The objective of this study was to determine the effects of milk flow on the vacuum characteristics in conventional and single tube systems by using the wet test method in the laboratory and under practical conditions. Different milking systems such as conventional clusters (1 conventional type, 2 types conventional systems with periodic air inlet), Automatic Milking Systems (AMS) (2 types) and MultiLactor (R)(1)) (single tube system with periodic air inlet) were tested using the wet test method in the laboratory and at different farms. Vacuum data at ten different points were recorded during the experiments and the calculations of the mean values and the vacuum fluctuations were made according to the guidelines from ISO 6690 Annex A. As a result from the study, it was found that the systems with periodic air inlet had stable vacuum conditions when receiving higher milk flow. The results also revealed that the introduction of a periodic air inlet for teat cups in single tube systems such as MultiLactor (R) can be useful. It was also further concluded that the development of other configurations for single tube systems as compared to the standard ones can be a useful approach.