Abstract: An air dryer for a vehicle air braking system comprises a container having first, second and third compartments, the first compartment having an upstream inlet for connection to a source of air under pressure, a vent for connection to the exterior of the container and a desiccant therein, the second compartment including a chamber having an inlet downstream of the first compartment with a non-return valve therein, a fluid connection to the first compartment having a restrictor therein, and the third compartment including a chamber having an inlet downstream of the second compartment with a non-return valve therein and an outlet for connection to a fluid pressure using device.

Abstract: A drain valve of an air braking system for vehicles has a drainage piston, a main sump and auxiliary sump. Moisture passes from the main sump to the auxiliary sump in response to pressure at a signal port which closes off air supply through ports. A reduction in pressure at the signal port causes the ports to be reconnected and allows moisture to be expelled through the drainage outlet.

Abstract: Air braking system of vehicles usually have a piston compressor (C) and a desiccant (D) for drying the compressor output air. The desiccant is periodically regenerated by downstream air from e.g. a reservoir (R). When a compressor is brought on load, the initial charge of air may be oil laden. The invention provides a delay mechanism to permit such initial charge of air to pass directly to exhaust.