A pneumatic RC circuit is a fundamental and important element in pneumatic control systems. This paper deals with the frequency response of a RC circuit taking the non-linear flow rate characteristics and the heat transfer in the chamber into account. Though this circuit is widely used in pneumatic systems it is not easy to calculate the dynamics of the circuit. This is caused by the non-linear flow rate characteristics of the restriction and uncertainty of state change of the air in the chamber. In this research, dimensionless non-linearity parameter composed of the amplitude of an input pressure signal and non-linearity coefficient of the flow rate characteristics has deen obtained theoretically.
Time has been m ade dimensionless by introducing pressure time constant. It is shown that the ratio of pressure time constant and thermal time constant is very important parameter in the circuit.
By the method of describing function, the dynamics of pneumatic RC circuit have been made clear. For the circuit designing convenience, normalized Bode diagrams with two parameter are shown in the figures.
In the experiments, frequency response tests of RC circuit have been conducted (0.5-7Hz)in different amplitude condition of input signals. Satisfactory agreements are obtained between theory and experiments.

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To study the incompressible axisymmetrical laminar swirl flow in a short vortex chamber with exhaust pipe, which characterizes the flow in a vortex diode, the full Navier-Stokes equations with the primitive variables are numerically integrated. For the singularity existing at the axis in cylindrical coordinates system, a novel technique is adopted. The generated flow pattern well agree with the visualized pattern. So, effects of swirl intensity and Reynolds number on the velocity and pressure field, which are difficult to be estimated by experiments, are discussed.
The general results obtained by this calculation are summarized:
(a) As the swirl intensity increases, the pressure field except for the core tends to take the gradient in radial direction only.
(b) Due to this gradient, the radial velocity profiles in the axial direction show unique profiles in the chamber. Near the walls where the boundary layers of tangential flow exist, the radial flow is accelerated towards the axis, while it is decelerated far from the walls and tends to become zero or even reverse for high swirl.
(c) Therefore, the flow to e xhaust pipe is restricted near the walls and flow resistance results as the swirl intensity increases.

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