Valve that allows the flow of liquid but prevent air escaping

[marokay]

Hello,
I do not really know if this is the right place to post this message ... if it's not then I'm sorry
I am looking for a valve that allows the flow of liquid but prevent air escaping out form let's say a sealed container ...
Is there such a thing?

 

[mfb]

Liquid and air in the same direction, at the same pressure?
Can you use some active elements?

 

[marokay]

The water is in a tank and I want them to flow through a pipe at the bottom of the tank (by the force of gravity)
Now I do not want that air will enters the tank back form the pipe while the pipe is open (in the pipe can be pressurised air)
What do you mean by active elements ?

 

[mfb]

So you just need a 1-way valve? Those exist.

Active elements would be something like a sensor to detect water and open the valve based on that sensor.

 

[Baluncore]

Automatic drain valves are available that mount below a compressed air reservoir. They have a float supporting a needle valve.
When water builds up in the lower float chamber, the needle valve at the bottom lifts and the water is vented by air pressure.