Interpretation ID: nht93-6.34

DATE: September 8, 1993

FROM: Christopher S. Spencer -- Engineering

TO: R. C. Carter -- U.S. Department of Transportation

TITLE: None

ATTACHMT: Attached to letter dated 4/25/94 from John Womack to Christopher S. Spencer (A42; Std. 121)

TEXT:

Allow me to introduce myself to you. I am an engineer at a manufacturer of air reservoirs for air braking systems. I am looking at modifying a present design. The new design is to improve the volume without increasing the need for more space. This design is to maintain a low cost as well. There is a problem with how to interpret the FMVSS-121 that I would like for you to help evaluate for me. According to FMVSS-121 Section S5.1.2.2 this reservoir should withstand a defined amount of pressure for 10 minutes. Generally speaking, this is 750 p.s.i. The safety standard does not clarify the test criteria specifically how the reservoir is to be sealed. We have tested two different ways. One shows acceptable results 100% of the time. The second way is not as impressive. Some people here say that both are valid test. My question to you is can we check reservoirs in either way. Why or why not. I look forward to hearing from you.