This paper concerns the control and the stability analysis of pneumatic actuators, which are nowadays of widespread use in the industry. A problem related to the use of such actuators is the so-called "stick-slip", due to the presence of dry friction in the system. In this paper we provide an empirical switching control law which avoids this phenomenon, as well as a general approach to the stability analysis of nonlinear systems which will let us prove the stability of the closed-loop system. The approach is based on casting the closed-loop system into a piecewise-affine form and finding a Lyapunov function for it. Such an approach will be able to cope with the special features of the controlled pneumatic system model, namely the presence of sliding modes, a whole equilibrium set and uncertainties on the values of a few parameters. At the end of the paper we will show how such a method can be successfully applied to our experimental setup under several different hypotheses. Index Terms-Piecewise-affine systems, piecewise-polynomial Lyapunov functions, switched control, fluid power.