"121" commonly mentioned in air brake talk refers to
the section of the United States Federal Regulations that pertains to air
brakes. The full designation if Title 49 (Volume 5) Part 571 Section
121 or 49CFR579.121.
These regulations set forth
many (but not all) requirements for air braked vehicles. The regulations
have evolved over the years hence the changes in the function of many valves.
Valves that were compliant for earlier trailers may not be so for later builds.
For this reason it is important that care is taken in valve
selection.
The text for the regulations can be be found on line with
some pertinent excerpts found in this section. |