A flow metering device (1) for milking plants, comprising: a cup body (13) a cover (15) a control membrane (17) transversely arranged in the cup body between the cover and the bottom (19) of the cup body a first hermetically sealed chamber (21) defined between the cover and the membrane and having an opening (23) that can be associated with the vacuum circuit of the milking plant a second hermetically sealed chamber (25) defined in the space enclosed between the membrane (17) and the bottom (19) of the cup body (13) and having a milk inlet opening (27) and a milk discharge opening (29) a valve (31) associated with the milk discharge opening (29) and equipped with a shutter (33) and a seat (35) for said shutter an actuating assembly (37) for the shutter, including a connecting member (39) associated with the membrane and the shutter wherein a third hermetically sealed chamber (41) is defined between the membrane (17) and the second chamber (25), which third chamber communicates with the external environment and is separated from the first chamber by the control membrane (17), so that the pressure inside the third chamber (41) is the same as that outside the device, whatever the pressure in the first and second chambers may be.
