The effect of machine milking on udder health has been recognized for the past 100 years. Among different milking systems, a new quarter individual milking system called the Multilactor(R) (MULTI) has been developed to eliminate some detrimental effects of conventional milking systems (CON) and conventional systems with periodic air ingress (BIO) on udder health. The objective of this study was to determine the effects of milk flow on average liner vacuum during the b and d phases of pulsation in all systems by using a wet-test method defined in ISO 6690 (2007). Measurements were conducted in three different milking parlours where CON, BIO and MULTI were installed separately. It was found that, at an average flow rate of 4.8 l min(-1), the average vacuum in the liner during the b-phase was 35.0 kPa in CON, 32.6 kPa in BIO and 31.1 kPa in the MULTI system, compliant with the desired average vacuum in the liner of 32-42 kPa mentioned in ISO 5707 (2007). The average liner vacuum values during the d-phase differs from one system to another and these values were calculated to be 34.2 kPa, 12.3 kPa and 14.8 kPa for CON, MULTI and BIO, respectively. The reason why CON differs as compared to MULTI and BIO can be attributed to the fact that both, MULTI and BIO use the BioMilker system that allows periodic air ingress under the teat.