# Degradation of Hydraulic System due to Wear Particles or Medium Test Dust
## 5 Conclusions  
Two durability tests of hydraulic systems were performed, one with wear particles and the other with test dust. A comparison of volumetric efficiency and leakage measurements between the two tests was presented. 1. The hydraulic system tested with wear particles failed after 624 h of operation because the pump could not reach a pressure higher than 149 bar, which is insufficient for most hydraulic applications. The hydraulic system tested with test dust failed after 5.3 min of operation because the pump could not reach a pressure higher than 27 bar. 2. The cleanliness of the oil, including the wear particles, was 22/21/19, and the cleanliness of the oil, including the test dust, was 21/21/21. The test results show that the wear particles are less abrasive than the test dust, which can be attributed to the different operating times of the two hydraulic systems and the relatively equal concentration of contaminants (wear particles and test dust) in the hydraulic oil in each system. 3. The volumetric efficiency of the pump tested with wear particles decreased from 0.83 to 0.64 after 623 h of operation with a decrease in efficiency of 0.18. For the pump tested with test dust, the efficiency dropped from 0.87 to 0.11 within 5.3 min with a decrease of 0.76. 4. The volumetric efficiency of the valve tested with wear particles decreased from 0.998 to 0.990, corresponding to a 0.008 decrease in efficiency, and the valve tested with test dust had a decrease from 0.995 to 0.986, corresponding to a 0.009 decrease in efficiency. Compared to the drop in efficiency of the pump, the drop in efficiency of the valve is negligible. The difference is due to the fact that the aluminum housing of the gear pump is a softer material than the cast iron housing of the directional 4/3 valve and therefore wears out much faster. It is also recognized that the valve is tribologically less loaded than the gear pump. 5. The wear parameter represents the amount of leakage as a function of various pressures and indicates the amount of wear of a particular hydraulic component. For the  
Figure 19: Wear parameter \(K\) depending on the time operation of the pump. pump tested with wear particles, the value is 4 \(\times\) 10\({}^{-13}\) m\({}^{3}\) at the beginning of the test and varies from 7.5 \(\times\) 10\({}^{-13}\) to 1.1 \(\times\) 10\({}^{-12}\) m\({}^{3}\). 6. An important part for improving hydraulic systems operation is filtering. Extra care should be taken when new hydraulic is put into the existing operating system in order to avoid contamination, especially with hard particles, such as test dust (SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), etc.). New hydraulic fluid should be filtered and the cleanliness of the fluid should be measured, and if the cleanliness is equal or better than the one in the system, only then can fluid be put in the system. Particles cannot be entirely removed from the hydraulic fluid because new particles are also generated due to components wear during the operation of the machine, and furthermore, the smallest particles cannot be removed with the filter because the grid of the filter material is too rough. 7. A higher concentration (greater number) of particles causes a higher possibility that these particles will damage the sealing surfaces and wear surfaces. With an increase in wear, the gap between the sealing surfaces increases and therefore the leakage increases. Test dust has a higher hardness than wear particles; therefore, it will cause a larger amount of wear than wear particles in the same operation time. With further testing at different fluid cleanliness levels with wear particles and test dust, the acceleration factor can be determined. _Novelty and Aspects of the Study_  
1. Two experiments and the comparison between test dust and wear particles were presented for the first time. 2. The two identical test rigs and test procedures with identical hydraulic components showed that the test dust has a more damaging effect than the wear particles present in the real hydraulic system. 3.