Pressure Tank Specifications

[cschippnick]

How do I properly spec out a pressure tank? Our current one is a WF45.

[Bob NH]

How do I properly spec out a pressure tank? Our current one is a WF45.

The simplest solution is to get a tank with a real volume that is 3 to 6 times the GPM capacity of your pump, with the ratio depending on horsepower of the pump.

Check the pump curve or run a test. If you have a pump that delivers 10 GPM at 50 psi, and you want your pressure switch settings at 40 and 60 psi, then you should have a minimum 30 gallon tank if your pump is 1 HP or less, and a 60 gallon minimum if your pump is greater than 1 HP. Those numbers are satisfactory, and larger is not a problem.

That will give you about 1 minute of pumping time for the 1 HP pump and about 2 minutes of pumping time for the larger pump.

You can read all of the arguments about smaller tanks and CSVs. A case can be made for using a CSV with a submersible pump, but I would never put one on a jet pump system because the jet pump already does about all that a CSV can do for you. A jet pump is so inefficient, and usually has so little pressure margin, that I believe that a CSV degrades a jet pump system.

[Bob NH]

Those size tanks are way smaller than I would use on a system without a CSV. You might get away with it if you never use water outside the house like with a garden hose or sprinkler. If you run a 5 GPM garden hose or sprinkler, it would cause your pump to run two minutes and be off for two minutes. There are 1440 minutes in a day so, if you leave the sprinkler running your pump would cycle on and off 360 times a day. That number really adds up over the life of the pump and causes your pump system to fail much too soon.

Of course if you really want to put 7200 gallons per day of water on your lawn you could connect two of those 5 GPM hoses and let them run half the day without ever cycling the pump, if you select a pump that delivers 10 GPM at something less than 60 psi. That same pump will deliver 18 GPM at 40 psi when you need to take a shower, flush a toilet, or do a load of wash.

[Raucina]

Another sales pitch. When will this poison be eliminated?

A typical sprinkler head running between 40 and 60 psi gives better coverage anyway as the pattern which is typically fixed varies to better distribute water droplets. Set the spray to the higher pressure.

[Raucina]

If you design to the largest diameter for the highest pressure, then you only suffer pattern shrink during the cycling. Since sprinklers still seem to have dead zones, that diameter shrink may be an advantage. In any case, unless its on a PGA green at pebble beach, your grass will still be alive and well.

If we are discussing acid heap leaching at a copper or gold mine, then the pressure and pattern will become very critical indeed. Time for the valve or the pump engineer to step in.

[Raucina]

Very generous of you to offer your services.

If you cannot tune your pump and zones to extend the pump run time during irrigation, then the csv is a good patch. I would put it on a 3 way valve for easy bypass during non irrigation times of the year, assuming you have the proper pressure tank and would like to save some electricity and hours on the pump components.

Tek supply sells some nice 3 way valves quite cheaply.