using pressure to circulate water
 

I want to circulate water by using air pressure. Imagine a vessel with air in and water out, the water then returns to the same vessel.
I know it takes a check valve but it might need to be very sensitive?
I'll be trying this with a mock up (small jar and a loop) to test it out. Its for cooling on a small scale.
Any thoughts?

You'll need to use the pressure to get the water to the highest point in the system, then vent the air. The water will then be free to drain back down via gravity. You'll probably need to turn off air for a bit to let the water back into the reservoire.

An air powered pump might be easier though.

Please think very small flow rate. The air pressure is from an aquarium pump. Pressurizing a small vessel with ice and water, then flowing to a loop and returning. The check is to prevent flow to the return, I think tiny head on that return so very sensitive check valve.

But how do you want to return the water to the vessel that's pressurized by the air? I don't understand how your system is supposed to be working.

Could you draw a small diagram?

Sounds like a job for a water farm column to me. Works like magic.

Zwerius; I was hoping the pressure combined with the slight head would return flow through a sensitive check valve to the vessel.
I may just use a second vessel for the return flow. I would use a pump but the flow rate is so very low I don't know where to source one.

A small peristaltic pump would work. You can get a 12 volt one which delivers about 70mls/min but you can run it at a lower voltage as long as you don't want to pump to a great height. It will then deliver a good bit lower flow.