I have sourced a gas pressure sensing unit that can accurately measure air pressure and read down to gauge pressure ( - 1 bar) vacuum, It has two nc/no relays and an analog output for PID, with programmable operating parameters, this can be easily integrated  into my current design and control circuit and can provide a visible display, and alarm supervision. The price was very reasonable for a unit like this, but as you are all aware it doesn't take long for those expenditures to add up. Depending upon configuration I think I may be able to monitor pressure and flow direction by using two of these units at different locations in the pneumatic scheme.

Progressing well.