1) How much does the volume of the rotary pump matter? Mine currently has the CA104z pump, which pumps 35gph at 130psi, and I'm considering replacing it with another compact fluidotech pump from the same series that pumps 25gph at 130psi. Should I expect any issues?

2) What is the function of the retainer spring (fluidotech part 23022) on the outlet of the pump? This spring is different than the bypass spring.

Brian

The flow rate difference won't matter at all.

If the spring is the one I think it is in the outlet, it's the retainer for the balanced bypass to allow fluid flow, but prevent it becoming displaced.