Interpretation ID: nht74-4.7

DATE: 06/14/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: The Berg Manufacturing Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your December 21, 1973, letter and subsequent communication with Mr. Sidney Williams of the NHTSA Handling and Stability Division asking if a check valve located at the isolated reservoir (as pictured in your schematic drawing) to protect the trailer service reservoir(s) would comply with S5.2.1.5 of Standard No. 121, Air brake systems.

The check valve may be placed at the isolated tank to protect the trailer service reservoir as specified in S5.2.1.5.

It appears from your schematic that a single failure in the service brake system could cause loss of service brakes on both trailer axles. It should be noted that if this arrangement is used and a significant safety problem result, it would be subject to NHTSA safety defect authority.