The two arches are installed in the wash area 2m further apart than the longest vehicle which is to be washed.

The vehicle is driven slowly to the first arch. As it approaches it actuates the under floor proximity sensor and the detergent/water pump starts up. The vehicle is then sprayed by the detergent mixture from the oscillating jets in the arch as it drives slowly through. As it leaves the arch and the proximity sensor the pump switches off.

After a pause to allow the chemical to act on the dirt film, the lights change on the rinse arch, and indicate to the driver to proceed slowly through the second arch, which is also automatically controlled by proximity sensors, and the vehicle is thoroughly covered by rinsing water from the oscillating jets, which finally index towards the rear of the vehicle.