Sciencemadness Discussion Board

Glassware Vacuum

aminotetrazole - 30-1-2016 at 08:27

I recently asked what vacuum a glassware kit could withstand from a seller on ebay. They responded 0.098 MPa. When I convert this I end up with 735 mmHg, which doesn't seem like it would be able to withstand any reasonable vacuum at all. Is there something that I am missing? Thanks.

Detonationology - 30-1-2016 at 09:17

One atmosphere of pressure is 760 mmHg. If the seller stated that it could with stand 735mmHg, that basically means it can withstand 1 ATM of negative pressure. HOWEVER, you should never exceed the rating posted, PERIOD! I have never felt comfortable nor the need to exceed ~450 mmHg. If you seriously need glassware to withstand serious pressures, don't skimp out... buy American. It ain't worth loosing your life over.

[Edited on 1-30-2016 by Detonationology]

Sulaiman - 30-1-2016 at 16:07

sorry to butt in, but this may be relevant,
I have wondered about this, using the above example of 1 ATM =760 mm Hg
and a rating of 735 mm Hg, implying a minimum absolute pressure of 25 mm Hg.

If ratings are exceeded and a vacuum of say 1mm Hg absolute is used
the stress is only increased by 759/735 = 1.033, a 3.3 % increase in stress
surely the safety margins are greater than this.

Then again, at 1000 ft. above sea level, -735 mm Hg gauge pressure is absolute vacuum ???

So what am I missing ?

[Edited on 31-1-2016 by Sulaiman]

vmelkon - 31-1-2016 at 15:29

Quote: Originally posted by aminotetrazole  
I recently asked what vacuum a glassware kit could withstand from a seller on ebay. They responded 0.098 MPa. When I convert this I end up with 735 mmHg, which doesn't seem like it would be able to withstand any reasonable vacuum at all. Is there something that I am missing? Thanks.


That looks weak. Yes, 0.98 MPa = 735 mmHg.
Even a PET plastic Pepsi bottle can handle 3 atm. I'm sure that the glassware should be able to do handle much lower pressures than 735 mm. However, I have heard of a case of a glass buchner flask blowing because of low pressure.