Working out how to do pressure

At this point i'm a bit lost on how to do pressure in the system. I know
that the pressure will decrease with each part in the system it pass
threw. Which means later i'll need to add a path finder to simulate
this. However, right now i can't figure out how to do pressure produced
and pressure load needed. The only way i know is with one source of
pressure but in minecraft people will not just add one source of
pressure for a system.