Interpretation ID: aiam2670
Director of Engineering
Power Controls Division
Midland-Ross Corporation
490 South Chestnut Street
Owosso
MI 48867;
Dear Mr. Denholm: This responds to Midland-Ross' July 8, 1977, request for confirmatio that the requirement that '[e]ach service reservoir system shall be protected against loss of air pressure. . .by check valves or equivalent devices' in S5.1.2.3 and S5.2.1.5 of Standard No. 121, *Air Brake Systems*, permits small losses of air pressure through the check valve of up to 2 psi per minute without constituting noncompliance.; The requirement for protection against 'loss of air pressure' doe permit a small amount of leakage, in recognition of the fact that no fitting can be perfectly air tight. While the standard does not presently specify a rate of permissible air loss in S5.1.2.3 or S5.2.1.5, the agency has adopted a maximum loss of 10 psi in 10 minutes as meeting the requirement for protection against loss of air pressure. The agency is considering adding such a specification to the standard in the future by interpretive amendment.; Sincerely, Joseph J. Levin, Jr., Chief Counsel