## 5 Testing Scope and Results  
The form of the seal to be tested is a torus of a square cross-section, and it deviates somewhat in that respect from the prescribed shape in the Standard that provides for the use of the O-ring. The dimensions are near to the prescribed O-ring, and only the cross-section is square. In this way, we get closer to the shape of the seals used in today's hydraulic systems--lip seals and X seals, suitable for higher pressures, which are in the role of dynamic seals (unlike O-rings, which are more intended for sealing fixed parts of components (static seals)). The test temperature was set to 90 \({}^{\circ}\)C, as this is the temperature that normally occurs in hydraulic components during the operation of the device. Due to the test rationalisation in view of test extension and cost management, the following test-duration times were selected, according to the recommendations within Standard ASTM D1414: 70 h, 250 h and 500 h.  
Volume swell and shrinkage, as two very important parameters when testing the compatibility of specified seal materials with specified fluids, were obtained indirectly by measuring the change in mass. The change in volume in respect of volume swell was calculated according to Equation (1), and in respect of volume shrinkage according to Equation (2). The change in hardness was determined based on Equation (3). The following shows a summary and the extent of individual measurements for each combination of seal material and fluid:  
Measurements of masses:  
* \(M_{1}\) = the initial mass of the specimen in air [g];
* \(M_{2}\) = the initial mass of the specimen in water [g];
* \(M_{3}\) = the mass of the specimen in air after immersion [g];
* \(M_{4}\) = the mass of the specimen in water after immersion [g];
* \(M_{5}\) = the mass of the specimen in air after drying out [g];
* \(M_{6}\) = the mass of the specimen in water after drying out [g]. Measurements of hardness:  
* \(H_{1}\) = hardness at position 1;
* \(H_{2}\) = hardness at position 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Seal Material** & **Code** & **Sample** & **Seal Material** & **Code** \\ \hline
1 & FPM/FKM & 1-1 & 5 & HPU USI & 5-1 \\  & & 1-2 & & & 5-2 \\  & & 1-3 & & & 5-3 \\  & & 1-4 & & & 5-4 \\  & & 1-5 & & & 5-5 \\ \hline
2 & POM & 2-1 & 6 & EPDM & 6-1 \\  & & 2-2 & & & 6-2 \\  & & 2-3 & & & 6-3 \\  & & 2-4 & & & 6-4 \\  & & 2-5 & & & 6-5 \\ \hline
3 & HPU FRANC & 3-1 & 7 & MVQ & 7-1 \\  & & 3-2 & & & 7-2 \\  & & 3-3 & & & 7-3 \\  & & 3-4 & & & 7-4 \\  & & 3-5 & & & 7-5 \\  & & 3-0 & & & 7-0 \\ \hline
4 & NBR & 4-1 & 8 & PTFE I & 8-1 \\  & & 4-2 & & & 8-2 \\  & & 4-3 & & & 8-3 \\  & & 4-4 & & & 8-4 \\  & & 4-5 & & & 8-5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Seal material and fluid type test combination code. All the parameters mentioned above were measured for the following test duration times:  
* \(t_{0}=\) before the testing;
* \(t_{70}=\) after 70 h of thermal loading;
* \(t_{250}=\) after 250 h of thermal loading;
* \(t_{500}=\) after 500 h of thermal loading. Fresh fluid was used to perform the tests, whereby, after 70 h of thermal loading, the same fluid was used for a further testing phase (up to a total of 250 h, and up to a total of 500 h). The results of seal-testing at 90 \({}^{\circ}\)C in durations of 70, 250 and 500 h, are summarised in Tables 5-10. The test results are shown for those test specimens that have with