No matter whether imbalances on the entire compressor, broken support rings, loose mechanical connections of the crankcase to the foundation or even cracks in the foundation: properly installed vibration velocity and vibration acceleration sensors detect these vibrations immediately. Therefore, vibration sensors are a key element in compressor vibration monitoring. The vibration sensors are mounted on the crankcase in a horizontal orientation both once on the drive side and once on the non-drive side. For further monitoring of compressor vibrations, we also recommend mounting acceleration sensors on the crosshead. The exact position depends on the direction in which the crankshaft is turning. Here, it is important from where the force of the connecting rod acts on the crosshead slide. If the force is directed upwards, the sensor must be installed above the crosshead slide. If the force is directed downward, the sensor must be installed below the crosshead slide. In the next step, we will concentrate on the valves. Statistically, suction and discharge valves in particular are the most frequent cause of faults on reciprocating compressors. Therefore, to monitor the valves per cylinder, we recommend installing a vibration acceleration sensor midway between the valves on the head end side and on the crank end side near the suction nozzle. These sensors allow the online condition monitoring system to detect all vibrations and anomalies caused by the valves. These are, for example, error patterns such as sticking valves, valves that do not close, or broken valve plates.