How exactly in detail do Trains Work?

5 Answers

  • 1 decade ago
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    Definitely a broad question as pointed out above. But, I'll take the time to give a detailed answer if you'll take the time to read it.

    There is indeed a lot of text. For that reason, I will enter the answer in parts so no work gets lost due to power failure, etc.

    Of course there are tons of variables at play, so lets set some parameters. For our purposes, we will be using for our model a consist of EMD SD45T-2s, as delivered to the SP, and standard freight car equipment, strictly for simplicity.

    Further, we will break the answer into three parts covering air, mechanical and electrical. There will be overlaps. Operating rules will only be touched on and only when necessary. There is no way the spell checker will keep up, so my apologies in advance for typos.

    Let's start with roadbed. The four basic parts of the rail are the base, the web, the head and the ball, which is the top of the rail. Most of today's main line rail is of the 139 lb variety. This means that a 3' section of rail weighs in at 139 lbs. Where some older branch line and yard tracks are still in service can be as light as 80 lbs.

    Standard gage, the inside distance between rail heads, is 4'81/2". The rails are laid on cross-ties made of wood or concrete, with tie plates underneath the rail where wooden ties are utilized or bolted to the concrete ties. Today, most rail is CWR (continuous welded rail), aka ribbon rail. These are laid in 1320' sections, with those sections being welded together after having been laid. This is done for a couple of reasons.

    The first reason is a maintenance issue. Where joints in the rail are there is a gap, albeit a narrow one, but a gap none the less. Over time, with constant pounding from the equipment passing over it, becomes a "depression" and requires frequent grinding to prevent further wear. Another reason is that since the joints are off-set, and either in 39' or 78' sections, when passing over a joint the equipment will take a little "dip" on one side, then on the other, then back to the other side, and so on. This creates a phenomonon called "harmonic roll" and is most prevalent at 15 miles per hour. It can become severe enough for equipment to actually turn over on its side. Consequently engineers try to avoid this speed when possible. But ribbon rail also has the defect of its virtue.

    Since the rail joints are welded up, there is little room for expansion and contraction due to fluctuations in temperature. Rail is held in place in the longitudinal axis by way of a device called a "creeper". This is a steel device, somewhat resembling a candy cane in shape, that is applied ahead or behind of the tie plate to keep the rail from expanding length wise. They usually do their job. But even so, there are still problems.

    Not as often as before, in extremely hot weather, the rail, trying to expand, would actually lift itself off the cross ties on the outside rail of a curve, without knocking down a block signal, since the rail remains unbroken. Even worse, when the temperature cools, the rail will lay right back down, only no longer secured to the ties. There was a derailment of an AMTRAK train near Corning, Ca., some years back where this is exactly what happened.

    The flip side is extreme cold. In this situation, as the rail tries to contract, it will actually pull apart, knocking down a block signal. Usually not more than an inch or two, a train can usually pass as long as the pull-apart is over a cross tie. If not, then maintenance of way personnel will temporarily reconnect the rail using an "angle bar". These are the rail joiners that one sees where there is jointed rail. Later, a welder will come along and weld up the gap.

    Temperature of the rail during being laid or repaired must be at a given temperature. Sometimes you may see a line of flame burning along the track. This is called "burning a rope". And that is exactly what it is. A length of rope is soaked in kerosene and lit to heat the rail to the necessary temperature before being re-welded.

    Track swirches enable the train to switch from one track to another. There are differnt types, such as slip, double slip, diamond, puzzle, moveable point frog, controlled, dual control, submarine, stub, spring and variable. The three basic components are the points, the movable part of the switch, the stock rail and the frog. The frog makes way for the flanges of the wheels (the flanges allow for the wheels to follow the rail, not necessarily keep it on the rail. That is accomplished by gravity. It is the weight of the equipment that keeps it on top of the rail. The forces involved are expressed as a ratio between longitudinal force and verticle force, L/V. As long as the verticle force is greater, the equipment will stay on top of the rail. If longitudinal force becomes greater, then the equipment will pull off to the inside of a curve, with a phenomonon called "string lining", when the train slack is stretched [draft], or jack-knife on the outside of a curve when slack is bunched [buff]).

    The whole shootin' match is on top of the ballast. The ballast serves multi-functions. It holds the ties and rail in place, provides for drainage, reduces build up of vegetation and mud, and a very important but often overlooked ability to "give" to a certain degree. This is an important attribute. The next time you observe a passing train, watch what happens each time a car's trucks pass over a length of track. You will see the rail and ties dip into the ballast. This give helps to reduce the amount of interactive force where wheel meets rail, dissipating some of the mechanical energy.

    Now that we have railroad in front of us let's climb aboard our consist, which is three SD45T-2s. I have chosen this model as it is the most generic, for our purposes.

    The heart of the locomotive is the "prime mover", in this instance a 20 cylinder, 3600 Hp, 45 degree V, water cooled, turbo-charged (this is actually a hybrid. Up to and including "run 5" it is mechanically driven, as a blower, by gear, equipped with a clutch which allows it to be driven by exhaust, as a true turbo-charger, in run 6, 7 and 8) with rack fuel injection. The prime mover actually sits in the engine compartment backwards, with the rear of the motor pointing forward, though both ends are business ends.

    People often interchange the words "alternator" and "generator", but they are two different things. In our locos the elctricity that supplies the traction motors is generated by the AR10 Main Alternator. The "10" refers to the number of diodes in the alternator. Since these are equipped with DC (direct current), D77 traction motors, the electricity has to be converted from AC to DC electricity. This is done by a bank of rectifiers. How much juice can one develop? How about 9,000 amperes across a 600 volt field. One can supply your neighborhood with all the electricity it needs, with some headroom to boot.

    An interesting difference between alternators and generators, outside of the fact one develops AC and the other DC, is that alternators, including the one in your car, needs some electricity to produce electricity. On our SD45s, this is called "excitation", and the electricity is produced by the "companion aternator". In additon, there in an auxilliary genertor that supplies electricity for low voltage needs (72vDC), such as battery charging, lights and electronics.

    Our traction motors are truck mounted, axel hung, and supply power to the drivers by a simple pinion and ring gear arrangement. The gear ratio is 62:15. Maximum safe RPMs of the traction motor is reached at 72 MPH. Above this speed centrifugal force can cause the armature windings to unwind, make contact with the magnets, and cause a ground relay fault. Our engines' "overspeed" (this overspeed is deifferent than the overspeed protection for the prime mover, these maxing out at around 915 RPM) protects against this by opening the PC and causing a penalty application of the brakes (more on this to follow). Engines designed for passenger service have a higher gear ratio which allows for much higher speeds.

    As we continue towards the rear of the engine compartment, we come to the front of the prime mover and the equipment rack. On the front we find the governor, lay shaft (a manual control for injectors), overspeed reset, low water/oil reset and crankcase overpressure reset (NEVER to be reset except by mechanical department personnel), fuel feed sight glass and fuel return sight glass.

    The governor opens or closes the injectors in response to throttle position, which increases or decreases motor speed, which in turn varies the amount of electricity being fed to the traction motors.

    The equipment rack holds the cooling water tank, sight glass for the same, water tank fill (with a pressure refief valve, manually operated) start switch, load meter, shutter control (for the radiator), water temperature guage and oil pressure guage. It is also a handy place to heat food.

    Next is found the air compressor. This is a two stage, three cylinder affair, air cooled with a large oil sump, driven directly by the drive shaft. I can't recall the capacity, but it is a lot of CFM. It is equipped with a manual unloader valve, should it malfunction.

    Next we find the radiator, cooling fans and a grill, just above the cat walk, that is see through. This is what makes it a T2, or "tunnel" motor. Conventional 45s had the radiator and cooling shutter at the top of the engine. The T2s had lower air intake, so that they wouldn't be gulping hot exhaust in the tunnels.

    Now that we are at the end of this engine, we come to the next one coupled to it. We are operating a multiple unit consist, which means all locos are operated from a single control. Starting from the top down, here are the connections that must be made.

    The first is the MU cable. This carries all the electrical signals needed to operate the consist, including throttle control, engine run, generator field, control and fuel pump, dynamic brake, headlight control, forward and reverse sanders and warning devices and alarms.

    There are a number of air hoses that must be connected as well. These are the brake pipe, main reservoir, actuating pipe and BC equalizing. The brake pipe carries the air through the train to charge the brake system as well as operate it, the main reservoir connects all of the consist's main reservoir together (nominally carrying 140psi), the BC equlaizing connects all of the engine's brake control together, and the actuating pipe, which allows the engineer to keep the engine brakes released while applying brakes on the train. Its pressure is zero until activated by the engineer by "bailing off" the independent, which will the put main reservoir air directly to actuating.

    Now that our consist is properly MUed, lets head into the cab.

    On the right hand side you see the hot seat, whith the control stand right in front of you. These were not "desk top" type controls so common today.

    On the left side, directly on the side, there is the pressure control valve commonly called the "feed valve". This controls the amount of air in the equalizing reservoir. Directly below, near the floor of the cab, is the MU2A valve, which either cuts in or cuts out the independent brake valve, which controls the brakes on the engine only.

    Next, on the left front of the control stand is the 26L automatic brake valve. This controls the brakes on the cars, as well as the engine. There are several detentes on the quadrant, which are, from left to right, release (or running), intitial reduction, service, suppression, handle off and emergency. Directly below is the 6SL brake valve, which controls the engine brakes "independently" of the train brakes, hence the term independent brake valve. Its positions are release, application and a detente for full application. In addition, when depressed, in an action called "bailing off", it will keep the independent brake released during an application from the automatic brake valve, by means of the actuating pipe we discussed earlier.

    Next, on the top front of the control stand are the guages the engineer needs to know what his train is doing. These are duplex guages, meaning there are two indicator needles for each dial. There is Equalizing reservoir (white needle), Brake Cylinder (red needle), Brake Pipe (white needle) and Main Reservoir (red needle), air flow indicator ammeter and speedometer. Some included accelerometer with the speedometer and tractive effort guages.

    Below that there are two throttle levers. One for power and one for dynamic brake. Below them is the reverser. Front right of the control stand has engine run, control and fuel pump, generator field and headlight control switches. Also on the control stand is the valve for the engine bell, a simple push/pull affair, sander control and whistle valve. Indicator lights include wheel slip, DB warning, hot engine and ground relay fault.

    Now we can couple to our train. Together, all the components are referred to collectively as "draft gear", which includes the cutting lever, pin, knuckle, drawbar, coupler pocket, keeper, end sill and center sill. The cutting lever will lift the pin, which opens the knuckle for coupling and uncoupling. The drawbar runs into the coupler pocket held in place by the keeper. They have a range of lateral movement. Some cars have end of car cushioning devices, where the drawbar is spring loaded, or where the entire center sill of the car moves, helping to dissipate the mechanical shock that runs through the train as slack is adjusted.

    In additon, air hose between the equipment are connected, manually, by means of the "glad hand", the metal fitting at the ends of the air hoses, which uncouples automatically when the cars are separated. Air flow through the hoses is controlled by the "angle cock" on the ends of each car. Okay, having been sensored, **** rhymes with rock but starts with the letter "C".

    Before one starts, one needs to know how to get the thing stopped where you want it to, which is the real trick. It must be noted that there is only one means of propulsion, but four braking systems. So, lets follow the air.

    Still with me? Good. We're half way home...........

    The air brake system of today operates on the exact principle as conceived by George Westinghouse when inventing it and producing it by the Westinghouse Air Brake Company, or WABCO, which still makes all of the systems. Rather than putting air in, it operates by letting air out of a system that is positively charged.

    The air that is produced by the compressor travels through pipes that are folded from end to end, called the aftercooler. As air is compressed, it heats up, and as it cools, it will form water condensation. The aftercooler cools the air, expels water via an inertial filter, before it arrives at the main reservoir. Once there, more condensation results. There are automatic condensation releases at the and of the reservoir, and when operating make the "sputtering" or blowing sounds heard. These are also manually drained, which is a good idea, since the acrs will plug up, and if its -20 degrees, water in the brake pipe is a really bad idea.

    The feed valve regulates the pressure in the equalizing reservoir. This is a container about the size of a 2 pound coffee can. By way of the automatic brake valve, the brake pipe will follow the equalizing reservoir pressure, wether increasing, decreasing or remaining constant, the latter being governed by the pressure maintainer.

    In release, we charge the train air to 90psi for freight, 110 psi for passenger, through the brakepipe. On each car there is an air tank, the smaller portion being the auxilliary reservoir, the greater being the emergency reservoir. On each car there is a control valve, now in release position and charging the reservoirs.

    Our train is 120 cars, 8,000' in length. Tonnage is a major part, but for our purposes is not a factor. A train of this length, starting completely deleted of air, will take 45 minutes or more to charge. Here is what happens when the brakes are applied:

    The initial reduction detente on the brake valve quadrant will decrease the pressure in the equlizing reservoir by 5 to 7 lbs. The brake pipe will follow, seeking to equalize.

    On the cars, when the control valve senses a decrease of 2 psi between the brake pipe and aux reservoir pressure, it moves, connecting the ports from the aux reservoir to the brake cylinder, putting in 10 psi before returning to "lap" position. This is called "preliminary quick service". After this, for each 1 lb the engineer decreases equalizing reservoir, the brake pipe follows, the valve functions again, putting 2 lbs more pressure into the brake cylinder. This follows until, with a 90 lb brake pipe, an air reduction of 26 psi is made in the equalizing reservoir. At that point, EQ reservoir, brakepipe, aux reservoir and brake cylinder all are at 64 psi. No more differential, no more brakes, except for "emergency", when the emergency reservoir puts a funal 10 psi into the brake cylinders. If you're still moving at this point, you have a problem on your hands. It is called (this may get sensored too, but it's what it's called) "pissing away the air". It happens due to improper cycle braking, sometimes necessary on descending grade.

    Our train is 8,000 feet long. Air propagates through the brake pipe at a rate, rounded off, of 500 feet per second. So, it takes a full sixteen seconds before the brakes begin to apply on the last car. If I've got a tonnage train and I'm clicking along a 60 MPH, it takes over 1/4 mile before the train begins to slow. That's the reason if I can see you, it's already too late to stop, even in full emergency, where propagation time is greater, at 1,00 feet per second.

    16 seconds to release. But, recharge time is one minute for each 12 cars or portion thereof. Hmmm. 10 minutes to recharge, but brakes release in 16 seconds. So, you come back after 'em. Remember, you have to go 2 psi below the brake pipe, to reapply from our initial reduction release. Now we're almost 10 psi into the brake pipe, with a soft set. Cycle again, more trouble and finally, equalization.

    The valves in the engine's air box is where all the real drama takes place, which is located right beneath the cab on the engineer's side. This where we find the EQ reservoir, and the PC valve. PC stands for "pneumatic control". It is a safety device, electro-magnetically activated and mechanically opening a vent valve to immediately exhaust EQ reservoir and brakepipe to atmosphere, sometimes at an emergency rate, or a full service reduction by way of penalty application, usually triggered by the train overspeed. The main difference between the two, in addition to outcome, is that in the emergency activation, the A-1 Charging Cut-off Pilot Valve is engaged, separating the main reservoir from the EQ reservoir, to guard against an undesired release of the brakes and resulting recharge.

    To recover from and emergency application, the valve must go to emergency on the quadrant, while a penalty application can be recovered by placing the handle in the suppression position for a length of time.

    In addition, activation of the PC will return the engine to idle immediately, if working power, with a delay of 20 seconds if in dynamic brake. This is to help control slack from a slack bunched (buff) position.

    The dynamic brake is an engineer's best friend. Simply, it reverses the process of the power, in essence turning the traction motors into generators, which provides retarding effort, and a good chunk of it to boot. The electricity generated must be dissipated, and in this instance it is by heat radiated from grids in the top of the engine compartment, over the prime mover, in just the same way as your toaster works. In addition, the electricity powers large cooling fans above the grid, which provide the distinctive "whine" of an engine in dynamic braking, which varies in pitch according to how much dynamic is being used.

    As Forrest Gump would say, "That's all I have to say about that."

  • 1 decade ago

    They have flanged wheels which are guided by the permanent way, 'the track'. They have either a prime mover, a locomotive, originally steam, now diesel or electric powered, to pull or push the consist along these tracks, or are self powered - a 'multiple unit'. These can be either diesel or electrical powered once again, but the engines are built into the carriages (cars), usually, but not always, under the floor. These days locomotive hauled trains are usually found on freight services, multiple units on passenger, the latter mainly because less terminal 'turn round' time is required.

  • soto
    Lv 4
    4 years ago

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  • Anonymous
    1 decade ago

    Your question is too general. There are many different types of train, and to describe each one in detail would take many pages of text.

    Can you be more specific, perhaps adding "additional details" to your question?

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  • disel motor runs and drives a large electrie generator the conductor pushes or pulls a leaver that puts voltage to a set of electric motors conected to the wheels ..... the more power the harder the motor turns and the faster the train goes

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