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Thread: DOS Bubbles in lines

  1. #1
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    DOS Bubbles in lines

    Hi Folks,

    I'm really struggling with bubbles being drawn into the dosing lines on my DOS units. The lines from the dosing containers to the pump head are clear, but from then on, they fill with bubbles.

    It's infuriating as the supplied pipe is being used and they appear fully sealed to the connector on the pump heads.

    I don't think I'm alone here, but has anyone found a good fix?

    Thanks

    Rob

  2. #2
    Frequent Contributor zombie's Avatar
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    If bubbles are coming well down the line, the tubing might be cracked.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Not cracked, tubing is also brand new. I have tried the Apex supplied tubing as well as a more flexible type of the same diameter

  4. #4
    Frequent Contributor zombie's Avatar
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    How high onto the dos fitting are you pressing the tubing on? I found any less than 2 barbs would produce lots of bubbles and less than 3 would sometimes produce bubbles for some.

    You might be an engineer if...You have no life and can prove it mathematically.

  5. #5
    Master Control Freak RussM's Avatar
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    Quote Originally Posted by zombie View Post
    I found any less than 2 barbs would produce lots of bubbles and less than 3 would sometimes produce bubbles for some.
    Huh? DOS Pump heads have smooth truncated cone-shaped fittings and compression nuts for connecting the tubing. No barb fittings.
    Please do not send me PMs with technical questions or requesting assistance - use the forums for Apex help. PM me ONLY if the matter is of a private or personal nature. Thanks.

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    I place non return airlines valves on the end of the dosing line

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    Frequent Visitor rkpetersen's Avatar
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    Air leaks from the incoming side of DOS head tubing connectors are common, and even when you get it fixed, they tend to recur. First, you have to cut the supplied tubing square on the end, and then push it all the way up on the smooth fitting until it hits the flange at the top. Then you must tighten down the compression nut very well. This will seal it, but the constant pressure on the tubing thins its plastic over time, so it will loosen. You need to retighten the connections the next day, and then again a few days later, in order to ensure a reasonably long term bubble free connection. If bubbles appear again later, retightening the nut may fix it temporarily, but eventually you'll probably want to redo the entire connection, cutting off the bit of thinned plastic tubing at the end.

    This all only applies to the incoming connections of each DOS head. The outgoing connections shouldn't take in air unless they're grossly loose.

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    Just to follow up on this, after relocating and using new Neptune DOS tubing, cutting cleanly and squarely, heating the end in hot water before fitting, tightening up and repeated checking to ensure the connections are still tight....

    I am still getting growing air bubbles in the lines...

    PS: rkpetersen - I think the bubbles in the outgoing tubing are being pulled through the pump from the ingoing side.

  9. #9
    Frequent Contributor zombie's Avatar
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    Check for cracks in the tubing.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by zombie View Post
    Check for cracks in the tubing.

    You might be an engineer if...You have no life and can prove it mathematically.
    No cracks whatsoever. The tubing is brand new, out of the box and I warmed the ends up before pushing over the fitting. Very frustrating.

  11. #11
    Frequent Visitor rkpetersen's Avatar
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    Did you have a period during which there were no bubbles? If so, it could be that your tubing has thinned and gotten loose again.

    Other things you could try:

    Replace the DOS pump head. Maybe some tiny leak in the head mechanism/tubing itself.

    Apply silicone caulk to both ends of the incoming connector on the pump head.

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    Quote Originally Posted by rkpetersen View Post
    Did you have a period during which there were no bubbles? If so, it could be that your tubing has thinned and gotten loose again.

    Other things you could try:

    Replace the DOS pump head. Maybe some tiny leak in the head mechanism/tubing itself.

    Apply silicone caulk to both ends of the incoming connector on the pump head.
    Yes, about a week lol. The pipe is brand new, the DOS units under a year old, so not keen to replace the pump head (and all four pump heads on two DOS units have had the issue, two seem to be stuck with it after replacing tubing). I didn't really want to use silicone on them, but I guess that's the only answer. Curious as to why it doesn't happen (or happen so much?) with other makes of doser and why it's happening even with Neptune's tubing.

  13. #13
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    Following I'm getting the same on the lines going into the aquarium. I DOSing triton so I need to make sure its working well. So far my parameters are well. Well my CA is a little higher then I want.

  14. #14
    Frequent Visitor rkpetersen's Avatar
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    I've never had another doser. So far, inspecting them at least weekly, over the last 5 months I've several instances of small air leaks from the inlet connection of 3 of 4 DOS pumps. In all but 2 instances, they were fixed by slightly tightening the fitting. The two times, I had to redo the connection by cutting off the thinned last 7 mm of tubing and reassembling it. Do most other dosers have barbed connectors? These connectors with the pressure fittings on the DOS would seem to be more secure than that for fluids, but maybe not for air.

    As far as pump accuracy, I am planning to recalibrate them at least quarterly. However, the last time I did so, all 4 pumps were right on the money.

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    Quote Originally Posted by GugsJr View Post
    Following I'm getting the same on the lines going into the aquarium. I DOSing triton so I need to make sure its working well. So far my parameters are well. Well my CA is a little higher then I want.
    Yes, so am I. Just make sure you are dosing into a very high flow area (like your return) and also dose as little as you can each time to minimise precipitation. Core7 is extremely concentrated

    Quote Originally Posted by rkpetersen View Post
    I've never had another doser. So far, inspecting them at least weekly, over the last 5 months I've several instances of small air leaks from the inlet connection of 3 of 4 DOS pumps. In all but 2 instances, they were fixed by slightly tightening the fitting. The two times, I had to redo the connection by cutting off the thinned last 7 mm of tubing and reassembling it. Do most other dosers have barbed connectors? These connectors with the pressure fittings on the DOS would seem to be more secure than that for fluids, but maybe not for air.

    As far as pump accuracy, I am planning to recalibrate them at least quarterly. However, the last time I did so, all 4 pumps were right on the money.
    I try to tighten mine weekly, but have never actually been able to tighten them. This is my second set of brand new Apex tubing.

    My last doser was a Marine Color PoS, can't remember if it had barbs or not, but it never had air bubbles. Calibration wise, the DOS is bang on (and very easy to do), however calibration means nothing if the lines are full of bubbles.

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    I was also getting A LOT of air in both lines. Fortunately, just cutting down the tubing (yeah, it thins quick) and cranking down the fittings seems done it for me, until next time. Thanks folks for the advice as always.

    Ditto above comments about recalibration coming out spot on.

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