Hi!
I'd like to preface my statement by saying that I am definitely not a pneumatics expert.
That being said, the main thing to know about pneumatics is that they are usually two-position actuators. This is mainly a result of the lack of precision involved in pneumatics. Teams often have small leaks in their systems, but ignore them because the main idea with pneumatics is the difference in pressure. This means that it is incredibly difficult to give the correct amount of pressurized air to the cylinder to make it stay at one point.
You can try the Dart Actuators
http://dartactuators.com/ which will provide you with some accuracy.
Best of luck to you, hopefully I helped a little bit.
TL;DR Pneumatics are 2-position actuators, if you want more positions go to linear actuators like DART.