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Thread: Low speed pumps causing gas bubbles

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    Low speed pumps causing gas bubbles

    Hi guys,

    I am in the market for a new pump - and I will buy an eco - variable speed pump (Viron P320) here is Australia. I discovered on the net - that when this pump is running at low speed - gas bubbles form in the salt cell.

    The issue identified from another site:
    I have had a VX9T chlorinator for around 12 months (no problems) and I have just installed a Viron EVO P320 pump. I am having a problem with the VX9 cell housing trapping gas bubbles when the pump runs at low speed. The bubbles soon form a larger bubble, which eventually exposes the cell plates. This could lead to a melted cell housing or possibly an explosion. The problem also occurs at minimum speed, but to a lesser extent (only on higher chlorinator settings). I'm currently thinking the EVO pump was a complete waste of money.


    The recommendation from the manufacturers - is to run the pump at higher speeds until the bubbles are gone - but for me - this defies the reason for buying a slow speed pump - if i have to run it at higher speeds - it is less efficient...or should i look for another chlorinator that doesn't have this issue? Can you guys run your pumps at low speed without this issue?


    My question:
    Can variable speed pumps run at the lowest speed without causing gas bubbles?

    (I initially thought you could turn the cell upside down - but i am told that the "gas trap" is needed to prevent gas building up in the filter. When it builds up in the cell casing - a safety mechanism turns it off....whereas if it build up in the filter - there is no safety mechanism.).

    Kind regards,
    Mil

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    mas985's Avatar
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    Re: Low speed pumps causing gas bubbles

    That is pretty common for multi-speed and two speed pumps and there is not much you can do about it but it should not cause a problem either unless it is collecting in an area where it could ignite. I get fairly large bubbles out of the returns on low speed as well but only when the SWG is running.
    Mark
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    Mod Squad jblizzle's Avatar
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    Re: Low speed pumps causing gas bubbles

    Just to add, if the SWG is downstream of the filter (as it should be ... the cell should be the last piece of equipment before returning to the pool) ... I can not see how gas would accumulate in the filter
    Jason, TFP Moderator
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    Richard320's Avatar
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    Re: Low speed pumps causing gas bubbles

    Is there some reason you can't slope the pipe run so any bubbles that form rise and travel away from the SWCG?
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Low speed pumps causing gas bubbles

    Yep I have the same problem - it was discussed at length on whirlpool forums, someone fixed theirs by mounting it so that it is at 90 degrees to normal, ill be doing the same with mine.

    http://forums.whirlpool.net.au/forum-re ... 874947&p=3

    Fix - https://dl.dropboxusercontent.com/s/gna ... AG0585.jpg

    Doesn't happen at medium speed, and it's unlikely that the gas buildup would ignite, but the lower utilisation of the plates in the swg would result in a higher current density = more wear, lower life and higher temps.
    Brand new 30,000 Litre (~8000Gal) inground Leisure Pools fibreglass, Astral Pool Viron 3 speed 1.5Hp P320 pump, Hurlcon VX 3 T SWCG, Hurlcon ZX100 cartridge filter.
    Two mustard algae events, lots of bad pool store advice - double the salt level it should be (sigh), large amounts of copper based algaecide, 50 litres of 12.5% liquid chlorine, 2 litres of clarifier. $300 in chemicals in two weeks.

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    Re: Low speed pumps causing gas bubbles

    Gas buildup should be prevented. In my opinion, the danger from explosion is probably not with just the hydrogen gas, but with the mixture of hydrogen gas and chlorine gas.
    When mixed, the combination is more easily ignited than just hydrogen alone. Simple UV light can ignite a mixture of hydrogen and chlorine gas. If the gas mixture is exposed to UV light, such as from sunlight, I think that it is more at risk of explosion than if it were not exposed.

    Clear cells are transparent to visible light, but I don't know if they are transparent to the portion of UV light that would have sufficient energy to initiate a reaction. However, from the anecdotal reports, it seems to me that clear cells are more likely to be involved in explosions than opaque cells. If you have a clear cell, I would recommend being extra careful to avoid gas buildup.

    In any case, prevention of gas buildup is important to help reduce the risk of explosion.

    This video shows that even blue light can trigger the reaction.

    http://www.youtube.com/watch?v=YNu2KeasN58

    Also see:

    http://www.youtube.com/watch?v=hrFKoq00kBk

    http://www.youtube.com/watch?v=NN82GoBG98s

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    Re: Low speed pumps causing gas bubbles

    Quote Originally Posted by jblizzle
    Just to add, if the SWG is downstream of the filter (as it should be ... the cell should be the last piece of equipment before returning to the pool) ... I can not see how gas would accumulate in the filter
    Apparently - the gas can still flow backwards to the highest point - especially at low speed. So if the filter is at the highest point - it will rest there.

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    Re: Low speed pumps causing gas bubbles

    Quote Originally Posted by Vectrix150V
    Yep I have the same problem - it was discussed at length on whirlpool forums, someone fixed theirs by mounting it so that it is at 90 degrees to normal, ill be doing the same with mine.

    .
    Wouldn't it be better to have it upside down ?

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    Re: Low speed pumps causing gas bubbles

    Systems in Australia usually use a gas trap design and a gas/water sensor as "flow" sensor. This means that they have to be installed as per the manual.

    The sensor detects a voltage difference between being covered with water, or not. If the cell runs with no water flow, gasses will build up and push water away from the sensor. This will cause the unit to detect the "No-Flow" problem and turn off.

    If the unit is not installed correctly, then the safety "flow" detector will not work properly.

  10. Back To Top    #10

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    Re: Low speed pumps causing gas bubbles

    This topic is starting to make a lot of sense to me in the way my SWG was behaving.

    I have a two-speed pump and I would try to run most of the time in low-speed, but my SWG would turn off every now and then due to "no-flow" after running in low-speed. I have since added an automatic speed switch along with my timer and my problems with the "no-flow" have gone away. I now start and shut off my pump in high-speed and I switch it to high-speed once during the day. I still run 80% of the time in low-speed, but I believe that the high-speed clears out the build up of gas in the line.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: Low speed pumps causing gas bubbles

    I'm in Straya & just installed that very pump!

    I get champagne bubbles out the jets but NO bubbles inside of the SWG.
    Its mounted vertical & is a Watermaid ez300 (i think?).

    Pump is sitting at 1370rpm on low & there's a HEAP of water flow to stop gas build up in my setup.
    50,000L Concrete with Pebblecrete
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    Re: Low speed pumps causing gas bubbles

    At low levels you don't really see much - a few whisps of 'smoke' that appear to come off the plates.

    Wind up the wick and they look like they are steaming.
    Brand new 30,000 Litre (~8000Gal) inground Leisure Pools fibreglass, Astral Pool Viron 3 speed 1.5Hp P320 pump, Hurlcon VX 3 T SWCG, Hurlcon ZX100 cartridge filter.
    Two mustard algae events, lots of bad pool store advice - double the salt level it should be (sigh), large amounts of copper based algaecide, 50 litres of 12.5% liquid chlorine, 2 litres of clarifier. $300 in chemicals in two weeks.

  13. Back To Top    #13

    Re: Low speed pumps causing gas bubbles

    I've been reading about this with fascination. Blue light has enough energy to break down Cl2 into highly reactive Cl. That's super cool. But are explosions really a problem? Cl2 is highly soluble in water (5 g per kg at pool temps). H2 is effectively insoluble (1.5 mg per kg). So these bubbles will be almost pure H2 without any oxidizer to allow them to burn. Certainly no where near the 50/50 ratio (by volume) needed to support a chain reaction. Have these explosions been documented to happen?
    20,000 gal in-ground plaster pool with sand filter. Replastered recently. Mostly adding bleach and acid. CYA was high when I took over.

  14. Back To Top    #14

    Re: Low speed pumps causing gas bubbles

    Explosions are not common, but they do happen. Several things have to go wrong to set off an explosion. First, there has to be little to no flow, second, the cell has to be energized and third, there has to be some sort of activation energy.

    If the cell operates with no flow and produces a mixture of chlorine and hydrogen gas, then there might be an explosion if sufficient activation energy was introduced. Light with a wavelength of less than about 490 nm (in the blue region) will have sufficient energy to photodissociate chlorine gas into chlorine radicals, which can set off the chain reaction.

    Systems are designed to not energize the cell when a no-flow condition is detected. Also, most systems are opaque and don't allow any light. Some cells are clear, which seems to me to be a bad choice. There are also some pieces of equipment that have clear parts, such as some check valves.

    If someone had a UV system that was operating while the gas built up, then it's possible that that could set off the chain reaction.

    Note: There is not a lot of reliable information regarding cell explosions. I am providing my best estimation of what's happening.

    swg-cell-explosion-t51234.html

    exploding-pool-t55561-40.html

  15. Back To Top    #15

    Re: Low speed pumps causing gas bubbles

    Yes, I could certainly see no flow causing an explosion, because then the water in the cell can saturate with Cl2.
    20,000 gal in-ground plaster pool with sand filter. Replastered recently. Mostly adding bleach and acid. CYA was high when I took over.

  16. Back To Top    #16

    Re: Low speed pumps causing gas bubbles

    Milbogo

    I have a Viron p320 pump and a VIron vph25 chlorinator which is basically the same the as the VX7 but includes PH control as well. I run my p320 all day on low speed with no gas build up, so I don't think you can say that it's always going to be a problem. I was careful however to follow Hurlcon's instructctions and make sure my pool builder installed 50mm returns pipes instead of their usual 40mm. Someone else posted on this site that he had problems with gas buildup but he attributed it to the design of the hurlcon chlorinator as it had some plastic bit stuck in front of the plates which seemed to trap the gas. I don't know if hurlcon have learnt from this but there is no plastic lip in front of the plates in my chlorinator. When I first got the chlorinator i watched it like a hawk to see if gas built up but I've not see any. In fact I would say that when the pump is slower theres less turbulence in the chlorinator and the gas seems to flow out more smoothly...
    33000L Concrete Pool, Viron P320 Pump, Viron-PH Auto PH Chlorinator, Viron CL400 cartridge filter, Sunlover solar heating, TF-100 Testkit and Taylor speedstir

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