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Discuss Greetings plumbfolk I'm on a bleeder gizmo hunt in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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beachkat

so the challenge is to come up with an automated inline gizmo for purging air which is regularly getting into the outlet pipes running from 2 vented coffin tanks. These supply a pair of flats below a new 2nd floor roof conversion.

BACKGROUND INFO... the copper pipes were neatly laid by an experienced and trusted plumber and (seemingly) regularly clipped / supported along 4mtr straight runs along the eaves before elbowing inward and down thru the subfloor to supply the hw cisterns in the flats below. We don't think they're sagging but maybe the runs were just a bit too long, who knows where the problem lies because...
the pipework is now well and truly buried within 30cms of acoustic insulation, fire barriers etc plus boarded & carpeted over. i.e we can't get to anything without destroying a lot of hard work. Sods Law the airlocks started happening after we finished everything so now the hunt is on ....

all replies most gratefully received, cheers James
 
What you done so far to try and remedy, beachkat? oh! & welcome to the forum :)
 
thanks.

yeah it did occur to me raising them up a bit but access is really limited around them i.e jammed up against the eaves. one flat (directly below) clears easily by using vacuum on CW supply but the other (2 floors down) is a pain. on that one we're connecting mains to hot water circuit and hoping to blast the air backwards into the roof tank. Both temporary solutions tho' and what we need is a permanent automated one. Also considering maybe installing electric inline pumps between downpipe and cistern CW inlet?
One possible explanation for these airlocks might be a drop in mains pressure - local water company has been doing major works in the area for past 12 months but they wouldn't confirm (or deny) that they'd lowered the pressure when we called them. grr
 
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if the the hw is tank fed and you can purge the air by blasting mains through system and then it is getting airlocks again it would suggest to me that there is air being drawn in from somewhere. i would be looking at any visible pipework connections compression etc. before ripping things apart. i would also check there is adequate clearance of overflow/warning pipe above water level.

also how would a drop in pressure affect air getting in the system? seeing as it is tank fed i would have thought any bubbles from supply would settle before draw off! also this can be checked by simply observing the water as it refills the tank after a draw off.

how would fitting a pump help??
surely if you are drawing in air from somewhere a pump is only going to do it more efficiently.


imho


KJ
 
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So do you think they're running dry and that's where the air is being introduced? Are they linked together or does each tank supply each flat?

If so is it possible to link the tanks so both flats have twice the draw and unlikely to be using water at the same time so less likely to be emptied?
 
thanks for your replies. some answers...

There's been much headbanging about the prob so some of our own 'theories'/'solutions' are most likely wild rubbish (please forgive). e.g
speculating that fluctuating pressure may be causing lowered tank levels or allowing dirt/particles in causing blockages. Tanks can't be linked as they're separate flats. Certainly the plumbing in both flats below ain't gd and we're checking for obvious air ingestion. But worth considering that neither had probs before the roof conversion and now BOTH do, so this is a problem that's common to both taking us back to the pipe runs. As for pumps - theory was it would help draw air down to where it could be bled off easily - another wild idea I guess ^^

pix before and after relocation
DSC00021.jpg DSC00024.jpg
 
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normally i'd consider linking them or changing for 1 larger combined tank but only as a last resort, the air has to be coming from somewhere....but it seems strange that both flats have this problem when they are on seperate/unlinked tanks!

how does the new tanks connect to the existing pipework? compression or soldered? check all nuts etc...

bit of a head scratcher!




KJ
 
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not sure how new links to old, will check with guy who did it - educated guess would def be soldered. Yep major headscratcher - you're not wrong there!! :thinking:

we're thinking along the lines that at some point along the run both sets of pipes are maybe levelling out enough to periodically idle the flow OR hitting a bend in a way that causes bubbling if that's possible? Airlocks seem to occur every few weeks.

Kinda leaning towards trying the raising-tanks-up-20mm idea to increase fall but still hoping u bright sparks here will come up with more suggestions.

thanks again.
 
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raising them will only do the same as fitting a pump which is to draw the air in quicker and more effectively. as for creating bubbles from hitting bends i don't think that would be possible unless there is a pinhole leak on the solder and as the water passes through air could then be drawn in, however with both tanks doing this it would be some coincidence.

i would definately look for any signs of bubbles in the cisterns while they refill after someone draws water off in the flats, is it possible that the turbulence in the cistern water as it refills during draw off coupled with a vortex created at the outlet during drawoff is enough to draw air down from the surface??? i think this would explain why the upper flat doesn't suffer as much as the lower flats because less head = less draw in of the air. if there ain't any bubbles passing from top to bottom and the overflows have clearance above water level then it has to be downstream of the tanks but then we're back to the coincidence thing


KJ
 
So do you think they're running dry and that's where the air is being introduced?

I'm with EPH on this one

How much water do the new tanks hold compared to the old ones ?
 
thx KJ, interesting & appreciated.

new ones 25 gal coffin and old look like 30 gal round (see photo in post#7) so should we try decrease/increase tank water levels? or maybe raise vent pipes higher?
 
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try running a bath tap ,while watching the water level in the tank - see if the tank goes anywhere near empty after a while.
 
Hello Beachkat and welcome to the forums I think personaly you have undersized tanks causing your problems BS6700 recommends that you need 115 ltrs for both hot and cold supplies i.e230 ltrs total although its hard to determine the size of the tanks you removed It looks to me that they are a lot bigger than the new ones . Also the pressure on the incoming main filling the tanks may not be as good if both tanks are calling at the same time especially when both flats are drawing water at the same time causing the tanks to empty quicker.Good luck and please let us know how you get on regards turnpin
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thx KJ, interesting & appreciated.

new ones 25 gal coffin and old look like 30 gal round (see photo in post#7) so should we try decrease/increase tank water levels? or maybe raise vent pipes higher?

first thing is to see if the tanks run dry during draw off and get air in that way. while watching the tanks during draw off watch for air bubbles travelling from the filling 'splash' travelling to the outlets i'm sure it has to be one of the two.

the coffin tanks should have enough capacity for hot water (is the cold in the flats mains fed?) but they are not tall/deep which means with increased draw from the head on lower flats there is more likely a possibility of bubbles being drawn down as said above. if this is the case position the feed at opposite side of tank to outlet then any bubbles would have to travel further ie across as well as down and should sort it. obviously if they are running dry then you will need bigger tanks

KJ
 
aha turnpin, blod & KJ think you've all cracked it - insufficient head and tanks periodically running too low.

that would explain a lot e.g.
intermittent nature of airlocks,
lower flat being worse than higher one - 1st floor never uses bath (infirm), ground floor does regularly. PS: feed is already well away from outlet vortex (1.4m)

now have to work out how to increase capacity in limited space. joy

will keep you updated and thanks again
 
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I would check the ballvalves are refilling at full pelt strip down and check for grit in the valve seat causing the tank to run dry this is a common problem after the water company have been working in the area. Even try and fit a fluidmaster fast fill valve side entry.
 
Thanks for input. Can't get back in there just yet for doublechecking but last week ballvalve flow looked fine, clean condition (pretty new) & smooth operation plus tanks have been flushed thru a couple of times - no trace of unusual/lingering sediment if it was there. Next step is close watching flow during max draw-off (as advised) and discussing FF valve. more I think about it, insufficient head does seem to tick a lotta boxes.
 
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Postscript. closely checked operation of tanks and fitted Fluidmaster valves (restrictors removed) - so far no probs.

If airlocks do reoccur (and since it's a major operation to squeeze larger tanks in) we figure we can get round it by connecting all bathroom CW to mains and leave roof tanks just for supplying hot cisterns.
 
Postscript. closely checked operation of tanks and fitted Fluidmaster valves (restrictors removed) - so far no probs.

If airlocks do reoccur (and since it's a major operation to squeeze larger tanks in) we figure we can get round it by connecting all bathroom CW to mains and leave roof tanks just for supplying hot cisterns.
this could cause more problems than youve got if there are mixers or showers
 
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