Possibly a silly question but hopefully an interesting one

Escapees

This is probably another silly question, but what am I missing in the following?!- I have a hot water tank at ground level and it's fed from a tank also at ground level along with a pump... and there's a tee off to the cold bathroom taps from the same supply...

So I noticed the other day that there's no flow from the cold taps if I turn off the pumped supply. That might seem obvious at first but... if the hot water tank is taller than the height of the cold taps and there's also an anti-vacuum valve at the top of the tank, then why doesn't gravity cause the tank water to drain through the inlet at the bottom and out the open cold tap??? I've tried turning on a hot tap just in case the anti-vacuum valve isn't doing its job, but still no water from the cold tap. And even if the pipes were routed for some crazy reason higher than the hot water tank, you'd think the water should just siphon out through the cold tap?

I know the water isn't meant to leave a hot water tank from the inlet obviously, but I'm baffled as to why it doesn't happen naturally in the above setup if there doesn't appear to be any non-return valves near the tank etc. It's like having a bottle of water with the cap off and making a hole halfway up the bottle but no water flows out??!

Tom44

Ask "Andy from Sligo"

Tom44

But the cap is not off your bottle (cylinder) in your scenario.


Same principle applies in photo.

Escapees

Tom44 wrote: »

But the cap is not off your bottle (cylinder) in your scenario.


Same principle applies in photo.

I want you to be right just so that I can stop scratching my head about this thing, but... the anti-vacuum valve at the top of the hot water tank should let air in or at least opening a hot water tap should be equivalent as it exits the tank at the top??

K.Flyer

Is the water level in your cold water storage tank higher than the top of the hot water cylinder?
Any chance of some pictures of the set up?

Tom44

Escapees wrote: »

I want you to be right just so that I can stop scratching my head about this thing, but... the anti-vacuum valve at the top of the hot water tank should let air in or at least opening a hot water tap should be equivalent as it exits the tank at the top??

Anti vacuum valve

Possibly a pressure relief safety valve.
Photo would tell a lot.

You have to take the cap off the milk carton for your scenario to work, or disconnect pipe at top of cylinder to let air in. Have fun.

Fill a milk carton with water, leave cap on, then punch very small hole in side and see how much water comes out.

That's the principle of the bird cage watering device. Air has to get in to allow water out.

Escapees

I meant anti-vacuum valve alright - it's to stop the cylinder from buckling in a closed system like I have, but that's an aside...

Anyway, cracked it - curiosity got the better of me so I opened the outlet connection at the top of the cylinder and sure enough water started draining from an open cold tap. I reckon the anti-vacuum valve doesn't open till a vacuum is formed that exceeds some minimum pressure so that's why it had no effect. And as for opening a hot tap somewhere to let air get to the cylinder outlet on top, umm... kinda overlooked the fact that there'll always be some water in the pipe run below the height of the taps, so there's no open path for air to get back to the cylinder outlet. So I'm guessing the pipe run becomes 'water-locked' - like the water equivalent of air-locked! Or else I'm just kidding myself with a BS explanation!!