Can a DMU be dragged by a loco safely beyond its maximum speed?

[NightatLaira]

In the case of a diesel hydraulic DMU (like a 158) - supposing this 158 was dragged by a high speed loco (something like a 67/90/91 etc) but with a modified coupling made to fit the BSI. Could it in theory be safe to haul the 'dead in tow' DMU to say 120mph even though the maximum speed under its own power is 90mph?

I know 158s aren't passed beyond 90mph, but has anything like this ever been tried before? If the impeller/torque converter/centrifugal pump was disengaged (as it would be by having the dead man's handle at rest?) and the brakes were off, surely the DMU would act just like a carriage with the wheels in free-spin without any drive-train resistance?


[I got involved in a similar topic to this last week concerning electric locos being dragged and some quite interesting discussion concerning motors acting as generators were had... http://www.railforums.co.uk/showthread.php?t=33692]

 

[LE Greys]

Not sure about being dragged, but someone once told me that he knew someone who had got into trouble for an incident where he got into his 158, and didn't notice that the rear unit was a 156 in the same livery. Thinking it was another 158, he took it up to the full 90mph. The unit suffered no ill effects. It sounds unlikely, but it might have happened.

 

[mumrar]

Absolutely not, you'll get in big trouble for it. It's a bigger no-no when the unit is properly coupled to another DMU, as usually both are running it will break stuff (happened with a 153 dragged by 170 under Central). Mk1 stock is passed for 100mph and you can't haul that any faster as that is the speed rating. The case for any train which is made up of multiple different speeds is that you always travel at the lowest speed allowed for any given part of the consist.

 

[Kneedown]

The max speed of a 158 is 90mph and that of 150/3/5/6 is 75mph. final, absolutely no exception

 

[TDK]

The max speed of a 158 is 90mph and that of 150/3/5/6 is 75mph. final, absolutely no exception

That is purely down to the braking capability of the unit.

 

[Kneedown]

That is purely down to the braking capability of the unit.

Maybe, maybe not, but the fact remains that they cannot legally exceed those speeds under any circumstances.

 

[NightatLaira]

I understand its illegal,

But mechanically speaking if the brakes were off and the unit was being 'dragged' would the wheels be in free spin or would they somehow still be connected up to the engine via the impeller?

I thought diesel hydraulics had to be 'engaged' like a clutch on a car for the motive power to be exerted?

 

[AlexS]

You might well need to disengage the final drive?

Do recall the big hoo har when a CT 153 was dragged at 100 mph across the country and arrived at Tyseley with a very shagged engine assembly.

 

[turbo mick]

Just like if you had a loco hauling a class 08/09 and you exceeded 15/25mph the rods would be wrecked

Dmus all have different drive shifts and fitted with governors not to go over the max speed.


cheers

 

[Old Timer]

The maximum speed authorised for any unit or item of rolling stock, in addition to the mechanical issues such as final drives, maximum traction motor revolutions, etc, will be guided by issues such as the wheel profiles, the suspension arrangements, and the riding characteristics.

I believe there has been at least one recorded case some years back of a traction motor disintegrating after the traction unit was being driven above the maximum permitted speed.

Irrespective of the linespeed, taking any rolling stock above its maximum permitted speed will increase the potential for a derailment or for the vehicle to strike a passing train or lineside structure.

The swept kinematic envelope addresses such issues as vehicle equipment wear, and track/infrastructure tolerances within maintenance intervention levels. It does not address situations where a vehicle riding characteristics respond badly to being hauled about at above its maximum speed.

 

[met331]

Not sure about being dragged, but someone once told me that he knew someone who had got into trouble for an incident where he got into his 158, and didn't notice that the rear unit was a 156 in the same livery. Thinking it was another 158, he took it up to the full 90mph. The unit suffered no ill effects. It sounds unlikely, but it might have happened.

Before Blackboxes were fitted speed limits were exceeded when running late without authority but now they are all fitted you wouldnt dare its not worth the risk. Certain early class 150 did have a maximum speed of 75mph however they were able to top 95mph.
the Central trains incident did happen ( no names) but yes the driver wasnt popular however he made a genuine mistake and didnt realise he had the 153 on the back. No-one told him it was there.
A Nottingham driver once reported in the fault book of a 153 and i quote
" Unit rough riding at 75mph okay at 85mph." A few questions were asked by the driver manager.

 

[43167]

I was once told about a driver who was clocked doing about 85 in a 142 & his reply to the letter was so what line speed is 90 between Colton Junction & Church Fenton. Never heard what the outcome was.

 

[LE Greys]

Before Blackboxes were fitted speed limits were exceeded when running late without authority but now they are all fitted you wouldnt dare its not worth the risk. Certain early class 150 did have a maximum speed of 75mph however they were able to top 95mph.
the Central trains incident did happen ( no names) but yes the driver wasnt popular however he made a genuine mistake and didnt realise he had the 153 on the back. No-one told him it was there.
A Nottingham driver once reported in the fault book of a 153 and i quote
" Unit rough riding at 75mph okay at 85mph." A few questions were asked by the driver manager.

I've heard about the occasional 158 reaching 100mph between Dundee and Arbroath. Never happened when I was on board, but I've timed a few that hit 92 or 93, although that could be a slight under-read on the speedometer.

The weird thing about the rough ride is that it used to happen with Westerns at 60-65. Something to do with the final drive at a specific speed. It seems to happen with 158s at 75 as well (or at least with the old Wales and West units ten years ago).

 

[route:oxford]

I've heard about the occasional 158 reaching 100mph between Dundee and Arbroath. Never happened when I was on board, but I've timed a few that hit 92 or 93, although that could be a slight under-read on the speedometer.

Shortly after the 158s were introduced in Scotland, they had to be withdrawn abruptly due to a serious component failure.

Anything and everything was used to cover the 158 diagrams - The 156s pushed to the max to meet the 90mph timetables. I was commuting between Stirling & Perth regularily at the time and the 156s were certainly going over their normal specified maximum.

I recall sitting in the front carriage of a Strathclyde liveried 101 (or similar) that had been pressed into service for a particularily lively southbound ride - we were absolutely hammering down from Gleneagles - my ears "popped" as we entered the Kippenross tunnel. Passing through BofA the guard came through and opened the drivers door and asked him how fast he'd managed... The reply was 90!

 

[TDK]

but yes the driver wasnt popular however he made a genuine mistake and didnt realise he had the 153 on the back. No-one told him it was there.

It is rule that a driver should check the taction and the length of the train before relieving another driver, if he failed to do this it is misconduct even if he forgot to check. It is a breach of the rules.
--- old post above --- --- new post below ---

The maximum speed authorised for any unit or item of rolling stock, in addition to the mechanical issues such as final drives, maximum traction motor revolutions, etc, will be guided by issues such as the wheel profiles, the suspension arrangements, and the riding characteristics.

I believe there has been at least one recorded case some years back of a traction motor disintegrating after the traction unit was being driven above the maximum permitted speed.

Irrespective of the linespeed, taking any rolling stock above its maximum permitted speed will increase the potential for a derailment or for the vehicle to strike a passing train or lineside structure.

The swept kinematic envelope addresses such issues as vehicle equipment wear, and track/infrastructure tolerances within maintenance intervention levels. It does not address situations where a vehicle riding characteristics respond badly to being hauled about at above its maximum speed.

So Old Timer, if say a class 67 was hauling 4 158's (8 coaches) (no traction motors) the top speed would be 90mph if the brakes were piped throughout?

 

[Old Timer]

So Old Timer, if say a class 67 was hauling 4 158's (8 coaches) (no traction motors) the top speed would be 90mph if the brakes were piped throughout?

I am not sure I can definitively answer that one, but......

If the maximum speed of the Class 158s is 90 mph then subject to any lower speed imposed by the maintenance fitters, or the unit working instructions, then yes it could travel at that speed subject to any lower line speed.

Differential PSRS relating to that class of train would not apply of course.

There may well be restrictions that I am unaware of though so the detail would need to be checked but the principle remains sound.

 

[met331]

Your spot on TDK it is a serious breach but under the old days of Central he somehow managed to get away with it.

 

[E&W Lucas]

So Old Timer, if say a class 67 was hauling 4 158's (8 coaches) (no traction motors) the top speed would be 90mph if the brakes were piped throughout?

If you stop and think about it, the only way you can get brake continuity with a Wescode brake unit, is with the use of translator vehicles. Once you start to introduce those into the formation, surely the loco hauled speed matrix is going to come into play?

When I've had to shift dead units with a loco, it's been at 5 mph to clear the line, as it was done with an adapter coupling, and there was no brake continuity. I've never had any dealings with translator coaches, but I would expect that you'd get a speed specified to you with a consisit like that. Not the sort of formation that you would want to go flying about with either.

 

[Newportmuscles]

When 155s first came out, a story that did the rounds was that a failure at Castle Cary was towed back to Westbury at a little more than the maximum 5 MPH! (70 more!)

Also, traction motors in an 158!!! (TDK if you are a driver, what are you talking about?)

 

[O L Leigh]

It is rule that a driver should check the taction and the length of the train before relieving another driver, if he failed to do this it is misconduct even if he forgot to check. It is a breach of the rules.

Not so.

I do not believe there is anything specifically laid down in the Rules about checking the consist of the train when relieving another driver. However, many TOC's (including my own) require that the driver being relieved tells the relieving driver about the formation and consist of the train, any faults and any specific instructions relating to the working of that train (among other things). Therefore it should have been the driver being relieved who should have told the relieving driver about the Scud in the formation, although it would have fallen to the relieving driver to remember that it was there.

As to the original question, any train is limited to the maximum permitted speed of the slowest vehicle in the formation. Therefore the Cl158 delivery runs from Derby to Haymarket would have needed to be governed to a 75mph maximum because the consist usually included a Cl150/1 to prevent the train disappearing from the signaller's panel (the Cl158's had not yet been fitted with TCA's at this point). Assuming that a loco hauled DMU formation had full brake continuity the maximum speed of the entire consist would be limited to the maximum speed of the slowest vehicle in the train, whether that was the loco or the DMU or the translator vehicles. However, if we're talking about a loco assisting a failed DMU out of harm's way using an emergency coupling adaptor, we'd be looking at the unit being unbraked and therefore a maximum speed of 5mph.

O L Leigh

 

[TDK]

Also, traction motors in an 158!!! (TDK if you are a driver, what are you talking about?)

No traction motors, obviosly 158's aint got none as quoted in my post, I think you may have mis read it! I used to sign 158's so know a little about them
--- old post above --- --- new post below ---

Not so.

I do not believe there is anything specifically laid down in the Rules about checking the consist of the train when relieving another driver. However, many TOC's (including my own) require that the driver being relieved tells the relieving driver about the formation and consist of the train, any faults and any specific instructions relating to the working of that train (among other things). Therefore it should have been the driver being relieved who should have told the relieving driver about the Scud in the formation, although it would have fallen to the relieving driver to remember that it was there.

As to the original question, any train is limited to the maximum permitted speed of the slowest vehicle in the formation. Therefore the Cl158 delivery runs from Derby to Haymarket would have needed to be governed to a 75mph maximum because the consist usually included a Cl150/1 to prevent the train disappearing from the signaller's panel (the Cl158's had not yet been fitted with TCA's at this point). Assuming that a loco hauled DMU formation had full brake continuity the maximum speed of the entire consist would be limited to the maximum speed of the slowest vehicle in the train, whether that was the loco or the DMU or the translator vehicles. However, if we're talking about a loco assisting a failed DMU out of harm's way using an emergency coupling adaptor, we'd be looking at the unit being unbraked and therefore a maximum speed of 5mph.

O L Leigh

Another thing to remember if having a 158/153 or 158/150 combo is if the 153/150 is leading you do not have auto sanders or WSP (Wheel Slide Protection) as for the length of the train itpossibly is a TOC rule as the Drivers Competence assessment had an ob for the assessor to witness the reliveing driver to check the formation of the train.

 

[455driver]

No traction motors, obviosly 158's aint got none as quoted in my post, I think you may have mis read it! I used to sign 158's so know a little about them

So you are a graffiti "artist" then, its al coming out now


Yes I do know what you mean; I have just got my funny head on today!

 

[brad465]

It might be able to, but the engines of that DMU being pulled shouldn't have its engines running if it can

 

[GB]

I dare say the axle boxes would get rather shagged if you did it for extended periods of time!

 

[krus_aragon]

Well here's a real life example along the theme of the OP (although I can't give an answer). When Merseyrail's 507s have been taken off to whichever depot for servicing/overhaul (via Wrexham, as documented by nwrail.org.uk) the consist would generally be:

67 + translater + n x 507 + translater

So this consist would be limited to the top speed of the 507, rather than the 67?

 

[mumrar]

Yes, as dragging the 507 (haven't checked, but they're 75mph I think) at 35mph over will cause all sorts of damage (although the translators will be 100mph at best, being mk1s). The train wasn't designed to be travelling that fast, so the suspension, rolling characteristics etc are all going to be affected for the worse. Trains speed limits are generally decided by two factors, ability to maintain the speed i.e. not thrashing full throttle better for maintenance, and the trains riding characteristics. It's never decided by the flat out achievable speeds, don't forget Deltic prototype hit 121mph and early tests with double 37s managed 104mph.

 

[E&W Lucas]

It's all very well quoting theoretical top speeds, but you have to recognise that the Rule Book often dictates what you are actually allowed to drive at. The consists described are essentially mixed formation trains, and when I've worked similar (albeit all air braked vehicles or assorted types), I have been expected to stick to the table on page 10 of this: http://www.rgsonline.co.uk/Rule_Book/Rule Book Modules/TW - Train Working/GERT8000-TW3 Iss 2.pdf

You also tend to get an inspector on the phone, reminding you that the brake performance might not be all that you would wish for.

I would expect that there is a specific instruction relating to permitted speed with translator coaches.

 

[Newportmuscles]

Apologies TDK, have reread your post.

I've seen some interesting speeds in the back cab, and heard a far few stories, an ex driver doing 100 through Upwey with an 155 20+ years ago

 

[mumrar]

Apologies TDK, have reread your post.

I've seen some interesting speeds in the back cab, and heard a far few stories, an ex driver doing 100 through Upwey with an 155 20+ years ago

A 155 as in what become Class 153s? There is never any chance of one getting up to 100 surely, unless it was full throttle down Upwey bank I suppose.

 

[O L Leigh]

The railway is full of stories, but it doesn't make them all true.

O L Leigh