You may neven seen the pneumatic stroke adjustment of reciprocating compressor

In rare cases, pneumatic stroke actuators are used. Therefore, the adjuster drive is primarily powered by compressed-air while generating torque or thrust for the stroke adjusting action. There are pneumatic actuators that work with air motors and threaded spindles and others that use a shifting piston to generate linear actuation. 

In pneumatic actuators the control signal may be available in both the electric as well as pneumatic form via a control pressure level. 

The advantage of these actuators is good explosion protection, as electrical drive energy does not have to be brought in nor converted and even the control signal does not necessarily have to be electric.

In figure , a motoric pneumatic stroke adjustment is illustrated on the left side. The right shows a solution with piston.