[Tristan Lall]

As of last season, the pneumatic cylinder rules were greatly relaxed—the best robot rule change in a while—and seem to pretty clearly permit all sorts of strange and wonderful cylinders. (Your stroke, diameter and pressure rating are still restricted.)

Since the GDC didn't say (in this year's or last year's rules) that single-action cylinders were distinct from double-action models, I don't think there's any issue with using the manufacturer's definition of a cylinder (which happens to be accepted in industrial practice). I therefore don't think there's any point in asking this one on the Q&A.

Of course, the robot must still satisfy safety rules with regard to energy storage, and the spring in a single-action cylinder will be inspected as such. That shouldn't be a major obstacle, however—lots of teams use springs.