To meet current challenges, manufacturing industries must develop precise designs for interactions of various components of production control systems, and in particular for behavior of the software controlling them. Several diagrammatic techniques, e.g., SDL, statecharts, and UML, have been utilized to represent the static and dynamic aspects of control systems. Still, a conceptual framework is lacking that would integrate components and allow assembly of applications from shared processes. This paper addresses the issue by providing schemata to be used in the conceptual modeling of production control systems. A flow-based specification that has been utilized in software engineering is proposed as a good vehicle in this area. The resulting description achieves uniformity by using a single flow system to represent all production system elements. The methodology is demonstrated by recasting the diagrams of two specific research projects in unified flow models.