Its the special little goodies inside that change or somehow modify the pattern of flow through the valve to get a particular desired characteristic, such as low noise, reduced cavitation possibilities, etc.
Can you give examples of what these goodies are tho? & does this mean that it DOES affect the capacity & therefore is also expressed as %capacity (instead of % trim)?
The trim pertains to components such as the valve plug, seat, and associated components. In the case of some "self-contained pressure-regulators, few options exist besides the actual regulator model selection. For example, perhaps the valve plug in a Fisher 620 or 630 "Big Joe" has a Teflon disc that seats against a nozzle similar to the seat on a pressure safety relief valve. However, with control valves there are many selections for metals, soft parts and the method that the pressure drop is made.
so how is the capacity determined from using different internals? that is, how do you determine the trim level (70%,80% or 100%) if you replace a part with a different part?? or how is that trim level number determined in the first place??
It is not clear to me whether those are trim choices or just properties of THE trim. This could be more like the tables for percent stem travel with the Cv for that percentage opening. Email the vendor to confirm such details.
you will see that there is one of two springs that you can select. Since each spring has a different spring constant, the percent open would be different for each spring at the same capacity, therefore (apparently) it made more sense for them to relate Cv to %Capacity rather than to %O. The typical method of showing Cv to %O would require two graphs, one for each spring.
