Ice is an insulator. So if ice or sleet forms on the third rail or trolley wire, as often happens during the winter, it can bring an electric railroad to an embarrassing and expensive halt. To solve this problem, we need the aid of Science. So if you like scientific details, keep reading!
We shall, of course, start with the CA&E. When the line was built in 1902, nobody had much experience with keeping a third-rail interurban running. In the early days they tried putting a tank of either brine or calcium chloride solution in the front vestibule and letting it drip through tubes onto the third rail. This was a real mess, as you can imagine, and it damaged the rails, the insulation, and so on. The third rail fixtures themselves were in a state of flux at this time, but by about 1913 or so the road had settled on the third rail beam design that was used until the end. This design includes pneumatic sleet scrapers.
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Here's what the standard sleet scraper looks like. The cylinder is fed through a flexible hose, and the piston pushes the cast iron scraper shoe down onto the third rail. There's one on each side of each truck, and all four operate in unison.
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The cylinder looks like this, upside down. The shaft goes down through a slot in the wooden beam, and the shoe is bolted onto the bottom. You can see the spring that pushes the piston up when air is released. I meant to measure the vertical travel, but it's about 6".
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The shoe looks like this. They tend to be pretty worn down. The shoe has an electrical connection so it will act as a current collector when in use.
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The scrapers on the lead car are controlled by a valve to the right of the brake valve. On the wood cars there's just a simple on-off valve as seen here.
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On the steel cars, however, there's a more complex valve that uses a second brake handle, of the same type as the M-23 motorman's valve. This is more than a simple on-off valve, but I'm not sure how it works since we never use it. I must confess that David was basically correct about this, although I doubt this was actually a motorman's brake valve of some sort.
Because of the great force the pneumatic cylinders could exert, I would assume it was necessary for the motorman to raise the scrapers wherever there was a gap in the third rail.
The CRT/CTA has always been able to use simpler means of scraping the rail, largely because traffic is much more frequent on the rapid transit lines, and during sleet storms they would send out extra trains just to keep the rails clear. .jpg)
Here's what one of the more modern scrapers looks like. At the top is a long leaf spring, which drives down the scrapers at each end. Ordinarily these are kept in the up position, as here, by means of a lever. By turning the handle, the scrapers drop into position. Of course, they are then always down and cannot be raised while the train is in motion. But that is evidently not necessary with the flexible scrapers used here. I think most of our rapid transit cars had these scrapers on only one truck.
Here's what one of the more modern scrapers looks like. At the top is a long leaf spring, which drives down the scrapers at each end. Ordinarily these are kept in the up position, as here, by means of a lever. By turning the handle, the scrapers drop into position. Of course, they are then always down and cannot be raised while the train is in motion. But that is evidently not necessary with the flexible scrapers used here. I think most of our rapid transit cars had these scrapers on only one truck. As for other third-rail equipment at IRM, the Michigan Electric car had pneumatic scrapers similar to the CA&E's mounted on the front truck only. The Com Ed 4 and the S motor used an under-running third rail where sleet would not be an issue.
But of course sleet can be a problem with trolley wire as well as third rail. The greater flexibility of trolley wire (particularly simple suspended) makes it easier to knock the ice off, but most cars can have only one pole up and you have to remove the ice and collect current at the same time. Somewhere we have examples of sleet-cutting trolley wheels and I'll try to get a picture of one. It looks sort of like a miniature turbine wheel.
Here's an interesting solution from the Illinois Terminal. Combine 277 has a trolley pole mounted near the front of the car with a special sleet cutting shoe. During the winter, a retriever would be mounted so the front pole could be raised. This would enable the rear pole to collect current reliably. Of course, if the front pole dewired, a crewman would have to climb onto the (presumably icy) roof to take care of it! We are certainly lucky that IRM can just shut down during the winter.