edit: Solved. Thanks guys
In: Engineering
Trucker here:
That noise you hear could be a few things. All relating to the brakes. The trucks brake system relies on pneumatic (air) pressure rather than hydrolic (fluid) pressure like in your normal car.
When the driver applies the brakes air pressure is applied to the system, the air expands inside the brake chamber which turns an S-cam which moves a rod that pushes the brake pads to make contact with the disk or drumb (usually drumb) and the truck stops. When the driver releases the brakes you can hear a hiss as the air pressure is released.
The hiss you hear that most people associate with trucks is when the driver sets their parking brakes. They pull out a valve in the cab that in turn sends a rush of air pressure from the air tanks to the brakes. And that holds in place as long as the trucks compressor is running. After a long while, the air may bleed off and once it reaches a predetermined pressure (20psi) the emergency spring brakes are automatically engaged. That truck ain’t going anywhere.
The last hiss ill talk about is a safety check valve on the air tanks. You’ll hear this hiss after pressure in the tank builds to 125psi. At that point the valve opens and quickly releases some pressure and a satisfying hiss and closes again once the tank is back below 125psi. This whole thing happens in less than a second.
Its a complicated system, but when dealing with heavier loads, air brakes are the bees knees.
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