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Author Topic: Can a vacuum helmet be created using an air compressor?  (Read 4358 times)

Offline mriver8

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What I mean is a vacuum between two layers that make up a helmet shell? Or will they collapse? And is so why don't vacuum sealed jars break while making them? What material must it be?


 

Offline chiralSPO

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #1 on: 18/10/2014 19:40:53 »
This depends on the material that the helmet is made of (also how the air compressor works--I would recommend a device designed for decreasing pressure, not increasing it), and how strong a vacuum is required.

There isn't any experimentally attainable perfect vacuum, so really what we are talking about here is reduced pressure. It is easiest to talk about this in terms of orders of magnitude: a household vacuum cleaner can get to about 20% of atmospheric pressure, and a cheap pump can probably achieve pressures about 1% of atmospheric pressure (102 atm). I routinely work with pumps that are about $5000, and can reduce pressure within a thick glass vessel to about 104 atm, and have occasionally used multiple pumps together to achieve pressures of 105 atm. I once worked in a lab that ran experiments in large steel boxes (>3 cm thick walls) under ultra high vacuum of about 1010 atm, but that required about $50,000 worth of pumps, sensors and regulation systems. I think deep space can have pressures as low as 1020 atm.

Given prior posts of yours I feel compelled to insist that you * DO NOT* try to put your head in anything that you have evacuated--even pressures achievable with a household vacuum cleaner can cause blood vessels to burst in your eyes, ears and face--I promise this is not pleasant!

If instead you wanted to make something akin to a thermos (an inner vessel and an outer vessel, with reduced pressure in between) that wouldn't pose as obvious a risk, but if you have ever broken a thermos you would understand why putting your head in such a contraption could still be very dangerous.
 

Offline syhprum

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #2 on: 18/10/2014 20:49:46 »
If it is thermal insulation that is required there are many light weight foam like materials that will provide a comparable degree of insulation to that provided by a vacuum.
 

Offline mriver8

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #3 on: 19/10/2014 02:38:13 »
If it is thermal insulation that is required there are many light weight foam like materials that will provide a comparable degree of insulation to that provided by a vacuum.

What materials?
 

Offline mriver8

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #4 on: 19/10/2014 02:44:33 »
This depends on the material that the helmet is made of (also how the air compressor works--I would recommend a device designed for decreasing pressure, not increasing it), and how strong a vacuum is required.

There isn't any experimentally attainable perfect vacuum, so really what we are talking about here is reduced pressure. It is easiest to talk about this in terms of orders of magnitude: a household vacuum cleaner can get to about 20% of atmospheric pressure, and a cheap pump can probably achieve pressures about 1% of atmospheric pressure (102 atm). I routinely work with pumps that are about $5000, and can reduce pressure within a thick glass vessel to about 104 atm, and have occasionally used multiple pumps together to achieve pressures of 105 atm. I once worked in a lab that ran experiments in large steel boxes (>3 cm thick walls) under ultra high vacuum of about 1010 atm, but that required about $50,000 worth of pumps, sensors and regulation systems. I think deep space can have pressures as low as 1020 atm.

Given prior posts of yours I feel compelled to insist that you * DO NOT* try to put your head in anything that you have evacuated--even pressures achievable with a household vacuum cleaner can cause blood vessels to burst in your eyes, ears and face--I promise this is not pleasant!

If instead you wanted to make something akin to a thermos (an inner vessel and an outer vessel, with reduced pressure in between) that wouldn't pose as obvious a risk, but if you have ever broken a thermos you would understand why putting your head in such a contraption could still be very dangerous.


What material would you suggest I was thinking a motorcycle helmet which is has a duel layered shell to form a vacuum of sorts while riding. I was thinking to seal the air vents with sealer, and use a compressor to reduce pressure.
 

Offline CliffordK

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #5 on: 19/10/2014 08:35:59 »
If you're talking about a vacuum between layers in a shell, you might consider simply an old glass thermos with two layers of glass separated by a narrow gap and a high vacuum. 

Vacuum pumps and compressors are similar, and sometimes are dual purpose machines, but are often slightly different in design, especially the air intake manifold.
 

Offline Bored chemist

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #6 on: 19/10/2014 10:03:44 »
The thermal conductivity of a gas is almost independent of pressure until you get to very low pressures (lower that you will get with a gerry-rigged vacuum pump) so there's no realistic way you can do this.
To keep that good a vacuum is very difficult and would need thick heavy walls made from glass or metal.

http://en.wikipedia.org/wiki/Thermal_conductivity#Simple_kinetic_picture
 

Offline evan_au

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #7 on: 20/10/2014 11:46:30 »
If you are thinking of using a vacuum as a shield against ultrasonic signals:
  • It is true that ultrasound cannot pass through a vacuum
  • However, the very rigid walls that are needed to contain the vacuum will conduct ultrasound around the vacuum fairly efficiently.
I think that the absorbent foam used inside a bicycle helmet would be a fairly good absorber of ultrasound, and a lot lighter than a vacuum helmet. Just don't use the air-cooled models with big gaps in them...

Seriously, you don't need to worry about ultrasound. But if you are worried, maybe a better protection is to get a dog? They can hear any ultrasound, and lead you away from it.
 

Offline mriver8

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #8 on: 21/10/2014 09:52:56 »
What about a dual layered titanium steel helmet with foam inside? I'm assuming it wouldn't be a perfect vacuum but you could get the pressure lower then a thermus without fear of ot crushing your head?
 

Offline RD

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #9 on: 21/10/2014 12:09:40 »
Seriously, you don't need to worry about ultrasound. But if you are worried, maybe a better protection is to get a dog? They can hear any ultrasound, and lead you away from it.

a bat-detector would be a better and cheaper way of detecting ultrasound,
[if one must have such a thing] ...

Quote from: wikipedia.org/wiki/Bat_detector
Bats emit calls from about 12 kHz to 160 kHz, but the upper frequencies in this range are rapidly absorbed in air. Many bat detectors are limited to around 15 kHz to 125 kHz at best.
http://en.wikipedia.org/wiki/Bat_detector

Note: air blocks ultrasound , so the idea that ultrasound can be beamed through air from a distance is a non-starter.

Bat Detector in action ...
« Last Edit: 21/10/2014 12:16:25 by RD »
 

Online alancalverd

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #10 on: 21/10/2014 12:14:20 »
Foam is not a vacuum. You can indeed evacuate a double-wall steel shell but the military find modern composites give better protection and lighter weight.

If you know the frequency of the alien ultrasound (use a bat detector to scan it) you can make "ultrasound chaff" with a car reversing transducer and baffle the buggers. 40 kHz travels reasonably well through air, and anything much higher than 1 MHz will be completely deflected and defocused at an air/Kevlar or air/steel interface, so grandad's WWII trophy will be perfectly adequate.
« Last Edit: 21/10/2014 12:20:00 by alancalverd »
 

Offline RD

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #11 on: 21/10/2014 12:25:47 »
If you know the frequency of the alien ultrasound (use a bat detector to scan it) you can make "ultrasound chaff" with a car reversing transducer and baffle the buggers.

Have the jamming-frequency sweep down to 17kHz and as a bonus you can repel teenagers  :) ... http://en.wikipedia.org/wiki/The_Mosquito
 

Offline mriver8

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #12 on: 25/10/2014 20:47:51 »
If you know the frequency of the alien ultrasound (use a bat detector to scan it) you can make "ultrasound chaff" with a car reversing transducer and baffle the buggers.

Have the jamming-frequency sweep down to 17kHz and as a bonus you can repel teenagers  :) ... http://en.wikipedia.org/wiki/The_Mosquito

feature=youtube_gdata_player
 

Offline mriver8

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #13 on: 12/05/2015 10:07:24 »
This depends on the material that the helmet is made of (also how the air compressor works--I would recommend a device designed for decreasing pressure, not increasing it), and how strong a vacuum is required.

There isn't any experimentally attainable perfect vacuum, so really what we are talking about here is reduced pressure. It is easiest to talk about this in terms of orders of magnitude: a household vacuum cleaner can get to about 20% of atmospheric pressure, and a cheap pump can probably achieve pressures about 1% of atmospheric pressure (102 atm). I routinely work with pumps that are about $5000, and can reduce pressure within a thick glass vessel to about 104 atm, and have occasionally used multiple pumps together to achieve pressures of 105 atm. I once worked in a lab that ran experiments in large steel boxes (>3 cm thick walls) under ultra high vacuum of about 1010 atm, but that required about $50,000 worth of pumps, sensors and regulation systems. I think deep space can have pressures as low as 1020 atm.

Given prior posts of yours I feel compelled to insist that you * DO NOT* try to put your head in anything that you have evacuated--even pressures achievable with a household vacuum cleaner can cause blood vessels to burst in your eyes, ears and face--I promise this is not pleasant!

If instead you wanted to make something akin to a thermos (an inner vessel and an outer vessel, with reduced pressure in between) that wouldn't pose as obvious a risk, but if you have ever broken a thermos you would understand why putting your head in such a contraption could still be very dangerous.

Do Igloo Coolers use reduced pressure as insulation? I think they do but probably not comparable to a steel dewar flask?
 

Offline Colin2B

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #14 on: 12/05/2015 11:03:55 »
a bat-detector would be a better and cheaper way of detecting ultrasound,
[if one must have such a thing] ...
i've got one, and for me it is a real 'must have'. But I use it for bat detecting and no worries about being attacked by unseen forces ;)

Do Igloo Coolers use reduced pressure as insulation? I think they do but probably not comparable to a steel dewar flask?
you still need to think about what Evan_au said re conduction through metal skin of a flask. Also think about weight.
I think a motorcycle helmet would reduce the level enough, I really wouldnt go to the trouble of a vacuum.
what will you do when you want to go to the bank? They wont let anyone in with a helmet!
« Last Edit: 12/05/2015 11:13:13 by Colin2B »
 

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Re: Can a vacuum helmet be created using an air compressor?
« Reply #14 on: 12/05/2015 11:03:55 »

 

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