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vulture
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Can we keep this on topic?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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ShadowWarrior4444
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| Quote: | Originally posted by vulture
Can we keep this on topic? |
Sure:
That wasn't vacuum tubing in those pictures. You're grievous acts of heresy have not gone unnoticed. It is quite important to use vacuum-tolerant
equipment while employing a vacuum, or you may have a nasty surprise when your discharge tube repressurizes or your chemical vapor deposition chamber
happily explodes throwing glass and diamond dust all about the lab.
That said, have you tested how high a vacuum you can achieve with the pump? And, does the collapse of the tube prevent further depressurization?
[Edited on 5-18-2008 by ShadowWarrior4444]
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bio2
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Nalgene tubing recommended for peristaltic pumps. Couldn't find a vacuum rating for this.
.........................................
NALGENE 280 PUR Tubing
Materials: ester-grade
NALGENE 280 Ester-based Tubing is an extremely tough product featuring excellent abrasion resistance, low-temperature resilience and flex-fatigue
resistance. Pure polyurethane-contains no plasticizers and low levels of extracables, which make it ideal for high-purity applications. Resistant to
atmospheric ozone, aliphatic hydrocarbons and petroleum products. Higher physical properties than PVC products (tensile strength, tear resistance,
elongation, etc.) makes it
ideal for peristaltic pump applications.
Not recommended for aqueous solutions. Note: NALGENE PUR tubing is not autoclavable, but can be gas-sterilized.
http://www.nalgenelabware.com/products/productDetail.asp?pro...
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indigofuzzy
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@vulture: are you referring to my pictures? I apologize if that was off topic, my intent was to share the results of constructing a peristaltic vacuum
pump, by showing that I had achieved a low enough pressure to support a continuous discharge.
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IrC
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"To be honest i have no idea what type of tubing should be used for good results."
Tygon would be the best of the choices I saw on the wiki page mentioned.
"It seems to me that a peristaltic pump should be capable of achieving a fairly low ultimate pressure...albeit at a very low throughput"
I do not think so, I imagine this design of pump would be very poor for high vacuums. Two stage pumps using high quality vacuum oil is a much better
idea for basic roughing. One more point, having put considerable time and money into a good vacuum station myself, you must use copper tubing or steel
brake line with flare fittings or you will never hold even a remotely decent vacuum, trust me on this one. A flaring tool kit and high quality tubing
cutters is a must have! You will find it is very quick and easy to plumb for whatever experiment you are doing with say 1/8 inch Cu tubing and when
you get good at flares leaks will not even be a problem.
One station I built uses a gast diaphram pump for the quick pump to 18 to 20 inches of Hg, then a oil rotary surplus medical pump gets down to 28
inches. It likely used to get down to 100 microns or so but being surplus the seals are in need of repair. After this I shut off the valve to the
above mentioned pair of pumps and turn on one I bought new from frostee freeze or whatever the ebay name was for an AC vacuum pump used in AC vacuum
work. This goes to 70 microns or less, and when it has been on a short while I open the valve to this one. All 3 pumps have a common high vacuum tank
about a foot in diameter with valving and guages to all 3 pumps. The next pump is a 4500 dollar new scientific pump which is oil 2 stage, and this
gets me down to a micron or lower. Below this I still cannot get as money has been too low for a while to have enough for a super exotic molecular
type pump. Maybe someday.
A test I did, I tried various tubings and fittings with my reservoir tank held at 100 microns, and in all cases the vacuum did not last real long,
whereas with my flare fittings and metal tubing I pumped the tank down to 100 microns just before I moved from Arkansas to Arizona. A year went by
before I even had any experiments to do using the pumps, and the guage was still sitting on 100 microns. After a year I could see no difference in
vacuum in the tank. Yes I let the air in a bit to make sure the guage was not just stuck or something, pumped it back down to 100 and shut the valve.
A year after this I moved back east again, having never needed the pump for any work I was doing, and you guessed it after reading this thread I went
and looked and sure enough it still sits on 100 microns. Metal tubing with flare fittings rule for doing high vacuum work in my opinion.
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indigofuzzy
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| Quote: |
That said, have you tested how high a vacuum you can achieve with the pump? And, does the collapse of the tube prevent further depressurization?
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Sadly, I don't have a vacuum gauge to test that with. All I can state is the length of discharge I can get from my mini Tesla coil. (And my volt meter
doesn't read kilovolts, nor do I have hefty enough resistors for a proper voltage divider.) What I know is this: the best vacuum I've gotten,
evacuating a 5cm diameter spherical lightbulb, was sufficient for diffuse violet plasma streamers to extend to the glass in response to touch. Without
touching the glass, there was a small (millimeter or so) ball of violet plasma around one electrode.
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indigofuzzy
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Ok, a few weeks ago, i acquired a hand operated vacuum pump with a gauge. Sadly, the gauge is a bit miscalibrated, and reads atmospheric pressure as
-60mmHg. My peristaltic pump will drag the needle to just below -760mmHg, so I'm guestimating the final pressure at around 50mmHg.
Now, IIRC, an aspirator using room temperature H20 will pull more vacuum than that. I think Evil_Lurker had some positive experiences with a waterbed
draining pump.
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Tacho
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The attached pdf describes the development of a peristaltic vacuum pump that can reach 5 x 10-2 Torr. That is a pretty impressive number for this kind
of pump.
At some point they suggest a possible improvement by using tubes with thinner walls imersed in a fluid under negative pressure to prevent colapsing
under vacuum. I think that negative pressure is not even necessary. Merely imersing the tube in an hermetically sealed fluid would prevent the walls
from colapsing.
Attachment: Peristaltic001.pdf (662kB)
This file has been downloaded 1947 times
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Swede
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I picked up a pair of pump drives off eBay for nearly nothing, and a pair of good Cole-Palmer pump heads. I've tried a number of quality St. Gobain
Tygon plastics, and the problem has already been stated.... if you set the pump head occlusion up such that you obtain a full seal between rollers,
the forces on the pump rollers are quite high, assuming you are using tubing stiff enough to handle vacuum. I think the best option is to have the
tubing INSIDE THE PUMP HEAD be as short as possible, and couple the stub leading out to a proper vacuum line, like braided vinyl, perhaps.
I think it can be done, but how low it can go, I have no idea. The best chance for a harder vacuum is a smaller pump with its associated smaller
tubing. Much slower, of course, but more able to handle the necessary forces.
A peristaltic pump is a handy beast. Even if it cannot create a vacuum hard enough for one's purposes, it'll always find use in some other project.
And peristaltic pumps that retail for $600+ can be had surplus for $20 to $40. Good deals all around.
Daisy-chaining pumps? Might be the key and is an interesting concept.
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Texium
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Thread Moved
19-11-2023 at 12:48 |
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