All refrigerator cars are insulated. One type is equipped with brine tanks at each end and used for carrying eggs, butter, vege tables and fruits. Some refrigerator cars are equipped so that they may be converted into heater cars during the winter. Heat ing systems employing coal, charcoal, alcohol and kerosene as well as steam have been developed.
Tank cars are used to transport gasoline and other inflammables, acids, alcohol, ammonia, oils, paints, milk, vinegar, pickles and other liquid and semi-liquid products. The most common design is the tank car for general oil or liquid serv ice. It consists of a steel tank mounted on a frame, or mounted di rectly on cradles over truck bolsters. Safety release valves are provided and it is emptied by valves at the bottom. At the top is a dome, with or without manhole, and the openings through which the tank may be filled. Milk in bulk is transported in cars equipped with glass lined'tanks.
Many types of special cars for maintenance of the track, and general construction work in con nection with railroad operations are necessary. These include dump cars, motor and hand cars, locomotive cranes, steam shovels, pile drivers, ditchers, flangers, snow plows, sweepers, supply cars, air-brake instruction cars. This rolling stock is known as non revenue equipment. Wrecking, instruction and dynamometer cars are included in the non-revenue group. Section or inspection cars are used to convey the section men to and from their work and to conserve the time of other maintenance employees.
Three general systems of electric car lighting are in service as follows : Axle-generator system, head end system, storage battery system. The axle-generator system is the most commonly used, and provides for lighting each indi vidual car by means of a storage battery charged by a generator under the car, and driven by a belt from one of the axles. The head-end system requires a generator located in a car at the head of the train where it may receive steam from the locomotive. The generator may also be driven by an internal combustion engine. This generator furnishes current for lighting the entire train. In some cases the generator may be driven by a belt from the axle or it may be mounted on the locomotive. The straight
storage battery system has a storage battery under each car as an individual unit or one battery for lighting several cars. The batteries are charged at terminals during a lay-over period.
Heating is accomplished by steam or electric heating apparatus. On steam operated railways vapor heating systems are usually used. Other systems employed are direct steam or pressure and combination vapor and pres sure. At terminals when a locomotive is not available until leaving time cars are heated from a central heating plant. The heating elements of a steam heated car consist of iron pipes placed along each side wall near the floor and protected by a grill. Live steam is supplied by the locomotive. Where cars are sub ject to isolation, a coal fired heater is installed in each car. Elec trically operated cars are usually heated by resistors taking cur rent from the power source.
the recent improvements in air-con ditioning, explained above, nearly all types of car ventilators in passenger cars were (and, in many cars in use in 1937, are) located either in the deck sash or in the main roof of the car. Their action was to admit or exhaust air to or from the car and depended upon the motion of the car for full action. This was later helped by the action of electric fans. Freight cars employed in handling certain commodities used a simpler system of ventilation consist ing usually of a series of slots at each end of the car and some times of ventilator side doors. For Air-Conditioning, see above.
To facilitate the economical movement of traf fic in America the railroads have for many years permitted car load freight to be shipped from consignor to consignee without the expense and inconvenience of trans-shipment at junction points. This has resulted in a vast interchange of traffic between the various railroad systems and in the gradual formation of the restrictions or rules under which this traffic interchange is con ducted. One railroad will repair the rolling stock of another railroad under a code of rules which governs this practice.