In air brake systems utilized in heavy commercial vehicles, what is the function of the 'Dual Foot Valve'?

1. To control the application of air to both the primary (rear) and secondary (front) brake circuits
2. To release air from the parking brake springs automatically when starting
3. To filter moisture and oil out of the compressed air reservoir
4. To regulate the air compressor cutout pressure between 100 and 125 psi