighta been EPDM. I don't think it was BUNA-N.
Eric - I took a look at Parker Seals' "O-ring Handbook". It now has a spot
on the book shelf, so to speak.
There was mention of a rotary speed limit of 1500 feet per minute, but
that was in a section about "hydraluics".
It was my understanding he has a solenoid valve in the shaft to
contol the air. Energized it puts air to the cyl to close the collet
chich, de-enrergised it puts air to the release cyl and vents the
close cyl. He needs to get the electical signal to the spinning
solenois - and the SIMPLEST way is to use a set of slip-rings to feed
the electrical signal into the 5000 RPM spinning collet eaaembly.
Well, the sealing diameter was about 2 inches, as I recall. So that
would be about 3000 RPM at 1500 FPM. I don't remember where in the
Parker book the information was that I used to design the rotary
union. But bit in there and the whole thing was pretty easy. Parker
had already done all the heavy lifting, so to speak.