vaccum pumping+bernoulli's eq

[dramarc]

In laboratories, there is a common “vacuum suction” thing (looks like a “T” working on the principle that tap water moving past a junction (T-junction) don’t know the name for it) will case a low pressure due to the high velocity (Bernoulli’s eq). This I can understand intuitionally, but with time as the pressure falls in the vacuum chamber, why doesn’t water flow into this part of the system as well since the pressure in the vacuum chamber is way lower than the atmospheric pressure?
What law of physics can be applied to explain this in a proper way?

Maybe it’s a similar problem as why a liquid will keep on flowing if you create a low pressure in the end of a hose and if the end part of the hose is lower than the part sucking the liquid. Could anyone explain this?

 

[quark]

That is called an ejector, but it is rather new for me that they are used in labs for evacuating chambers. Mostly, we use vacuum pumps.

The only and one physics law(or natural law rather) that can be applied here is that flow always occurs from high head(don't dilute this with pressure) to a low head region. The throat of the venturi (or the connecting point of horizontal and vertical bars of T) has the lowest head, lower than the chamber.

Please read the rules carefully. We generally don't discuss these kind of fundamentals.

 

[25362]

Dramarc, quark's explanation is clear and sufficient. One of your examples is an eductor (=ejector) and the other is a siphon.

I reckon the following quote applies.

It's elementary, my dear Watson.
Sherlock Holmes.

 

[TedLinsle]

They're called aspirators...at least the ones that connect directly to lab faucets.