Interpretation ID: aiam1246
P.O. Box 560
Oshkosh
WI 45901;
Dear Mr. Kamath: This is in reply to your letters of August 7 and August 23, 1973 concerning the conformity to Standard No. 121 of certain features in air brake systems submitted to you by suppliers.; Your first question is whether the volume of a supply reservoir tha lacks a check valve is to be included in arriving at the required reservoir volume of 12 times the full-travel service brake chamber volume. Our reply is that S5.1.2.1 includes the volume of all service and supply reservoirs, regardless of valving, and that the volume of the supply reservoir in question would therefore be included in the combined reservoir volume.; You next ask whether a system that has no isolated emergency reservoi can rely on its service reservoirs to provide air for the two emergency stops proposed as S5.7.3 by Docket No. 73-13, Notice 1 (38 F.R. 14963). Under this proposal, the stops would have to be accomplished with a single failure of a part (other than a common valve, manifold, brake fluid housing or brake chamber housing) designed to contain compressed air or brake fluid. If the system is designed so that no single failure, other than a valve, manifold, or housing failure, will cause a loss of air in both tanks, it would seem to be capable of meeting the proposed requirement even though it does not have an isolated emergency reservoir. However, if a single failure in a brake line would deplete the air in both service reservoirs, the system would be unable to meet S5.7.3 unless an emergency isolated reservoir were provided.; In answer to your last question, the emergency stops proposed in S5.7. would be conducted from an initial pressure in excess of the compressor cut-in pressure. The reservoirs would not be depleted by prior stops.; Yours truly, Richard B. Dyson, Assistant Chief Counsel