## 2 Test Methodology and Measurement Technique  
The authors tested valve stems that were 12 mm in diameter (see Figure 1c) and made from 317 Ti austenitic steel with the properties and chemical composition (EN 10088:2007 compliant) listed in Tables 1 and 2, respectively. This steel is a highly corrosion-resistant material used in valve stems and glands in various types of valves, including control valves (Figure 1a), applied in the flow control of liquids, vapours, and gases. During operation of this valve, the stem (1) slides within the sealing part (3), the length of which is \(L\) (Figure 1b). Sealing of the joint between friction elements (1) and (3) is ensured by tightening the gland (2) (with a pressure of \(F\), Figure 1b). With the passing of the operating time, the wear of the mating surfaces increases until a leak occurs. The faster the rate of wear, the higher the frequency of gland (2) retightening and seal replacement, and the shorter the service life of the valve. The tested seal was a pack assembly formed from stranded, square-section graphite cords woven from yarn made from expanded PTFE with incorporated graphite at a maximum share of 50% and lubricants (i.e., the seal standardly applied in industrial valves) and a valve stem. The study compared the properties of standard stems (removed from commercially available valves) with those additionally finished by diamond burnishing. It was performed on a universal turning lathe using a PCD spherical-tipped burnishing tool. Based on the recommendations given in refs. [31; 35], burnishing parameters were selected to ensure surface roughness Sa < 0.2 \(\upmu\)m, similar to that of standard stems. This surface roughness was achieved with the following processing parameters: workpiece rotational speed of 630 rpm, feed rate of 0.03 mm/r, burnishing force of 100 N, burnishing tool tip radius of 3 mm. Surface condition tests were carried out in the zone of cooperation between the stem and the gland packet (in zone 3 Figure 1c). The surface texture was tested using a Taly Scan 150 profilometer with Taly Map 2.0.15 surface analysis software, by the contact gauging method using a 5 \(\upmu\)m profilometer tip, and the measurement results were processed in the form of contour line maps, surface photographs, 3D surface views, curves of material shares and load-bearing capacities, distributions of localised elevations, auto-correlation functions, and power spectrum density distributions. The surface layer stresses were tested using an X-ray diffractometer (X3000 Stresstech 0Y) by applying the standard method of \(sin^{2}\psi\)[36], whereas the stress levels were calculated by applying a method of fitting with parabolic background subtraction. Axial and circumferential stress values were measured in four locations of each valve stem, and the results were expressed as the mean measurement \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Fe** & **Cr** & **Ni** & **Mo** & **Ti** & **Mn** & **Cu** & **Si** & **V** & **Co** & **C** \\ \hline
66.86 & 17.13 & 10.58 & 1.903 & 0.054 & 2.016 & 0.492 & 0.459 & 0.096 & 0.077 & 0.021 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition (in mass %) of 317 Ti steel. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Hardness, HB** & **Yield Limit,** & **Tensile Strength,** & **Elongation A\({}_{5}\), [\%]** \\ \hline
217 & 200 & 600 & 40 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Some mechanical properties of 317 Ti steel. values. Microhardness measurements were performed in accordance with ISO 6507:2007 using the Vickers method on the Sinowon HVS-1000 device. The indenter was loaded with a force of 1 N for 15 s. The durability of the valve stems were tested by simulating normal operating conditions of a control valve with a standard gland, a flow rate of \(K\)\(\approx\) 0.63 m\({}^{3}\)/h, and a valve stem displacement of h = 20 mm. These tests were performed on a test stand (Figure 3) based on a milling machine, which actuated the valve stem in a reciprocating motion.