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Borehole pressure vessel change

bladder failure

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pgk pgk07/04/2020 10:24:13
1729 forum posts
287 photos

This is 100L horizontal tank inconveniently located in a cupboard under a sink. Trying to rebladder it is not advised apparently..because it's a cuss to do and if there's any internal corrosion then the roughness destroys the new bladder fast.
I have a new tank on order (hopefully today).

If I just undo the old one then that;s 50L on the floor and still trying to muscle the remainder plus tank weight out. That would have been easy 20rs ago.

So far i've come up with 2 options..drill a hole as near to the top as I can get and shove a hose in to siphon it outdoors or drill a small hole at the top and make up adapters to drain via the low down repressurising valve - would be slow.

The tank spec shows they are pressure tested to 15Bar so I guess the walls are going to be a reasonable thickness?

Any other suggestions?


Speedy Builder507/04/2020 10:45:45
1985 forum posts
139 photos

Go to IKEA and buy a new kitchen ?

can you connect an air line to the hot water inlet and flush the rest of the water out through the "cold" connection. Limit the pressure to just a few PSI although our tanks run at 3.5 Bar (approx 56 psi)

The tanks I have seen have a wall thickness of about 2mm and once out, can be cut in half lengthwise to make barbecue troughs.

Kiwi Bloke07/04/2020 11:23:14
403 forum posts
1 photos

If it's like the thousands all around NZ, typically in rural properties, there's a valve to which a foot-pump is connected, to pressurise the vessel. Even if the water-containing bladder is leaky, the vessel will still pressurise, of course. Close off the inflow (from the pump) and open a tap on the outflow. It may be necessary to pump more than you expect, to get all the water out. If you're really unlucky, the collapsing bladder could possibly block the outflow, or it could collapse in a way that doesn't allow it to empty fully, but I think this is unlikely. Forgive me if you have a completely different arrangement.

Did ours (a big one!) a couple of months ago. Typical of NZ, the new, Italian-made vessel cost many times the UK price (in real terms).

SillyOldDuffer07/04/2020 11:26:31
5633 forum posts
1157 photos

Posted by pgk pgk on 07/04/2020 10:24:13:


The tank spec shows they are pressure tested to 15Bar so I guess the walls are going to be a reasonable thickness?


I doubt the walls will be particularly thick especially if the container is steel. My wild guess about 3mm, could be wrong!

15bar is about 220psi, which isn't far off the working pressure of a model loco boiler made of relatively thin copper. Cylinders take a lot of internal pressure: a 2 litre lemonade bottle bursts at about 12bar, and the plastic is about 0.23mm thick. The pressure vessel will be proportioned to take a working pressure plus allowance for heat and pressure cycling (if any), and probably corrosion. (Does the cylinder have a specified life like rechargeable gas bottles?) Then multiplied by a hefty safety factor. For ordinary items x2.5 is common, x5 if safety is involved, and x10 or more if safety critical.

I know absolutely nothing about boreholes!


pgk pgk07/04/2020 11:27:46
1729 forum posts
287 photos

A single water inlet on this one to prevent the borehole pump constantly switching on/off. Nt actually in the kitchen - utility room and wife would love a new set of units there but the mare of all the cutouts to cope with washing machine drains, sink drains borehole plumbing, electrics and this tank - don't even whisper...
As for Ikea.. hate the place. It may have imporved but when i looked at kitchen there (many may years ago) I did my usual test of pull a drawer part out and sit on it.- the one's at Magnet can take my weight.

Kiwi Bloke07/04/2020 11:48:24
403 forum posts
1 photos

Are we at cross-purposes? Swapping a tank isn't difficult - provided some thoughtless person hasn't built it into an inaccessible location... The 100 litre tanks here are an easy one-man lift.

A single water connection is standard. The pressure vessel is Tee'd off the pipe between the pump and the services supplied. There's a one-way valve in the system to prevent back-flow into the pump, when it's not running.

Kiwi Bloke07/04/2020 12:06:27
403 forum posts
1 photos

Ah, OK, perhaps I'm being slow, and we're not at cross-purposes. If the water has escaped from the bladder, to part-fill the tank, I now understand the possibility of 50 litres remaining in the tank, but not on the floor. It should be possible to drain the tank down to the level of the water connection.

You say the air valve is low-lying. Can you pump up the vessel and let water out via the air valve - several times? With enough puff behind it, it should only take half the morning...

Edited By Kiwi Bloke on 07/04/2020 12:08:36

pgk pgk07/04/2020 12:48:21
1729 forum posts
287 photos

Well i figured with the bladder gone (as in water out the valve) then switching borehole tap/mains off and running the tap woud have relieved any pressure.
Not so!
As drill went through a high pressure spray covered me from head to foot followed by a fountain spraying all over the utility room. Once OH has calmed down and the puddle is reduced I shall get back to it...
Wall is quite thin.. upping to 12mm drill to get some tube in there..


Former Member07/04/2020 13:03:27

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pgk pgk07/04/2020 13:06:56
1729 forum posts
287 photos

..the cooling benefit of a shower.smiley.

12mm hole in and siphoning. Drill jammed going through and my 15yr old woolworths drill puffed some blue smoke but still works. A waiting game right now bucket by bucket..


Neil Wyatt07/04/2020 14:54:57
17722 forum posts
697 photos
77 articles
Posted by Bill Chugg on 07/04/2020 13:03:27:

Sounds like you are getting it sorted OK.

I have the greatest respect for anybody who can stay cool when under pressure wink


Probably not the time to say a squirt is a drip under pressure...


pgk pgk07/04/2020 15:32:05
1729 forum posts
287 photos
Posted by Neil Wyatt on 07/04/2020 14:54:57:

Probably not the time to say a squirt is a drip under pressure...


Let him who is without sin cast the first mallard.

The theory let me down. I did drain down by siphon until it wouldn't drip and then disconnected... the blasted bladder still had heaps in it - obviously the leak was more than half way up. Not so much as issue with more water leakage - just muscling the weight of the thing out - had to stretch out to settle the backpain after.
OH just finished cleaning up behind the old tank so my turn back under there to fit the new..


pgk pgk07/04/2020 16:35:20
1729 forum posts
287 photos

OH and I call that a joint back, her knees and hip.

All done.


Former Member07/04/2020 17:23:16

[This posting has been removed]

pgk pgk07/04/2020 17:41:59
1729 forum posts
287 photos

Working fine- no leaks,


Former Member07/04/2020 17:49:14

[This posting has been removed]

pgk pgk07/04/2020 18:18:47
1729 forum posts
287 photos

I mighthave it wrong but as i understand it the borehole pump operates to a pressure and turns off. Pressure/volume of water in the pressure vessel is allowed out by a pressure sensing valve and when it drops below a value the pump is switched back on. By using the pressure vessel the main pump doesn't have to operate for small volumes or clatter on/off on the contactors when topping off.

Our borehole is around 250ft deep. Contrary to my original belief the hole at the bottom is quite narrow and short but the refill rate is significant. Oviously a forcepump down the bottom. (I hate to think what that costs to replace).

It is possible to empty the borehole - I managed it once by leaving a hose running overnight and then we see sludge and that can also damage the pressure vessel lining. Some boreholes need to have filters to remove solids and may need some disinfection system (such as UV light?). the original specs we inherited with this property showed very low bug levels and high purity in our supply. Since we have our own reed bed sewage system there are no water/waste rates but costs of running the system since the sewage tank has a constant pump cycling water from the first reed pond through that tank washing the top off as the solids decompose and aerating the pond via a swirly waterfall. Then the reed ponds do their bit before final approved discharge via ditch to stream.


Former Member07/04/2020 18:30:07

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Former Member07/04/2020 18:30:08

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