The Department of Transportation (DOT) mandates safety for persons and goods that travel roads, waterways, and the skies. DOT compliance follows the federal regulation standards which are intended to reduce potential risks in transportation.
Understandably, a large focus of the DOT are commercial motor vehicles such as trucks used for transporting goods and buses for transporting people, where weight limits and other guidelines are specified to keep our roads and highways safe. The DOT standards for a vehicle’s total weight are set by individual states, with the federal government having the final authority on interstates. Highways and roads in the U.S. are regulated in a number of ways, one of them is weight limits for trucks, semis, and buses. Where regulations are set at the state levels one state may allow higher weight limits than another. That’s why we often see weigh stations along interstates as we pass from one state into another. For instance, the maximum gross vehicle weight for a tractor trailer in Michigan is 164,000 lbs., while its neighboring states of Indiana and Ohio have a maximum limit of 80,000 lbs. And many states such as Texas, California, Alabama, and others have no individual weight restrictions. Yet the federal vehicle limit for an 18 wheel tractor-trailer is 80,000 lbs. gross vehicle weight, which takes president over interstate highways in all states. Restrictions can also be placed on single axil weight. For instance, a typical 18 wheeler has five axles, three on the tractor and two on the trailer. Federal restrictions are a maximum of 20,000 lbs. on a single axle (though the front axles on the tractor are lower), and 34,000 lbs. on a tandem axle group. So why is Michigan able to exceed federal regulations? It’s due to a "grandfather clause" in the federal law. However, there is a specific restriction that makes up for this —a truck carrying 164,000 lbs. in the state of Michigan must have 11 axles, and each one of those axles cannot carry over 13,000 lbs. However, by those standards a 164,000 pound truck cannot pass from Michigan into Ohio no matter how many axles it has. And to confuse issues even more, consider Ohio as an example. Though Ohio’s max weight is 80,000 lbs., according to the Ohio Turnpike Commission the maximum gross weight allowed on that section of interstate without a special hauling permit is 90,000 lbs. as long as the axle weights are legal.
Of course, all of these guidelines are in place for safety. A truck that is carrying too much weight can be it difficult to brake and maneuver, posing a danger when trying to slow down, safely navigate going down a hill, or in bad weather.
With regard to transporting people on a bus, if carrying more than eight people for compensation (pay to ride), then the bus must comply with DOT regulations. The same goes if transporting fifteen people without compensation, such as a school bus. Therefore, trucks, trailers and busses must be up to DOT standards. Which includes ensuring that air brakes, and the tubes and fittings used to operate them, meet DOT specifications requiring air brake connections using nylon tubing that has an inner tube support.
DOT Approved Air Brake Fittings
Air brakes are vital in the proper operation of a large vehicle’s ability to safely slowdown and stop.
If the brakes fail, there is usually injury to passengers and the driver, sometimes even resulting in a fatality, and of course cargo. Eighteen wheel tractor trailers typically require 60 to 100 air brake fittings to conform with regulations and allow for proper stops. Air brakes need to have a high heat threshold to deal with high-powered engines. They also need components that can withstand vibration resistance, have an effective tensile strength and corrosion resistance to ensure they have a long service life to withstand the demands the road.
Brass is the standard metal for air brake push-to-connect fittings. Brass fittings for air brake systems are specifically designed to connect the tubes in the pneumatic braking system of commercial vehicles and trailers. After a tube is connected to the fitting, the tube can be easily removed while remaining mounted in the threaded port of the air brake system. And some air brake systems mix brass with a polymer to create a lower cost lighter weight fitting. However, brass fittings are preferred for strength and corrosion resistance. Plus, air brake systems with brass push-to-connect fittings are easier to assemble, have a more reliable operation and are easier to maintain than brass compression fittings. The compact design of robust brass push-to-connect fittings is typically the first choice for use on most commercial vehicles and trailers.
DOT brass fittings are most frequently used in air brake systems yet can also be found in applications as varying as fifth wheels, windows, door locks, wipers, air operated seats, air horns, mirrors, operating gauges, gear shifts and heater controls.
Reusable air brake hose fittings must meet DOT specifications and incorporate hose ends that attach hoses to other components of the air brake assemblies and have the following specifications, features, and benefits:
- Brass body material capable of withstanding -40°F to +120°F (-40°C to +48°C).
- Capable of use for virtually any air brake hose line and ease of assembly with proper selection of hose ends.
- Provides excellent corrosion resistance.
- Meet SAE & DOT specifications, DOT H3380 for brass fittings.
- Operate at up to 125 PSI as determined by the maximum working pressure of the hose size.
Gladhand Couplings
Another important component in air brake systems are gladhand couplings. Gladhands (a.k.a. gladhand connector or gladhand lock) are devices used to connect the service and emergency air lines from the tractor to the trailer. These couplers have a rubber seal which prevents air from escaping. A gladhand is an interlocking hose coupling fitted to the hoses which supply pressurized air from a tractor unit to air brakes on a semi-trailer, or from a locomotive to railway air brakes on the railroad cars.
Gladhand locks prevent unauthorized or unintentional movement of a tractor-trailer by sealing the air intake valve of the trailer's emergency brake system. A gladhand lock serves as a primary safety device in airbrake systems.
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