Pressure Sensor Feedback loop

I'm trying to build something that will more or less maintain a constant, but adjustable level of pressure, probably driven by an electric motor. I've seen pressure-sensors on this site that increase conductivity with more pressure applied to the sensor, but mechanically I can't think of any way to get my device to work without a pressure sensor to decrease in conductivity with added pressure. Sadly I don't know enough about electrical components or circuitry to make it work with the former.

If anyone here would happen to know how I could create such circuit, or can suggest of a purely mechanical alternative I would appreciate it.

I've made a unit that does what you are looking for, using a pressure sensor and a peristaltic pump, connected to some electronics.
Charlie_Szasz (author)  steveastrouk5 years ago
Do you know where I could get a cheap peristaltic pump? Everything I search for online seems to cost hundreds of dollars.

I was pretty tired when I wrote this, but I didn't even think to use an ordinary potentiometer. With a little tweak to the design I could use that instead. I have another, similar project that could use a little vacuum pump.
I got mine for 20 bucks on Ebay.