Page:NTSB - Railroad Accident Report - Derailment on May 25, 1989.djvu/58

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Rule 2. Dynamic Brake.

Helper locomotives entrained may not use dynamic brake unless road engine has operative dynamic brake.

The number of axles of dynamic brakes of the helper engine(s) will be added to axles of dynamic braking of the road engine to determine the tonnage that may be handles in accordance with applicable Air Brake Rules.

Dynamic brake on head end of freight trains must not exceed 24 axles. Each helper entrained must not exceed 36 axles.

Rule 17. Retaining Valves.[1]

The Superintendent will prescribe the number and locations where retaining valves must be used.[2]

Instructions in Timetable No. 2 indicate that for the descending grade between Hiland and West Colton, retaining valves will be used under certain conditions. For trains being operated down the grade without operative dynamic brakes, one retaining valve will be used for each 80 tons in train. If gross tonnage exceeds 80 tons per operative brake, retaining valves must be used on all cars and speed must not exceed 15 mph. For trains being operated with operative dynamic brakes, use of retainers is not required if tons per axle of dynamic brake does not exceed 375 per standard range or 450 per extended range.

Rule 33. Tonnage Per Operative Brake.[3]

The maximum tonnage per operative brake that may be handled on descending grades of 1.8 percent or over will be prescribed by the superintendent.

  1. As defined in the Air Brake Association’s Management of Train Operation and Train Handling, a retaining valve is "a control device through which brake cylinder air is exhausted completely or a predetermined brake cylinder pressure is retained." In short, the retainers provide the engineer with braking capability while the air brake system is being recharged.
  2. Typically, when a company rule (in this case an airbrake rule) indicates that the superintendent will prescribe certain operating parameters, the superintendent will accomplish this through instructions in the timetable or by special bulletins.
  3. Tonnage (or tons) per operative brake is computed by dividing the gross trailing tons by the number of cars in the train. The weight of the locomotives is not included in the gross trailing tons.