Tender brakes air pressure and leverage

[Fender]

Another variable to include in the analysis is the brake lining material. For example, McMaster Carr lists linings of various widths and thicknesses, with coefficients of friction between 0.14 to 0.55, so changing to a different lining will make significant difference in braking. If the shoes are not lined, it will make a large difference if they are bronze, aluminum or cast iron.

[cbrew]

I guess i can chime in,
I run auto air on the train while the locomotive, tender and fuel tender are on the indy system.
I run a 50 psi line pressure with 110 psi in the main tanks (via regulator)
all the linkages use the 2.5 to 1 lever on a .75 bore cylinder per truck. the shoes are alum on steel wheels for all the cars. bronze shoes on steel tires on the locomotive.
Russ can speak to how effective the brakes are on my truck

[NP317]

Chris Brew wrote:
"Russ can speak to how effective the brakes are on my truck" (I think he meant Train.)

Totally true! Saved our proverbial bacon!
RussN

[DaveD]

Thanks again for the comments. I'm learning a bunch about where to go with this. But my focus for now is getting it right mechanically for the tender, and I believe I'm on the right track. Chris Brew's comment somehow got me to a thread that is now eight years old, Air Brake Question at http://www.chaski.org/homemachinist/vie ... ?t=96484. , which, in addition to a thorough discussion of automatic air brakes, has a lot of general information about what I am looking for, certainly something that I have to aim for farther down the line. I'm sure there are other threads that I haven't found.

My plans at this point are to attach the propane car with a drawbar to minimize the danger of separation and to have a compressor there with a storage tank, using air brakes on all three units.

[Berkman]

As long as you have safety chains there is no reason for a drawbar connection.
Many transfer tables and turntables will likely not be long enough for the locomotive + propane car, and the draw connection will get old quick when you have to uncouple it multiple times a day. Follow chuck hackett's advice on the type of propane connection to use. I believe his automatically close if the connection is pulled apart.

Straight air on the drivers, tender and a couple of trailing cars will be enough braking power for a number of cars. For the trailing cars just go with something off the shelf from Titan or Tom Bee. Now if you plan to pull the public on heavier riding cars or have a bunch of pullmans, you might want straight air on all of them. Many on here recommend a viair compressor.

True automatic air brakes add a lot of complexity, and you are just asking for leaks in the system with the additional components. Straight air using clippard fittings/tubing works really well and is bulletproof reliable. Plus if something breaks, it's easy and cheap to order a replacement.

Having a trailing propane + air compressor + tool car will be quite handy. This could also be a RPO/ or baggage car.

[DaveD]

I piped it up and applied air pressure. I placed a return spring with seven pounds force in the cylinder, so this return force should be subtracted from the apply force. At 20 PSI (13 PSI effective) I could barely turn the five inch wheels, at 35 PSI they were firmly locked against my effort to turn them. It appears that fairly low air pressure will do the trick.

The ruler is there to keep the trucks from swiveling against brake pressure and they swiveled perhaps 0.010" each when measured at outside end of wheels. With this setup the total piston movement against the 35 PSI was about 1", with a full movement possible of 1.6", so the piston movement max appear to be OK. But I have a question: There generally is lots of play between the rail and wheel flange width when built to spec, and I'm wondering whether hard brake application with several hundred pounds of tender, water, and operator on the trucks will cause them to swivel a bit, requiring additional piston travel to fully apply the brakes. I don't suspect that this is a problem, as most of the brake cylinders I've seen, mostly vacuum, have very little travel by comparison. But just to be sure...