Interpretation ID: aiam3545
Executive Engineer
Vehicle Regulations
Engineering Division
Mack Trucks
Inc.
P. O. Box 1761
Allentown
PA 18105;
Dear Mr. Robson This responds to your January 19, 1982, letter asking whether the hos 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 o 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 hoses 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 the ai 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, Frank Berndt, Chief Counsel