How did they remotely throw trolley switches back then?

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How did they remotely throw trolley switches back then?

Postby bostontrainguy » Mon Sep 10, 2018 11:32 pm

Watch at 2:09. Does anyone know how they remotely threw switches in the old days?

https://www.youtube.com/watch?v=ylAmAjRELXc
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Re: How did they remotely throw trolley switches back then?

Postby diburning » Tue Sep 11, 2018 12:02 am

Its an old system where the (single) switch point is thrown (magnetically?) based on whether power is drawn from the overhead. I think it was coast to go whichever route is on the left, operate under power to take the other route. Then, the switch either has a timer, or the car traversing the switch has a release lever mounted to the rear, to return the switch to the default position.
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Re: How did they remotely throw trolley switches back then?

Postby jaymac » Tue Sep 11, 2018 2:43 am

For pre-PCC cars, the power for throwing the switch was applied or not applied by the controller. For PCCs with their "automotive" controls, there was a switch -- among many -- on the desktop edge, made distinctive by a large coiled-spring toggle: no movement of the toggle, no power, but if the toggle was pushed forward, power to the detector.
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Re: How did they remotely throw trolley switches back then?

Postby Disney Guy » Tue Sep 11, 2018 7:53 am

In the old days, probably into the 1980's there were Green Line subway switches that were pneumatically thrown. At those you could hear the hiss of air as the switch points moved.

There would have had to be some form of track occupancy sensing to keep the second or third car of a train from throwing the switch the other way. When the switch and some track beyond it was no longer occupied then the switch might return to the "left" position. If the next car or train approaches the switch and too closely to the car or train ahead, the switch would not throw and the operator would have to get out with a switch iron.

Less wear and tear is put on the switch if it remains where it was last thrown. The throwing sensor can be made to detect the small current draw of a car coasting up and throw to the left at that time.

Trackless trolley overhead frogs can be made with just one throwing coil tor lighter overall weight. (For Boston) the coil and sensor sets the point for the "right" movement and the trolley shoe hits a release lever to return the point to the "left" movement after passing through.
Last edited by Disney Guy on Tue Sep 11, 2018 8:14 am, edited 5 times in total.
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Re: How did they remotely throw trolley switches back then?

Postby bostontrainguy » Tue Sep 11, 2018 7:58 am

diburning wrote:Its an old system where the (single) switch point is thrown (magnetically?) based on whether power is drawn from the overhead. I think it was coast to go whichever route is on the left, operate under power to take the other route. Then, the switch either has a timer, or the car traversing the switch has a release lever mounted to the rear, to return the switch to the default position.


So the same as a trackless trolley. Interesting. Thanks!
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Re: How did they remotely throw trolley switches back then?

Postby CRail » Wed Sep 12, 2018 1:05 am

Power right, coast left. The location in the video referenced still operates this way. You didn't have to power over the switch, but through the overhead sensor that detected the power draw. This is how cars operated on the street and in the subway until the AVI system was introduced in the 90s. Type 7s still have a track switch button on the dash (even post overhaul), though it no longer serves a purpose.

For Trackless Trolley electric switches, the switches always rest left. They are thrown right by current draw and reset by the passing of the pole through the frog.
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Re: How did they remotely throw trolley switches back then?

Postby jaymac » Wed Sep 12, 2018 6:59 am

CRail-
Tnx for confirming my Arborway -- with Types 4 and 5 and PCCs -- and Riverside/Cleveland Circle -- with just PCCs -- memories of the 50s and 60s.
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Re: How did they remotely throw trolley switches back then?

Postby typesix » Wed Sep 12, 2018 12:45 pm

PCC cars can also use the power right, coast left method. Starting with the LRVs, this method is not reliable, as the electronic motor controls draw less power at low speeds and the sensor cannot always determine which way to set the switch.
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Re: How did they remotely throw trolley switches back then?

Postby Disney Guy » Wed Sep 12, 2018 7:30 pm

Any kind of car can be equipped with a button or toggle on the dashboard (Type 7's had this as mentioned above) to put a resistance grid as a separate subcircuit directly from positive (overhead) to negative (wheels; frame) and guarantee a power draw sufficient to activate the switch (for "right" in Boston). What is tricky is setting the "coasting" threshold in the switch throwing mechanism so the air conditioning and other equipment in a coasting car does not draw enough power to throw the switch as if the car approached under power.
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