Malfunctions in hydraulic systems can be tied to contaminations being the most prominentfactor for them to occur. Contaminations in hydraulic systems can lead to shorter lifetime forhydraulic components, oil leaks that can pollute surrounding environments and also increasethe risk of accidents happening if the systems do not work as intended. Cleanliness in hydraulicsystems is therefore an important success factor for organisations producing hydraulicallyoperated products, because if neglected it can negatively affect economic, environmental andsocial sustainability factors.This study was conducted at a production facility where market-leading hydraulically operatedproducts are manufactured. The purpose of the study was to investigate how activities such ashandling, storage, and assembly of hydraulic components in a production facility can affect therisk of contaminations being built into hydraulic systems. Experiments and observations wereused as the main data collection methods to collect different types of data and also to strengthenthe overall results obtained from the two different methods.The results showed that the assembly stage of hydraulic systems is where the most risks lie withpersonnel and production facility and equipment used being the most influential risk factors.This was also coupled to that all assembly activities, including the hydraulics, were performedin the same area for the product. It also showed that sedimented particles from the ambientenvironment at the assembly stage could mostly not be linked to particles found in analysedhydraulic oil samples taken from assembled products. The majority of sedimented particlesfound was also deemed to pose little risk of damaging the hydraulic systems.This study contributed to research by providing a real-world example of how internal processesin a production facility can affect the risk of particle contaminations being built into hydraulicsystems.