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 10:50 PM.