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How many pounds of air need one expansion tank

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  • How many pounds of air need one expansion tank

    I wonder how many pounds of air must have an expansion tank and how much water.

  • #2
    Re: How many pounds of air need one expansion tank

    For a well tank - 2lbs less the cut in pressure


    • #3
      Re: How many pounds of air need one expansion tank

      If it is a thermal expansion tank you want to charge it to the line pressure coming into the house and not to exceed 80#
      Last edited by TOPDAWG; 02-24-2011, 05:20 PM.


      • #4
        Re: How many pounds of air need one expansion tank

        I am happy pepito 10 asked that question because I have alway wondered if there was a formula. At camp I have what I think is called a jet pump. The pump is cone shaped and it is sitting on top of some type expansion or storage tank which has an air valve on the back. I am not too good at estimating volumes but the tank is smaller than a five gallon pail, probably 3 - 3 1/2 gallon size. I bought it at Home Depot a few years ago. One of my neighbors, a union plumber steamfitter plumbed it for me because I don't have a clue about plumbing. As I recall the water pressure is set to switch on at 30# and off at 50#. How do I know if it is a thermal expansion tank? Also what is inside the tank? Is the tank compartmentalized with one side for air and the other side for water, separated by some sort of flexible gasket? If not, what prevents the air from entering the water line? The tank seems to be welded so how did the manufacturers install the gasket and then weld the tank closed without melting the gasket? During the winter months I bring the tank home and keep it in my basement. That means, I think, that there is no water pressure inside the tank so the gasket, if there is one, is expanded fully, is that OK? Is there some type of maintenance, maybe something to spray inside the tank to keep the gasket flexible?

        In the old days I remember my father used to replace what he called "leathers" in our water pump. I think he called it a two piston pump as opposed to what I don't know maybe a single piston pump. The pump was attached to a storage tank maybe 15 -20 gallons in size. The tank would get what my father called 'water logged'. This caused the pump to cycle more often that he liked. He would drain the tank and then refill it. There was no way, as far as I remember, to add any air. You could always see the water level in the tank because the condensation on the outside of the tank would stop at the interface of the water and air within the tank. After the pump was replaced it was kicking around for years collecting dust. My neighbor, who helped me install the new pump, refused to take any money for helping me but said he would really like that old water pump which I gladly gave up. As I recall there was a plactic bag wired to the pump that had some of these 'leathers' in it. I remember thinking at the time that they didn't lool like leather to me, more like some sort of manufactured, non-naturally-occuring, man made material. We always knew when the pump came on because the lights would dim. I can still hear that old water pump chugging away. I have no clue about how old is was but it served us faithfully for at least 45 years.
        Last edited by Tom W; 01-29-2009, 02:13 PM.