TM 55-203
Figure 11-4. Zone system of car heating.
temperature-controlled vapor automatically operated
b. Essentially, the vapor zone heating system
vapor cutout valve is employed instead of the two
consists of one or more steam-supply loops of pipe
manually operated valves previously discussed.
underneath the car. Each loop is supplied by a single
vapor regulator which releases live steam from the train
11-6. Direct Steam or Pressure Steam
pipe and converts it into vapor at 212 F. The steam-
supply loop in turn furnishes steam (vapor) to two or more
In the direct steam system of car heating, the steam from
radiators, which are of the extended-surface, unit-fin type.
the locomotive is carried directly to the radiators or
Steam from the trainline is conducted from the trainline
heating pipes in the cars. The term is used to distinguish
strainer tee (or cross) to the vapor regulator, where it is
this system from those in which steam is vaporized before
reduced to a pressure of 40 pounds. A shutoff and drain
entering the heating system or is employed to heat the
valve is placed ahead of the regulator to permit the steam
water which circulates in the radiators or heating pipes in
to the vapor regulator and steam-supply loop to be shut
the hot-water system of heating.
off if required.
11-7. Electric Heat
c.
Each steam-supply loop is controlled in
On electric motorcars, the common method of heating is
accordance with steam requirements by a flow valve
by use of resistance coils usually placed beneath the
incorporated in the regulator. The steam loop is divided
seats or along the walls. These coils become heated
into a feed portion and a return portion by a vapor loop
when electric current is passed through them, and the
retarder, which creates a reservoir of steam in the feed
heat is transmitted to the surrounding air in the car. The
portion to insure an immediate delivery of steam to the
coils are sectionalized so that varying degrees of heat
radiator whenever the radiator steam-admission valves
may be obtained. On cars operated by direct current, it is
are open. The radiator condensate is piped to the return
customary to use the line voltage for heating. On
portion of the loop, and the condensate is open
alternating-current cars, a transformer is employed to cut
continually to the atmosphere through a return-pipe drain
down the voltage for heater use.
tube adjacent to the regulator. One type of automatic
11-3
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