Interpretation ID: 1984-2.32

TYPE: INTERPRETATION-NHTSA

DATE: 07/20/84

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Kentucky Manufacturing Company

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Robert J. Crail Kentucky Manufacturing Company P.O. Box 17185 Louisville, Kentucky 40217

Dear Mr. Crail:

This responds to your letter seeking clarification of the testing requirements of paragraphs S5-3-3 and S5-3-4 of Federa1 Motor Vehicle Safety Standard No. 121 , Air Brake Systems.

You state that you have always tested all of your trailers with the 50-cubic-inch test reservoir connected to the rear of the trailer, downstream of the trailer test rig and the trailer. This is the correct testing method, because the purpose of the 50-cubic- inch test reservoir is to represent the volume of lines in the following vehicle.

You also state that a customer suggests that the correct reservoir connection is between the trailer test rig and the control coupling on the front of the trailer. This location of the reservoir in front of the trailer would indeed negate the purpose of the test requirement, because in this position the reservoir could not simulate the volume of lines in the trailing vehicle. Your interpretation, not the customer's, is correct for testing vehicles equipped with air brake systems for compliance with the standard.

Sincerely,

Frank Berndt Chief Counsel

February 15, 1984

Chief Counsel National Highway Traffic Safety Administration 400 7th Street, S.W. Washington, DC 20590

Re: 49CFR 571.121, Air Brake Systems

Dear Sir:

This letter is to seek clarification on sections 5.3.3 and 5.3.4. These require that on a vehicle designed to tow another vehicle equipped with air brakes, meet brake actuation and release time requirements with a 50 cubic inch reservoir connected to the control line coupling. We have always tested all of our trailers with the 50 cubic inch reservoir connected to the rear of the trailer, that is downstream of both the trailer test rig and the trailer.

A customer insists that the proper location for the 50 cubic inch reservoir is between the trailer test rig and the control coupling on the front of the trailer. This, of course, negates the whole reason for placing the 50 cubic inch reservoir on the control coupling, which is to simulate the towed vehicle.

Since the standard is not clear as to where the 50 cubic inch reservoir is connected, we are requesting an interpretation as to the proper control coupling to which it should be connected.

Sincerely,

Robert J. Crail Director of Engineering

RJC/maf