Hey Boom, I have a question for you about Water pressure tanks, or anyone else that knows.
As I posted earlier this year, my bladder in the pressure tank broke this winter, spring is here, and it is time to replace it, so I was wondering what is the minimum sized tank I should look at.
Currently the tank I have is a 44 gallon tank, but in looking at specifications of my well, I was wondering if I could go smaller, or if I need to go larger.
Well spec's are 498 feet deep, static water level is 40 feet below land level, 3/4 HP pump with a flow rate of 2 GPM(draw down 120 PH), 7 faucets in the home, the switch is set at 30-50LBs
So any insight anyone can offer before I purchase the new tank?
Thanks.
Right here, Bro! Whoa! Who spent all that money to drill 498 ft when the static water level is at 40 ft? I do not understand (draw down 120 PH)? Without looking at a chart and without knowing how far down your pump is installed it is hard to say what the ground level GPM's of your 3/4 hp is, but I question the 2 GPM. That sounds way too low unless you have a miserable recovery rate in the well, while the pump is running. Most residential pumps are sized (taking into account head and water availability) to deliver 10 GPM at the point of use.
That being said, there is a minimum tank size that you want to use. It is calculated to keep the well pump from turning on and off excessively. Pumps like to run. It wears them out to keep starting up. The rule is that you should have a minimum of 2 minutes of pump run time to refill the draw down water volume in a pressure tank. The amount of draw down gallons, for any given size tank, is a factor of the pump switch setting and the tank precharge pressure. So for example, if you have an 86 gallon (total volume) P/ tank with a switch set to operate between 40 and 60 lbs, that tank will have about 22 gallons of draw down. If the well pump can deliver 10 gpm, that gives you a 2.2 minute pump run time to refill the tank. That is the minimum that is considered reasonable for the longevity of the well pump. A lower switch setting will require a lower pre-charge in the tank and alter the draw down volume upward, in any given size tank.
Now, if you think your well output is really a 2 gpm, I would try to consult any well pump records (should be on file with the pump company that installed the pump or the county when the well was permitted. OR you could disconnect the line before the pressure tank, get some 5 gallon buckets and time the flow yourself.
If your flow is actually 2 gpm's and you cannot reasonable alter that, then you would not really concentrate on the minimum size pressure tank but on the maximum size or combination of tanks you can accomodate. There is no downside to having too much except for space constraints and cost. The more tankage you have (properly balanced) the more drawdown you would have available to compensate for the low well output.
Further more there is no practical reason not to run your system at a setting of 40/60. You can either adjust the switch you have OR get a new one. If you go to a Home Depot, you will find Square D switches in both 30/50 and 40/60. The switches are identical except for factory settings and labling. 40/60 is considered to be the standard today. If the plumbing is sound, I have adjusted many systems (for customers) to run at 50/70. There is nothing in the home that will not easily live with that and your faucet performance is so much better. You just have to remember to adjust your pressure tank precharge (with tank empty) to 2 psi below the pump cut in pressure.
