A CSV works like a pressure reducing valve as long as you are using more than the built-in minimum flow of the particular CSV. A 2" would have a minimum flow of 5 GPM. As long as you are using more than 5 GPM, the CSV will hold a set pressure. But if you use less than 5 GPM the downstream pressure will continue to increase until it equals the upstream pressure.
This internal bypass in the CSV is why it is self flushing. The bypass allows the CSV to function much faster than a PRV, so screens for needle valves and small tubes are not necessary. But we use CSV's for pressure reducing all the time like in municipal jobs where the flow never gets below 5 GPM.
