Nose wheel on Alco RS units

[thomasjmdavis]

I find it embarrassing that I need to ask, but I can't find anything in any of my references-

Alco RS1s and later RS units have a wheel on the nose of the short hood. Usually attached directly to the nose, occasionally on a stanchion at the railing.  It looks like a brake wheel on a freight car.  But I assume the brakes on a loco are in the cab under control of the engineer.  What is the purpose of this wheel?  One does not see this on many other types of locos- or at least, not so prominently placed.

[dem34]

I find it embarrassing that I need to ask, but I can't find anything in any of my references-

Alco RS1s and later RS units have a wheel on the nose of the short hood. Usually attached directly to the nose, occasionally on a stanchion at the railing.  It looks like a brake wheel on a freight car.  But I assume the brakes on a loco are in the cab under control of the engineer.  What is the purpose of this wheel?  One does not see this on many other types of locos- or at least, not so prominently placed.

Still a brakewheel, its just less prominent on most locomotives. Seen here on these EMD and GE short hoods.

[Lemosteam]

Mechanical fail-safe in case of total pneumatic system failure?

[thomasjmdavis]

Still a brakewheel, its just less prominent on most locomotives. Seen here on these EMD and GE short hoods.

Thanks.  So it is, literally, the emergency brake?

[cv_acr]

Hand brake/parking brake. Every engine has one. (Some engines used a ratcheting lever design instead of a wheel, so it's less prominent.)

[Ed Kapuscinski]

Mechanical fail-safe in case of total pneumatic system failure?

I wouldn't even say "failure". A locomotive still uses air brakes for "variable" braking while in operation. But shut it down and eventually the pressure naturally bleeds off. Since locomotives aren't always on there's got to be some method to secure them and regular hand brakes fit the bill.

[cv_acr]

I wouldn't even say "failure". A locomotive still uses air brakes for "variable" braking while in operation. But shut it down and eventually the pressure naturally bleeds off. Since locomotives aren't always on there's got to be some method to secure them and regular hand brakes fit the bill.

Exactly. Engine no run = no air = no brakes.  So you hand-brake it when you shut it down, and probably also when you tie it up idling somewhere it case it shuts down while you're gone. (Megantic anyone?)

[Lemosteam]

Exactly. Engine no run = no air = no brakes.  So you hand-brake it when you shut it down, and probably also when you tie it up idling somewhere it case it shuts down while you're gone. (Megantic anyone?)

Makes sense, conversely Heavy trucks with air brakes automatically engage with loss of pressurized air. I always thought that locomotives (trains) would work similarly, but I guess if that happened on a moving train, the brake shoes would burn off quickly.

[Kentuckian]

I thought if air pressure was lost in the train line, the air brakes would be applied because of pressure from the each individual car air reservoir? Is this correct?

[Ed Kapuscinski]

I thought if air pressure was lost in the train line, the air brakes would be applied because of pressure from the each individual car air reservoir? Is this correct?

Yes. But eventually that bleeds off and the brakes release.

[Kentuckian]

Thanks, @Ed Kapuscinski. To see what this looks like inside a cab unit, see page 10: https://www.alternatewars.com/BBOW/Railroads/EMD_FT_OM.pdf#page4

[nkalanaga]

Chris:  Megantic was my first thought as well.

Kentuckian:  Modern automatic airbrakes are a little complicated, but I'll try to keep it simple.  Old straight-air brakes released when the brake line was unpressurized, and applied when the air pressure increased, which forced a piston to extend on the brake cylinder.  A spring returned the piston when the pressure decreased.

That's still true today, as far as the brake cylinder is concerned.  But today, there's a rather complicated "triple valve" that controls everything.  When the train is first made up, there is no pressure in train line, or in the individual car reservoirs, if they've been "bled off" for switching in the yard.  The brakes are fully released.

As the pressure increases, the triple valve allows the air to fill the car reservoir.  The brakes are still released, as there's no pressure in the brake cylinder.

Once the system is fully pressurized, the train can go.  If the engineer then applies the brakes, the train line pressure drops by a measured amount, triggering the triple valve again.  It senses the pressure drop, disconnects the reservoir from the train line, and connects it to the brake cylinder, applying the brakes. 

When the engineer releases the brakes, the train line pressure increases again, the triple valve senses that the pressure is now greater than the reservoir pressure, and recharges the reservoir.  At the same time, it releases the pressure in the cylinder, allowing the spring to release the brakes.

On a parked train, in theory, the brakes will stay applied.  But all brake systems leak, and eventually the reservoir will run out of air, the cylinder will depressurize, and the brakes will release.

[randgust]

And, with that a known fact, any stopped train is required to have a minimum number of handbrakes set depending on length, and then many railroads require a 'tug' on the power before the crew is released to make SURE the train can't roll off as the air dies off. 

Megantic was the first tragedy from bled-off train brakes and insufficient handbrakes.   Parked train was left idling to keep air in the line, but unit caught fire in the turbo, fire department arrived to put out the fire and shut down the units.  Left, and a couple hours later the entire train drifted downgrade into Lac Megantic and exploded on the curve.
Similar to that, the CP spiral tunnels derailment happened when the parked train bled off on the hill, an new crew came on, and couldn't get the air back up in the trainline fast enough, down they went into an epic wreck into the river.

This whole handbrake thing is one of the key issues on one-man crews and long trains..... it's a lot to ask for one man to cover to both set and test.

Loco handbrakes can be in a lot of places but they have to be somewhere.  When you are flat switching, the only 'air brakes' you often have in a yard is the locomotive independent, and if you've been in the cab you can really get bounced around pretty good on slack run-in moving dead-air cars (which is legal).   On switchers, having the handbrake right there in the cab is kind of nice, because if the independent fails you literally have no brakes in a yard situation.  First time I was in the cab flat-switching I was told 'hang on' and good reason.

[u18b]

While we are on this subject, there are some locos that have no visible brake.
I'm thinking like some U25Cs.

Like these:

http://www.rrpicturearchives.net/showPicture.aspx?id=2384172
http://www.rrpicturearchives.net/showPicture.aspx?id=2384163


If the brake is not external, where is it?

In the cab?   In the nose?  On the back like some SD40-2?

[SD452XR]

I wouldn't even say "failure". A locomotive still uses air brakes for "variable" braking while in operation. But shut it down and eventually the pressure naturally bleeds off. Since locomotives aren't always on there's got to be some method to secure them and regular hand brakes fit the bill.

Crazy to think some L&N units had no hand brakes.