Railroads are normally pretty tolerant of ice and slow with even the snowiest lines through the Sierra Nevada or Rocky Mountains needing the use of specialized rotary snow ploughs only about once a decade. However when rails need to move back and forth at the point of a switch, snow and ice can quickly gum things up and that is where the wonderful world of switch heating comes into play. Despite there really being only two main heating methods and a handful of fuels, the solutions employed still show a fair bit of diversity, even within the railroads themselves.
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| SEPTA losing a bet on the necessity of point heaters at 16TH ST Jct. |
The two main methods of clearing the movable parts of switches are heating the rails directly or blowing hot air in and around them. These two categories are then divided by the type of fuel beings used to do the job. Currently the most common are electricity, gas (methane or propane) and kerosene. The decision of which point heating solution to use is typically based on the severity of the winter events any given interlocking is likely to encounter. Erring on the side of caution may result in unnecessary maintenance and capitol expenditures. On the other hand insufficient point heating capacity may not only fail in its intended role, but also succeed in making the problem worse. Railroads may further adopt the use of snow plans where the use of top quality snow melting is restricted to certain locations with the remainder being straight railed and taken out of service for the duration of the snow event.
The most basic type of point heating solution is that of the
smudge pot. Named for an agricultural device designed to ward off the effects of frost, a railroad smudge pot is a long, flat metal tank holding 2-5 gallons of kerosene with a wick at one end. Placed under the running rails and ignited, the open flame will heat the rail sufficiently to ward off snow and ice accumulation within a certain vicinity.
Smudge pots can be left in place year round or deployed by maintainers in advance of a weather event. Regardless of the placement, smudge pots must by lit and extinguished manually and are generally not used anywhere a switch needs to be in service during a significant snow/ice event. They also replaced the practice of igniting oil or other flammable liquids directly on the track structure, although that can still be used to free frozen points in an emergency.
Moving up a notch in power, the electrically powered rail heater works in much the same fashion as a smudge pot, but without the need for on-site manual operation or fuel oil and with a significantly larger area of effect. The hardware device could not be simpler, usually consisting of an electric-range style heating elements strapped along the length of the outer rail.
In the above example of an electric resistance point heater in operation, the water has evaporated along the entire length of the heating element. When encountered in the nighttime the elements glow a cherry red, again similar to a household electric range.
Where heating elements on the outside rail prove insufficient, additional coils can be placed under the points themselves where the radiant heat would work to keep the mechanism clear. One major drawback to electric contact point heaters is the somewhat limited amount of BTUs available. A practically sized heating coil can only output so much heat and in extremes of temperature and precipitation and electric contact point heater will not only fail to melt the snow as it accumulates, but the snow that does melt may re-freeze between the ties and the points making mechanical clearance nearly impossible.
Electric heaters also require a fair amount of railroad and utility infrastructure. Not only do the interlocking locations need a power supply with sufficient current available to power tens of feet of heating element, they also need additional cabling between the power supply and the switches themselves and in the long run high voltage electrical cabling in wet conditions can become a maintenance issue.
When the electricity supply either isn't available or isn't enough then it's time to break out the burner bars that apply a gas flame directly to the rail. Generally impractical to use except on the outside rail, it was common to add an additional shroud to trap the heat around the rail, although these since fallen out of favor due to issues related to inspection or snagging equipment.
The propane heaters shown above generally succeed in hiding the flame and and often create a whistling noise while in operation. Some older installations that use municipal natural gas lines create more visible flames, sometimes to the alarm of passers by who think that something has gone wrong.
