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  1. #11
    Join Date
    Aug 2007

    Default Re: Well pump short cycles


    Everything sounds fine to me. I looked at the pump curve chart for your pump, motor size and depth (roughly 500') and you're fine. You are not outside the recommended range at all...and your output to pressure tank size should be fine...provided that you don't allow the tank to become "overly waterlogged". You'll know if it does cause your drawdown between pump cycles will become diminished enough that you'd notice if you're paying attention at all. (*Shouldn't* need to check more than every 3-4 months or so unless the tank develops a pinhole leak somewhere.)

    With a 120 gallon tank, your optimal drawdown on a passive airhead recharge (like what you just did) will be approx 30% of the total tank capacity....or approx. 36 gallons. (Will vary slightly depending upon what range of pressure switch you have installed) This is in regards to a "closed" tank without an air/water volume control such as yours has. Since the float of this A/W control doesn't close until the water is high enough to float-the-float.....your airhead is not as large to start with...and so your drawdown won't be as great.

    Note that even if your pump was putting out 15 gallons a minute....it would take over two minutes of run-time to replenish that. That's great for the life of the pump-motor. The 90 seconds you report is okay also. (Don't know if you closed the hydrant the instant you heard the PS kick in or not. If not... you might try running your refill test again and do just that.)

    (Needless to say...what size the pipe is that leads up/down from the pump to the tank will also vary the output/delivery gpm....but with what you report....there's no need to change anything. Whether it's hanging on 1 1/4" or 1 1/2" now is irrelavent cause you're well within acceptable ranges.)

    Sounds to me like you're good to go......and were just a little confused about how to recharge the tank. The objective (as you now know) is to get all the water out and allow all of the passive air (at atmosphere) back in that the empty tank can hold. Then turn the pump back on and let the incoming water compress that passive air-charge.

    If you wanted to go for max drawdown...you can pre-charge a galvy tank just like you would a baldder tank. IOW, drain the tank and then get out your compressor and put an air-charge in it (via a Schrader/tire valve) that equals two psi less than the cut-in pressure of your pressure switch. This will give you greater drawdown than a simple passive recharge, but.......unlike a bladder tank where the air is separated from the water by the bladder material.....your air and water will still be in contact with one another and so the air will still get absorbed over time. This means that you'll still have to periodically recharge the airhead, but not as often and you'll have greater drawdown for quite a while.

    However, the only way that you'd likely succeed at pre-charging your galvy tank (if you so choose)... is if you removed the "bleeder" (air/water volume control) from the tank all together (replace with a 1 1/4" plug). Unless you do that it will more than likely leave out any "excess" charge and you'll be right back to passive/atmospheric airhead recharge.
    Last edited by goldhiller; 02-07-2009 at 09:50 PM.

  2. #12
    Join Date
    Aug 2007

    Default Re: Well pump short cycles

    My bad on my previous post, folks. Hence an alternative definition for the term "post haste", I guess.

    Drawdown on a "passively" charged tank will be approx. 10% of total tank capacity. (*if* the total tank volume is available for pre-charging)

    Drawdown on a pre-charged tank will be approx. 30% of total tank capacity. (*if* the total tank volume is available for pre-charging)

    (Also assuming conventional points of tank connection to the water piping)

    These can be calculated more closely using Boyle's law, but the rough percentages should be close enough for all "normal" applications.

    Exact drawdown in either situation will vary some depending upon the pressure settings and spread of the pressure switch kick-in/kick-out settings, where the input and output pipes are connected to the tank, etc.

    The difference between a passively charged tank and properly pre-charged tank is dramatic and well worth the time and effort with a single compartment galvy tank.......even though (on the average system) the water inside a single compartment galvy tank will eventually absorb the air...requiring recharge.

    An exception is a well or well system which injects "excess" air into the tank each time the pump runs. You shouldn't try using a bladder type tank on such a well system as that air will be trapped inside the bladder and will then frequently come ejecting out of your fixtures in the house. A galvy tank is the better option here. However, even a galvy tank can/will actually become air-logged over time. While installing a common (cheapy) air-water volume control is better than nothing in these cases, it relegates the airhead "charge" to that of atmospheric pressure because it will open the tank to atmosphere when the float drops. This means less drawdown than with a higher precharge on the airhead, of course.

    The better option if an excess air-injection situation exists is to install an Ametek US Gauge WJ type control as it is pressure-release adjustable. IOW, once properly adjusted in relation to the kick-in pressure of your particular pressure switch and then precharging the tank.....it will only release excess airhead from the tank when the water volume drops below the float level *AND* if the airhead pressure is too high. Nice device for only around $20 - 25. (As with any air-water volume control, it will only operate properly if its float remains operable & its orifice does not become clogged with "goop" .......such as iron algae, calcium deposits, etc.) You won't likely find one at a big-box, but rather at your local plumbing supply house or perhaps from a local well-driller.
    Last edited by goldhiller; 02-09-2009 at 01:31 PM.

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