I really appreciate all of the input everyone has provided. I'm not sure when I'll be able to get into it again, but I'll check the pressure. Now that I've taken all the stuff apart I have a little bit of a feel for how the system works. I'm going to check the mixer next, and I'll just replace the diaphragm while I'm at it. It's a model 100, so the parts are cheap and probably easy to find here in So Cal.