I’m currently filling out my iMechE application to become a MEng

Do you mean CEng?

…with a brake which is sprung on the spring or the brake pad could fail…

Three axle trucks and trailers usually have two axles braked. It would take all four springs to fail at the same time to leave it with no parking brake at all.

Any explanation of a braking system that includes the words “Many runaways have resulted from…” suggests there is a fault with the system.
There are far more trucks in the world than trains, yet they are not regularly running away.

Does CEng FInstMC count ?

There’s a link (from the link I posted earlier) that’s specific to North American Freight Train brakes
http://www.railway-technical.com/brake2.shtml
This is more frightening than the first link

😯

I’d always assumed that air pressure held the brakes off, and if that pressure went away the brakes were applied by a spring.

What that article doesn’t seem to cover is why they are how they are. I assume it’s in order to achieve even application of brakes across all cars, which would be very hard to achieve with springs.

What that article doesn’t seem to cover is why they are how they are. I assume it’s in order to achieve even application of brakes across all cars, which would be very hard to achieve with springs.

Well it would be, but for the fact the air pressure still pushes against a spring to apply the brakes, hence there’s still going to be some variation. I’m struggling to see any advantage over having brakes simply applied by springs and held off by air pressure.

Yes, but the spring in that system can be trivially weak, as it’s simply to move the pad back when the brake is released, so variations in spring rates will have negligible effect on the braking force.

With brakes applied by springs and held off by air pressure, I suspect that you could easily end up with some brakes being firmly applied with others not being applied at all, which would probably lead to the applied brakes overheating.

?Really? Why not just wind the springs the same or add some adjustment allowing for calibration in the factory?

Well, I’m guessing that the fact that a train may be made up of different cars from different factories makes that a harder problem. I don’t really know, but I’m trying to figure out why an entire industry would adopt such a complex approach if there’s a simpler and safer alternative. I’m sure there’s a good reason for it, and my best guess so far is brake balancing.

Fair enough bru

Thinking about this a bit more,from a truck mechanic’s point of view, I’m guessing that system is the best they could come up with using a single pipe between wagons.
A basic two pipe system, as used on trucks since the 1930s would be an improvement.
As would spring brakes, as used on trucks since the 1960s.
Another problem that comes to mind, is that all wagons in the train are braking equally, whether they are loaded or empty. This means that either the empty ones will lock their wheels under braking, or the loaded ones will not be braking as hard as they could.
A simple mechanical load sensing valve as used on trucks since the 1970s would solve this.
As would ABS, as used on trucks since the 1980s.
Better still, considering the length of a train and the time it takes for a variation in air pressure to travel from one end to the other, EBS, as used on trucks since the 1990s.

As long as they stick to 100 year old technology, articles about train brakes are always going to have to explain what causes runaways, while articles about truck brakes don’t.

But how would you introduce a new standard without making it incompatible with the existing rolling stock?

I’m no expert on trains, but I do take an interest in them.
I believe trains can have either air or vacuum brakes and steam or electric heating.
As long as the locomotive is equipped for both and the train is made up of one type of wagon or the other, it’s not a problem.
I don’t know about the US, but in the UK, the days of mixed goods trains are long gone.
Most goods trains are made up of identical wagons coupled together in permanent sets.
It shouldn’t be too hard to upgrade the wagons in sets.

I can tell you’re impressed with how up to date their technology is, aren’t you Graham?

I was genuinely shocked when I read about how they work.
It really is a crap system and it seems to be accepted that the driver has to use his skill in estimating how much air is left in the reservoirs to compensate for the crapness and avoid a runaway.

If a trailer behind a truck loses its air it will stop.
It might rip the tread off all six tyres as they lock up and the car behind might run in to it as screeches to a sudden halt, but it will stop and the brakes will remain applied until someone connects an air supply or winds them all off manually.
That’s a proper fail safe system.

I’m actually a qualified safety engineer. And that is truly shocking, right up there with the helicopters that suffered rotor detachemnt on gearbox failure.

Oh, and we did the whole engineer/mechanic thing a year ago.
http://singletrackworld.com/forum/topic/what-i-do-at-work-bus-in-bits-content

I remember thinking at the time that I ought to refer to myself as an engineer more often, knowing as I do now how important some people think job titles are. 😉

I’m actually a qualified safety engineer.

I’m not, but I don’t think I’d could even get a risk assessment passed if it was relying on that train braking system.