Derailers & Retarders....

[Anonymous]

I've noticed on some tracks yellow derailers. What
are they and how are they used? My second question is what are retardersAnd how are they
used?

[Anonymous]

The yellow derailers you see are used to protect main tracks from being fouled by cars or locomotives spotted on a side track. They work by guiding the flange of the wheel up and over the railhead, causing the car or locomotive to derail before rolling onto a main track. A retarder is something used mainly in gravity hump yards, which mechanically squeezes the flange of the wheel against the rail to slow, or retard, the car being humped. I am not sure, but I believe that the car being humped is weighed as it begins to roll, and then the retarders are applied at different pressures against the flanges depending on the weight and how far the car has to roll. Anyone have a good answer to that?

[thirdrail1]

Re; retarder force. Several methods are used to determine the amount of force applied using retarders. The most common is Doppler radar, which measures the acceleration of the car down the hump and applies the retarders accordingly, with the computer controlling them aware of the track and spot the car is destined. A simpler method uses notches in the rail. The computer measures the rise in the frequency of the clicks to determine the acceleration of the car. The weight is secondary to the rolling characteristics of the car.

[Anonymous]

Thanks Gregg. I wasn't aware that doppler radar was used. Where are the transmitters typically located? Along the trackside, or above. I would guess that they need to be aimed at the end of the car fairly strait to get a good reflecting surface for optimum return signal.

[thirdrail1]

The radar is usually located either between the rails or just alonside at about the first switch below the hump. The car really only has to move about 10 feet for the rate of acceleration to be determined accurately enough.