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Digital blood pressure monitor Answered

Do you guys think a digital blood pressure monitor would be capable of pulling a strong enough vacuum for a vacuum chamber if it was modified?

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Disasterificpetercd

Reply 4 months ago

Would that be enough to fool around with? Would having a smaller chamber do anything?

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petercdDisasterific

Reply 4 months ago

No not really, a smaller chamber is still only going to have a 36% vac, just would be quicker to get to that level than a large one.
If I remember correctly, it took about a 70% vac to make a marshmallow puff up, with no real visible effect even at 50% vac.

For all my tinkering needs, I used a rotary scroll compressor for an aircon unit that I picked up at the scrapyard, then modified it in order to vac bag model aircraft wings, purge air out of wood for resin stabilizing etc.

matsushita rotary compressor 1.jpgmatsushita rotary compressor 5.png
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Downunder35m

4 months ago

Nope.
The pumps used are designed to provide positive pressure only.
In theory you could try modify the mechanism or revers the valve but it leaves the problem of the design.
Get a cheap vacuum food sealer, they are far from perfect but at least offer a half decent vacuum.
For anything that should come close to a real vacuum and not just low pressure you would need a proper pump though.
To get bubbles out of resin the above should work.

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Jack A Lopez

4 months ago

Strong enough vacuum? It depends on what you want to use it for.

The image attached to this post, is a graphic showing vacuum quality, on a logarithmic scale, versus ways that vacuum is produced, measured, and what applications it is used for.

I borrowed this graphic from the belljar-dot-net's page, "Vacuum Basics", linked here:

http://www.belljar.net/basics.htm

From this graph it becomes apparent that all the really, like "hard science" applications of vacuum, e.g. particle accelerators, require really hard vacuum.

Moreover there is a whole range of stuff in between; e.g. sputter coating, neon signs, removing water vapor from refrigeration plumbing, et al.

Actually it kind of makes sense there would be such a wide range like this, when you consider a liter of air, at standard temperature and pressure, has roughly N = 10^22 molecules it, and if P*V= N*K*T then every tenfold reduction in pressure reduces the number of gas molecules by tenfold.

I'm just saying there is a lot of room to do that, to keep reducing pressure by a factor of 10, before there is absolutely perfect vacuum, i.e. exactly zero gas molecules, or statistically less than one, gas molecules in that liter of space. So the log scale on that graph is appropriate.

I suppose I could also recommend looking at the Wikipedia article for, "Vacuum"

https://en.wikipedia.org/wiki/Vacuum

This article is sort of telling the same story, dividing vacuum quality into regimes like, "low", "medium", "high", "ultra high", and the various applications for these different regimes.

vacuum-quality--production-measurement-application--fig1b.gif