<p>A vent valve for an air braking system of a vehicle comprises an elastomeric valve member (11) held in relation to a vent (17) and having a restricted vent passageway. A continuous depending rib (23) is engageable with a valve seat (28) to close the vent passageway as increasing pressure acts on the head (21) of the valve member (11). The valve member (11) permits a fluid chamber to be connected to exhaust until pressure in the chamber reaches a predetermined level.</p>
