Air Block in Suction line

Discussion in 'Pumps and Tanks Well Forum & Blog' started by danny25, Sep 30, 2009.

  1. danny25

    danny25 New Member

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    Hello ,




    Let me explain the scenario. I live in a building. We have a water pipe supplying water from the city mains running parallel to my building. This horizontal water pipe is shared between my neighbour and me. We both have water pumps that suck water and fill our overhead storage tanks.

    [​IMG]


    Please refer to the key in the diagram to understand the shapes .

    If the figure does not load, please click : http://img36.imageshack.us/i/pumpdiagram.jpg/


    I have a check valve just about half an inch from the begining of the vertical pipe. Off late, whenever I start my pump,after say a gap of 20 hours, I get a very shrill sound from the pump for 2-4 seconds and I do not get any water. If I leave the pump on after this sound, about 4-7 minutes later, I will get a perfectly normal flow of water.

    Alternatively, I can open the priming tap( which is connected to the suction line of the pump) and pour some water in the suction line, a shrill sound comes once again lasting about 2-4 seconds and then I get the normal flow of water.

    Another thing, I've noticed is if we switch off the pump after its run for 30-45 minutes and after the water started flowing, then restart it after 15- 30-45-60 minutes ( never tried beyond 60 minutes), I would never have to do any of the things I have mentioned above. The water would just flow normally.

    We have not had any problem with this setup all these years, however this problem started the day my neighbour extended the main pipe & took a seperate connection from the mains till his house. Earlier we had a mutual understanding where one pump ( placed in my house ) would supply water to both houses.

    Now since we have seperate pumps, we start pumps one after the other, never together.

    When my neighbour did this seperation I saw that I had a leaking check valve which was leaking like say 30 drops a minute or less. I did not bother changing it that day.

    I did another test because I felt that even if it was leaking, since it was connected so close to the source it would not matter. I filled the suction line completely using the priming tap near the pump and then monitored it for 12 hours, I did not notice any noticeable drop in the level of water. Can this method be used to check for a leak in a check valve ?

    I still have not replaced the check valve.

    I feel its a air leak somewhere, but I cannot figure it out.

    I hope I have explained the problem well enough and I hope we can find a solution to this daily priming activity.

    Thanking you

    Danny
    Last edited: Sep 30, 2009
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,378
    Location:
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    If the check valve is leaking water out, it will even more easily leak air in. You have a suction leak that is letting air in, and causing the pump to loose prime.
  3. danny25

    danny25 New Member

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    This is what I find most confusing, if the horizontal water line contains water where does air enter it, so that it can enter the vertical line.
    Last edited: Sep 30, 2009
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,378
    Location:
    Lubbock, Texas
    The same place that leaks water out under pressure, will let air leak in when the pump creates a vacuum.
  5. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    The red line should be suction, if I am reading the diagram right...and the air is being sucked in somewhere on that line...
  6. danny25

    danny25 New Member

    Messages:
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    No the black line is the suction, the red is the delivery line.
  7. danny25

    danny25 New Member

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    Does this give me correct results ? Or is it incorrect ?

    Correct me if I am wrong : if the check valve is leaking water when the pump is off, then air enters the vertical line through the same place where water is leaking, but what causes confusion in my mind is how does air manage to get below the check valve when there is water supposed to be in that horizontal line, also how does the air cross the check valve and enter the vertical line when that line is full with water.

    I'm sorry for the pestering.
    Last edited: Sep 30, 2009
  8. valveman

    valveman Moderator Staff Member

    Messages:
    4,378
    Location:
    Lubbock, Texas
    Water flowing past a leak in the pipe can draw in air just like a bubler in a hot tub. And if there is a vacuum created, air comes in much easier than water. You need to fix the leak.
  9. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    OK then it is somewhere on the black line...between check valve and pump...
  10. danny25

    danny25 New Member

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    I have checked the pipes visibly for any leakages & there is no leakage of water through the pipe.
  11. Bob999

    Bob999 In the Trades

    Messages:
    448
    Location:
    Pennsylvania
    Is your neighbor having the same problem or only you?

    If only you the leak must be in that part of the system unique to you. If both are having the problem the leak is in parts of the system that are common to you both.
  12. danny25

    danny25 New Member

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    Sadly, its only me :(
  13. masterpumpman

    masterpumpman New Member

    Messages:
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    Location:
    Virginia Beach, VA
    You're getting air in the suction!

    Valveman is right. Any water leaking the suction line at rest will cause air to enter the suction line when it's pumping. The pump may pump air and water while it's running but when it's at rest the air bubbles in the water will rise and settle in or near the pump. Then when the pump starts again after setting for a time the air in the pump causes the pump to be partially air logged. Repairing all the leaks should solve your problem.

    Porky
  14. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Put a vacuum gauge on it and start checking for a leak.
  15. danny25

    danny25 New Member

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    Hello,

    Well, I checked the pipes for visible leakages and I could not find any leakage from where water is leaking. I can see all the pipes .

    But, what I do know is the check valve does not shut 100% tight so it leaks water into the pipe below the check valve. Can this be the problem ?
  16. valveman

    valveman Moderator Staff Member

    Messages:
    4,378
    Location:
    Lubbock, Texas
    Now you say you can't find any leaks. What happened to the 30 drops per minute? If this is not your air problem, then it could also be air coming in from the priming plug on the suction line. Priming plugs should be on the discharge of the pump to prevent another place for a potential air leak in the suction line.
  17. danny25

    danny25 New Member

    Messages:
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    Location:
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    I'm Sorry ! I think there is some miscommunication.

    Looking at my diagram the check valve is connected at the bottom of the vertical pipe an inch above the horizontal pipe.

    The check valve is leaking at about 30 drops a minute from the vertical line into the horizontal line. The water is not leaking outside the pipe at all.

    This is where I think there has been some miscommunication. Sorry for the trouble .

    Is this the same leak you are meaning or were we thinking differently ? Can this leaking check valve be the reasons for my worry , if yes , please read this post : http://www.terrylove.com/forums/showpost.php?p=223903&postcount=7 .


    Thank you once again.
    Last edited: Oct 1, 2009
  18. valveman

    valveman Moderator Staff Member

    Messages:
    4,378
    Location:
    Lubbock, Texas
    A check valve leaking back will only cause the pump to cycle on, even though no water is being used. Air is getting in somewhere, I suspect the priming plug on the suction side.
  19. Bob999

    Bob999 In the Trades

    Messages:
    448
    Location:
    Pennsylvania
    Because the check valve that is leaking is below the pump there is probably another check valve above the pump and before the cistern that is not shown in the diagram. The control for the pump is probably a switch that operates based on the level of water in the cistern. So the leaking check valve may not cause the pump to cycle on in this case.

    I think that in order for water to drip from the check valve something has to replace the volume of water that drips--in this case it is being replaced with air. Perhaps the air is coming from the supply line if you are unable to find any leak in the pipe between the supply line and the pump.

    Replace the leaking check valve!
  20. danny25

    danny25 New Member

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    Ok.. I will check them both. Thanks for all the help.
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