If you gently press the brake pedal in a car, you get a gently increasing braking action. The car stops - eventually. If you nail it hard, you get a rapidly increasing braking force. The car stops, pretty quickly. With only two levels of air introduction into the system, you have just those two options - gently add more, or rapidly add more. With a more typical proportional valve, you have any rate of braking force you want, from the slightest amount to a "we gotta stop NOW". The NYAB document I linked below goes into the construction of the brake valve and how it actually works (also covers the train brake). It does make great use of air system schematic symbols, which I've forgotten most of, so at a quick glance I can't really decipher the whole thing. There are also cutaways of the valves, so more than a quick glance may reveal the answers.
The brake application across multiple units is faster than might be expected, since the independent brake includes air relays. Applying the air in the lead loco doesn;t have the same delay if it were actually supplying pressure to the 4th unit back in the cosist - instead it supplies a signal to the relay which supplies the air to the brake cylinders from the loco air reservoir.
Microsoft Word - IP-74 Supp 1.doc (nyab.com)
CONTENTS (wplives.org)
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerYeah that would be like driving a car where your only options are a light braking force or stomp the pedal as hard as you can.
not sure how you're coming to that conclusion.
there's a slow and quick application setting that would more slowly and more rapidly increase the air flow into the independent brake cylinders increasing the brake force until setting the brake handle to LAP.
similarly, slow and quick release allows braking to be decreased without dropping immediately to zero (%).
while this model has specific slow and quick settings, it seems that other units (e.g. S-40 pg B-6) have a continuous range of settings from lap to full release and lap to full-application, some self-lapping.
with a continuous self-lapping model, i'm curious how long it would take to reach the self-lapping pressure for a specific setting and what the brake % is
greg - Philadelphia & Reading / Reading
Overmod zugmann I like having full control of my independent. Hey, wait a minute... is that Australian system description saying it has only two rates of application and release? And that it's not self-maintaining? And by implication there's no relationship between the position of the independent brake handle and the amount of brake currently applied? I'd think that might suck.
zugmann I like having full control of my independent.
Hey, wait a minute... is that Australian system description saying it has only two rates of application and release? And that it's not self-maintaining? And by implication there's no relationship between the position of the independent brake handle and the amount of brake currently applied?
I'd think that might suck.
Yeah that would be like driving a car where your only options are a light braking force or stomp the pedal as hard as you can. Granted, my boss at my first job drove pretty much like that - time to move, stomp the gas pedal. Hold until halfway to destination, then let go and stomp brake pedal. Dunno if that is some typical style of Romanian driving (he was from Romania) or what - he was an EE, but not a digital specialist so I don't think it was just a binary thing.
Everything I've seen with indepedents is they are proportional to the amount the valve is opened, unless you press the handle down to bail off so the incoming slack doesn't slam into the loco, which will stop a lot faster than all those cars behind you. I need to ask next time I get to the museum if the LEMTU (Locomotive Engineerr Mobile Training Unit) car is actually functional, if it can be powered up so the controls actually do something instead of move - it has control stands for two types of EMD, an Alco, and a Baldwin I think. All housed in a converted baggage car. There are also lots of contactors and even cab signals. Back when it was in use, they would take it to various places to teach new enginemen how to run the various locos. Half is a classroom, the other half has the various control stands. Can't pull any info from the web page any more - half says under construction. A bunch of years ago, I was in the running to take over maintaining the web site, but they gave it to a guy who is more of a web designer than I am. And now it sits... and I'm assistant treasurer (ok, everyone, even engineers, had to take Eco 1 in college...).
trying to understand how a loco is controlled. i'm an EE. i ask technical quesitions and hope to get technical answers from people with experience
BigJimIn other words, the response time of a single unit is immediate,
does that really mean you have 100% braking immediately in the first unit or a single switching loco?
based on application-quick and application-slow, my impression is that brake % increases gradually the longer the brake is held in an application setting.
so it takes some time to increase brake % to some desired level (i.e. %) and it takes some time for a train to stop with the brakes set to some level (%)
Greg,
Where do you come up with this oddball stuff?
Now, to answer your question about independent brake response times...the response time is directly proportional to the number of diesel units in the consist that are mu'ed with the "A&R" hose cut in.
In other words, the response time of a single unit is immediate, that of five units cut in takes much longer. That is because the air signal between units must travel and fill a much longer air line.
.
zugmannI like having full control of my independent.
OvermodInteresting premise, though. Zug, would there be practical advantage here to having a two-range proportional brake?
I like having full control of my independent.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
zugmannold stuff.
Interesting premise, though. Zug, would there be practical advantage here to having a two-range proportional brake?
Ok, so you're talking about old stuff.
1946 Victoria Railways Westinghouse Automatic Air Brake
description of driver's straight air brake valve
gregcmy understanding is ithere are 5 independent brake settings: quick-release, slow-release, lap, slow-application and quick-application.
no, that's not how that works on anything I've used or seen?
gregcmy understanding is there are 5 independent brake settings: quick-release, slow-release, lap, slow-application and quick-application.
It would be interesting to see how 'quick' application or release differed physically or pneumatically from ordinary independent application -- is this something specific to large MUed consists (e.g. the reason you keep the ring up a second or two 'for every unit in the consist' on a P42)?
Lap of course would hold the straight-air application 'applied' (less any leakage of course).
my understanding is independent brakes directly control the brake cylinder pressure of the brakes on the locomotive.
my understanding is ithere are 5 independent brake settings: quick-release, slow-release, lap, slow-application and quick-application.
roughly, how quickly (seconds) would each setting change the amount of braking as a percentage. for example, would quick-application take 5 seconds to go from 0 to 100% braking?