Pump Run and Off Times
The inrush current from starting a motor creates heat in the core of the motor. It takes about a minute of run time for this heat to transfer to the skin of the motor and be dissipated to the water. Then when the pump shuts off, the motor is still warm, and it takes about a minute for the motor to cool down where it is safe to restart. So a minute on and a minute off has always been the minimum rule of thumb. Two minutes on and two minutes off is just that much better for the motor.
With the old conventional pressure tank method, the pressure tank fills at the rate the pump can produce, less the amount of water being used at the time. So if you have a 10 GPM pump and a tank with 10 gallons of draw down, the tank will fill in 1 minute if no one is using water. If there is an 8 GPM hose running, then the tank will fill at 2 GPM and give 5 minutes of run time to fill the tank. Then because there is still an 8 GPM hose running, the tank will be empty in 1.25 minutes and the pump will be restarted. This is 5 on and 1.25 off or 230 cycles per day.
If you only have a 2 GPM hose running, the tank will fill at 8 GPM in 1.25 minutes, and be off for 5 minutes. That is 1.25 on and 5 off, which is still 230 cycles per day. Either way you are just barely getting the 1 minute on or the 1 minute off that the motor needs. Doubling the size of the tank to 20 gallons of draw down will also double the run and off times but, is still 115 cycles per day. The less cycling, the longer the pump will last.
With a CSV the process is a little different. As long as there is at least 1 GPM being used, the CSV will keep the pump running continuously. This means absolutely no cycling for systems that use more than 1 GPM for 24 hours a day, such as with heat pumps. When there is no water being used, the CSV then fills the pressure tank at 1 GPM, from the pressure setting of the CSV to the off setting of the pressure switch.
A 4.4 gallon size pressure tank only holds 1 gallon of water. Every time you use more than 1 gallon of water the pump must start. So the pump does not usually need to start while you are rinsing your toothbrush or the ice maker is filling. However, the pump will start when a toilet is flushed or the shower is running. With a 40/60 pressure switch and the CSV set at 50 PSI, that is only 30 seconds of run time to fill the tank. However, when you flush a toilet, it takes about 30 seconds for the toilet to refill, then the CSV refills the pressure tank for another 30 seconds, and this gives you the required 1 minute run time. When a shower is running, the pump will continue to run as long as the shower is on, then when the shower is turned off, the CSV will refill the pressure tank in another 30 seconds and shut off the pump. This will always be more than 1 minute of run time.
The off time required by the motor is also figured a little differently with the CSV. Since the CSV keeps the pump running as long as you are using at least 1 GPM, the pump only shuts off when you are no longer using water. Since you are no longer using any water, when the pump shuts off, it stays off until you start using water again. This gives you much longer than 1 minute of off time. The only way you could make the pump come back on in less than 1 minute, is to shut off all water use, sit and wait 30 seconds for the pump to go off, then quickly open a faucet that uses more than 2 GPM. This will still give you more than 30 seconds of off time. In reality, if you shut off all water use, then start using water again in less than 30 seconds, the pump has never shut off and does not cycle. If you shut off all water use, then restart using water 1 minute later, the motor has already had it's 1 minute to cool down. Only if you start using more than 2 GPM, between 30 and 60 seconds after the last water outlet was closed, can you make the pump stay off less than 1 minute. This may happen on a rare occasion but, it is not something that can be repeated, or can even happen often enough to cause any damage to the motor.
With the CSV and a tank that holds 1 gallon of water, the pump must start every time a toilet is flushed. As long as you flush again within 30 seconds of the toilet refilling, the pump does not cycle again even for multiple flushes. With the CSV and a tank that holds 1 gallon of water, the pump must start every time the shower is on. However, the pump will stay on for the entire time the shower is running, instead of cycling on and off 4 or 5 times during a shower, as with a standard tank system. With a CSV and a tank that holds 1 gallon of water, the pump must start every time the sprinklers or heat pump is running. However, the pump will stay on the entire time the sprinklers or heat pump is running, instead of cycling hundreds of times per day as it would with a standard pressure tank system.
The pump must start every time a toilet is first flushed. However, the CSV eliminates so many cycles during showers, heat pump or sprinkler zones, and other long term uses of water, that even though the pump cycles every time a toilet is flushed, it is still cycling hundreds of times per day less than a regular pressure tank system with a large tank.
A CSV with a 4.4 gallon size tank (1 gal draw down) will cause the pump to cycle about 40 times per day on the average house. Using the CSV with a 20 gallon tank (5 gallons of draw down) will cause the pump to cycle about 20 times per day on the average house. In most cases, this is not enough difference to justify the use of any larger than a 4.4 gallon tank. The way the CSV controls the pump system, there is really no justification in using a larger tank. Then if you consider the cost and space needed, there is even less justification for using a larger tank.