I'll read through this thread later when I have some more time. There's still a lot of pneumatics in my area and a definate lack of people that know how to work on it. We were busy today and I ran a call myself at a building down the street. Another company had come in and bypassed all the summer/winter selector switches that controlled the outdoor air dampers. The note they left said this was done to "close" the dampers but sending air to them opens them. Then they went to the outdoor air dampers and saw they were open so they disconnected all the linkages and threw the dampers shut (well, some were open and some were shut). On one air handler, both the return and outdoor air dampers were shut so the duct was imploding. On another air handler they couldn't get the hot deck warm enough (because they had outside air wide open) so they jacked up the setpoint sky high. The building's simply a mess.
Back on subject, pneumatics are great, and they don't lock in a sole source service provider but they do require constant calibration. Anyone that thinks DDC doesn't isn't living in the real world either though.
The building I mention above is up for sale and could be remodeled or could be torn down. The air handlers(Westinghouse), chillers (Worthington), and boilers (came over on the Mayflower) are all in the sub-basement (that's right, two floors underground). This equipment doesn't lend itself to replacement because of it's location. What suggestions do you have? We've converted hot deck/cold deck pneumatic systems to DDC VVT or VAV systems before but not on this scale. Ever done anything like that?