Interpretation ID: aiam2671
Crane Carrier Company
1925 N. Sheridan
P.O. Box 51191
Tulsa
OK 74151;
Dear Mr. Sizemore: This responds to Crane Carrier Corporation's June 8, 1977, questio whether the maximum time limits specified by S5.1.1 of Standard No. 121, *Air Brake Systems*, for build-up of brake system air pressure from 85 to 100 psi includes the time taken to build up air pressure in an accessory reservoir (for an air starter) that is replenished only when the truck is started.; The answer to your question is no. Section S5.1.1 is a performanc requirement that assures that repeated use of the brakes during vehicle operation will not deplete the available air supply because of insufficient air compressor capacity. The purpose of this requirement only indirectly relates to the initial air pressure build-up that occurs when the vehicle is first started.; The agency's existing laboratory procedure for compliance testin provides for fully charging the air brake system (and any accessory reservoirs which charge automatically in the process) before the test is begun. The engine is shut off while brake system air pressure is reduced to a level that permits a subsequent build-up for measurement purposes. In order to properly test vehicles with air starters, the agency is modifying its procedure to keep the engine running throughout the test, so that the air starter reservoir remains fully charged throughout the measurement period.; Sincerely, Joseph J. Levin, Jr., Chief Counsel