Pressure builds on its own inside this water tank?

[saeppi]

Hey guys,
It‘s been a few years since I had my last physics class so please be kind to me. I came here to ask you about a phenomenon I recently discovered in a design of mine.
The object in question is a stand with 3 arms, holding a water tank (see pic below).
All openings are pretty tightly closed and for a few hours there‘s no water leaking. But after a while, some pressure is building which pushes water out via the bottle screw (encircled in black). Another evidence of increased pressure is that when I let water out via one of the arms it would gush out if I wait for several hours. But soon after it would calm down and water flows smoothly again. Any ideas what‘s happening here?

 

[Baluncore]

Welcome to PF.

How do you fill and close the reservoir?
Please give us a link to the product on the web.
If you fill it with cold water, that will warm over time, and the air will expand, building up pressure.

 

[saeppi]

If you fill it with cold water, that will warm over time, and the air will expand, building up pressure.

Hi Baluncore,
Thanks, I think you‘re on point. The pressure build up happens overnight when we turn our AC off and the room warms up. How could I potentially counter that? Small hole at the top of the glass bottle?

 

[Baluncore]

How could I potentially counter that? Small hole at the top of the glass bottle?

I have never seen one before, so I do not know how it is built or operated.

How can water drain out if air cannot get back in?
As water is removed, a reverse flow of air would need to enter and bubble up to the surface, or a partial vacuum will form, that will prevent it dispensing.

A 1 mm hole in the top of the reservoir might be drilled, and could have an air permeable plug, to prevent dust entering.

 

[sophiecentaur]

How could I potentially counter that? Small hole at the top of the glass bottle?

How can water drain out if air cannot get back in?

Exactly. All the office water coolers you see work because air is allowed in. That air need not come from the 'top' but is allowed in through wht must be a non-return valve that's at a level above the water outlet. They all make that characteristic bubbling sound when you fill your cup. ~They must all have some pressure relief and so should @saeppi 's dispenser. The problem could be a design fault (form over function? - it looks nice but) in his 'interesting' model. I guess the commercial ones have a drain (for the cooler unit ?)

Don't try for a hole in the top /bottom of the bottle. You will have problems between filling it, carrying it and turning it upside down.

There is one possible solution, I just thought of, and that is to have a narrow vent tube leading down from inside the top of the bottle (just above the water level when ' full), down into the metal collar and out from side of the collar ( above the three outlets. The vent should be very narrow so that the entertaining bubbling takes place whilst still allowing a very slow rate of air to equalise the pressure at the top as the device warms up.
That would call for some DIY skills and it would depend on what's actually in the collar which the bottle sits in. OR you could just fashion a ring of sponge or felt to sit on the base and catch the drips.