Tek Faucet aspirator - preventing backflow?

[Deleted Member 1643]

The faucet aspirator:

Remember these from lab? Work great with Buchner funnels, why not purge? Initially very impressed. Checked 30 minutes later, still big bubbles - but oil was under water in evaporation dish. (Apparently no mixing, so easy to recover.)

These work simply - faucet pressure forces water through a constriction where a hose barb is attached, pulling impressive vacuum. Some have backflow valves (whatever they are) - obviously, not this one. What causes backflow? Any way it can be prevented? In comments for a cool glass aspirator: "Water outlet at the bottom is angled nicely to prevent backflow." How would this work? Rig something up on the end?

 

[herbivore21]

The faucet aspirator:

Remember these from lab? Work great with Buchner funnels, why not purge? Initially very impressed. Checked 30 minutes later, still big bubbles - but oil was under water in evaporation dish. (Apparently no mixing, so easy to recover.)

These work simply - faucet pressure forces water through a constriction where a hose barb is attached, pulling impressive vacuum. Some have backflow valves (whatever they are) - obviously, not this one. What causes backflow? Any way it can be prevented? In comments for a cool glass aspirator: "Water outlet at the bottom is angled nicely to prevent backflow." How would this work? Rig something up on the end?

Interesting man, backflow contamination is a substantial problem with using typical oil lubricated rotary vane vacuum pumps (ie: what 99% of you guys on FC are using) for purging. So many folks would benefit from avoiding this problem and learning to prevent backflow!

 

[Deleted Member 1643]

Tried extending with a hose. Got pull-and-snap from QWET, using foodsaver container as vacuum chamber and watching for back-flow. Blurry.