Pound Sand, Sucky Motor Club

[bankworking]

Boy, sounds like this auto club is going to be answering to it's members and soon!



There's one case I would give the owner a pass on. I can change my own tire except when the last idiots who changed my tires ignored my explicit instructions and used an _air hammer_ to put the lug nuts back on. When they do that my short tire iron can't get nearly enough torque to get the @#$*#&^$ things off and I'm pretty much screwed...

And yes, I made them pay for my tow...

THIS. I was hugely embarrassed to have to call a tow driver to help me change a friggin' tire. Since then, I always make certain I can physically move the lugnuts after a mechanic does anything with my tires.

[mathnerd]

Scared to get out of the car?

This is PENNSYLVANIA lady, not TRANSYLVANIA!

And I'm not surprised, as technology in theory is working from one end to make life easier, people are simply deciding to abdicate more and more effort on their end so the end result is the same as it always is.... stupid.... helpless.... MORONS wanting to know why you won't help them in such SIMPLE situations!

Learned helplessness. It drives me freaking batty.

[Ophbalance]

Gah, that freakin turnpike... I broke down on that, December 05 outside of Harrisburg and across from the highway patrol. My poor little elantra blew a coil pack (leaving me with just 2 out of 4 cylinders). That was a very cold wait for a tow that day, but at least I knew the mile marker I was at. The turnpike gives meaning to the phrase "limited access highway."

[Chromatix]

Train brakes are in fact quite simple, if you limit yourselves to considering American freight trains.

There *is* a spring in the brake rigging, but it actually acts to keep the brake shoe *away* from the wheel (or the brake disc) when the brake cylinder is empty, thus preventing dragging brakes. It's not a strong spring, and is overcome by about 1psi of pressure in the cylinder. The brake cylinder itself is a simple, single-chambered affair.

There is a reservoir attached to the "triple valve" which sits between the brake pipe and the brake cylinder. This stores the energy required to apply the brake against the spring. The brake pipe serves two purposes:

1) It supplies the air needed to charge the reservoir to service pressure.

2) It provides the control signal (a reduction in pressure to apply, an increase to release) upon which the triple valve acts to transfer air from the reservoir to the brake cylinder, or from the brake cylinder to atmosphere.

The triple valve itself is very simple in its most basic form. When the brake pipe is at a higher pressure than the reservoir, it slides into the "release" position, venting the brake cylinder completely and recharging the reservoir. Conversely, when the brake pipe is at a lower pressure than the reservoir, it slides into the "apply" position, emptying the reservoir into the brake cylinder. When the pressures equalise, the triple valve goes into the "hold" position, sealing all three elements off from each other.

The triple valve makes train brakes "fail safe" by ensuring that if the brake pipe bursts or parts, the brakes automatically apply throughout the train. In this case the triple valves on each wagon will settle in the "apply" position, with equal pressure in both the reservoir and the brake cylinder, because there is no pressure in the brake pipe.

The triple valve does have a major flaw, however. The brakes will automatically release *completely* if the brake pipe is charged even slightly above the reservoir pressure. On a long train, it can take several minutes to regain full pressure after initiating a brake release - but the brakes can still be re-applied by reducing the pressure further. Eventually however, if this cycle is repeated, there will be insufficient pressure in the reservoir to provide effective brake force - the train driver has "pissed away his air" in railway-speak. This is the cause of most manned runaways.

The above problem is solved by the distributor valve, which is more complex and requires recharging the brake pipe fully in order to get a full brake release. Distributors, or some equivalently capable system, are used on passenger trains in America, and all trains in Britain and Western Europe (with increasingly rare exceptions). Drivers usually prefer distributors because they can get a partial brake release very easily, but I understand they are a bit more expensive to fit.

When shunting wagons, it is normal to drain the brake system of air and use only the brakes on the locomotive, supplemented by handbrakes on stationary wagons. There are thus manual release valves on each wagon, which vent both the reservoir and the cylinder for this purpose.

Some locomotives have a spring parking brake similar to the one described. The spring is held off during normal operation by main reservoir pressure and/or a manual catch, and a normal brake cylinder (as described above) takes over.

[mathnerd]

I believe I just had a nerdgasm.

[Argabarga]

Not yet, we haven't even gotten to the subject of locomotive dynamic brakes!

[mathnerd]

Not yet, we haven't even gotten to the subject of locomotive dynamic brakes!

*drools* Don't tease me like that!

[Argabarga]

They work similarly to how the engine or "jake" brake works on a semi truck.

Instead of using engine power to generate electricity to turn the traction motors in the locomotive's axles, the wheels are allowed to turn on their rolling inertia only. This essentialy turns the system around, and while it's running in reverse, the electricity generated is dissipated as waste heat out electrical resistor grids while providing an overall braking effort.

If I'm not explaining it well, think of it as downshifting in manual transmission car when you're coming down a hill.

The transmission is your dynamic, the brake pedal is the air brake.

Using them both like this on a grade is known as "blended braking"

And for one better, the locomotive has an "independent" brake, brakes for it's own wheels that operate, well, independent of the rest of the train, think of that as your parking brake.

[mathnerd]

I do have a passing familiarity with how jake brakes work, so that makes sense. While I'm nowhere close to an expert, I do know more about semi's than your average 4-wheel driver. I dated a trucker for a while and have several trucker friends. Unfortunately, most of them don't like taking on the teacher role when I start asking a billion questions, so what I know is limited to what I've been able to pick up in passing conversation or during the ride alongs I've done in a truck. I really know very little about locomotive mechanics, so the previous discussion has actually been quite exciting for me. When I was in university, I hemmed and hawed between pure math and mechanical engineering. I went pure math, but never lost my love of mechanics.

[dalesys]

... but never lost my love of mechanics.

And their things?

[mathnerd]

And their things?

Only if they're mechanics of the male variety.

[protege]

If you really want to have fun...electric locomotives have regenerative braking. That is, unlike the diesels with dynamic brakes...which *waste* the energy produced...electrics can actually send the energy back into the power grid.

I too appreciate engineering. In fact, I nearly went into it. But, I couldn't get my head around trig and calc

[mathnerd]

If you really want to have fun...electric locomotives have regenerative braking. That is, unlike the diesels with dynamic brakes...which *waste* the energy produced...electrics can actually send the energy back into the power grid.

I too appreciate engineering. In fact, I nearly went into it. But, I couldn't get my head around trig and calc

And, I think I know how I'll be spending my free time over the next few days. If you have any additional links that would be good reads, feel free to share them with me.

The math for me wasn't an issue. I got more interested in biostats and switched gears. My bachelor's is actually a double major in Mathematics and Biology, with minors in Chemistry and English Lit. My master's is Math with a concentration in Statistics and Probability theory, and I've taken the required coursework for a Ph.D in the same thing. It really boiled down to competing interests. Math won.

[ADeMartino]

Regenerative braking is used on electric cars, if I'm not mistaken, since it recovers a portion of the kinetic energy of the moving vehicle. I think most electric models also have traditional friction-type brakes which apply for greater braking effort.

[RealUnimportant]

A lot of hybrids will switch to regeneration almost as soon as your foot's of the gas, with the brake being used to activate the conventional brake system. If you ever get a ride in one, you'll usually see this mentioned on their in-car info screens when it occurs.