On Sep 14, 4:22*pm, "Ed Huntress" wrote:
"Mark Rand" wrote in message

...







On Mon, 14 Sep 2009 09:35:10 -0400, "Ed Huntress"

wrote:

Hey, here's something curious. I just tried this, and got funny little
drops, much smaller than I would get with an eyedropper, for example.

I took a 30-unit syringe, filled it with water, and counted the drops in 5
units. I got 11 drops -- close enough to 10 -- but they were really teeny.
These were drops that would detach themselves and free-fall as I held the
syringe point-down; just ordinary drops.

That's exactly 1/10 the size you're describing -- one drop from this
syringe
is 5 microliters. I see from some references online that this is the same
size as a drop of water dispensed from a Pasteur micropipette.

So is the size of the drop that dependent on the opening from which
they're
dispensed? This was a 30-guage needle. I'd have to mike it to see the
size,
but it's *really* thin.

Might get smaller if you ground and lapped the end square. Or not...

I'll bet it would get bigger. I'll try it, but not now.



PS Are you throwing the things away after only one use? *I get a couple of
weeks out of mine.

I don't use them at all anymore. I have a pump. But I typically used them
three times. The old 28-guage ones lasted longer. 29-guage is my favorite..
With the callouses I have, the 30-guage sometimes bends right over at a 90
degree angle when I try to push it in.

I used to use them until you had to screw them in. d8-)

I have sharpened a few, when I was in a pinch, on a black hard Arkansas
stone. It works pretty well.

--
Ed Huntress



Mark Rand
RTFM

Geeze, how many people here have diabetes? Show of hands?

I don't but my brother does (and my mother did as well). Last time I
checked (a couple of months ago), my blood glucose was 85 an hour
after a large-ish meal so for the time being, I appear to have dodged
that bullet.

But back to the matter at hand. How about making a screw-activated
plunger pusher? You'd have some stiction problems in the syringe, but
maybe not too bad. Also, Ed, are the cartridges in the pump
refillable? They're usually operated by a stepper motor driving a
screw, and can deliver pretty small increments. It should be pretty
straightforward to concoct a device with a fine-thread screw, maybe
with a 10:1 vernier dial drive for good measure.

The old glass syringes were very slippery, but I don't know if they
make them in very narrow bores.

If it's too hard to control the movement of a syringe plunger, you
could use a diaphragm instead, which would have pretty close to zero
friction.

Just some random thoughts from a tired former designer of anesthesia
equipment.