Interpretation ID: aiam1519
Chief Engineer
Automotive Products
Wagner Electric Corporation
6400 Plymouth Avenue
St. Louis
MO 63133;
Dear Mr. Kourik: This responds to your May 7, 1974, request to know whether check valve or equivalent devices must be placed immediately adjacent to or within each service reservoir in a trailer air brake system to comply with S4.2.1.5 of Standard No. 121, *Air brake systems*, and whether the standard intends each axle subsystem to have a separate service reservoir and check valve system, with particular regard to arrangements for liftable axle systems. S5.2.1.5 states:; >>>S5.2.1.5 Each service reservoir shall be protected against loss o air pressure due to failure or leakage in the system between the service reservoir and its source of air pressure by check valves or equivalent devices.<<<; The answer to both of these questions is no. In an April 3, 1974 letter to Great Dane Trailers, Inc., we interpreted S5.2.1.5 to permit location of the check valve at the isolated reservoir, permitting that valve to also guard the service reservoirs on that axle system. The language of S5.2.1.5 is unclear in this regard, and may be amended in the future. In response to your specific question, it is permissible to use a single check valve to protect more than one reservoir in a subsystem.; Standard No. 121 does not require a separate service reservoir chec valve for each axle system in a tandem axle. As you point out this could decrease total vehicle reliability, and abuse in this area could lead to amendment of the provision. In answer to your fourth question, a single check valve could be utilized to protect the air reservoir or reservoirs required for a liftable axle system or subsystem.; Yours truly, Richard B. Dyson, Assistant Chief Counsel