Hayward EcoStar - Air in Filter Basket

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Well, I checked the shaving cream when I got home today and everything looks exactly as I left it except the water level in the strainer basket was about an inch of more lower. No sign of any of the shaving cream being drawn into the pump, pipe joints or valve or disturbed in any way. Now I'm really confused. :scratch: It doesn't seem likely that it's my pipes because #1 - they're only 6 mos. old, #2 - I didn't have the problem with the old Pentair SuperFlo from last Sept until a month ago. The strainer basket area stayed full of water all the time, and #3 - it occurs whether I'm drawing solely from the skimmer/main drain pipe or solely from the vacuum port pipe. It just seems too improbable that both of those pipes decided to start leaking air when I installed the new pump.

The only thing I can think of at this point is to pressure test both pipes. Anyone know how many psi is safe to test with? I figure with a little ingenuity I can rig something up with some capped off PVC to screw into the skimmer, a 0-30 psi guage, a schraeder valve, a big rubber bung and a small compressor with a pressure regulator.

Anybody have any other ideas? :idea:
 
From your picture, it looked like the water was outgassing dissolved air in the pump basket. So I did a few quick calculations, and assuming I did them correctly, here is what I get.

Dissolved air at 0 PSI = 22.7 mg/l
Dissolved air at -0.5 PSI (1" hg) = 21.9 mg/l
Volume of water at 30 GPM over 10 hours = 18k gallons
Weight of released air over 10 hours = 0.12 lbs
Density of air at -0.5 PSI = 0.0715 lbs/cu-ft
Volume of released air over 10 hours = 1.7 cu-ft

Some of the air bubbles will make their way out the pump and air is released slowly from the water so not all of it may be released but it looks like it could be possible that outgassing alone explains the collected air. At higher speeds, there is not enough time for the bubbles to form and if they do, the flow rate probably pushes them out of the pump.

The simple solution would be to run a priming cycle for a few minutes a day to purge the air.
 
Thanks for doing that Mark, but wouldn't it follow that all the people running VS pumps would be experiencing this to a greater or lesser degree (depending on the speed they run the pump) and it would be a rather widespread phenomenon? I really don't recall anyone else on the forum reporting this. Also, I had no problem with the previous pump though, granted, it was running at a higher rpm all the time so that may be a moot point.

In regards to running a priming cycle it does that already each day when it starts up, though to completely clear the basket of air I have to run it longer at the higher rpm.

I'm not trying to argue with your figures, but it still seems a bit excessive. I would also think that the manufacturers would make mention of this in the owner's manual to avoid a slew of support calls from customers if this were a part of normal operation.

Can the amount of dissolved air vary significantly from one water source to another? Would this make an appreciable difference in your calculations?

Gary
 
Actually, this has been reported on several forums but usually with people using 2 speed pumps. I have the same issue with my pump on low speed. High speed does not draw any air at all but on low speed, air will accumulate very slowly over the coarse of the run time. Also, I noticed one day that my spa jet pump had accumulated air while sitting idle during a hot day. This is exactly the same effect when placing a cold glass of water in the hot sun and soon you have lots of little bubbles. The amount of air that water can hold is dependent on both temperature and pressure. Your picture with the tiny bubbles is exactly what happens during outgassing which gave me the idea that this may be the cause of your issue and I emphasize MAY.

As for the example I gave is for ideal conditions so I wouldn't expect that much air but the point was that it may be possible for air to accumulate due to just outgassing.
 
[EDIT] This is under a review so may be wrong in that it does not consider ALL of the dissolved gasses taken together at saturation. Though clearly carbon dioxide or oxygen alone are not enough, nitrogen also at saturation and the full complement of gasses in air may be. [END-EDIT]

One thing is for sure is that the outgasing bubbles aren't carbon dioxide. Though the water is over-saturated with carbon dioxide, that concentration is not high enough to form bubbles near normal pressures. As for "air", I presume you mean dissolved oxygen, but here again I don't believe one would see bubbles forming without the pressures getting lowered significantly.

The concentration of a gas at 1 atmosphere of pressure may be found from PV=nRT where n/V = P/RT so (1 atm)/(0.08205746 l-atm/(mol-K) * 303) = 0.0402 moles/liter. The typical concentration of carbon dioxide in a pool with normal TA and pH is around 0.0001 moles/liter while the equilibrium concentration of oxygen in pool water is around 0.00026 moles/liter. Basically, the pressure would have to be reduced by a factor of around 150 or more in order to form bubbles of these pure gasses. Part of potential bubble formation is water vapor which by itself is only able to form bubbles at boiling temperature, but if combined with super-saturated amounts of the other gasses then bubbles can form. The vapor pressure of water at pool temps is around 0.045 atmospheres or 0.0018 moles/liter.

Supersaturation is not the same thing as bubble formation. It takes a lot of supersaturation to get bubbles as with carbonated beverages. Water distribution systems sometimes see "white" water or bubbles due to taking supersaturated water that is very cold and then putting it under pressure in the distribution system which allows for even higher concentrations of dissolved gasses so when it gets to your tap, some of the dissolved gasses become visible as bubbles.

So I don't believe the slight lowering of pressure is going to form bubbles from dissolved gasses. In a pool, you have to get to very low pressures before this happens which is what starts to happen in the earliest stages of cavitation though in that case the extreme is a complete vacuum which implodes at great force (and damage).

[EDIT] Though the above analysis is correct for INDIVIDUAL gasses, it is incorrect if one considers the SUM of all dissolved gasses. In particular, since nitrogen gas is the largest component of air, if the water is saturated with nitrogen gas, then the other gasses including dissolved oxygen need not be highly super-saturated in order to form bubbles. If all gasses from air saturate the water, then any excess can start to form bubbles. [END-EDIT]
 
First, by dissolved air I mean dissolved oxygen and nitrogen as discussed in this reference. Using Henry's law, a change in pressure of 1" Hg, would result in a change of soluability of about 4%. I am not saying that 4% of dissolved air would come out of solution but some certainly would. But according to the link, water has about 22.7 mg/l of dissolve oxygen and nitrogen and if 4% came out of a 26k gallon pool, that would be a lot of air. Even if a 100th of that came of solution, that would still cause an air gap in the pump basket.
 

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My guess is that what you're seeing is the normal behavior from reducing your flow by 1/3 or 1/2. Suction leaks would be worse at high speed as they would be under greater vacuum. If the strainer basket is full of water at 120gpm, it may not stay completely full at 80 - 60 gpm.
 
I finished installing Intelliflo VS (8 speed) couple of days ago. I am experiencing the same issue with air bubbles. They are really tiny bubbles and accumulate over time in the lid. Lid has ribs on it and they get trapped. I run my pump at 1000 rpm (275 watts) and every hr ramp it up to 2200 rpm for 1 min. That creates enough turbulence in the strainer to suck the bubbles out. I am still learning about the pump and will post my findings.
 
I was incomplete in my analysis in my post above and therefore it was wrong. Though the above analysis is correct for INDIVIDUAL gasses (especially those in low proportion in air such as carbon dioxide or even dissolved oxygen by itself), it is incorrect if one considers the SUM of all dissolved gasses. In particular, since nitrogen gas is the largest component of air, if the water is saturated with nitrogen gas, then the other gasses including dissolved oxygen need not be highly super-saturated in order to form bubbles. If all gasses from air saturate the water, then any excess can start to form bubbles.

So yes, Mark's analysis looks correct where a lower pressure could create bubbles from water saturated with dissolved gasses. The slower flow rates prevent such air pockets in the pump basket from being physically disrupted and pulled through the pump. I don't think there is any harm with this since there will be a limit as to how much air can form in the pump basket before the water flow pulls it through the pump.
 
chem geek, what does it mean for the water to be "saturated" with nitrogen or other gases? Would this be the normal condition of the gas in the water or does it require special conditions for saturation to occur? If so, what are the conditions leading to saturation for a particular gas?

Thanks for the info,

Gary
 
If your pool has a lot of aeration such as a spillover or waterfall or even return jets, more air can get dissolved into the water making it easier to outgas within the pump. Think fish tank aerator.
 
No change yet. Just this morning I'm pressure testing my suction lines. I cobbled up a couple of PVC test tubes over the weekend with 0-60 psi pressure gauges and schraeder valves.

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I screwed them into the skimmer and vacuum suction ports and plugged the other end at the pump with a 2 1/4" expandable pipe plug. I used the pump to draw out as much of the water as possible and then filled the pipes with 10 psi of air. I'll let it sit all day and check it when I get home from work tonight.

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Gary
 
Also, if the pipes leak on low speed, they would leak even more on high speed so you should be able to see bubbles in the pump basket and out the returns.
 

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