It can be assumed that the system illustrated up to this point is the air brake system of a truck unit. If a trailer was coupled to this unit, the brakes of the trailer would have to be operated from the tractor.
The following diagram shows the piping of a unit, similar to the tandem axles of the truck unit. The trailer has a single axle equipped with brake chambers.
A ‘TEE’ has been installed in the application line between the foot valve and the truck axle system. A line has been connected from this tee to the trailer by a set of couplers called ‘GLAD HANDS’ (20).
This term refers to the coupling device used to connect the service and supply lines of the trailer to the truck or tractor. These couplers have a snap lock position, and a rubber seal prevents air from escaping.
Before connection is made, couplers should be clean and free of dirt and grit. When connecting the glad hands, start with the two seals together and the couplers at a 90 degree angle to each other. A quick snap downwards will join and lock the couplers. Vehicles equipped with ‘dead-end’ couplers should have these protection plates in use whenever the vehicle is used without a trailer. This will prevent water and dirt from entering the coupler and lines.
If the unit is not equipped with dead-end couplers, the glad hands of the service line can be locked to the glad hand of the supply line to keep water and dirt from entering the unused lines. The cleaner the air supply is kept, the less chance of brake problems.
Glad hands and lines should also be secured to prevent the line from bouncing off the vehicle. This could seriously damage the couplers.
