Unstable behavior accompanied by vibration of control movable elements, scratches in friction couples and loss of accuracy of controlled parameter often arise during development and operation process of pressure automatic control systems (ACS) of power plants. The task of providing required quality of ACS dynamic characteristics is complicated by high requirements on its accuracy in a wide range of consumption especially for the control systems with a pilot valve in a feedback channel. Previous researches aimed at the study of the main valve dynamics have suggested the possibility of nonlinear lift causing vibrations in ACS. The report presents the research results for the pilot valve influence in the feedback channel on ACS static and dynamic characteristics. Non-linear and linearized mathematical models of the feedback channel have been developed with its static and frequency characteristics determined on the basis of those models. Stability margins for ACS having the pilot valve in the feedback channel have been evaluated. Recommendations on parameter selection for the feedback channel to provide ACS stability and required accuracy of the controlled parameter have been proposed.
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