## 6 Discussion and Conclusions  
An effective seal built into the hydraulic component ensures reliable, long-lasting, and energy-saving operation, not only of the component itself, but of the entire hydraulic system. That is why seal designers and manufacturers are constantly looking for ever new, better seal materials that would cover most of the possible operating conditions and also be compatible with different types of fluids used. A new challenge arises when either new seal materials or modified formulations of a known type of fluid (e.g., a new additive package) appear, and especially when a completely new type of hydraulic fluid appears. Such a challenge arose in the case of using a completely new type of hydraulic fluids, ionic hydraulic fluids. The decision on the most suitable sealing material in the case of using ionic hydraulic fluid followed the requirement that the material must also be suitable for mineral hydraulic oils, which are the most common medium in today's hydraulic systems. In this case, the mineral oil could be replaced with an ionic hydraulic fluid in the existing hydraulic system. At the forefront of the assessment were materials suitable for both static and dynamic seals--the sealing of moving parts (e.g., pistons and piston rings). The material-compatibility test was carried out in accordance with the Standard ASTM D1414, which specifies the method and conditions of testing in more detail. Eight of the most commonly used seal materials, FPM/FKM, POM, HPU Franc, NBR, HPU Usi, EPDM, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No.** & **Material** & **Code** & **Change (70 h) [\%]** & **Change (250 h) [\%]** & **Change (500 h) [\%]** \\ \hline \multirow{4}{*}{8} & \multirow{4}{*}{PTFE I} & \multirow{4}{*}{8-1} & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 \\  & & & Shrinkage: 0 & Shrinkage: 0 & Shrinkage: 0 \\  & & & Hardness: \(-2\) & Hardness: \(-2\) & Hardness: \(-1\) \\  & & & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 \\  & & 8-2 & Shrinkage: 0 & Shrinkage: 0 & Shrinkage: 0 \\  & & & Hardness: \(-2\) & Hardness: \(-2\) & Hardness: \(-3\) \\  & & & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 \\  & & 8-3 & Shrinkage: 0 & Shrinkage: 0 & Shrinkage: 0 \\  & & & Hardness: \(-2\) & Hardness: \(-2\) & Hardness: \(-2\) \\  & & & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 \\  & & 8-4 & Shrinkage: 0 & Shrinkage: 0 & Shrinkage: 0 \\  & & & Hardness: \(-2\) & Hardness: \(-2\) & Hardness: \(-1\) \\  & & & Volume swell: 0 & Volume swell: 0 & Volume swell: 0 \\  & & 8-5 & Shrinkage: 0 & Shrinkage: 0 & Shrinkage: 0 \\  & & & Hardness: \(-1\) & Hardness: \(-1\) & Hardness: \(-1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Thermal testing compatibility method—PTFE I summary of results. MVQ and PTFE, were tested in combination with four ionic liquids, and, for comparison, with conventional hydraulic mineral oil. The emphasis of the test was on changes in basic parameters, such as the swelling and shrinking of the seal volume, as well as changes in the hardness of the seal. These parameters are primarily of decisive importance for a reliable seal. Based on the results of material-compatibility testing with ionic hydraulic fluids, the following materials would be considered for seals: FPM/FKM (1), POM (2), NBR (4), EPDM (6) and PTFE I (8). MVQ (7) caused excessive material shrinkage, which caused the cylinder to leak due to inefficient sealing, and the seals from both HPU materials collapsed in contact with the ionic liquids. If we rely only on the numerical values of the performed tests, the most suitable material would definitely be PTFE, both for the use of mineral hydraulic oils, as well as the considered ionic hydraulic fluids. The test results additionally revealed that even the tested HLP quality oil has certain weaknesses, especially in terms of the shrinking or swelling of the seal.