A height control valve for an air spring of an air-ride axle/suspension system of a heavy-duty vehicle includes a body. The valve body is pneumatically connected to an air reservoir of the vehicles an ail spring, and to atmosphere A control arm actuates the valve to direct air from the reservoir into the air spring, when air is to be added to the air spring When air is to be exhausted from the air spring, the valve, actuated by the control arm, directs air from the air spring to atmosphere The valve includes a throttle assembly that can regulate the rate of pneumatic flow from the air spring to atmosphere when the vehicle is loaded and the air spring is in an extended condition. A throttle assembly can also be used to regulate the rate of pneumatic flow from the air reservoir to the air spring.