Can't increase air pressure in Watts Expansion Tank

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Ccoles, Nov 18, 2008.

  1. Ccoles

    Ccoles New Member

    My water heater has been leaking out the TP Valve. We installed a new one to see if this would help, but the new valve leaked as well. I tested my Expansion tank to see if it had air in it and the pressure would not register on my gauge, so i took the needle out to see if there was any air and there was no air, but there was also no water leaking out as well so the bladder must still be good. For some reason i am not able to increase the air pressure. I have put my trusty tire pump on the tank and it won't air up. It is as though the valve stem is not long enough for the mechanism inside the pump to unseat the needle and allow the air to go into the tank. Can someone help me because i think the tank is still good and i don't want to spend the $40 on a new tank if i don't need to.
  2. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    You may need to turn the water off and drain down some before you can pump air into the expansion tank.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    The easiest way is to remove the tank and pressurize it. Right now, you would need more air pressure than that of your water system to get ANY air into the tank.
  4. You didn't mention anything about how much air you're putting in this tank.

    That would indicate that you don't know how much to put in it.

    Let us know what it is.
  5. Gary Swart

    Gary Swart In the Trades

    Yakima WA
    If you are following the directions for adding air, you are using a bicycle pump or similar type hand pump. That is advised by the tank manufacturer because the volume of air needed inside the tank is quite small and a large air compressor could easily overcharge the tank and rupture the bladder. Do not confuse volume with pressure. If you are trying to add air this way with the water pressure against it, a small hand pump would not have the power to push air into the tank. Remove the tank and my guess is you will be successful. The air pressure should match the water pressure the PRV is set on. If you are using an air compressor, be extremely careful and apply air in very short bursts, checking the pressure with a good gauge after each. I'm not suggesting that this is a safe practice, just warning you to be aware of the potential of blowing out the bladder.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Some bicycle tires use VERY high pressures, so a bicycle pump may be able to do it, but it could take a LOT of strokes.

    The static pressure in the tank (without any water pressure on the other side water off and a valve opened to relieve any pressure) should be the same as the normal water pressure in the house. So, to properly adjust the air, you really need a water pressure gauge. They aren't expensive.

    An alternative is to use your tire pressure gauge (same as for checking your tires). With water turned on, the pressure in a functioning bladder tank will be the same as the incoming water pressure.

    To minimize the flexing of the bladder, if it is about the same as the normal water pressure, the bladder just sits there at its midpoint when the pressures match. This gives it the design volume to account for volume increases when your water heater is on and the hot water expands.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    when the tank air pressure is the same as the water pressure, the bladder is expanded and fills the entire tank. Water cannot get into the tank until its pressure increase and overcomes the air pressure. The closer it is to the system pressure, or if it is higher, the less water that can enter the tank before the two pressures equalize.
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