pressure loss

Discussion in 'Pumps and Tanks Well Forum & Blog' started by clymberboy, Nov 13, 2006.

  1. clymberboy

    clymberboy New Member

    Messages:
    5
    i've been losing pressure as the tank drains down to the cut-in pressure. the pressure switch trips, but there seems to be a lag before the pump recharges the tank. the pressure switch trips, around 30, but the pressure suddenly drops below 20 & sometimes to zero before the pump seems to spin up. any ideas?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,815
    Location:
    New England
    With the pump turned off and a faucet opened, after any trapped water in the tank flows out (how much does come out?), check the pressure on the bladder tank.
  3. clymberboy

    clymberboy New Member

    Messages:
    5
    i've checked that pressure a few times. it always reads ~28# or whatever i've pumped it up too. the tank is the same as when we moved in, so its at least ~5 yrs old. i'm pretty sure that is got a slow leak to the point that i need to add a few #s every 2-3 months. there isn't any water coming out of the valve, so i don't think that the bladder is blown. i've also noticed that the pressure gauge mounted on the line reads ~10# less than what i read at the schrader valve with a typical tire gauge.

    whats odd is that the pressure switch trips ~30#, but then the pressure on the in-line gauge instantly drops to 20# or less (sometimes nearly to zero). its only 2-3 secs before the pipes jiggle a little & the pressure quickly shoots up. i'm not sure if the is a delay in the pump spinning up or if there is a delay in the power getting to the pump, or sticky check vavle, or . . . ?
  4. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    You should get a tire gauge you can trust. Turn off the pump (electrically). Let all the water pressure out of a faucet near the tank. When it is empty of water check the air pressure in the tank. Then turn the pump back on and let the pump shut off. Now check the pressure in the tank again. Tell me what it is. Then run the water until the points close on the pressure switch and again quickly check the pressure in the tank with the same gauge. Tell me what that pressure is.

    bob...
  5. Deb

    Deb Plumber

    Messages:
    200
    Location:
    Idaho
    When you check the pressure at the Schrader valve, there should be no water in the tank and the inline gauge should be at zero. I suspect a blown bladder.
    Deb
    The Pipewench
  6. clymberboy

    clymberboy New Member

    Messages:
    5
    empty = 28#
    full = 37#
    cut-in = 32#
  7. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    I don't think I trust your gauge.

    I don't think you can get the pressure switch to have that low of a differential. 17 psi. is about the lowest differential I have seen.

    Your telling me your differential is only 5 lbs.

    bob...
  8. clymberboy

    clymberboy New Member

    Messages:
    5
    no it doesn't make sense. i used 2 different tire gauges on the pressure tank valve & got the readings as posted. the in-line pressure gauge reads ~20# when the tank is empty, cut-in is ~30# & cut-out ~50#.
  9. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    That's more like it. 30/50. Your air pressure should be 28 lbs.

    bob...
  10. clymberboy

    clymberboy New Member

    Messages:
    5
    i've pumped the tank up to 40# measured with 2 tire gauges, but the in line gauge never reads any higher than 26#. the pressure still drops at the cut-in with every cycle. somethings amiss.
  11. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    I think you need a new pressure gauge:

    Read this:

    Explain how a bladder tank works
    A. When a bladder tank is installed, before putting power to the pump. The tank has a pre-charge of let's say 38 lbs. Ideally the pressure switch should be set to turn the pump on at 40 lbs. and off at 60 lbs. or more. What physically happens is; with no faucets open the pump is turned on. The pump will try to send water somewhere. The tank is the only place the water can go (since water cannot be compressed like air can). The bladder is being pressed against the inlet\outlet at the bottom of the tank with the 38lbs. The inlet\outlet in the tank can't take in any water until the pump over comes the 38 lbs. of pressure that is already in the tank. Now at 38.000000001 lbs, the tank starts letting in water and at 60 lbs. the pump shuts off. The tank has now taken in its total cache of water.
    Since the builders - centers started calling tanks by their physical size instead of their equivalency to galvanized tanks. The size can be about anything. In reality a 40 gallon galvanized tank and a 40 gallon equivalent bladder tank can physically give about 6 gallons of water between 40 and 60 lbs. The builders - centers sometimes call this 40 gallon a 20 gallon because that is what it will hold if you cut a big hole in the top and fill it up with water. Of coarse nobody really cares what a bladder tank can hold from top to bottom, because that's not how one works.
    As you open the faucet at 60 lbs. the pressure is going to go down gradually. When the tank reaches 40 pounds the pump kicks back on. At that point the system pressure is at 40 psi, and there is a 2 lb cushion to keep the tank from bottoming out and stopping the water flow temporarily. Now the pump starts pumping and trying to either keep up with water demand or getting ahead of demand and sometimes getting to 60 lbs and starting all over again.
    The main reason for a tank is to keep a pump from cycling and damaging the pump motor.
    There are constant pressure devices that will keep a constant pressure in your house and keep the system from cycling the pump too much. They are inexpensive compared to constant pressure pumps and they work in conjunction with a tank. When using a CP device you can use a much smaller tank. This can sometimes offset the price of a much larger tank.



    Q. How do I set my bladder tank air pressure?
    A. A bladder tank comes from the factory with pressure in the top of the tank. This air pressure will just about never be what the label says it’s supposed to be. So adjustments are necessary.

    Pressure switch’s that tell your pump motor when to start and stop are normally factory set at either 20PSI on and 40PSI off or 30 - 50, 40 - 60. I personally like 40 - 70. That gives a little more water between pump cycles. Regardless of the high pressure setting, the on pressure setting is the one that matters to the bladder tank. If your tank has 30lbs. in it and you want your pump to turn on at 30lbs. You will need to let out two pounds making the bladder tank air pressure 28PSI. The same with 20 on or 40 on. Make the tank pressure two pounds less than the on setting of the pressure switch.The reason for this is to have the pump turn on just before the tank reaches it’s air pressure setting. This prevents the tank from going completely empty when the air bladder hits the bottom of the tank. If this were to happen, the pressure in your plumbing would immediately go to zero since there is no more water to be pushed out of the tank. This condition is not desired when your in the shower. Of coarse the pump will kick on at this point making the zero condition only momentary, but nevertheless aggrivating.
    Last edited: Nov 15, 2006
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