What do you call this type of air control valve?

I am looking for a valve to control pressurized air, up to 120 psi or so.

I don't want just on/off. I want to be able to squeeze a lever and have the valve allow a proportional amount of the air pressure through. A small squeeze -> a little pressure. A big squeeze -> a lot of pressure.

I am using it to control a pneumatic cylinder that drives an extruder. I want to be able to control the rate of extrusion by how hard I squeeze on a control lever (sort of like the brake lever on a bicycle).

What is this type of valve called?
Are there any that are already set up for hand control or will I have to work that part out myself?

this is called a "servo-valve" . whether its pneumatic or hydraulic, you still want to use a double spool type.

there should be plenty available on the web.

look for pneumatic servovalves. (they may not be cheap)

wer

You could use a conventional diaphragm control valve that takes a 3 to 15 psi signal. 3 psi can be either fully closed or fully open depending on the configuration of the diapharagm while 15 psi would be fully open or fully closed.

You would feed this valve with a manual 3 to 15 psi air regulator that is designed for this purpose. You can set the regulator at any pressure between 3 and 15 psi.

You could also interpose a pressure controller into the circuit and set the pressure you want and the controller would adjust the control valve to achieve that pressure.

A company such as the one at this site could do that.

http://controlsouthern.com/