Interpretation ID: 1982-1.33

TYPE: INTERPRETATION-NHTSA

DATE: 03/30/82

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Mack Trucks, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 19, 1982, letter asking whether the hose that connects the air pressure gauge to the service reservoir system must comply with Standard No. 106, Brake Hoses. You also ask whether the air pressure gauge is part of the Standard No. 121, Air Brake System.

The air pressure gauge to which you refer is required by S5.1.4 of Standard No. 121. Accordingly, it is considered as part of the air brake system. With respect to whether the tubing connecting that gauge to the air supply reservoir must comply with Standard No. 106, that standard defines brake hose as:

"a flexible conduit, other than a vacuum tubing connector, manufactured for use in a brake system to transmit or contain the fluid pressure or vacuum used to apply force to a vehicle's brakes."

The agency has previously determined that hoses connected to air pressure gauges need not comply with Standard No. 106 if they do not transmit or contain the brake air pressure used to apply force to a vehicle's brakes. To determine whether your system transmits or contains the pressure, you must determine whether a failure of the hose to the gauge would result in a loss of air pressure in the system. If you use a check valve or some other device to prevent loss of pressure, then the hose would not contain or transmit the air pressure and would not be required to comply with Standard No. 106. This answer would also apply to other air pressure gauges that you may install to monitor other portions of the brake system performance.

SINCERELY,

MACK TRUCKS, INC.

January 19, 1982

National Highway Traffic Safety Administration Office of General Council

Gentlemen:

Subject: Requirements for the Air Brake System Air Pressure Gauge and Supply Line Ref: FMVSS 121 and FMVSS 106

Mack Trucks, Inc., as a major producer of heavy duty vehicles, is in the process of releasing for production a new cab-over-engine vehicle designated as the MH model.

Section S5.1.4 of Standard 121 requires that we install in these vehicles a pressure gauge to monitor the service reservoir system air pressure. Since Standard 121 is entitled "Air Brake Systems", we have considered such a gauge to be part of the air brake system.

In light of the above facts, and since the supply line to the gauge does contain brake system air, we have assumed that the hose or tubing used for the supply line should comply with the requirements of Standard 106, Brake Hoses.

We are, therefore, requesting clarification on the following subjects:

(a) Is the air pressure gauge required by S5.1.4 of Standard 121 considered part of the air brake system?

(b) If the answer to part (a) is yes, must the supply line (hose or tubing) to this pressure gauge comply with the requirements of Standard 106, Brake Hoses?

In a related situation, we will be supplying, as an option, an air application gauge in these new models that will monitor the

Subject: Requirements for the Air Brake System Air Pressure Gauge and Supply Line Ref: FMVSS 121 and FMVSS 106 air being applied to specific parts of the brake system (e.g., front brakes, rear brakes, or trailer brakes). We would assume that if the answer to part (b) above is yes, then the supply line to these gauges would also be required to comply with Standard 106. Is our assumption correct?

We would appreciate a timely response to our questions since the manufacture of certain preproduction MH models is to take place in the very near future.

S. Robson Executive Engineer-Vehicle Regulations