Buying products related to the heavy trucking industry is a significant responsibility, impacting not only truckers’ safety but also everyone else on the road. This is why your trust in manufacturers is crucial; buyers need to be confident that manufacturers comply with government regulations. This is the second edition of Alkon’s three-part series about DOT air brake fitting regulations and what it takes to be compliant.

When it comes to DOT-compliant fittings, there are two major regulatory bodies that drive DOT compliance: Federal Motor Vehicle Safety Standards (FMVSS) and Society of Automotive Engineers (SAE). The specific regulations that guide compliance are 49 CFR 571.106 and SAE J2494-3, respectively. These specifications are designed to cover a wide range of environments in which trucks and trailers operate—ranging from everyday conditions to extreme scenarios. It is crucial for your equipment to function reliably, especially in harsh conditions. You certainly don’t want to be stranded in subzero temperatures because a fitting isn’t working properly.

For a fitting to be certified compliant and meet DOT requirements, it must undergo a variety of tests that simulate real-world environments and conditions. Many of the required tests in both specifications are focused on proper retention of the air line in the fitting and maintaining pressure without leakage under many conditions.

Tensile/Pulling Tests:

High Temperature Test: In this test, the fitting and tubing are subjected to boiling water for 5 minutes and then pulled to determine when the tubing or fitting fails. The purpose of this test is to make sure that the fitting will retain the tube during hotter operating conditions.

Conditioned Temperature Test: The fitting and tube are cycled through cold temperature to room temperature and then to hot. This cycle is repeated a few times and then the pull test is performed at room temperature. This test will ensure that the fitting will retain the tube across varying operating conditions throughout the life of the equipment.

Water Absorption Test: The tube and fitting are submerged in water for a long period of time and then tensile tested. This tests the fitting and tube’s ability to resist environmental conditions such as rain and snow.

 

Air Leakage Tests:

Cyclic Pressure and Temperature Test: In this test, the pressure is cycled from very low to very high pressure continuously.  The temperature undergoes a defined cycle and hold process, varying from -40°F to 220°F over a span of 20 hours. The fittings are subjected to a pressure test after this conditioning and are required to meet certain leakage criteria.

Frozen Water Test: This test ensures the fitting will not leak in the presence of frozen water.  The fitting is submerged in water, then conditioned at 14°F until all of the water is frozen.  When pressure is applied, the assembly must remain within specified leakage limits.

Vibration Test: Pressure and temperature are varied throughout the full 1 million vibratory cycles.  Air leakage is monitored both during and after the test, and it must meet the specified criteria.

Side Load Test: This tests the fitting’s ability to withstand high side loads due to extreme bends in the airline routing. The airline is bent to a specific radius and then subjected to a certain pressure. The fitting is required to maintain pressure during this test.

Corrosion Test: In this test, the fitting and tube are subjected to 72 hours of salt spray.  This test not only assesses the fitting’s resistance to corrosion but also requires it to meet specific leakage criteria afterward.

Reassembly Test: This test verifies that the fitting can be reassembled correctly after disassembly, ensuring it will operate properly after normal equipment maintenance. In this test, a tube is pushed into the fitting, pressurized, and then removed. Once this process is repeated 6 times, the leakage rate is measured.

 

Additional Tests:

Separation/Burst Test: This test determines if the fitting can withstand remarkably high pressures. The fitting assembly must maintain tubing grip at pressures up to 800 psi.  This will ensure that the full assembly will maintain structural integrity during an over-pressure situation.

Oil Compatibility Test: This test is intended to evaluate the effects of contaminated compressor oil on the fitting.  This is done while conditioning the fitting through a specific temperature and pressure cycle across 96 hours. The fitting and tube must remain connected when subjected to 150 psi after this process.

While the testing to verify that fittings are DOT compliant is rigorous, it is necessary to ensure the tractor and trailer braking system function properly under all environmental and operational conditions. However, it should be noted and cautioned that there is no overseeing body that reviews the test results and confirms the fittings are suitable for sale in the US market. In fact, the only enforced requirement is to register with the National Highway Traffic Safety Administration (NHSTA) and mark fittings accordingly. This means that being DOT compliant is essentially an honor system.

In other words, it is possible for a manufacturer to unknowing, or knowingly, not meet DOT testing requirements and still mark their fittings as DOT.  Alkon has found through competitive testing that many copycat products fail to meet DOT testing standards. This is because copycat manufacturers often replicate designs without understanding the purpose of certain features, leading to missing elements that are crucial for passing these tests. For example, copycat products frequently failed the burst and air leakage tests at cold temperatures. In some instances, these manufacturers even failed to meet the lowest hurdle of properly marking their fittings.

Overall, the testing for DOT compliance is thorough and simulates extreme and everyday conditions. However, Alkon wants you to understand that claiming compliance with DOT requirements is one thing, but consistently producing fittings that meet those standards is another. Fittings that are marked DOT is not a declaration from the government or any other overseeing body that they pass all of the required tests. Many copycat products do not. It is crucial to know not just who is selling your products, but more importantly, who is making and manufacturing them. You need to trust that what they say they do is genuinely being done.

Do you know who manufactures your DOT fittings? Remember — lives depend on it.