With an old style pressure tank system, you need a tank that will have at least 1 gallon of draw down for each gallon per minute the pump will produce. Ie; a 10 GPM pump needs a tank with 10 gallons of drawdown, which is about a 40 gallon size tank. This should let you wash toothbrushes, fill the ice maker, or flush about 5 or 6 times before the pump is started. Adding a CSV to this system will still let the same thing happen. However, any use more than 10 gallons and the CSV will match the demand, which keeps the pump running continuously until the faucet is closed. You donít need to bypass the CSV for this to work. Just set the pressure switch and CSV so it takes the right amount of time to refill the pressure tank. Ie; 40/60 switch, CSV set at 55 PSI.
With the CSV and small tank system, you only need a 4.4 gallon tank, that has 1 gallon of draw down. 1 gallon will keep the pump from having to start for small amounts of water like, washing a toothbrush or filling the ice maker. Any demands more than 1 gallon, and the CSV will match the demand, which keeps the pump running until the faucet is closed.
Actually the CSV and big tank are the best of both worlds for the pump. The big tank supplies water for smaller uses, while the CSV prevents cycling for long term uses of water. This delivers the minium cycles per day possible for any system, and extends the pump life considerably. The only draw back is that you have to wait for all the water in the tank to be used before you see constant pressure. Usually a person will be about half way through with their shower before the tank is empty and they experience constant pressure. Once you have experienced constant pressure, you will learn to hate waiting for it. Constant pressure is so much stronger than tank pressure for a shower, that you will quickly learn to like it. Many people have told me that with constant pressure, they no longer need soap in the shower, as the pressure will simply blast the dirt off of them.
The CSV and small tank are usually best for the home owner. The 4.4 gallon tank is less expensive and takes up less space. The pump will cycle a few extra times per day compared to the large tank system. However, you donít have to wait for the constant pressure. When taking a shower, the pump will be running and delivering constant pressure, before you get the water temperature adjusted. With a larger tank, you would be continually adjusting the temperature of the water as the pressure dropped from 60 to 40 for the first half of the shower. With a smaller tank, the CSV will maintain 50 PSI constant and you will not need to adjust the temperature for as long as you are in the shower.
The CSV takes out so many cycles during long term uses of water, that you can afford a few extra cycles per day for short term uses of water. The CSV will work with any size tank, and the decision is ultimately up to your own preference.