The paper presents strategies for control of parallel gravitational coal separation processes in dense media vessels and jigs. These strategies are designed to maximize the yield of the final product at the desired ash content. The principle of circuits operating in parallel at equal incremental ash contents has been discussed from the point of view of its practical application. In the case of an ideal separation process this principle can be reduced to the requirement of equal separation densities for parallel circuits; so far, however, it has not been applied in real industrial processes. The paper includes a discussion on the concept of a separation density and incremental ash for computer simulation of parallel processes and their control. Conclusions from this discussion, presented in the paper are not available in open literature especially as regards the optimal control of jigs operating in parallel: (a) the separation density (elementary ash) defined as the density of the feed fraction reporting in half to the concentrate and in half to refuse and incremental ash (density of the elementary mass of material recovered in a process in which the yield is increased by an infinitesimally small amount) can be used for real time control in dense media baths and in jigs; (b) the autogenous separation process in jigs makes it possible to determine the incremental ash as the ash content in the separation layer of the material as measured by the correlation between ash content and the density of the separation layer. The concept of a new control system which may be used in practice, based on a radiometric density meter with a properly collimated radiation beam and located at the level of the separation layer has been discussed. The radiometric density meters, applied to monitor the density of the separation layer in jigs on-line and to monitor the density of heavy media in dense media baths can be used effectively in real-time control systems optimizing the yield of product. (C) 2017 Elsevier B.V. All rights reserved.