Watched a train move with disconnected air lines

Donald Van Slambrook 013018 posted:

A few days ago in Spring TX I watched a string of cars being moved and was surprised to see that not all air hoses were connected.  It was near the big yard there and there were several cars connected, but there were disconnected hoses every 5 cars or so.  What's up with that?

They obviously were switching the cars without air, i.e. the cars were all drained of their air, and only the brakes on the locomotive/locomotives were being used during the switching.

Thanks for the reply.  My novice level of knowledge thought there had to be train brakes as well as locomotive brakes for movements.  

Donald Van Slambrook 013018 posted:

Thanks for the reply.  My novice level of knowledge thought there had to be train brakes as well as locomotive brakes for movements.  

Well, yes and no.

No, there is not a physical reason that cars cannot be switched without air brakes cut in and the air system charged.  One of the features of the automatic air brake is that, if there is a break in the continuity of the brake pipe, air brakes throughout the train automatically become applied at an emergency rate.  You can't kick a car and let it roll into a track like that.  If the brakes were charged, then each car kicked into a track would have to be "bottled", i.e., angle cocks closed on each end to prevent discharge of air from the brake pipe.  Leakage would eventually set the brakes, and the car would have to be bled off before it could be pulled out again.  Lots of time would be wasted bleeding off the brakes multiple times during switching, so the crew walks the track and bleeds it once, before switching the cars.

So, the usual process is to use the bleeder rod underneath the car to bleed all air out of the reservoir and brake system, and switch the cars that way.  If the cut of cars is very heavy, a few cars next to the engine might have air brakes in operation to help the engine stop the cut.

Yes, a train must have the air brakes cut in and tested to verify that they are operating properly, before departing its initial terminal and until it is delivered at its final terminal.

This might be a good place for a truly knowledgeable RRer to post a quick explanation of how air brakes work in RR applications.

palallin posted:

This might be a good place for a truly knowledgeable RRer to post a quick explanation of how air brakes work in RR applications.

Google might be more helpful, and more understandable.

Think of an automobile. The brake pedal is like a brake pipe on a train. The pedal or pipe pressure  regulates how much force is applied to the brake shoe. Now think of the  automobile brake fluid as the main reservoir air that each rr car has. The main reservoir is a seperate air chamber from the brake pipe air, that is regulated through brake valves.

Now, if you remove the brake fluid from an automobile, the brakes will not apply as there is no transfer of force by way of the fluid, which is now absent. The main reservoir air on a train car is like the brake fluid on an automobile. It travels by way of the pipe to the brake shoes, applying them.

Now, You can drain the main reservoir  air out of the railroad car, using a duplex release valve, thus rendering the brakes inoperative. That allows movement with out needing the brake pipe hooked up and charged. It also means that the handbrake is the only way to control or stop a railroad car.

This method is often used in hump yards where brake applications are not desired as each car is cut away from the train being classified.

When a train is assembled and brake hoses are connected and the system is charged, the main reservoir on each car is resupplied by the brake pipe air through the railcar airbrake control valve. It takes a while to recharge the brake system on freight trains as the main reservoir on each car fills up slowly.

I could go on, and I am sure this answer isn't totally correct, but this is the basic idea of how train brakes work...

Tom