Diesel driving question

[scottishchris]

Can anyone explain why when a diesel loco is pulling away, the driver tends to take power, ease off, then take power again at a higher level?
Thanks in advance.

 

[andrewkeith5]

I can't say for sure, but I would imagine it is to do with using enough power to generate sufficient torque to get the train moving then holding back a little so that once the power takes hold the passengers don't all end up in the trailing cab?

Or if you're talking about at this time of year specifically it's probably to with traction on poor rail surfaces.

 

[scottishchris]

Thanks for that! So it just makes the take-off a bit smoother and a bit less 'all or nothing', getting the wheels moving before putting the full power down?

 

[plarailfan]

I should imagine that applying the power gradually reduces the possibility of broken couplings and wheelslip.
Also, the transmission (hydraulic / electric, etc) is not subject to quite as much stress and strain, which can save on general wear and tear.

 

[HSTfan!!!]

We don't really ease off unless you experience slip, tend to start off in notch 1 and slowly move through the throttle notches as appropriate. If you're on a gradient you'll perhaps need notch 2 or 3 to get going.

 

[HarleyDavidson]

I was taught on 15x series to start away in notch 2 or 3, particularly when it was damp to avoid wheelslip and the transmission light coming on & eventually locking the transmission out.

I use the same principals on EMUs too and it does seem to work (at times).

 

[andrewkeith5]

Thanks for that! So it just makes the take-off a bit smoother and a bit less 'all or nothing', getting the wheels moving before putting the full power down?

Please don't take my word as gospel, I am not a train driver! But yes that was pretty much what I was getting at.

I was just suggesting what sounds logical to me. There are also likely to be differences between how you'd drive a DMU and a locomotive.

I base my thoughts on how I drive my car - I have a car with a fairly sporty engine setup where the power and torque come late in the rev range - so to get a smooth start with a nice, comfortable acceleration rate (instead of launching off into the distance) without stalling or lurching around, I have to apply a short blast of high power level then ease off quickly to a more reasonable rate so that the engine bites enough to get going but doesn't launch me into the car in front! Makes everything much smoother and more comfortable.

 

[neilb62]

What you can also hear is the revs change as the load-regulator brings field-diverts in with no action from the Driver, on 47's for instance in the dry I used to select 'on' wait for power then go to about half power, the revs would build and die off as the charge air from the turbo and the load regulator acted on the engine governor. Up to about 30-35 then select full power and let it do its stuff...

 

[Jamesb1974]

Deleted

 

[ComUtoR]

Is it specific to a location ?

Pull away to 15mph, coast, clear station, crank it open ?

 

[scottishchris]

I've noticed it most on 47s and Valenta engined HSTs as they were the mainstay where I come from when I was growing up. I'm sure I've seen it on 67s since, though.
It's most noticeable audibly, but also visibly on an HST when it's clagging. You get the 1st burst of smoke with the 1st power application, a bit of clear air, then a more constant stream of smoke as the power's re-applied.
--- old post above --- --- new post below ---
No specific location, ComUtoR, but your description does sum it up well.
--- old post above --- --- new post below ---
So, neilb62, you're saying that the loco knows how much power it needs, sets the revs to get that power off boost, then along comes the turbo and messes up the calculations?
Simply put, I know but at least I understand what I mean. Lol.

 

[455driver]

Probably the Alternator magnetic field building up putting a load on the engine.

 

[Jamesb1974]

Deleted

 

[E&W Lucas]

I can't say for sure, but I would imagine it is to do with using enough power to generate sufficient torque to get the train moving then holding back a little so that once the power takes hold the passengers don't all end up in the trailing cab?

Or if you're talking about at this time of year specifically it's probably to with traction on poor rail surfaces.

And also:
--- old post above --- --- new post below ---

I should imagine that applying the power gradually reduces the possibility of broken couplings and wheelslip.
Also, the transmission (hydraulic / electric, etc) is not subject to quite as much stress and strain, which can save on general wear and tear.

These boards are plagued by ill informed comments, from those with no clue about the realities of railways.
Why oh why do you people post about things you know nothing about?

 

[CharlieSpotted]

These boards are plagued by ill informed comments, from those with no clue about the realities of railways.

Why oh why do you people post about things you know nothing about?

A bit unfair, both of these posters qualified their comments with "I would imagine that..." or similar.

 

[scotsman]

It's most noticeable audibly, but also visibly on an HST when it's clagging. You get the 1st burst of smoke with the 1st power application, a bit of clear air, then a more constant stream of smoke as the power's re-applied.

What you actually saw was the result of incomplete combustion whilst the engine was idling, and this was cleared out as the power was taken. The power is retained and then gradually increased.

 

[E&W Lucas]

A bit unfair, both of these posters qualified their comments with "I would imagine that..." or similar.

Not really.
They "imagine", ergo they do not know the answer. Therefore, why bother posting ill informed nonsense?

 

[neilb62]

Not really.
They "imagine", ergo they do not know the answer. Therefore, why bother posting ill informed nonsense?

Don't be too harsh, many thousand of people are interested in what we do and how the we do it with machines work. Ill informed or not. Every question has an answer after all!

 

[Strat-tastic]

It can be good to speculate

 

[andrewkeith5]

Don't be too harsh, many thousand of people are interested in what we do and how the we do it with machines work. Ill informed or not. Every question has an answer after all!

I wouldn't bother even replying - it's almost impossible to post anything to this forum these days without being battered down by someone who's not willing to accept that forums exist for discussion.

Dozens of people on these boards seem to think they know how to do the jobs of railway management better without qualifying their comments. I don't work in the railways, and I'm quite honest about that, but that doesn't mean I can't have an opinion, speculate or engage in a discussion that means I might learn something.

Sorry, a little rant that effectively is in support of your post - but I am getting sick and tired of everything in the universe apparently being an attack on front line railway staff. I bet a lot of other people who use the railways regularly are, too...

 

[SPADTrap]

I wouldn't bother even replying - it's almost impossible to post anything to this forum these days without being battered down by someone who's not willing to accept that forums exist for discussion.

Dozens of people on these boards seem to think they know how to do the jobs of railway management better without qualifying their comments. I don't work in the railways, and I'm quite honest about that, but that doesn't mean I can't have an opinion, speculate or engage in a discussion that means I might learn something.

Sorry, a little rant that effectively is in support of your post - but I am getting sick and tired of everything in the universe apparently being an attack on front line railway staff. I bet a lot of other people who use the railways regularly are, too...

You're must be new :razz:

Dont get sick and tired of what you read on forums and the Internet take a break and go outside, come back and carry on

 

[Dazza3732]

When I depart on an HST, I always apply notch 2 or 3 if needed, then when speed is about 20-25 mph gradually open up more power.... Unless it was back in the Valenta engine days and there were a few spotters wanting to hear the Valenta scream......... Then it was full wack

 

[andrewkeith5]

You're must be new :razz:



Dont get sick and tired of what you read on forums and the Internet take a break and go outside, come back and carry on

Haha, 'fraid not - I've been posting for years!

I don't get sick and tired of reading by any means - but I am getting sick and tired of 'discussion' forums being allowed to be railroaded by people who cannot accept that other people may have good ideas or points of reason in case it means their tirade against the industry/it's management/the public/suppliers might not be so punchy! So many threads on this forum just degenerate into playground arguments and petty insults instead of being discussions...

 

[hulabaloo]

Personally I find the professionals' views on here incredibly interesting - it's a great forum to get your side of things across, and has educated me no end about the logistical difficulties faced.

Now when I get friends and work colleagues complaining about train related things, such as short trains, no drivers etc, I can at least tell them why is isn't that simple just to throw on a few extra carriages that are lying around in the yard or grab a driver who is sitting around doing nothing.

Sometimes their eyes just glaze over, sometimes they don't!

 

[No Fault Found]

I would imagine it's to overcome the initial inertia to get the vehicle / set moving. Once it's actually moving you don't need it to be in notch 2/3 to pull away at a moderate speed.

 

[Juniper Driver]

I do sometimes on 159's on a gradient but pulling out of Waterloo platforms I apply power gently low notch...It really depends on a variety of factors and the chance of overloading in slippery conditions...I could start high and drop it back from 7-6-5 and so on so I don't go overspeed.

 

[AndrewE]

What you actually saw was the result of incomplete combustion whilst the engine was idling, and this was cleared out as the power was taken. The power is retained and then gradually increased.

There's a bit more than that (from my technical involvement 20 yrs ago.)
I believe the initial white cloud after idling is/was unburnt fuel and other condensates being evaporated out of the exhaust as it heats up, then on old diesel-electrics there was

a) turbocharger lag, so when you wanted more power you put more fuel into the cylinders, but the physically-driven turbo didn't supply enough air/oxygen to burn it all until the revs had built up, (the reason for intermittent black smoke out on the road) and

b) I used to see the "regulator" opened steadily by the driver who watched the amps build up. When they reached the top of the yellow he would stop increasing, the power unit would continue at that setting but the amps gradually dropped back as the back emf built up in the motors as we accelerated. The driver would then notch up again (creating black smoke again) to bring the traction current up to the limit. The notching up could be almost continuous in small steps if the maximum acceleration was wanted (consistent with adhesion etc), or intermittent if a good story was being told!

 

[Phil.]

And also:
--- old post above --- --- new post below ---


These boards are plagued by ill informed comments, from those with no clue about the realities of railways.
Why oh why do you people post about things you know nothing about?

OK, let's have the explanation then O expert one.

 

[zn1]

Listen to the front seaters, they know what they are doing, until u actually done the job of driving a rail vehicle, dont comment, listen and read their knowledge...