# Forum Home Renovation Pools, Spa & Water Features  airbubbles forming in my poly pipe

## pellicle

Hi 
I'm using black poly pipe and a small solar powered impeller pump to move water around. 
The system requires a siphon operation to work as the pump will not lift the water high enough without that. Things start off fine then it starts to slow down water flow, after  about a week it stops. 
Flushing the system with the garden hose reveals bubbles of gas is forming in the pipes, I am expecting this to be dissolved gasses in the water coming out, as there is no sign of leaks and all joints are very secure. 
I'm thinking that the only solution is to run a higher volume pump now and then to "flush the system" but that would require a more complex setup than I have. 
Does anyone have any ideas? 
PS: *this* is what I'm using it for

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## watson

Ok Questions:
Using what you have does the water get hot enough in the collector for your requirement? 
I reckon the bubbles in the pipe when flushed with the hose are a Red Herring (I.e. Not caused by dissolved gasses in the water  :Shrug: ). 
I also reckon that siphons are great......but I think you have a leak in that system. 
Just my thoughts (IMHO).....you might have to go a bit heavier in the pump area and modify the siphon somewhat.

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## pellicle

Hi 
thanks for your suggestions.   

> Ok Questions:
> Using what you have does the water get hot enough in the collector for your requirement?

  yes ... within 2 hours of sun hitting it you can feel warm bars in the wood under the floor, by 2pm its warm enough you feel inclined to open windows AND I only have 2 of the 4 circuits working at the moment   

> I reckon the bubbles in the pipe when flushed with the hose are a Red Herring (I.e. Not caused by dissolved gasses in the water ).

  the bubbles are the cause of the siphon stopping, the only issue is where they come from. The places where there are joins are lower than the places where there are no joins I see no trace of moisture in leaks and there is no loss of water (I can monitor that carefully) and I still get bubbles. 
I know that gasses go in and out of solution (chlorine for instance in the water supply) when temperature goes up and down.   

> I also reckon that siphons are great......but I think you have a leak in that system. 
> Just my thoughts (IMHO).....you might have to go a bit heavier in the pump area and modify the siphon somewhat.

  siphons are indeed great. It goes great guns for 2 days then starts to fizzle out. 
Joins are done with "spear joints" (or what ever they're properly called) "barbed end" or what ever to call them press two pipes onto it joiner. This is then sealed with silicon and then wrapped carefully under tension wide electrical tape (I used to seal Antenna cables in a similar way) and then double cable tied "just to make sure" 
so if there is a leak I'll eat my undies

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## Danny

First, let's talk about water beds!!! 
A water bed uses a small heat pad between the bottom of the bladder and the bed's base. The bladder needs regular air purging and 'burpers' are sold to make this task easier. The air is caused by the pad heating the water and water bed bladders do not produce the air because of leaks! 
Your poly wheel uses the sun as its heating pad. 
You have used 13 mm poly pipe and its required air flushing velocity is (not much) greater than the 2.33 lpm that is supplied by the pump although a pipe's air flushing velocity is actually measured as metres per minute. The generated entrained  micro bubbles will travel through the poly pipe circuit and bond with other entrained micro bubbles. In time, a bubble will lodge in a small kink at the top of one of the coils as kinks generate vortices (low pressure areas) on the lee side. Other micro bubbles will then be captured and eventually you will have an air lock situation which in your case takes about a week.  
The only way to avoid this happening is to devise a method to provide a 5 minute purge cycle once a day or generate a higher flow rate. Note that your poly wheel is nothing more than a long pipe with numerous undulations that are conducive to harbouring an air bubble in each apex if the air flush velocity is below requirement. As such, air locks will still form at each apex, albeit slower than if a kink was present to concentrate entrapment. 
EDIT: Have you tried using filtered rainwater and an algicide? 
DOUBLE EDIT: Your coil is currently mounted at a 90 degree angle. If you could remount it at an angle similar to that required by PV panels, you would (I think) improve heat generation PLUS reduce the severity of the pipe line undulations. To purge may then only entail laying the coil flat for several minutes every few days.

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## watson

> so if there is a leak I'll eat my undies

   :Rotfl:  ..Strawberry???

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## pellicle

Danny 
thanks for the reply   

> First, let's talk about water beds!!!

  well geeze mate, we hardly know each other and you're showin me the bedroom.    

> A water bed uses a small heat pad between the bottom of the bladder and the bed's base. The bladder needs regular air purging and 'burpers' are sold to make 
> ...
> Your poly wheel uses the sun as its heating pad.

  didn't know that about water beds so that's an interesting point and to my mind explains my position. I'm guessing the poly pipe is also gassing to some extent too    

> You have used 13 mm poly pipe and its required air flushing velocity is (not much) greater than the 2.33 lpm that is supplied by the pump although a pipe's air flushing velocity is actually measured as metres per minute.

  well now that's bloody interesting. Did you make that figure up or do you have some sort of reference for it? 
either way it confirms my suspicion that I need to leave the system running 24/7 and sort out ways to power that.   

> The generated entrained  micro bubbles will travel through the poly pipe circuit and bond with other entrained micro bubbles. In time..  and eventually you will have an air lock situation which in your case takes about a week.

  sounds perfectly consistent with my experience   

> The only way to avoid this happening is to devise a method to provide a 5 minute purge cycle once a day or generate a higher flow rate.

  yes, been entertaining either or both as an option.    

> EDIT: Have you tried using filtered rainwater and an algicide?

  not yet and intending to when the system is stable.   

> DOUBLE EDIT: Your coil is currently mounted at a 90 degree angle. If you could remount it at an angle similar to that required by PV panels, you would (I think) improve heat generation

  perhaps ...  as winter comes along the sun dips lower as the days get colder, I intend to mount the the panels such that it gets that and also such that as we approach summer (and its not needed during the day) the eaves will block more of the sun.   

> PLUS reduce the severity of the pipe line undulations. To purge may then only entail laying the coil flat for several minutes every few days.

  that part would be a pain in the proverbial and I'd like to set the system up to be as low maintainence as possible  
thanks for all your good advice

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## pellicle

> ..Strawberry???

  I'm guessing a cross between sea bird flavour and with a hint of cheese 
;-) 
Albatross ....  http://youtu.be/Z_u7VGiMO0U

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## Danny

Hi pellicle, 
The water bed analogy gives a quick understanding, thought it would be memorable!   

> Did you make that figure up or do you have some sort of reference for it?

  Ooops! Made a mistake here. I got the figure of 140 lph (2.33 lpm) for your pump off your linked blog but after revisiting the blog and enlarging the pump's instruction sheet, I see that 140 lph is the static head pressure flow rate. I now also see that you mentioned further down under the photo as per the quote below that your flow rate is about half this rate. I should have realised.   

> I thought I'd  provide a little more details about the pump. As I mentioned I bought if  from Jaycar and it cost $49.95  Its the 7v model which moves about 140L  / hour of water (_in full sunlight_). I thought that this was a 'good number' (_upon experimentation_)  to start with and the more expensive 12V model (twice the price) moved  200L / hour which I thought may be too fast for heat gathering. 
> As  it turns out I think that the 140 would be too fast, but as it also  turns out there is enough resistance pumping the water around that it  works out to be about half that in practice.

  A 1/2" pipe's air flush velocity is theoretically 2.3 lpm but theorum and practice rarely align. A problem your system has is that whenever the circulation is shut down, any micro bubbles will rise to the pipe's many apices. A bubble larger than 1 mm rises at a rate of about 1 metre every 4 seconds. 13 mm poly pipe holds .133 of a litre for each 1 metre length which means that 7.5 metres of 13 mm poly will contain 1 litre. This means that (keeping it simple) a bubble *will retain buoyancy* against a flow velocity of 15 metres per minute or as in the case of 13 mm poly; a flow rate of 2 lpm. This lower flush figure however doesn't align with the 2.3 lpm required flushing velocity as a bubble rising in still water is not subject to laminar flow as it would be if in a pipe. The velocity also needs to exceed the bubble's buoyancy figure of 15 metres per minute if it is to carry the bubble downwards.  
Note that the air flushing rate for horizontal pipe work is lower than for pipe work with vertical rises and falls, hence my recommendation to substantially reduce the current 90 degree face to assist purging.  
For your situation, you should aim for a flush rate of about 2.5 lpm to be safe. With pumps, to double the flow rate requires X4 the energy. Also, does the return line feed into the reservoir close to the existing pump; i.e., is there a chance that the return line is generating bubbles? It would only take one small bubble ingested by the pump to cause problems. In the meanwhile, I would suggest a small dose of algicide. 
BTW; I was interested to read your blog entry re the difficulty of buying Australian made and your observation about the packaging of Nudie Juice. Of particular interest was the linked news article posted by writergenn regarding previous action taken against Nudie Juice by the ACCC in the Federal Court re misleading labelling. As I said...Interesting. Good blog!

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## pellicle

Hi 
well I think I would like to buy you a beer for all your kind and beneficial help   

> Hi pellicle, 
> The water bed analogy gives a quick understanding, thought it would be memorable!

  perfectly   

> Ooops! Made a mistake here. I got the figure of 140 lph (2.33 lpm) for your pump

  ahh, that's a shame, as I was thinking it was a good figure and would be close to what my pump produces.    

> I now also see that you mentioned further down under the photo as per the quote below that your flow rate is about half this rate. I should have realised.

  I did a little ferreting on your first suggested key words and also found some resistance calculations ... handy stuff 
so do you reckon that given I'm pushing it through 80 or so meters the flow rate is about right? Seems like it is to me.   

> A 1/2" pipe's air flush velocity is theoretically 2.3 lpm but theorum and practice rarely align.

  old favorite quote: 
This is where theory and practice meet: it doesn't work and we can't explain it.   

> A problem your system has is that whenever the circulation is shut down, any micro bubbles will rise to the pipe's many apices.

  which is why I've been wondering if it may not be better just to keep it running all the time...   

> 13 mm poly pipe holds .133 of a litre for each 1 metre length which means that 7.5 metres of 13 mm poly will contain 1 litre.

  thanks, its what I calculated and had been about to measure it ...   

> Also, does the return line feed into the reservoir close to the existing pump; i.e., is there a chance that the return line is generating bubbles? It would only take one small bubble ingested by the pump to cause problems. In the meanwhile, I would suggest a small dose of algicide.

  very good points ... and I'll get some algacide into it this weekend   

> Of particular interest was the linked news article posted by writergenn regarding previous action taken against Nudie Juice by the ACCC in the Federal Court re misleading labelling. As I said...Interesting. Good blog!

  I agree! and thanks for the kind comments on my blog

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## Danny

> I would like to buy you a beer for all your kind and beneficial help

  I would need one after the long drive. Might be heading up for Bundy Thunder in November though!   

> ahh, that's a shame, as I was thinking it was a good figure and would be close to what my pump produces.

  A trap for new players. A pump's flow rating needs friction loss deductions to arrive at the actual flow rate.    

> so do you reckon that given I'm pushing it through 80 or so meters the flow rate is about right? Seems like it is to me.

  It is actually very hard to calculate this because of the coils and the very low flow rate. Friction loss at a litre or so a minute is very, very low. It would be good if you measured the flow for one minute. The desired velocity would be best determined by also recording the return temperature.   

> I've been wondering if it may not be better just to keep it running all the time...

  How would you run a solar pump at night?    

> its what I calculated and had been about to measure it ...

  It is all fairly simple once you understand some basics.

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## pellicle

Hi   

> How would you run a solar pump at night?

  battery and change my photovoltaic system. I think that would negate some of the elegant simplicity, but clearly something needs change right now anyway.

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## Pitto

interested to hear where you got the PET sheet from. I am in the middle of building a similar poly pipe solar collector for my Spa. It works pretty good, however, i really want to tidy it up and build a proper enclosure with a clear plastic sheet over it to help trap the heat in. 
G

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