Interpretation ID: aiam1641
Director of Engineering
Power Controls Division
Midland-Ross Corporation
490 S. Chestnut Street
Owosso
MI 48867;
Dear Mr. Denholm: This responds to Midland-Ross' October 8, 1974, clarification of it February 8, 1974, petition for an amendment of S5.1.2.1 and S5.2.1.2 of Standard No. 121, *Air brake systems*, that would establish separate air reservoir volume requirements for several brake chamber types generally available in the air brake component market. You point out that Midland-Ross was referring to chamber stroke and not chamber diameter as the chamber dimension which could affect the safety of a brake system. You also requested that we adopt SAE Standard J10b instead of J10a as our specification of a reservoir that 'withstands' certain internal hydrostatic pressure.; In our denial of your petition, we did understand your point tha additional stroke could be discouraged by a reservoir capacity requirement based on chamber size at maximum travel of the piston or diaphragm. We found that the stopping distance requirements in effect mandate the installation of high performance components, and we do not anticipate a safety problem. If a safety problem does arise in the future, we would consider a modification of S5.1.2.1 and S5.2.1.2.; SAE Standard No. J10b is identical to J10a in its requirement that n rupture or permanent circumferential deformation of the reservoir exceed one percent. Therefore, for purposes of S5.1.2.2 and S5.2.1.3, we are adopting SAE J10b as our specification of 'withstand' until we undertake further rulemaking.; Yours truly, Richard B. Dyson, Acting Chief Counsel