This paper explains the possible occurrence of the "sticking and restarting phenomenon" observed with electropneumatic positioning systems. This is carried out from the notion of partial equilibrium, with the analysis of the model which incorporates two parallel phenomena which are used to generate a pressure force subjected to dry friction forces. Also, an experimental result has been studied in a particular pressure force plane which shows the origin of the problem more explicitly. The theoretical results give a necessary and sufficient condition for the restarting phenomenon not to occur and, if this condition is not validated, there is an estimation of the restarting time. Understanding this undesirable phenomenon will be the basis for further work which will attempt to find solutions to a void its occurrence.