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The draft gear is a device that allows for a certain amount of play in the couplers. But it doesn’t really seem to be a gear. What is it really?
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When brakes are applied they are done so progressively so that each car breaks before the next. Does the progression start at the front of the train or the rear?
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“Gear” means “equipment” or a collection of property, not necessarily a toothed wheel.
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When a train goes into emergency the pressure of the brake pipe is released. The pressure in the pipe does not drop to zero along the entire length at the same instant. It takes a finite period of time to progress along its length, thus the brakes are applied in progression from the point where emergency was applied. If from the locomotive at the front of the train then the first cars get braking action prior to cars following. If from a seperated hose somewhere along the length of the train then braking action propagates from that point in both directions.
There is a special version of the triple valve that, if it senses an emergency application of the brakes, will dump air from the main pipe itself which increases the speed of the pressure drop and thus increases the speed of the propagation from one car to the next.
I am sure those that work with this stuff can correct or expound on what I have said here.
The “gear” refers to “related equipment” such as fishing gear, reather than gear with teeth. I can’t answer the second question.
Tom
1.) I have an old prototype coupler planted in my back yard. It was removed from an old flat car that was serving as a bridge over a small creek. The fellow that brought it to me also brought all the ancillary hardware, which included - a gear!
More likely, it’s the same thing as SCUBA gear. No gears there either.
2.) I’m pretty sure that the train brakes apply from the front to the rear. This allows the slack to be drawn in gradually. If it were the other way around, the rear end would separate from the train in most brake applications - especially in emergency.
Just my guesses!!
the other chip
On passenger trains equipped with EP (electro-pneumatic) brakes, the brakes in all cars apply simultaneously. Also, a freature called EP hold allows the brake pipe to recharge the system without releasing the brakes,thereby allowing the brakes to release quickly when it’s time to go.
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“gear” would refer to equipment.
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train brakes would be applied from the point where the brake pipe reduction was initiated. usually that’s from the locomotive or a back up hose on a caboose or separation.
How about the synonym “apparatus”?
The air brakes apply when there is a difference in pressure between the train line and the auxilary reservoir on the car.
That difference in pressure is caused by venting the air in the brake pipe to atmosphere. The most common way is with the air brake valve on the engine. In that case the pressure drops from the front of the engine so the cars next to the engine apply their brakes first. If there is a remote control engine on the rear (common in modern coal trains, then the engine on the rear also initiates a reduction so the brakes apply from both ends. If the movement is being protected by a conductor on a caboose or a pasenger train with a tail hose the conductor can initial an emergency application and the brakes will apply from the rear. If the train line breaks the application will move outward from where ever the break occurs.
Dave H.
Chip, the illustration shows a typical steam-era arrangement of coupler, yoke and draft gear.
Cheers,
Mark.
Valve gear, running gear (locomotive), running gear (sports), military gear (helmet, webbing, body armour, etc.)… [:)]
I learn a lot over in the trainsmagazine forum next door, and they had a good thread about couplers and brakes over there not long ago. Fascinating. Who woulda thunk a coupler was so complex?
It needs to be strong to resist 500,000 pounds pressure at times.
I hope I got that right more or less in the ballpark.
The variant of damage-free coupler mounting that used a moving center beam inside the usual freight car center sill had a standard draft gear installed on each end of the moving beam. The less-complex version simply used a draft gear with longer coupler travel (in a fore-and-aft direction.)
I vaguely recall that, with standard air brakes, the pressure reduction wave front travels at about 500ft/sec, so on a 5000 foot long train FRED will sense brake application about ten seconds after the air brake handle is moved in the cab. (This is 1970’s technology. More recent systems may propagate faster, but they are still a long way from instantaneous.)
Chuck (modeling Central Japan in September, 1964)
Interesting. I’d have thought that the pressure wave would travel at the speed of sound (1056 ft/sec) less some friction loss for the pipe. This would be closer to 5 seconds for a 5000-foot train.
Chris
I believe air systems that “Pass the word” from engine to fred is at the maximum possible… roughly 900 feet/second?
To gain faster response will be necessary to allow each individual freight car to be connected via fiber optics and allowed to work togehter as a sort of a massive capstan crew all pulling together to one fiddle (Computer)
Airbrakes on a big rig only need a few seconds max to generate maximum braking horsepower availible depending on road conditions. We are already seeing electric braking with very large drums and rumors of electro generative braking which are nothing more than wild fantasys from the few who have been around desiel fumes a bit much.
I may be off base on my thinking but you’ll read it anyway…[:-^]
You are dealing with more than has been brought up so far. Not only is the brake hose pressurized but you also have the brake diaphrams (or equivalant RR name) that is pressurized. This creates additional volume, and if you factor in the obstructions (hose fittings, pipe fiitings, etc…) in the way of the airflow this slows down the pressure drop even more.
Just my thoughts from me…
On train brakes, the actual braking pressure is applied from the reservoir on the car. The train line recharges the reservoir through the triple valve, which also controls the application by sensing the pressure differential between the brake line and the reservoir. So, the pressure drop for the entire train is not slowed appreciably by the reservoirs and brake cylinder piston volumes…
That makes sense…
any idea on the psi used and what the differential needs to be to activate the brakes?
There are no “diaphrams” as in road vehicle brakes. There is a piston operating with the brake cylinder. The only time the brake cylinder is pressurised is when the brakes are applied - or when the application is held by putting the automatic brake handle in to the lap position. The crucial difference between train and vehicle brakes is that brake pipe pressure must be REDUCED to make an application.
Cheers,
Mark.
The pressure of the brake pipe/train line will vary according to the railroad and the type of service, so these figures I quote - used by the railway I work for - are given as examples only.
When I was running freight, brake pipe pressure was set at 500kpa, or about 72psi. Loco-hauled passenger trains were to carry 600kpa, or 87psi. The electric multiple units I run now carry 450kpa, about 65psi. In addition, these EMUs have Westcode electropneumatic brake.
The amount of pressure differential needed to make an application is not large. Our typical minimum reduction in normal service on freight was about 7lbs. A full service reduction was generally 25lbs. Owing to the difference in volume between the auxilliary reservoir and the brake cylinder, a 25lb brake pipe reduction will put 50lbs in the cylinder, assuming the piston travel is properly adjusted.
Cheers,
Mark.
Dozens of pounds PSI.
In trucking the diagphram springs are rated in the thousands of pounds to overcome the loss of pressure and lock the brakes down should there be a dangerous loss of air. I realize my numbers are pitfully small, but to apply the service brake would be 10-30 pounds and compressor supplies about 90 to 120 into the dry tank ready to use. Once below 60 pounds the springs start to take over and if left alone, eventually stops the vehicle.
The brake chambers are two halfs. One is where air is forced into against a synthetic membrane. On the other side of that is the spring and the foundation rod that applies force to the drum through a cam system.
In the small cars brake fluid does the same job. But would not survive the very high temperatures potentially reaching a thousand or two of degrees. The fluid would burn up and catch the car on fire. That is one benefit of air. You can heat it quite a bit and still be in service on that mountain.
In order to stop a rig you chose a service application of about 20 pounds give or take a few roughly 8 seconds prior to your chosen stopping point at the light. You can make it max application at any time during that stop but at the price of air loss.
Mountain downgrades are a simple contest between brake application over time versus what you are supplying back into the air tank verus brake temperature and thermal damage. If everything is in balance you are ok. Should one exceed it’s physical limits… well… that is what you are trained for eh?