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    Overhead Tank - Air Vent on tank delivery pipes

    Asked Mar 4, 2009, 10:41 PM 11 Answers
    Hi,

    I'm currently constructing my own house and presently we have started plumbing. Our plumber told me that we need to put a air-vent on the tank's delivery pipeline in order to release the air-lock. Please find the attached image. [Overhead cold water tank is the common method in India]

    I already have a air-vent on the top of the tank and my questions are:
    a) do we need to have another air-vent on the tank's delivery pipes?
    b) since this is for air-release, will it work out if we take a diversion on the vertical pipe? Shouldn't it be on the horizontal pipe? Another problem we have is that the there is no room for air-vent in the horizontal pipe. It is placed in the ceiling of the under-tank room. More preciously, from tank to the gate valve, I have no room for any additional fittings.

    Could you please advise me, if this air-vent is necessary, and properly placed (as in the image)? If not properly placed, could you please advise me the correct position?

    Thanks in advance.

    Regards,
    Hari

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    11 Answers
    ourhari's Avatar
    ourhari Posts: 4, Reputation: 1
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    #2

    Mar 9, 2009, 03:00 AM

    Hi, can I get any help? Thanks.
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    speedball1's Avatar
    speedball1 Posts: 28,581, Reputation: 1908
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    #3

    Mar 9, 2009, 05:26 AM


    Quote Originally Posted by ourhari View Post
    Hi, can I get any help? Thanks. a) do we need to have another air-vent on the tank's delivery pipes?
    Is thnis gravity fed or is there a pump involved. Because if there is the tank delivery line now becomes the suction line and you don't vent a suction line.
    The vent on the tank prevents air lock. I can see no reason or advantage for a vent on the delivery line. Regards, Tom
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    ourhari's Avatar
    ourhari Posts: 4, Reputation: 1
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    #4

    Mar 9, 2009, 06:42 AM

    Hi Tom,

    Thanks for the response. But the tank inlet is fed by a pump and the tank delivery is actually utilized by utilities such as bath, kitchen taps and by washing machines.

    Regards,
    Hari
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    speedball1's Avatar
    speedball1 Posts: 28,581, Reputation: 1908
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    #5

    Mar 9, 2009, 07:30 AM


    the tank delivery is actually utilized by utilities such as bath, kitchen taps and by washing machines.
    The tank vent will exhaust air as the pump fills the tank and vent it as a draw is made. Since you indicate the house i8s gravity fed I can see no reason to vent the delivery line. Regards, Tom
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    ourhari's Avatar
    ourhari Posts: 4, Reputation: 1
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    #6

    Mar 9, 2009, 07:42 AM

    Hi Tom,

    Thank you very much for the answer.

    Regards,
    Hari
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    Milo Dolezal's Avatar
    Milo Dolezal Posts: 6,039, Reputation: 393
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    #7

    Mar 9, 2009, 08:35 AM



    Some plumbers install air vent, like WATTS (see photo) on pressurized plumbing system, especially if your system uses pump. It automatically removes air from your pipes. It is a small, compact unit, installed on vertical riser
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    speedball1's Avatar
    speedball1 Posts: 28,581, Reputation: 1908
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    #8

    Mar 9, 2009, 08:44 AM
    Quote Originally Posted by Milo Dolezal View Post
    Some plumbers install air vent, like WATTS (see photo) on pressurized plumbing system, especially if your system uses pump. It automatically removes air from your pipes. It is a small, compact unit, installed on vertical riser
    Milo,
    This is not a pressurized system. It is gravitry fed. If you can see the advantage of venting the gravity feed then educate me. What would be the advantage? Regards, Tom
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    speedball1's Avatar
    speedball1 Posts: 28,581, Reputation: 1908
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    #9

    Mar 11, 2009, 04:49 AM
    Setting in my livfng room last night this post came to mind. I was thinking, "what's wrong with this picture? (see image).
    And tthen I flashed on the answer. This pipe your misguided plumber wants to install on the house feed is just plain useless. Simple physics! If the top of the pipe is left open as a vent then the moment the valve's opened the water will flow, by gravity, to the house. However once it reaches the house water will do what water does. And that is it will seek its own level and fill that pipe up as high as the level in the tank.
    Now, even if he puts a AAV on top and only allows air to enter the pipe pressure will build up and compress the air and you will nbe left with the biggest air chamber in the entire world. There is no way this pipe will act as anything but a embarrassment to the plumber that planned it.
    I apologize for not seeing this earlier. Tom
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    alexcalter's Avatar
    alexcalter Posts: 1, Reputation: 1
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    #10

    Feb 28, 2011, 10:30 PM
    The air vent on the over head tank takes care of air above the water level .The vent in the delivery line will take care of air in the delivery line as water will try to rise the level of water level in the overhead tank and as such there will be no air gaps in the delivery line.Generally for a small building like yours it does not matter or you may get water hammering and hissing sound.
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