This paper aims to present the results of the testing a single-stage electrically actuated throttle valve, in which a piezoelectric stack was used for adjustment of the flow section area of the throttle aperture. The valve prototype was built based on a proprietary design, using the components of a standard manufactured overflow valve. The complete valve was designed on the basis of the results of simulation tests performed on a mathematical model. The constitutive equations presented herein, describing all critical phenomena and influences present in the component, were applied for the modelling of the piezoelectric stack. Laboratory tests were carried out to establish the valve’s characteristics, describing its usefulness for control of flow intensity. LabView software was used for measuring the data gathered. The test results, after conversion, were developed using the Matlab/Simuling software package. This paper presents the most notable results of the tests of a normally open valve equipped with a high-voltage piezoelectric stack. Based on the results obtained, the functional correlation between the volumetric flow rate, pressure drop in the throttling aperture and control signal input to the piezoelectric stack were determined. Due to the comprehensive approach involved, the material presented herein may be prove useful to designers of valves and hydraulic units using piezoelectric stacks for controlling their operating units.