View Full Version : Brake physics and Bin -- Part Deux
01-05-2007, 09:44 AM
The previous thread on brake physics got me wondering: what's the real scoop on running releases on a freight train (from a normal slowdown using air rather than dynamic)?
The RW rule -- or so it says in North American freight train handling manuals -- is that running releases should not be attempted unless a brake pipe reduction of at least 10 pounds has been made, or else sticking brakes could result.
When I was working for a shortline, our trains were so short that 10 pounds was our usual minimum reduction (with a 24RL), so I never really got to test that theory. Neither have I discussed the matter with a RW hogger. But I do remember that the old Commodore 64 "Engine 64" simulator did enforce the 10 pound running release rule -- trying to release from a reduction of less than 10 pounds caused sticking brakes. MSTS doesn't, so I've been following the practice on my own -- making a ten pound reduction and pulling the train against the set, releasing, and using power to keep the train stretched (and at a steady speed) until the brakes fully release.
Hence, my question: since MSTS allows clean running releases from a mimimum set, is this another area that needs to be looked into, and if so, is it an issue that Bin could resolve? Or is it a purely physics issue? Or is it a non-issue?
01-05-2007, 12:51 PM
Many of the newer cars are so light that on wet rail a ten pound set could cause wheels to slide. I too remember the 10psi set rule and the 24rl brake valve from my hogging days. That valve was notorious for doing to two things. Causing newer cars to kick off their brakes randomly after being set and cars not releasing when removing the set. I still do a 2psi drop to ten pounds even in the sim. The cars are getting so realistic so I just follow RW trainhandling techniques.
01-05-2007, 01:50 PM
This is a direct quote from the current CPR GOI-Book 2 Section 16; 5.0-Minimizing Sticking Brakes
5.1 c) The total brake reduction should be at least 10 psi or more before the release is made. An overall reduction of less than 10 psi should therefore be increased to 10 psi before releasing. Brake pîpe exhaust must be stopped for at least 20 seconds before releasing.
5.1 d) Whenever air brakes are used to stop a train, if a 15 psi brake pipe reduction has not been made, it must be increased to that and comply with GOI Section 13. item 10.3-Continuity Test Procedure.
My old railroad had a similar requirement and after 25 years in the right-hand seat, for me it is an automatic gesture when making a running release of the train air brakes. Almost all railroads have similar instructions.
01-07-2007, 05:30 PM
Interesting thread for us over here (UK).Our minimum brake pipe reduction (initial application) is 0.4 bar which is about 6psi (from 72.5/5 bar) and we are told to do most of our braking in initial only.To stop dragging brakes,after the brake test the brake pipe is overcharged to approx 5.5 bar.I have had a couple of instances of dragging brakes,both caused by defective wagons.
01-08-2007, 10:33 AM
On this side of the pond, minimum reduction is 6 to 8 pounds (usually). The idea for a normal slowdown is to make your minimum set, then make additional 2 pound reductions until you reach the required speed, then release (or work power against the set, or whatever you have to do to maintain speed AND not screw up the slack).
I guess the reason I brought this all up in the first place (and maybe the Bin forum was the wrong place to do it) is that many of us run MSTS routes from different eras when different train-handling philosophies were in vogue. I have a Frisco train handling rule book from the 70's that emphasises the use of air for normal slowdowns, even with dynamic-equipped locomotives (slack control was the primary reason). My 80's-era Chessie System book emphasises dynamics over air for fuel conservation. Today, I'm told (by a Class 1 conductor) that engineers are not to touch the air unless they're stopping.
Since we're getting closer and closer to real-world physics, our methods of train handling are changing to keep pace. So as long as we're getting used to more realistic braking (and more realistic coupler and slack action), I wondered if it was time to address the "10 pounds before release" rule and if it was something that future editions of the Bin patch might cover.
01-08-2007, 11:19 AM
The only reason that Dynamos are the required method of slowing a train is fuel conservation. It is not he better way to slow a train. It is the slow way to slow a train down. With stretched braking you can come into slow areas faster and start your slowdown later but you will use more fuel due to having to power brake that train when it gets close. I for one preffered using the Dynos on long downhill grades and for an alternative way to slow a train down just to do it differently or in some special instances where it worked better then stretched braking. The rules for how you do either of the types of braking methods have not changed over the years. Just the preference the railroads have to what methods you do use out there. You run that old Frisco train and the engines have dynamos, thenuse them. The method of bunching up and applying headend braking is the same today as when the first Dynamic equipped trains showed up on the scene.
The method of stretched braking noted above is absolutely correct, but with new RW physics, the delay times before taking that next shot of air are longer and patience must be excercised before going for more or you will have a real dragging train on your hands. These are exciting times for this old sim and it's cool to see it rival the big dollar similators that Class 1's have had all to themselves these years. Now we can apply their methods or train handling to our trains and see it work as efficiently as in the RW.
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