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?
This is interesting, as I thought the independent was a proportional (and inherently graduated-release) straight-air brake. I presume this is different from positions on the Westinghouse one-pipe control valve where the independent is ‘co-actuated’ as a general rule during certain types of brake application (and can then be ‘bailed off’ with its own separate release) – the question then becoming ‘how much is the independent set in each of the five Westinghouse brake valve positions you mentioned’. I don’t know enough to answer that definitively.
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).
no, that’s not how that works on anything I’ve used or seen?
1946 Victoria Railways Westinghouse Automatic Air Brake
description of driver’s straight air brake valve
Ok, so you’re talking about old stuff.
Old Australian stuff.
Interesting premise, though. Zug, would there be practical advantage here to having a two-range proportional brake?
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.
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.
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
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 (%)
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 variou
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
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)
–Randy
I suspect this is not an MU system.
I have operated brake like this on old electric railway equipment. My guess is it was meant for running trains without an effective trainline.
you seem to be suggesting that application-slow or quick are two pressures applied to the brake cylinder instead of the “rate” the brake pressure increases.
application-slow will increase the brake % until it reaches 100%. it takes less time with application-quick. you can stop increasing the brake % by moving to LAP
did you look at the link to 26L Brake Equipment in my previous post
Randy,
If you are speaking of the OP comment, maybe so.
Greg,
If you are speaking of a U.S. loco, forget all of that crap that you posted in your first post. It does not apply here.
“does that really mean you have 100% braking immediately in the first unit or a single switching loco?”
Yes! On a single unit, you will feel every move you make, from full release to full application and everywhere in between, with the independent brake valve as soon as you make it. It is when you add more units with their brakes cut in that you feel the response time slow down.
"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 "
rrinker,
Well, that is a bit confusing!
The independent brake is controlled by the lead unit (usually). The lead unit sends an air signal to the control valve of every unit in the consist. That signal has a maximum air pressure of 60 psi. That is why you can have multiple unit operation. That “signal” is then translated by the locomotive control valve, of which there are many types and each operate the brake cylinder at a different pressure. But this is not the point.
The point is, that the “signal” from the controling unit has to pass to each unit that the independent brake is cut in on. Consquently, the more units, the longer it takes to fill the "Apply & Release&q
“my understanding is ithere are 5 independent brake settings: quick-release, slow-release, lap, slow-application and quick-application.”
Maybe on steam engines, and early diesels and electric-powered switchers, but not on any engines I ever ran (starting in 1979, and some of them were switch engines dating back to the late 1940’s).**
On engines from the late 40’s onward, the independent brake had (from left to right)
release (you could also remove the handle in this position)
application zone (cylinder pressure increases as handle moved to right)
full application (handle couldn’t be moved any further)
… and that’s all. No “lap” at all.
In addition, depressing the handle (at any position) was the “bail off” feature, and would either partially or fully release the engine brakes regardless of the automatic brake application.
** I was on an old New York Central S2 electric once at Croton, dating back to the original NYC electrification of around 1904 (or 06?), and I believe it had an older-style independent with a “lap” position.
Just for the record, I think the “Westinghouse” referred to here is the British Westinghouse Ltd., which was run by Metropolitan-Vickers after 1919. It may bear little resemblance to anything the Westinghouse company here offered by 1946.
I can see how desire for foolish consistency might want the locomotive brake to work ‘the same’ as locomotive-and-train brake – and how a slow-speed position either side of ‘lap’ would be a fine answer to having to build a proportional setup.
I used to run an engine equipped with #6 ET brakes. The independent was as simple as simple can be. It responded as quickly as the air pressure could build up against the brake pistons (3 in this case) to about 45 pounds. Probably twenty to twenty-five seconds. Half that time in Quick Apply. I don’t recall having to use quick application very often.
100% braking will just get you flat spots in most cases and probably won’t get you stopped any sooner.
The positions between running and release were spring loaded to return the handle to the running position. Likewise the position between Slow Application and Quick Application was spring loaded to return the handle to Slow Application.
I hardly ever recall using the lap position, maybe a little if you wanted to hold a light application but there was seldom a need to. The independent was primarily used when the engine was running light OR to keep the engine brakes bailed off (there was no bail-off on the automatic) while applying the train (automatic) brakes.
Overheated driver tires were frowned upon.
6_ET_0001 by Edmund, on Flickr
Good Luck, Ed
