airbreak pressure tanks

[Dr_Doggy]

obviously an air tank can support high enough pressures for air breaks, one i was looking at goes up to 150psi, obviously its structure is sturdy but i wonder how they would stand as a vacuum chamber??

could it be a simple calculation of:

stp = 15psi;

1/150psi= 0.0066psi


a chart i found implies that 0.0066psi is between 750 - 100 microns, an online calculator says 340 microns , is this correct, can i use an air tank this way??


also if i drilled in a hole for a plexiglass view port what kind of sealant should i use to "glue" the plexiglass down, when im at that kind of pressure?

 

[JimB]

could it be a simple calculation of:

stp = 15psi; What is "stp" ?

1/150psi= 0.0066psi Yes, so what?

a chart i found implies that 0.0066psi is between 750 - 100 microns, What? That is nonsense

There is no relationship between PSI and Microns.
PSI is Pounds per Square Inch, a unit of pressure.
A Micron is on millionth of a Metre, a unit of length.
There is no equality between the two.

As for whether an air tank can withstand a vacuum, it is a bit difficult to say.
But as a 100% vacuum is no more than 15PSI and the tank is rated to 150PSI, it is a risk worth taking, the worst it could do is implode.
Having said that, I would not want my fingers near to it when it did implode.

The stresses involved in a vessel under vacuum are somewhat different from those on a vessel under pressure, it needs someone with a bit more stress experience than me to analyse it.

As for cutting a hole for a viewing port, that will raise the stresses quite a bit.

As for an adhesive to hold on a plexiglass window, I would suggest silicone rubber, something with a bit of elasticity.
The window should of course be placed on the outside of the tank so that air pressure forces the window onto the tank tightening the seal when there is a vacuum.

JimB

 

[MikeMl]

If the tank is rated for 150psi. Std atmospheric pressure (1 Atmosphere) is 14.7psi, so the tank is rated for a tensile load of 150-14.7≈140psi. If you evacuate it to a perfect vacuum, there will be a compressive load of only 15psi, so no problem at all...

 

[Dr_Doggy]

wow, really! so with this tank i can simulate outer space pressure? I have been looking around for a suitable vacuum chamber, and have found that for a chamber to go to 99.999% or 10 torr, which is my requirement, but cost goes up to 1000's $ , that will be bonus if i can just use a 100$ air tank off a truck, in fact screw the view port.

would that mean a tire pump hooked up backwards would also be able to evacuate said tank to create my outer space pressure as well?

here is the chart im following:
https://www.engineeringtoolbox.com/vacuum-converter-d_460.html

 

[MikeMl]

Look up pressure achievable with a "roughing pump" (mechanical pump). It takes a "diffusion pump" to get to 10micron pressures..

 

[alec_t]

Vehicle vacuum-brakes are commonplace, so perhaps a conventional vehicle vac tank would meet your needs?

 

[Dr_Doggy]

https://www.ebay.ca/itm/90066-2V-11...788?pt=LH_DefaultDomain_0&hash=item58a02ed8e4

is the pump im looking at, 15 microns is close enough, which is what the ad specified, i doubled checked, but diffusion is not required until after < 10 microns.

I was unaware that vehicles now used vacuums on the breaks, however after investigating such device it is too small, plus i will need the access ports, which may be too small on the tank as well. but im going to try to swing something anyway, which will cut cost down alot alot.

 

[tenfingers]

How much vacuume a tank can withstand is related to the size of the tanks surface area. Yes, the pressure differential is only up to 14.7 psi but that is 14.7 pounds on every square inch of the outside of the vessel.

I saw a video of a rail tanker car that was steam cleaned, then let cool withe the tank sealed. Not pumped out, just the hot air shrinking as it cooled. It imploded the tank car.

If your looking for a cheap tank and don't need a window, how about a propane tank from a gas grill?

 

[ClydeCrashKop]

An old compressor from a refrigerator or air conditioner will evacuate a tank to 28" of mercury or better.
A propane tank will definitely do it.

 

[tcmtech]

Most any tank rated for 150 PSI or greater will have no issues at all with being taken down to a high vacuum. I have done it many times to clear water out of tanks I have cleaned and intended to repurpose.

I have a air conditioning vacuum pump that will pull a vacuum high enough to boil water at 40 F which is around 29.5" of vacuum.

Now on a more dangerous note I have also done the same with old glass canning jars as well which are in fact designed to handle a moderate amount of vacuum when used in canning processes. During the canning process the foods being caned are usually put in the jars hot which are filled right to the top then the lid is put on so as the food inside cools and shrinks the jar is put under a moderate vacuum.

The smaller round 1 quart and less heavy glass ones will easily take being drawn down to high vacuum levels as long as they have no cracks or chips in them.

If they do at worst they simply implode into bits with a loud pop!

 

[Dr_Doggy]

**broken link removed**

is the tank i plan to use, and im kind of steering towards a view port again, which i would put right across the top center rite where it says "length", but plexi is flat, and tank is round,

what if i were to just use surface plastic off 2l pop bottle? those can handle up to 60-80 psi,

and pls confirm type of silicon i can use, would threadlock or gasket seal be best? or should i not worry about that and just go with standard silicon??

(i willl ofcourse be generous with my surface area)

 

[alec_t]

what if i were to just use surface plastic off 2l pop bottle? those can handle up to 60-80 psi,

Because of the bottle shape the plastic does not noticeably distort when under internal pressure. But if you were to evacuuate the bottle it would crumple under the external atmospheric pressure. Your plastic window would crumple inwards.

Will the window be removable so that you can insert things into the tank?

 

[Dr_Doggy]

well preferably a door/removable window would be good, since there are always margins for error while constructing insides, and it probably would be a good idea, but it seems to me that a door would make things increasingly more difficult, so i was thinking of a window that i could remove temporally while tinkering, then re-seal after.
i was thinking of basics just to get me through a few tests, but maybe i should add the access port, i fear cost mostly with this,

i was thinking about cutting a 3-4" diameter hole on the top of tank, then cutting the center part of the bottle to get a flat-semi curved sheet, then with the silicon, would that work?

 

[alec_t]

Alas, no. That bottle plastic would bulge inwards and crease at the window edge.

 

[tcmtech]

WIthout reinforcement putting a hole in the side of one of those tanks is the same as putting a crease in the metal. As soon as the vacuum gets high enough the whole thing will crush in on itself like a stomped on pop can.

A small viewing port would work best on the end where the stresses are held more securely due to the domed shape.

 

[alec_t]

The reinforcement tcmtech mentions could be provided by a ring-shaped flange welded to the opening.

 

[crutschow]

Why not make a glass bell jar vacuum chamber? That way you can readily see whatever is happening to anything inside the chamber. Here's a description of how to do that.

 

[Dr_Doggy]

actually that is the very vid i was watching, and what lead me to wonder about how to properly seal things in, but will that will go down to low enough pressure...?

 

[alec_t]

Just google for 'glass bell jar vacuum' and you'll see many hits for vendors of jars and seals. Those jars can take a full vacuum.

 

[crutschow]

actually that is the very vid i was watching, and what lead me to wonder about how to properly seal things in, but will that will go down to low enough pressure...?

Yes, a heavy glass dome will take a full vacuum. "Vacuum grease" can be used to seal the interface between the dome and the flat base. For hobby experiments you may be able to get by with a thin coat of petroleum jelly.