An air control valve comprising: a valve plate for controlling airflow through a main passage; a control passage for supplying control air to the control valve, the control passage including an inlet and an outlet transverse to the inlet, the inlet and outlet opening into a chamber that receives a filter assembly, the filter assembly disposed within the control passage to block particles and other contaminants; characterised in that the filter assembly comprises:; an outer housing supported at least partially within the control passage an inlet tube disposed along an axis common with the inlet of the control passage and including a seal for preventing contaminants from entering the inlet, the inlet tube extending from the inlet into the outer housing, the inlet tube including a bottom shoulder that fits over the opening to the inlet, the shoulder including the seal, the seal adapted to seal against an inner surface of the chamber to separate airflow through the inlet from airflow exiting through the outlet; a filter housing disposed about the inlet tube, supported within the outer housing and spaced apart from an inner surface of the outer housing to define an annular passage in communication with the outlet and sealed against an outer surface of the inlet tube, the filter housing including a filter medium for trapping contaminants within the filter housing; and an outlet passage in communication with the outlet, the outlet passage having a first portion defined between the filter housing and the outer housing, and a second portion defined between the inlet tube and the inner surface of the chamber. a valve plate for controlling airflow through a main passage; a control passage for supplying control air to the control valve, the control passage including an inlet and an outlet transverse to the inlet, the inlet and outlet opening into a chamber that receives a filter assembly, the filter assembly disposed within the control passage to block particles and other contaminants; characterised in that the filter assembly comprises:; an outer housing supported at least partially within the control passage an inlet tube disposed along an axis common with the inlet of the control passage and including a seal for preventing contaminants from entering the inlet, the inlet tube extending from the inlet into the outer housing, the inlet tube including a bottom shoulder that fits over the opening to the inlet, the shoulder including the seal, the seal adapted to seal against an inner surface of the chamber to separate airflow through the inlet from airflow exiting through the outlet; a filter housing disposed about the inlet tube, supported within the outer housing and spaced apart from an inner surface of the outer housing to define an annular passage in communication with the outlet and sealed against an outer surface of the inlet tube, the filter housing including a filter medium for trapping contaminants within the filter housing; and an outlet passage in communication with the outlet, the outlet passage having a first portion defined between the filter housing and the outer housing, and a second portion defined between the inlet tube and the inner surface of the chamber.; an outer housing supported at least partially within the control passage an inlet tube disposed along an axis common with the inlet of the control passage and including a seal for preventing contaminants from entering the inlet, the inlet tube extending from the inlet into the outer housing, the inlet tube including a bottom shoulder that fits over the opening to the inlet, the shoulder including the seal, the seal adapted to seal against an inner surface of the chamber to separate airflow through the inlet from airflow exiting through the outlet; a filter housing disposed about the inlet tube, supported within the outer housing and spaced apart from an inner surface of the outer housing to define an annular passage in communication with the outlet and sealed against an outer surface of the inlet tube, the filter housing including a filter medium for trapping contaminants within the filter housing; and an outlet passage in communication with the outlet, the outlet passage having a first portion defined between the filter housing and the outer housing, and a second portion defined between the inlet tube and the inner surface of the chamber.