What equipment/technology does a train use to brake?
Anyone who looks at my profile will see this is the second train-themed question I have asked today! I just had some questions spinning around in my head when I was on one today! How does a train brake? It is so heavy thats surely any brake caliper would just burn to cinders. Do they use an electronic back current in the wheels (I think I read something about this at physics A level) or do they rely on some other electronic things? How much do trains rely on pure wind resistance to slow them down? And finally (lots of questions!) in an emergency and at full power, what is the stopping distance of an average train – say a train like the paddington to bristol temple meads FGW train. Thanks everyone! And no, Im not train mad! Or a spotter haha
A train has a safety system for the brakes.
They are 'Air released and Spring applied'.
Thus when there is air pressure available, the brakes can be released and applied by the driver.
If there is no air then the brakes lock on.
A train in motion has energy input by the power plant (what ever form that takes) that accelerated the train from rest and keeps it moving. When the driver wants to slow the train the energy of the train is has to be removed, as energy cannot be lost it has to be converted from motion energy to some other form. The measure of the ability of a train to convert the motion energy on braking is referred to as its brake force.
The brake force available is dependant on a number of factors; the weight, and speed of the train, the amount of friction available between the brake blocks and the wheels, the amount friction available between the wheels with brakes and the track, and condition of the track itself all connected with the amount of air pressure available to force the brake blocks against the wheels.
In short the more braked wheels and the greater the friction between the wheels and brake block and the wheels and the track (also improved by increased weight) coupled with the amount of air pressure, the better.
On modern stock (South West Trains) There are 3 main types.
455 – 450/444 and 458's.
The physics of the brakes are basically the same.
455 trains are more controlled by air pressure. There are 4 'steps to the brakes being applied. Step 1 is around a third of available air, Step 2 around 2/3rds and Step 3 is Full Service. There is also an Emergency setting which applies the brakes on all coaches and all bogies (where the wheels are)
450/444 are more computerised and have a progressive brake setting. This means that the more the brake handle is moved, the greater the force is applied to the braking system.
458's are a mix of 455 and 450/444 braking systems.
The stopping distance would depend on the track, weather, length of the train, whether the train is empty or not.
It 'could' stop in anything from 100 yards to 3 miles in bad conditions.
:~}
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Here you go this should tell you exactly how
http://en.wikipedia.org/wiki/Air_brake_(rail)
http://www.spikesys.com/Trains/brk_faq.html
References :
I Imagine a lot of braking force is developed by calipers or similar (be it air or hydraulic), a certain amount of braking can be delivered by the engine itself (assuming it is a diesel train). A full speed intercity train could easily exceed a mile in going from full speed to a standstill in an emergency. Don't get in the way of one! See also the Westinghouse patent braking system, employed by many trains.
References :
A train has a safety system for the brakes.
They are 'Air released and Spring applied'.
Thus when there is air pressure available, the brakes can be released and applied by the driver.
If there is no air then the brakes lock on.
A train in motion has energy input by the power plant (what ever form that takes) that accelerated the train from rest and keeps it moving. When the driver wants to slow the train the energy of the train is has to be removed, as energy cannot be lost it has to be converted from motion energy to some other form. The measure of the ability of a train to convert the motion energy on braking is referred to as its brake force.
The brake force available is dependant on a number of factors; the weight, and speed of the train, the amount of friction available between the brake blocks and the wheels, the amount friction available between the wheels with brakes and the track, and condition of the track itself all connected with the amount of air pressure available to force the brake blocks against the wheels.
In short the more braked wheels and the greater the friction between the wheels and brake block and the wheels and the track (also improved by increased weight) coupled with the amount of air pressure, the better.
On modern stock (South West Trains) There are 3 main types.
455 – 450/444 and 458's.
The physics of the brakes are basically the same.
455 trains are more controlled by air pressure. There are 4 'steps to the brakes being applied. Step 1 is around a third of available air, Step 2 around 2/3rds and Step 3 is Full Service. There is also an Emergency setting which applies the brakes on all coaches and all bogies (where the wheels are)
450/444 are more computerised and have a progressive brake setting. This means that the more the brake handle is moved, the greater the force is applied to the braking system.
458's are a mix of 455 and 450/444 braking systems.
The stopping distance would depend on the track, weather, length of the train, whether the train is empty or not.
It 'could' stop in anything from 100 yards to 3 miles in bad conditions.
:~}
References :
Train Driver – South West Trains
No most trains use disc brakes like a car but bigger…have a look at FGW HST's and you can see the discs in the middle of the coach wheels.
Other units use discs that are on the axles under the train,they are operated like truck brakes by air.
More modern electric trains do use regenerative braking…where the motor becomes a generator and puts the current back into the overhead wire…but still use air brakes as the re-gen current becomes lower.
References :
Whatever it is, it doesn't work very well, a train travelling at high speed takes well over a mile to stop, even on flat land, more if it's downhill. What this means is that even on a straight track, in good sunlight, a passenger train will not be able to stop within the driver's field of vision. Scary, huh?
http://www.davros.org/rail/signalling/articles/intro.html
References :
Most modern trains use disc brakes, applied using air pressure in a brake cylinder. Full service braking is typically about 3.5 to 4 bar.
Diesel units can stop very efficiently, but can still take over a mile (from 100 mph in the case of a 170). However, if the railhead is contaminated, this distance will be much greater, as either the wheels will lock up, or a system call WSP (Wheel Slip Protection) will activate, which is analogous to anti-lock brakes on a car. Automatic sanders can also help in such a situation.
Sorry, I can't answer about HSTs or loco hauled stock, I'm not trained in those.
References :
Train driver