Nolan has it right that narrowing the pressure switch bandwidth would make a large tank act like a small one. That would just be wasting the extra money spent on the large tank. Plus a pressure switch that can do 10 PSI between on and off will cost more as well.
Wondering has a good idea to try the 4.5 gallon tank so you can see it in action, which will make it easier to understand. Then if you decide you want a larger tank you can just add a 20 gallon size tank anywhere after the CSV. You can even plumb the 20 gallon tank to a faucet and open the faucet. Since the 4.5 gallon tank is on the CSV and close to the pressure switch, an additional tank can be added anywhere in the plumbing past the CSV. Then you would have 24.5 gallons of tank size that would deliver about 6 gallons of drawdown.
It has always been said that a "properly sized tank" that will make the pump run for one minute and be off for one minute will reduce the pump cycles enough to make the pump last a long time. The only time this doesn't work is when using the pump for irrigation or something long term and using less than the maximum output of the pump. This would cause the pump to be destroyed from cycling on and off repeatedly for hours.
With a CSV you don't have to worry about running water at less than max pump output for long periods of time. The CSV will not let the pump cycle when using more than 1 GPM no matter what size tank you have. Add to that the fact that the CSV and 4.5 gallon size tank will cycle the pump the same number of times per day for house use only as a "properly sized pressure tank" without a CSV. Then it stands to reason that the CSV with the 4.5 gallon size tank will make the pump last just as long as the non CSV system with a larger tank as long as it has perfectly matched irrigation zones that don't cause cycling.
A lot of people will tell you that most pumps will last 20-30 years with a "properly sized pressure tank" and perfectly matched irrigation system. In the 25 years we have been using Cycle Stop Valves with small tanks, we have found they will last the same 20-30 years as the old style systems, and it doesn't even matter if the sprinkler system is sized to match the pump. It does stand to reason that the CSV with a large tank can reduce the cycles for house use even more. But I don't think it will make the pump systems last any longer than 20-30 years, as something besides cycling will probably cause the system to fail in that length of time. Even if the pump last more than 30 years, a wire will break, a pin hole will develop in a pipe, a check valve will fail, or something else will cause the system to stop making water. Plus I am now 57, if it last that long some one else will have to worry about it.
HI Cary,
Will you please answer my previous comment:
I don't understand the house equivalency usage here. Can you please explain? How does tank size relate to the number of houses? Would you say that a fair estimate of flushing a new toilet and washing hands leads is a 2.5 gallon draw? So in the ideal scenario starting with a full capacity 20 gallon tank, the pump would allow two toilet uses before starting. In a more realistic scenario with some water already being used up, the pump would start at every use, in which case there's no point in increasing to 20 gallons from 4.5 gallons. Is that right?
I want to get a CSV and need to replace my tank. I just need to figure out which size tank to get to avoid the pump starting at every flush and still take advantage of the constant pressure.
Can you please tell me if I were to get a separate tank, which parts I'd need and what the cost would be for the CSV?