When a car is on the road, the dirtiest and hardest parts to clean are the lower sides — the skirts — and the wheels. To get these parts clean, besides the basic wetting, high-pressure spray and detergent, you need the friction of a brush, and with real force, before you get a worthwhile result.
That calls for a part of the tunnel car wash machine that looks unremarkable, yet matters a great deal: the rocker panel brush.
The rocker panel brush is designed to clean the sides of the car and the area around the wheels. It takes up little space, and it rotates against the direction of travel. As it washes, the brush, working with water and detergent, cleans the sides of the car through friction and agitation.
The lubricating film made of wash water and detergent both lubricates and wraps the dirt, so that the rocker panel brush can protect the paint as much as possible while cleaning the sides.
Two mounting styles
Tunnel car wash rocker panel brushes come in two main designs: top-mounted and bottom-mounted.
The top-mounted rocker panel brush is simply designed, with an extremely low failure rate. Its only weakness is that if a car’s mirrors are not folded in, the top-mounted drive motor risks knocking a mirror.
In the bottom-mounted design, the centre of gravity sits at the bottom of the brush, and because the force arm is short, the car’s push-back feeds back quickly to the cylinder that controls the brush arm. That gives a more stable cleaning force, and it is safer to use.
Variants in height
Most Chinese makers build rocker panel brushes about 750 mm tall, but in practice they design different heights for different needs, to get the cleaning result the customer wants.
For the very bottom of the car and the wheels, the rocker panel brush is only about 500 mm tall. For the area below the mirrors, it is about 900 mm tall. The American company PECO and the German company HOLZ have both brought out rocker panel brushes around 1.9 metres tall, to clean large vehicles better.
The cleaning effect of the rocker panel brush is obvious — but the stronger cleaning force also brings more vibration. That vibration affects the life of the gear motors, cylinders, bearings and other parts. To deal with it, most makers build in shock-resistant design, to extend component life and make the machine more stable.
So we know that the dirtiest parts of the car are cleaned by the rocker panel brush. That is also why, in an earlier article, we advised customers choosing a machine to pick a longer tunnel rather than a short one. A short tunnel is the first to lose rocker panel brush space — and two fewer rocker panel brushes means much lower cleanliness.
So when I talk to customers, I usually advise them not to stick to the popular 9-brush tunnel design, but to add another pair of rocker panel brushes if they can — even on a machine that is already installed. At a low cost, and without adding later maintenance, you get much higher cleanliness.