tnhrbtnhb
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Pressure testing a vessel.
I'm thinking I might try to pressure test a vessel for vacuum use by dropping it in 10 m of water. It's winter here, though, so the only way I can is
by tying it to a rope and a rock and dropping over a bridge.
Think they'd haul me in as a terrorist? There are no boats passing below.
BTW it's one of those 29 litre pails for winemaking, I don't know if it will hold.... Anybody got any better ideas for cheap vessels? Has to be about
30 litres or more.
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chemoleo
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Forgive the obvious question, but why don't you just apply the vacuum, since you must have it as you intend to apply it at some point in the future?
Just cover it with a blanket if you are scared of fragments.
Vacuum isn't that tough...as long as the container isn't made of some plastic such as PE/PP, but instead of glass, metal, epoxy etc there shouldnt be
much of a problem. But just test it. We apply vacuum to 5mm-walled glass bottles without a problem. Admittedlty, the larger the bottle, the more of a
problem I suppose.
You could also coat the container in some sort of air-proof cement, even if that's hard model plaster, giving extra strength.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Organikum
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The problem with large vessels is not the vacuum whats cheap, but temperature and not overall temperature whats even cheaper but stress through
unequal heating/cooling.
/ORG
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Magpie
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What about a stainless steel beer keg? You might be able to find a used one for a reasonable price. I'm thinking it would likely be strong enough
for full vacuum.
The single most important condition for a successful synthesis is good mixing - Nicodem
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tnhrbtnhb
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| Quote: | Originally posted by Magpie
What about a stainless steel beer keg? You might be able to find a used one for a reasonable price. I'm thinking it would likely be strong enough
for full vacuum. |
That's an idea. Might be expensive, though. I just thought submersing it all in water would be a quick way to test a vessel. That way I don't add
connections, go through the trouble of sealing it all if it will implode anyway  .
It is PE  . About 2-3mm thick I guess. But isn't PE stronger than glass?
I think I'll just go for it. Who cares if they haul me in for a couple hours. Could take some explaining, though.
[Edited on 18-2-2007 by tnhrbtnhb]
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Mr. Wizard
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You can pull a rather quick vacuum with an automobile engine by hooking a hose to the intake manifold. It won't be a hard vacuum of any description,
but it will be enough to test a container, and it is rather fast too. You get the lowest pressure during the time the engine is going fast without the
throttle being open. I know it's obvious.
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chemrox
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I don't understand the problem. A vacuum pump will pull down to a mm or less and these kinds of pressures haven't caused any problems with my glass.
A water pump seems a lot more accessible and efficient than hooking up to an engine and a hand pump can be had at the auto supply.
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Mr. Wizard
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| Quote: | Originally posted by chemrox
I don't understand the problem. A vacuum pump will pull down to a mm or less and these kinds of pressures haven't caused any problems with my glass.
A water pump seems a lot more accessible and efficient than hooking up to an engine and a hand pump can be had at the auto supply.
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Obviously there is more than one way to pull a vacuum on a stainless steel beer keg, or a glass container. The vulume of the containers might matter.
A two foot length of vacuum hose will cost you a dollar or two to hook up to a vacuum port on the intake manifold. A hand vacuum pump will cost about
$30. I don't know what a glass water aspirator would cost, if you can find one locally. You might be able to substitute a plastic water bed pump or
aquarium water aspirator.
I'll bet I can pump a keg down with a car engine in the time it takes you to get tired of pumping that hand operated pump or 30 pumps, whichever
comes first. 
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bio2
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If it's PE 2-3mm thick low density like most buckets it will
collapse under vacuum. If HDPE it will crack and bend
sometimes catastrophically Internal braces might help.
I once built a vacuum dessicator that was made from a big
PP cake pan. Ran for a few minutes full vacuum
when the domed cover shattered instantly.
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Sauron
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If you look at a good glassware company's catalog you will find vacuum maxima for various sizes of RB flaks that were designed for vacuum.
You will quickly see that the larger the flask the less vacuum it can tolerate because the mechanical strength of the sphere decreases as radius
increases.
Also it should be equally obvious that any flat bottomed vessel like your pail will be inherently weak to vacuum as compared to a radiused bottom
cylindrical vessel (which is still weaker than a sphere would be) and the required strength has to be compensated for with wall thickness. And this
introduces the pesky problem of thermal stress from unequal heating and cooling. The manufacturer will have guidelines for max temperature
differentials at different vacuums, as these stresses are additive.
Not a trivial problem and really not likely to be one with a cheap improvised solution.
How much vacuum do you want to pull, how fast is the displacement (like, you do not want implosion) and what about temperatures (or contents, of
environment etc.) What kind of pump? Have you got gauges and vac controls or is it just turn on and let it pump down?
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tnhrbtnhb
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I got it solved now, I'm pretty sure. I just bought a pressure cooker, after going through the pain of trying to construct an airproof box from
plywood. Thanks for the replies. It did implode, as suspected, but it was the sides that buckled. I just used my vacuum pump, though maybe I
shouldn't since the reason I didn't want to was that I don't have an oil mist filter on the output yet.
I have gauges and so forth. If you care to know what I'm doing, there are details in the "how to bond polyethylene" thread.
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Texium
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Thread Moved
19-11-2023 at 11:54 |
Texium
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Thread Moved
19-11-2023 at 11:55 |
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