Re: pump cycling-pressure tank volume-irrigation system
Posted by Steve on December 10, 2001 at 13:35:32:
In response to Re: pump cycling-pressure tank volume-irrigation system
Thanks More,
Sorry, I didnt make it clear, but I have the plain steel syle pressure tank ie, no precharge, no diaphram. A little bit of air is pushed into the tank everytime the pump turns on, and a float valve lets a little bit of air out to maintain a constant volume of air at the cut in pressure. pressure valve is set to 40 cut in 60 cut off. With this style system, a 9 gallon sweep volume is about normal for an 86 gallon tank.
: I don't want to burst your bubble, but maybe you can get a nice Christmas gift out of Terry's free advice page. If you have an 86 gallon steel pressure tank that only provides you 9 gallons of drawdown capacity, then you're operating it at higher than 100 psi precharge pressure, and thats excessive. Turn the pressure down to about 30 - 50 psi and you'll have 25 gallons available drawdown water. There is a possibility that if your pressure gauge reads 40 and you only have 9 gallons, that you have ruptured the nitrogen diaphragm in the tank. Have you consideed restricting the output on the sprinkler heads which will increase water atomization and aereation while reducing water volume and pressure needs? Have you considered drip tube irrigation which will reduce the water usage and pressure needs even more?

: : I have a 1 HP submersible of about 16 gpm capacity and an plain steel pressure tank of 86 gallon capacity. It has always worked fine. Recently, I began adding a sprinkler system to the yard, and began realizing some things I had'nt thought about before. With the 86 gal tank, there is only a usable volume of about 9 gallons. I did some calculating and convinced myself that this is correct. (does this seem about right to you?) Anyway, I am concerned about excessive pump cycling, it looks like with this arrangement the pump would cycle more than 30 times per hour during irrigation (with the sprinkers running at about 9 gpm).
: : I've come up with an idea that is either very clever, or will lead to some kind of unforeseen disaster. I figure that if I obtain a second 86 gallon plain steel tank and connect a pipe from the top of the first tank to the top of the second tank, then the additional air volume stored in the second tank will more than triple the usable capacity of my present tank, to about 36 gallons. (Only air would be contained in the second tank) By my figures, at the pump cut-off pressure just about the entire volune of the present tank will be filled with water, and at the pump cut in pressure, the water would be about 28 inches below the top of the water tank.
: : Does anyone see any pitfalls in this approach? Has anyone seen an arrangement such as this?
: : Thanks for any feedback,
: : Steve

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