Does it take more, less, or equal power for a locomotive to push a train rather than pull it? What would be the difference?
If the train is too long they won’t be able to get it started it they’re pushing it. When the train stops all the cars ‘stack’. That is, all sort of pile up next to each other. There’s a bit of slack in the connections and they all come together. When the locomotive, in the front, starts to move, it’s only moving itself…then it pulls the first car, then it only pulls the first two cars, then only the first three cars and so on until the entire train is moving.
If the locomotive were in the back it would have to get the entire train moving all at the same time and likely wouldn’t have the power to do this.
Now, if you put one in the front and one in the back so you could get it started, then cut the power to the front one and switch to the back one, that would be a different question.
ETA, you’d have to transfer the power slowly, now that I think about it, if you just killed the front one and turned on the back one that ‘stacking’ might be kind of violent.
Probably somewhat more to push, so far as I know, for the reason listed in the previous post. With that said, many commuter type passenger trains in North America and Europe are run as push-pull operations, with a locomotive on one end and an unpowered ‘cab car’ on the other. This saves on turning the train at its termini. It helps that the trains are relatively short and have relatively tight couplings
Issues with slack between the couplers of freights, and an increased potential for derailment with the train in compression rather than tension, mitigate against powering freights solely from the rear, except for low-speed switching moves. There is some mechanical and operational advantage, however, to the concept of distributed power: radio-controlled mid-train or tail-end helpers that augment the lead locomotives. These have become quite common on heavy freights in recent years.
[quote=“Joey_P, post:2, topic:692389”]
When the locomotive, in the front, starts to move, it’s only moving itself…then it pulls the first car, then it only pulls the first two cars, then only the first three cars and so on until the entire train is moving.
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Except when the train is on a slope, and all the wagons are held tight and therefore would move as one… Then the locomotive has to fight the force of static friction of all the bogeys all at once.
Force.
The static friction force is not much compared to taking (pulling or pushing) a full loaded train up hill … so there’s no reason to discuss static friction.
On a very flat and level surface , anyone can make a wagon move… very very slowly. You can do it with your teeth if you like. Its barely significant what mass the wagon is… “He is so strong he can make a 10 tonne wagon move with this teeth!” :~ And all the jumbe jet tugging and so on… of course its only the force of friction … which is greatly reduced by the high quality bearings in use in these devices… 
Commuter… most commuter wagons contain engines…Passengers sit in the same wagon that has the engine…
The train industry term is “electric multiple unit”. Basically its a bunch of trams joined together… “An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power.” However many designs do not have all carriages with a motor…so not all designs are like “trams joined together” these days
I was specifically referring to (mostly diesel-electric) locomotive-hauled trains, not multiple units of the type you describe. Locomotive-hauled commuter services are quite common in the US (and in some parts of France, where I lived for a time).
They’ll stack together because the braking is from the front. If the engine were always in the back, and doing most of the braking, the cars would stop stretched out. Then an engine in the back would start by pushing one car, then two cars, etc. In that case, an engine in the front would have the problem of starting all the cars at once.
But a pusher locomotive could just reverse far enough to pull them apart (unstack them) one by one, then start out forward, motivating each car in order as they get restacked by the start of motion.
I hadn’t thought about that. Makes sense in theory, I wonder if it works in practice (maybe they do it all the time, I have no idea).
Had beer, so brain not at 100%, but if the braking is at the front, the couplings will compress when you slow/stop which is what you want when you set off?
This way, there’s the slack between compress and stretch to get each car moving before the next coupling is pulled?
What’s to stop them all stacking back together when reversing stops?
Do it (start and stop) slowly.
Certainly not “most”. As El_Kabong states, locomotive-hauled commuter trains are common in the US and elsewhere. Around here commuter trains used to all be of the push-pull configuration, with (as mentioned) a cab car at the opposite end for engine control when the locomotive is pushing from the rear. Though now I’m seeing a lot of double-ended trains with a locomotive at each end.
I’m not convinced it would be practical without brakes on all the carriages - they would have to stop simultaneously, or in precise order, for it to work.
Well, there are brakes on all the cars, so there’s that. Maybe you can lightly apply them, or (if it’s possible) apply the brakes on only the last car.
Imagine a whole bunch of (regular, vehicular) cars all connected with a few feet of chains and all the bumpers touching. Don’t you think you could, very slowly, stretch them out so the chains are taut, then slow down slowly enough that they don’t all bump back into each other?
Either way, I’m sure there’s a ‘real’ way to do it. In all the years trains have been around, I’m sure them getting pushed together or spread apart when the engineer wants them the other way must happen on a somewhat regular basis.
OK. I’ll try to clear up a few things. There are three types of brakes available to the engineer. The first type is dynamic braking.This is generally used while the train is motion so it isn’t really germane to the discussion about starting and stopping. It uses the traction motors to act as generators and shunt the current up to a set of resistors in the roof of the locomotive which then dissipates the energy as heat. It’s nice because it doesn’t cause any wear on the brake pads or disk rotors.
The second type is the independent brake system. This is a set of air brakes that only affect the locomotive, or set of locomotives if more than one are “lashed up” in a “Multiple Unit” set.
The last type is the train brake system. These are controlled from the locomotive and affects all of the cars in the trainset. When these are applied each car applies its own brakes more or less equally. You can apply these to any degree you choose. The engineer moves a lever that, in effect, sends a pneumatic signal to each car to apply its brakes the amount that the engineer has moved the brake lever. The brakes can then be held at that degree of braking as long as the operator wishes. (There is also emergency braking (called the Big Hole which applies the train brakes to their maximum).
I don’t know that much about trains but don’t all the cars have brakes? I thought the cars were coupled with hydraulic lines for the brakes.
Way back when, the engines were much bigger for people trains than freight trains.
Freight does not care about small jerks so much. People on the other hand…
So for people trains, they need to stretch them out so there is a non-jerking start. It takes a bigger engine to dead start the whole train at once even if it is much less train then the average fright train. For an equal weight, the people train needs a bigger engine.
And yes, the jerking is a big deal for passenger trains, especially cross country trains from the past. Ever try to stand in an empty rail car when they pull out? 100 cars = a lot of bumps of different intensities but all can be felt by the passengers. If they are paying, their preferences are usually taken into account.
Pulling creates a stress point. Think of a trailer hitch. All the energy is focused on that one point. Pulling means friction is trying to separate at that hitch point. <-----H<------
Pushing - the forces combine. The front of the locomotive is pressing into the train. —><-----
Pushing and pulling both create stress points.