A diaphragm valve for shutting off milk flow through a claw (13) of a vacuum driven milking machine has, in a preferred embodiment, a lever (5) linked (6), outside the milk flow, to the diaphragm (4), thereby avoiding any bushings which are prone to leakage. The lever (5) can be swung manually to a position holding the diaphragm away from its seat thereby permitting milk flow. In the automatically closing embodiments, the lever is swung in this case against the bias of a spring (7) and is retained in this open position if the suction force acting on the diaphragm (4) and the link (6) is sufficient to overcome the bias of the spring (7), which will be the case when there is normal milk flow through the valve. Upon detachment of the tea from the animal's teat only air will flow through the valve, thereby reducing the suction force exerted on the link (6) and allowing the spring (7) to swing the lever away from its valve-open position to a diaphragm-release position where the air suction will pull the diaphragm to seal against its seat and cut off potentially contaminating air-flow through the system. This inventive principle can, for example, also be embodied in a rotary knob (21) linked to the diaphragm (4) and interacting with indined grooves (23) and springs (24) biasing the knob to advance to a diaphragm-release position when there is insufficient milk flow. Such a system is particularly useful in sheep or goat dairies where there is frequent attachment and detachment of the clusters.
