Western Railroad Discussion > How do locomotive sanders work?

The "what's wrong" image with lots of piles of sand on the ground
caused me remember a question I've been meaning to ask for a while.
What is the setup that gets sand out of locomotive sandboxes and
delivers it to the rail? I'm guessing it's not straight gravity,
as that would dump too much sand on the rail too quickly, and any kid
who has ever played in a sandbox knows the stuff likes to jam up in
a funnel.

The sand hoppers narrow to a point at the bottom. There is a trap there that allows sand to flow out by gravity, kind of like a bird feeder releases seeds. The rate of sand flow is controlled by a manually-set valve that meters the flow. Sand will flow until the trap is filled, then stop. Once in the trap, the system uses main reservoir air to shoot the sand down the tubes to the sand nozzles in front of the wheels. The sand will then gravity flow from the hoppers into the trap to replenish the supply as long as the air is blowing the sand out the nozzle.

The railroads purchase sand with very even-sized grains to prevent it from caking when it's wet and when it flows through the tubes.

On our light rail vehicles we use a silica sand, very fine grained. When you activate the sander button sand dumps as described above, but the wheels grind it into a fine powder and it gets rather dusty at times. There are certain lrv operators that will use that to your detriment if they catch you at track speed on the mainline if you get my drift.

There is a more forgiving type of sander that does not drop great gobs of sand on the rail. To me it seems sanders were "dumbed down" when they started being part of the brake system. All operator finesse was taken away, and believe me I've seen it used in the "old" days and today on older locomotives so equiped by old timers that know what they are doing.
The attached shows an "older" non EMD sand trap.

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And to add to the discussion. In locomotive facilities where you see sand piled up to the axles it is beacuse when a locomotives brakes are being tested by the loco. shop they place the loco. into emergency and sand is automaticly applied to the rails to aid in stopping. So when the workers leave the loco. in emergency you get the piles of sand. I heve seen too where engineers accidently leave the sanders on again leaving large piles of sand.

KJ Larson;UPRR
Chciago

You might be interested to know that one of the reasons steam locomotive sandboxes (sand domes) were placed atop the boilers was to keep the sand dry via the warmth of the boiler. I'm not sure if the lagging was intentionally left off that part of the boiler shell upon which the sandbox rested.
Have fun, be safe
Doc Jones

Here's a question. Does anyone know why sand works for adhesion? It is not because of grit. I'll wait awhile and let you know later.

It gives the wheel more adhesion area? (Grabbing at straws here. I too have often wondered.....)

Is it because it creates a different friction source than the rail surface presents? IIRC friction is the reason perptual motion is not possible. Wow--how long ago was high school physics?? Bartender-another round please!!!~~~Ed

Thanks for the attachment (patent drawing?), ge13031. That tells the whole story.

The sand is blown onto the rails with air pressure. Modern sanders have been considerably redesigned, compared to the diagram presented earilier, in the interests of ease of maintenance and increased reliability. Sanders are either on or off, and the rate of sand deposition is dependent on other factors like moisture, alignment of the nozzles inside the sander, etc. That burst of air which occurs right before it stops is designed to clean the sand out of the pipe between the wheel and the bottom of the sand bin.

The piles of sand you see are caused either by leaving the sanders on (virtually all modern locomotives have a button rather than a lever, a situation which more or less stops this) or leaving the locomotive in emergency.

When the silica (sand) is crushed between the wheel and rail, there is a plasma arc that is set up that attracts the wheel and rail to each other. This in a way temporarily "welds" the wheel and rail together. This "weld" action is broken by the effort of the traction motors and the weight and momentum of the Locomotive. This action is repeated over and over again hundreds of thousands of times while sand is being applied. Sounds strange but tests have shown this action happening.

Re AIRBRAKE post; Sounds interesting but do you have any data to back that up? Who did the work and where? Got any references like books or other reports? A plasma arc implies a lot of other effects that are pretty complex. This should be visible and leave a magnetized domaine. Got any more information?

This effect was establised in the 1960's in England. The railroad's have tried to use other sand that is cheaper but this is why they have to use silica sand - it is the only type of sand that wil aid in traction as it is the only sand that will produce this effect. I am told as the crystal breaks down, there is a plasma discharge. There is a company that was experimenting with a device that would electronically give the same effect. If I can find out the name I will post it here.

Back to AIRBRAKE reply: Fantastic! Learn something new everyday. If you have any other information I would sure like to learn about it. My email box will make sure I see it. Thanks again.

I'd heard it mentioned since I first started my stint in this industry back in '73 but did not sit down and discuss it until one of the RSA shows in Chicago about 3 - 4 years ago. Like I said I'll find out who the company is and let you know probably early next week via your Email here at TO or if others want more info I can post a new thread next week.

I'm not sure anyone is following this thread anymore but I'll take a chance: Now, if the plasma arc "welds" the wheel to the rail then why is it when a train stops on sand it is not then "welded" to the rail and cannot start. I have heard if you put a quarter in front of each driving wheel of a locomotive (all units) it will stall the train since the locomotive cannot "climb" the fraction of an inch thickness of the quarter. Not sure if this is absolute fact. So, then why wouldn't a few good "welds" of wheel to rail do the same job? Also, I've heard maximum adhesion occurs just as the wheel breaks loose from the rail. Electronics have already been developed to take advantage of this. I'm told that's why modern GE locomotives "sing" when they are working down and dirty. Any comments solicited.
Thanks
Have fun, be safe
Doc Jones

I was curious when operating in heavy snow conditions when the rails are covered, wouldn't the lead locomotives sanding be kind of useless, spraying the top layer of snow and not the rail?

DocJones Wrote:
-------------------------------------------------------
> ... I have heard if you
> put a quarter in front of each driving wheel of a
> locomotive (all units) it will stall the train
> since the locomotive cannot "climb" the fraction
> of an inch thickness of the quarter. Not sure if
> this is absolute fact.

To prove or disprove this old wives tale, I placed 8 1"x1"x1/4" steel blocks, one tucked against each wheel on a GP-38, and climbed over them when I got to run 3.

-LD

The wheels probably squashed the front end of those 1/4" bars a bit, so the amount to climb was probably less than 1/4" instantly, thus somewhat flattening the grade. Ignoring that however:

If I did the math right, a 1/4" jump with 40" wheels is a 7.9% grade for a short instant. Considering the whole grade is only 1/4" high, it isn't going to take a huge amount of HP to overcome it. Assuming the engine was 200K pounds and you climbed the 1/4" in one second, it looks like you needed 364 HP to do it.

I suppose this might have been a concern with a rod engine in the steam days, but I have a little trouble believing that would stop a reasonable sized engine. Again assuming a 200K pound steam engine, you need 16K lb-f drawbar pull to start up that hill. Maybe that could be a probelm for some engines.