## 4 Experimental Test-Bed  
### Reciprocating Compressor  
A reciprocating compressor model EGB-250 driven by a 5.5 hp induction motor was used in the experiments. Mechanical rotatory motion at 3470 rpm is transmitted to the compression chamber using two V-belts. The compressor has two stages, both with two valves: one for inlet and one for discharge. The second stage enables the transfer of the gas to the tank. The compressor used in this research is shown in Figure 8. The main elements studied in this research are the roller bearings and the valves. Tapered roller bearings are used due to their ability to withstand high combined loads. They are mounted on 'X' (face to face) one on each side of the crankshaft. An schematic view of the tapered roller bearing showing each of their parts is presented in Figure 9. The type of valve used is presented in Figure 10a and the assembly form in Figure 10b. This valve works as an intake valve or as a discharge valve. Its operation mode depends only on the orientation in which it is assembled.  
In this research, fault combinations in bearings and valves were considered. Faults were introduced in the roller bearing B1 which is located closer to the fan pulley and in the discharge valve located in the second stage. Three type of faults are included for the roller bearing: (a) inner race crack, (b) roller element crack and (c) outer race crack. The cracks are created through the Electrical Discharge Machining (EDM) technique. The inner and outer race cracks are aligned with the rotation axis and covers all the raceway. They have a width of 2.0 mm and a depth of 1.0 mm. The roller element crack is also aligned with the rotation axis. It has a width of 1.0 mm and a depth of 0.5 mm.  
Concerning the valves, four types of faults were included: (1) valve seat wear, (2) corrosion of the valve plate, (3) fracture of the valve plate and (4) broken spring. The different conditions of the valves are shown in Figure 11. The valve seat wear is attained by machining on the face of the valve seat and reducing its depth 1.44 mm. The corrosion of the valve plate is simulated by performing a through hole with a diameter of 2.5 mm. The fracture of the valve plate is performed by cutting the plate, the diameter of the thread is 1.6 mm. The break of the spring is obtained by cutting the spring with a thread of 1.6 mm of diameter.  
In total, 13 different multi-fault classes were considered. P1 denotes the healthy class and classes P2-P13 correspond to 12 combinations of one fault type in the roller bearings with each one of the four possible faults in the valve. The fault combinations are described on Table 1. The internal and external parts of the reciprocating compressor used for dataset acquisition are shown in Figure 12.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Label** & **Valve, 2S–DV** & **Bearings, B1** \\ \hline P1 & Healthy & Healthy \\ \hline P2 & Valve seat wear & Inner race crack \\ \hline P3 & Corrosion of valve plate & Inner race crack \\ \hline P4 & Fracture of valve plate & Inner race crack \\ \hline P5 & Broken Spring & Inner race crack \\ \hline P6 & Valve seat wear & Roller element crack \\ \hline P7 & Corrosion of valve plate & Roller element crack \\ \hline P8 & Fracture of valve plate & Roller element crack \\ \hline P9 & Broken Spring & Roller element crack \\ \hline P10 & Valve seat wear & Outer race crack \\ \hline P11 & Corrosion of valve plate & Outer race crack \\ \hline P12 & Fracture of valve plate & Outer race crack \\ \hline P13 & Broken Spring & Outer race crack \\ \hline \hline \end{tabular}
\end{table}
Table 1: Multi-faults in valve and roller bearings.  
Figure 8: Compressor model EGB-250 available at the Universidad Politécnica Salesiana.  
Figure 9: Parts of the tapered roller bearing in the reciprocating compressor.  
Figure 11: Different types of valve conditions.  
Figure 12: EBG250 compressor: (**a**) external parts; (**b**) An internal view of the compressor.  
Figure 10: (**a**) Parts of the valve; (**b**) scheme of the assembly form.