An air dryer (24) for a vehicle air braking system comprises a container (26) having first, second and third compartments (34, 50, 48), the first compartment (34, 34a) having an upstream inlet (28) for connection to a source of air under pressure, a vent (44) for connection to the exterior of the container (26) and a desiccant therein, the second compartment (50) comprising a chamber having an inlet (36, 36a) downstream of the first compartment (34, 34a) with non-return means (38, 38a) therein, a fluid connection (40, 40a) to the first compartment (34, 34a) having a restrictor (42, 42a) therein, and the third compartment (48) comprising a chamber having an inlet (54) downstream of the second compartment with non-return means (52) therein and an outlet (30) for connection to a fluid pressure using device.