I know right? Like I said, it is so simple it is hard to understand. The CSV works the same as any ball valve, it just opens and closes. It is just spring controlled instead of having a handle on it. Less than 50 PSI pressure in the house opens the CSV and more than 50 PSI closes it.
When you valve back on a pump, it makes the pump think the well is deeper. That is a 7 GPM pump because 7 GPM is the optimal flow for that particular size impeller. But, it will pump 1 GPM in a 410' deep well, 7 GPM when lifting from 280' deep, and 9 GPM if the water in the well is only 180' deep. With the understanding that 115' of that total head is needed to make the 50 PSI pressure needed at the house, you can size the pump as needed for the depth of water in the well.
A 3/4HP, 7 GPM pump will produce 7 GPM at 50 PSI at the house while pumping from a depth of 165'. When the CSV makes the pump produce only 1 GPM as is needed for a sink at the house, the CSV holds back water until the pump thinks the well level has dropped to 295', even though your well is not that deep. The well could only be 10' deep with a water level of 1' from the surface and the pump still thinks it is lifting from 410' when needed. See the performance pump curve attached.
OK, now if you understand that your next question is going to be, "What happens to a pump in a 10' deep well when it is being restricted to think the well is 400' deep? Isn't that going to make the pump work much harder?" No. Just the opposite is true. That is the part that is hard for our brains to understand. It is completely counter intuitive, just the opposite of what our brains want to think. Some peoples minds are just never able to accept it. Lol! Restricting a centrifugal impeller pump with a simple valve makes the amp draw/watts used decrease, not increase. See the power section of the curve supplied to see this pump uses 1.1HP to pump 9 GPM when it thinks the well is shallow, and only 0.6HP pumping 1 GPM when it thinks the well is deep.
If the well is only 10' deep, that would cause there to be 177 PSI on the inlet side of the CSV while it is supplying 1 GPM at a constant 50 PSI on the other side of the CSV to the house. The deeper it is to water the less pressure on the inlet side of the CSV by 1 PSI for every 2.31'.