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johncc330 06-08-2013 01:00 PM

Air continues to appear in pipes
I believe this is a new variant on the problem. and I read loads of mails on the normal cause of air bubbles in plumbing.
We have a water tank on the roof, which fills from the city water distribution. It contains about 1000 litres, so there is little chance of running empty.
This also means that there is constant pressure on the internal piping.Normally, if any work is done on the tanks, I just purge and that's that.

For some reason, I am still getting air in the plumbing and no amount of purging seems to solve the problem. This has been going on for weeks now - there cannot possibly be that much air in the pipes. The water tank is full, so I can't really imagine how air could possibly get into the plumbing.

Any suggestions or ideas?

joecaption 06-08-2013 04:45 PM

Both hot and cold water?
Please go back and add your location to your profile.
Just go to quick links to edit.

johncc330 06-08-2013 08:13 PM

Yes - both hot and cold. Which makes it even stranger - both come down from the tank with separate pipes. I first suspected steam bubbles from the heater, but the cold water sputters even harder than the hot water.

Will edit profile...

old_squid 06-09-2013 10:51 PM

Does it supply just your residence or other homes? Have you opened all of your faucets at the same time to purge? Sounds like there is a line somewhere (hasn't been used or purged) that is holding air and everytime you open another faucet you're pulling some of that air into your system. Just a thought.

johncc330 06-10-2013 09:38 AM

Air continues to appear in pipes
Well, yes... I tried about everything I could think of. The original tank was made of brick and cement, and someone had the bright idea of reinforcing the walls with iron. The iron rusted and as such increased in volume, causing leaks. So I replaced the tank with plastic containers, changed all the tubing, purged and was happy for a couple of years. Now:

- Air seems to regularly appear again and again. The house piping is not very complicated - and the house isn't too large either. The supply is private - our house only.

- Yes, as mentioned before, I purged everything. and there simply is not enough piping in the house to explain what's happening.

Thanks for the suggestions though!

Ghostmaker 06-10-2013 06:12 PM

Could one of your pipes possible be in and out of water. Like wave action in your tank?

johncc330 06-10-2013 11:21 PM

Hi Ghostmaker,

Not really. The water outlet is about 90 cm below the surface and tanks are
full. Tank is closed with a lid, and is inside a brick enclosure (the old tank, in fact).

TheEplumber 06-11-2013 08:17 AM

199 Attachment(s)
How is the system pressurized? Booster, gravity, municipal....

johncc330 06-11-2013 01:58 PM

Input is municipal, but that shouldn't make a difference while the tank is full. Output is gravity-only - the tank is the highest point,

Akpsdvan 06-11-2013 02:08 PM

Are the tanks in an area that gets hot in the day time?

Where the water is pulled from in side the tank is that floating or always at the bottom of the tank?
Single tank or multi tank set up?

How much air is showing up in the lines?

old_squid 06-11-2013 04:26 PM

With a gravity feed system there really isn't any way for air to get into the system other than coming from the tank(s). So...... if we assume that all of the supply lines from the tank(s) to the faucets have been adequately purged, but yet air keeps appearing at the faucets then it's getting into the lines from the tank(s). When you plumbed in the new tanks did you introduce a trap in a supply line that is trapping air? The trap in this case being an inverted or upside down trap with the "U" being turned upside down that would trap air in the top part and make it very difficult to purge with just gravity flow....... could be something as simple as a flexible length of tubing with a hump in it's length somewhere.

Is it possible that the city water fill is some how stirring up the tank when it's filling and introducing a lot of air into the water and at the same time you're drawing water from the tanks?

The only other way I've ever seen "phantom" air appear in lines is from a chemical reaction between something in the water and something in the system (metal) that caused a gas to be given off.

johncc330 06-11-2013 07:37 PM

We're in autumn, so we are at 25C (hottest moment of the day) and about 10C during the night. There's a good roof over the tanks, so temp should be in between both temps.

Two tanks, directly connected, Both connection and output is about 8 cm above the bottom to avoid sediment.

How much air? That is difficult. Over days more than could be trapped...

johncc330 06-11-2013 07:50 PM

Yes, I understand all that! I'm a real practical guy (at least I like to think so ;) but this has me really confused.

I can't imagine the incoming water making enough bubbles to cause air in the output tube. They'd have to go down about 25 cm through a tube before finding the horizontal part. And, for this theory to work, I'd estimate that there would have to be consumption at the same time.

No trap as far as I know - there may be smallish diameter changes from the valves and such. Not enough to trap lots of air though.

MTN REMODEL LLC 06-11-2013 09:23 PM

Just exploring.... no theory/idea as yet..... but does your tank breathe, ie: it is not airtight.????

Do any of your outlets, inside or out, leak to any degree.???

This is a good mystery.

johncc330 06-11-2013 11:36 PM

Yes, the lids are far from airtight, they are just to keep dust and contamination out. And, as far as I know, none of the outlets leak. It is difficult to check the washing machine, I guess, but even after a couple of days, it is dry inside.

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