Continuous flow vessel system of pilot scale was constructed and provided with computer control for programmed variation of flow rate and volume of liquid. Radioisotope and chemical tracer pulses were used for determination of residence time distributions (RTDs). It has been shown earlier that the RTDs of such vessels are invariable under variations of flow or volume and flow, if they are presented as functions of an appropriate, integrated variable, and if the process flow pattern is not affected by the stated variations. The experimental responses of the individual vessels tested were therefore converted to RTD functions of such a variable. It turned out that they converged close to each other within a wide range of steady states and dynamic variations of flow and volume. This is considered to indicate the expediency of the integrated variable used and invariance of the vessel flow pattern within the same range. Additional tests with continuous, randomly variable tracer feed support these conclusions.