Questions re braking

[Deggesty]

Friends, in my learning about braking, I somehoe missed something--what is the PCS? 

Thanks

[BigJim]

Deggesty

Friends, in my learning about braking, I somehoe missed something--what is the PCS? 

Thanks

 

Pneumatic Control Switch: That is what knocks the power down when there is a penalty or emergency brake application.

[Lithonia Operator]

What is the theory behind the system cutting out the dynamic brakes during an emergency air brake application?

[ruderunner]

and a minor hijack since we've gotten into emergency braking...

I know the eot can activate the emergency function and it also does so if the locomotive goes into emergency. But can the engineer make the eot initiate emergency braking without placing the locomotives in emergency?

I would expect the results to be sort of like stretch braking a passenger train.  Would this have any practical application?

[Overmod]

Emergency applies brakes on the locomotive as well as the train.  This will cause wheels already significantly 'braked' by inverter action or back EMF  to slide very quickly.

If from a UDE, a crew might not respond quickly enough to bail off the independent, and the actual bailing off might not then be quick enough to avoid some flat-spotting, even a little of which means grinding of expensive wheelsets.

If in actual declared emergency, the crew might not take the time to do the bailing off; some might be 'distracted' enough not to prioritize it as company management might like.

[Overmod]

ruderunner

But can the engineer make the eot initiate emergency braking without placing the locomotives in emergency?

The Amtrak P42 has an explicit control that does precisely this, described in the orientation video (I watched it yesterday so it is fresh in my mind to confirm).

[BigJim]

Overmod

If from a UDE, a crew might not respond quickly enough to bail off the independent, and the actual bailing off might not then be quick enough to avoid some flat-spotting, even a little of which means grinding of expensive wheelsets.

The engine brakes don't apply so fast that you can't bail them off before any sliding occurs. Even before I retired, the newer engines would not let the dynamic load very much if there was any pressure in the brake cylinders.

[jeffhergert]

BigJim

 

 

Deggesty

Friends, in my learning about braking, I somehoe missed something--what is the PCS? 

Thanks

 

 

 

 

Pneumatic Control Switch: That is what knocks the power down when there is a penalty or emergency brake application.

 

 

That's how I originally learned it, from reading railroad manuals before hiring out.  The glossary in our Air Brake and Train Handling rule book now calls it the Power Cut-Off Switch.    

Jeff

[Lithonia Operator]

Early in the thread, Tree suggested this to me:

If you haven't already read Al Krug's excellent primer on railroad air brakes, you'll find it well worth your while. http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/north-american-freight.html

I've now read it, and it IS excellent. I'd highly recommend it to anyone curious about air brakes. Thanks again, Tree.