Retarders explained

@Tom Tee posted:

Some of these questions may be or sound stupid, I am just curious as to their workings.

Would someone with actual working knowledge please explain in detail how the Master and Group retarders work?
I worked at the Pittsburgh & Lake Erie Railroad back in the 60s. I've pulled many a pin at the crest of the hump at Gateway Yard in Struthers, OH. See more pictures here.

What portion of the wheel has pressure applied?  How high above rail head do the gripping jaws grab?
The retarder clamp squeezes the wheel in the bottom few inches of the wheel. It clamps on the inner flange area and the outer rim, squeezing the wheel.

How much pressure is applied?
I don't know.

How does the actual weight of the car affect applied clamping force?
The weight of the car will affect the clamping force. On a typical hump, the car is weighed in motion as it moves over the hump crest. That weight is sent to the computer. The computer then uses that weight to calculate the clamping force needed to achieve the desired exit speed from the retarders, both the Master and the Groups.

How much of this operation is more of an art form based in experience?  Is there a weight/grade/length of run computer formula?
The hump that I worked on was computerized, even in the 1960s.  Not too much of an art form...just numbers crunched in the computer. The hump conductor had manual override controls to use if necessary, but he rarely needed to do anything.

How does temperature and precipitation affect operation?
Not sure.

Would too much clamping grip pressure cause a pop up derailment?
No, it would just stop the car. The clamping force is not vertical, it is horizontally applied against the wheel rim and the back of the flange.

Are the follow up group retarders for fine tuning the car's speed?  Other purposes?
Yes. The Master Retarder (the one ALL the cars go through) will have a computed target exit speed. The Group Retarders would then fine tune the speed before the cars actually enter the track they are headed for. This speed fine tuning is needed because as the track fills up, the coupling point moves closer to the hump end of the track. The final track entrance speed of a car that only has to roll another four or five car lengths to couple would be less than a car that might have to roll forty or fifty car lengths to a coupling at the far end of the track.

What is the desired closing speed upon recoupling?
Less than 4 mph.

How is the stopping point of very first car in an empty track determined?
There is a fixed retarder at the far end of each track. If the speed has been set correctly by the master and group, the car will roll to a stop a few car lengths from the end of track, stopped by the fixed retarder placed there.

What classifications determines hump yard bypassing?  I have never seen photos of tank cars on humps.  Real or not real.
Haz Mat Loads and any other car marked "Do Not Hump."

Thank you.

Wow!  Now that is an answer!!  Thank you.

Here in Roanoke, the N&W used "skates" to stop the cars at the far end of the hump bowl. SKATES

Well the O.P.s questions were definitely NOT STUPID. I believe more people than I learned something new by reading this thread.

In the 1974 (?) Penn Central 'we need $' film,  I believe men were manually placing pieces of wood in front of the railroad cars wheels to stop them at the top of the hump

The retarded was worn out

I also learned a lot. I understood the basic idea but didn't know the deets of how it was accomplished.

This guy Definitely humps.

@prrhorseshoecurve posted:

Well the O.P.s questions were definitely NOT STUPID. I believe more people than I learned something new by reading this thread.

Right, and thank you for the reply, Rich!