Interpretation ID: nht73-4.34

DATE: 07/19/73

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

TO: Kysor of Cadillac

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of June 22, 1973, concerning the applicability of section S5.1.4, Pressure gauge, of Standard No. 121, to an electronic gauge that displays the air pressure under normal conditions only when the driver pushes a switch but that provides continuous display at pressures below 70 p.s.i.

Section S5.1.4 requires a pressure gauge to be "readily visible." Used in this context, "readily visible" means visible whenever the driver wants to see it. It does not mean that the air pressure level should be continuously visible. As we understand your system, the driver could determine the air pressure at any time by pushing the "air pressure" button. We have concluded that this operation satisfies the intent of S5.1.4 and that your system would be permissable under that section.

The low pressure warning signal is required by section S5.1.5 and must be separate from the pressure gauge. You state that you provide a flashing red light and an audible alarm, in addition to providing continuous readout of air pressure below 60 p.s.i. This would appear to conform to S5.1.5.