Interpretation ID: 1983-2.22

TYPE: INTERPRETATION-NHTSA

DATE: 07/01/83

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Grumman Flxible Corporation -- Charles R. Sidner, Product Safety Engineer

TITLE: FMVSS INTERPRETATION

TEXT:

Charles R. Sidner, CPSM Product Safety Engineer Grumman Flxible Corporation 970 Pittsburgh Drive Delaware, Ohio 43015

Dear Mr. Sidner:

This responds to your March 31, 1983, letter asking about the lo-air pressure warning device that is required by Standard No. 121, Air Brake Systems. In particular you ask whether the requirement must be met with two switches, one on the primary and one on the secondary air tank, or whether one switch on the supply tank would be sufficient.

S5.l.5 of the standard states that a warning signal shall be provided to give a continuous warning of a loss of pressure in the service reservoir system below 60 p.s.i. The intent of the section clearly is to provide a warning to a driver of any instance that results in a loss of pressure in either the primary or secondary service reservoir system.

Dependinq upon the design of any individual brake system, it might be necessary for more than one switch to ensure that the driver will be alerted to such an air loss. For example, a single switch on the supply tank might be inadequate to signal a loss of pressure in the primary or secondary service reservoir system if the action of the compressor masks such loss of pressure. It is up to the manufacturer to determine whether its system is designed in a way that requires more than one switch.

Sincerely,

Frank Berndt Chief Counsel

March 31, 1983

Office of Chief Counsel National Highway Traffic Safety Administration 400 Seventh Street, S.W. Washington, D.C. 20590

Reference: (a) FMVSS No. 121, Air Brake Systems S5.l.5 Warning Signal

Dear Sirs:

Your assistance is requested with respect to an official interpretation/ clarification of reference (a) above as it relates to the installation of lo-air pressure switches on our Flxible-METRO transit coach.

In accordance with S5.l.5, as we interpret the standard, when the ignition is in the "on" or "run" position and the pressure in the service reservoir system is below 60 ps, there shall be a signal either visible....or both audible or visible.

In order to attain this signal, we have positioned a lo-air pressure switch, electrically operated at both the primary and secondary air tank (service reservoir system).

The issue for interpretation is whether the two lo-air switches on both the primary and secondary tanks are necessary to meet the requirement, or if one lo-air switch on the supply tank only to activate the warning signal is adequate to meet the requirements of S5.1.5.

We shall continue to locate a lo-air switch on both the primary and secondary tanks until we are advised otherwise.

Sincerely,

GRUMMAN FLXIBLE CORPORATION

Charles R. Sidner, CPSM Product Safety Engineer

cc: E. Kravitz J. Bolton L. Musser T. Schubach