Most proportional directional control valves currently in practical use are piston spool valves. A disadvantage of this type of design is the occurring leakage between spool and sleeve or housing. A second disadvantage is that the service life is limited by wear on the control edges. The ceramic flat slide valve is a promising concept, which allows to reduce the mentioned leakage and to increase service life. In contrast to piston spool valves, the main stage of the flat slide valve consists of three plates. Two control plates and a movable slide plate, which is located in between. An external force is applied to the plates by the so-called pressure compensation, which presses the plates together and thus counteracts a gap expansion and thereby an effective reduction of occurring leakage is accomplished. The plate-by-plate design of the main stage allows the use of technical ceramics, which are more resistance to abrasive wear and can thereby extend the service life of valves. A challenge in the realization of the flat slide valve is the design of the pressure compensation. If the force applied by the pressure compensation is not sufficient to prevent a gap formation between the plates, an increased leakage will occur, which results in a reduction of efficiency. In case the applied force is too high due to the pressure compensation, high frictional forces between the plates occur and an adjustment of the slide plate position through an actuator is no longer possible. Therefore, the design of the pressure compensation is essential for the success of the concept. This contribution presents the results of testing a main stage, which consists out of two metallic control plates and a slide plate made of special brass. The main stage is designed in such a way that a 4/3-way directional control valve with a proportional characteristic can be realized, as it is also achieved by valves currently available on the market. Therefore, in addition to the pressure forces, further influences on the resulting force of the pressure compensation were determined and their influence was estimated based on test bench results. With a program written in MATLAB, the forces prevailing in the valve can be calculated time-efficiently for different geometries and are validated with test bench trials.