###### Abstract
Studies on the effect of pressures on the polymer-graphite filler friction node have shown that as the pressures increase (0.5, 1 and 1.5 MPa), the value of the coefficient of friction and wear decreases [22]. However, some studies report that at relatively low pressures, the formation of a graphite protective layer is not possible [23; 24; 25]. Analyzing the effect of speed on the operation of the graphite-stainless steel friction node, it was shown that at higher speeds there was a decrease in the coefficient of friction, which was explained by the formation of a thicker sliding layer [18]. At the same time, the aforementioned studies showed that wear increased with increasing speed. The above studies are confirmed by the authors of the paper [26]. The operating environment is also of great importance for the operation of graphite. Graphite wear changes with an increase or decrease in relative humidity [21; 26; 27; 28; 29; 30]. In practice, tribological associations in which one of the materials is graphite are widely used in work in the aquatic environment [13; 31; 32]. Due to the adsorption of water, graphite has good lubricating properties [33]. The adsorbed water molecules on the main sliding planes reduce the adhesion between them and thus reduce the coefficient of friction during their sliding. On the other hand, studies indicate that a larger amount of water in the tribological combination contributes to too rapid wear of the tested surfaces [34]. Water leaches out the resulting wear particles, which are necessary for the formation of a sliding layer [35; 36]. According to [PERSON] and [PERSON] [34] and [PERSON] et al. [37], water hinders the formation of a transfer film on the graphite mating surface. It should be noted that in many sealing and bearing applications, the friction pairs are immersed in liquids, and the mechanism of low friction is still not very clear. [PERSON] et al. [38] studied the effect of graphite as a filler in polymer, which showed that the formation of a sliding layer was hindered when lubricated with water, resulting in lower friction and wear than with pure polymer. The presented research shows that there is no clear answer to the question of how water affects the resulting graphite sliding layer. There is a significant lack of research on the operation of the expanded graphite-stainless steel tribological pair in an aqueous environment. Meanwhile, this pair is widely used in popular piston valves. In this type of valves, a cylindrical piston made of stainless steel moves between graphite sealing rings. The sealed medium is usually water. Practical knowledge indicates that these valves have problems related to frictional resistance and accelerated wear of cooperating parts. To confirm this fact, literature was cited indicating the existence of practical problems related to the reliable operation of the analyzed pair of materials [39; 40; 41; 42; 43]. The sliding layer created during operation of the expanded graphite-steel combination affectsthe effectiveness of the friction process. Knowledge of the factors determining the properties of the sliding layer will make it possible to reduce friction resistance in the future through the proper design and selection of sliding pairs for given applications. The large number of factors affecting graphite transfer means that, it is difficult to determine which of the elementary friction phenomena dominates under specific conditions. The lack of scientific research on the mentioned tribological pair makes it difficult to properly select operating conditions. Therefore, the novelty in the presented research is primarily the set of materials used for the research. Moreover, due to the wide use of expanded graphite in industry, the research performed can be used not only in sealing technology, but also in many other industries. In construction, for example, expanded graphite is a key ingredient in fire-resistant building materials such as fire-resistant coatings, plasterboard, and insulation.