# Rule of thumb of how much vacuum does lab glass stand?

Sometimes I have to apply vacuum to all kind of different borosilicate glass equipment like:

• liebig condensers

• fractional distillation apparatus

• spiral condensers

• chromatography column

• and so on...

While I know that a thick walled round bottom flask will pretty much stand any vacuum my vacuum pump can produce, I am not so sure for something as fragile as a spiral condenser.

Is there a kind of rule of thumb how much mBar thin walled glass equipment like spiral condensers or chromatography columns can stand without risk of implosion?

• The risk of implosion is always here, even properly certified glassware may get a tiny crack and implode. Always assume that the risk exists. Be especially suspicious with flasks above 100 ml except for very thick-walled ones for vacuum filtering. That said, there is no much difference from 0.01 kPa and 10 kPa as the outside pressure is 99+ and 90+ kPa respectively (10% difference), so if a piece of glassware can be evacuated by water ejector to meaningful degree, it usually can withstand any vacuum within. Jan 29 '18 at 21:14
• That said, you should be suspicious of large flat and almost flat surfaces and sharp angles.Small tubes are fine. Glass condensers are usually meant to be used with vacuum. Jan 29 '18 at 21:14
• How can you use a chromatography column "in vacuum"? Are you meaning to clean/dry it? Jan 30 '18 at 10:18
• Scratches and cracks have a much larger effect on strength for internal pressures than for external pressures, due to the nature of compression strain verses tensile strain. Apr 18 '20 at 22:16

The basic rule is that the stress on an evacuated glass vessel is pretty much the same at 0.01 mbar (oil pump), 1 mbar (membrane) or 25 mbar (water jet) absolute internal pressure. 0.99999, 0.999 or 0.975 bar $$\Delta p$$ to the outside make very little difference if the thing goes pop.

And basically everything made out of borosilicate and with no flat surface is safe. Condensors definitely, they're not delicate at all. It's basic procedure to make them oxygen-free by evacuating.

Be careful with chromatography columns and flasks in the > 1 liter range. They're principally safe to be evacuated, too, but then are also a bomb, armed and ready to drop. If it goes off, you better not stand next to it. The danger from evacuated vessels is more or less proportional to their volume.

• The primary danger of imploding flasks is the hot/cold/toxic/corrosive/reactive substances inside. The glass itself will make a startling noise and small chips could get in the eyes if you are very close with no goggles but the nature of implosion is not nearly as dangerous as explosion. Apr 18 '20 at 22:13
• @Karl: Is regular glass much less resistant to vacuum vs borosilicate (I think the lower elasticity plays a big role for internal pressure, but I'm wondering if it makes much of a difference when the pressure is external). I have a 50,000ml flask with medium thick walls I'll like to take down to -25Hg.
– Hans
Aug 8 '20 at 10:24
• @Hans 50 liters? Wow, no idea. -25 Hg means ~35 mbar below ambient? That could occor by itself within 12h if you put a cork on during a thunderstorm. Don´t think anything could happen there.
– Karl
Aug 8 '20 at 11:11
• @Karl -25mmHg (~ 125 Torr I think). Yes, 50L
– Hans
Aug 8 '20 at 17:04
• If you go using ancient units, you´d better know what they mean. ;) Torr and mmHg are the same thing.
– Karl
Aug 8 '20 at 17:51