Push - Pull with top & tailed locos

[melmerby]

Hi all

 

How does a loco at the top of a train control the one on the tail when used for push-pull services?

 

e.g. DRS are using 2 class 68s topping and tailing a three coach Mk2 set for Northern services on the Cumbrian coast route and both locos are powering the train.

(7,600 hp with a load of 100 tons max seems a bit of overkill!)

 

Cheers

 

Keith

[E3109]

The rear one is not usually 'controlled' at all, it's basically turned into another carriage or wagon via isolating cocks.

 

The main exception is of course HSTs, which were designed this way and legitimately 'top and tailed' by design.

 

Edit: I just noticed you said both locos are powering.

I dunno much about 68s but I would ask if you're sure about that? As you say, seems overkill.

Why bother?

I suspect the trailing engine is just on tickover or maybe supplying ETS, but if not, and it is powering, I'd also like to know how, and more importantly, why!

Edited June 16, 2018 by E3109

[Bomag]

As far as I am aware the DRS set have been fitted with through cabling for remote control. I have no idea if this is compatible with the system fitted to the non-Chiltern Class 68; but I would not be surprised.

 

As for only providing ETH (the data panel on the one I saw last month does not mention ETS), if you have two locos then in most cases you will get better fuel economy with both at 50% output than 1 at 100% and one on low revs. 

[great central]

The pair of 37s working to Great Yarmouth are usually in multiple, the coaches being through wired with the same system as used between locos. Usually if they're not working in multi it is due to a problem with the through wiring on the coaches.

The first time it was done,I think,was by EWS for Northern's Leeds-Carlisle service around 2003-4(?). Only mod to the locos is remote operation of the fire suppression system I believe.

Not knowing what type of multiple working system the 68s employ I can't comment I'm afraid, although as Russp of this parish is a DRS driver, I'm sure he can give the definitive answer

Edited June 17, 2018 by great central

[leopardml2341]

In the '70s when the Glasgow/Edinburgh services were operated by top and tailed calass 27s, the coaches were through wired 'Blue Star' and through piped somewhat paradoxically, with a white 'reg air' pipe.

 

I have a web reference to a photo of a MK2, maybe 2a, FK which clearly shows said pipe - if only I could recall where it is.

 

The reason for this is that although 'Blue Star' mw control makes provision in the 27way jumper for three engine control lines, these weren't used and the (rear) engine revs were controlled by this white pipe running the length of the train.

 

I'm envisaging a certain amount of lag with this.......

 

Not so bad when accelerating, the rear loco would just take a while to catch up. When decelerating however......

 

AFAIK, 'Blue Star' wasn't used for engine speed control on any so equipped locomotive.

 

On 'modern' diesel locos, using the AAR system of mw control introduced (and therefore becoming the de-facto standard) with Class 66, electric control of engine revs IS accomplished, but for top and tail it would of necessity also require through wiring of the coaching stock. Ergo, without through wiring the locos can only operate 'push-pull' with a driver at each end.

 

Rgds

Edited June 17, 2018 by leopardml2341

[pheaton]

There would be a lag accelerating, not much though because reg air is 54psi max and it wouldn't take long to achieve that even over the push pull mk2s unless there is a leak of course. Deceleration wouldn't be affected by lag at all because the air is exhausted by the valve in the power controller of the loco being driven. Then you have the 27 way wires which operate things like the fire alarm, possibly fault and wheelslip lights (but not sure on those) reverser and the power control relay. Blue star is relatively simple system, compared to tdm and the Drs proprietary system. However blue star is prone to false feeds caused by damp which can cause a lot of problems.

Edited June 17, 2018 by pheaton

[melmerby]

Ironically the 3 coach set included a Mk 2 DBSO of which the controls are apparantly incompatible with the Class 68 MU set up hence topping and tailing.

The tail loco definitely sounded like it was powering as the engine pitch increased as the train accelerated.

 

There was another set working on the line with a DBSO one end (controlling) and a class 37 the other.

 

Keith

[keefer]

In the '70s when the Glasgow/Edinburgh services were operated by top and tailed calass 27s, the coaches were through wired 'Blue Star' and through piped somewhat paradoxically, with a white 'reg air' pipe.

 

I have a web reference to a photo of a MK2, maybe 2a, FK which clearly shows said pipe - if only I could recall where it is.

It's on Brian Daniels' Flickr: https://www.flickr.com/photos/brianews/5837144002/in/album-72157626969809416/

[russ p]

The 68s are not in multiple when doing topping and tailing but the rear one is often left running in trail mode where the fire suppression equipment becomes automatic.

We try to use the ETS equally between the two locos so the fuel levels stay about the same so its 50/50 which one is supplying power.

One downside with topping and tailing with 68s is the rear one often snatches with the dynamic brake under light braking ,so if anyone gets a jolt on this afternoons Yarmouth specials its nowt to do with me mate!

[Davexoc]

There were certainly a few Mk2 air-cons blue star multi-wired and control air piped, which were used in Wessex I believe with pairs of class 31s (famous pink livery). Were they also not used for Bletchley - Bedford at one point?

They were definitely trialled for summer Saturday Skegness services in 2005, but in the end EMT opted to use spare HSTs.

 

Dave

[leopardml2341]

It's on Brian Daniels' Flickr: https://www.flickr.com/photos/brianews/5837144002/in/album-72157626969809416/

That's the one, thank you.

[w124bob]

When First Northwestern used the FMrail cl 31's, I'm sure the coaches had an additional MU cable added.

[Gwiwer]

There are different systems in use or having been used.

 

Commonly the leading loco is the only one powering but the trailing one is left switched on and idling which keeps it warm and ready for use.  In many cases of Top and Tail (TnT) working the trip times are short and diesel engines are less efficient when cold and when switched on and off regularly.  According to some sources the same thinking applied to leaving first generation DMUs idling for hours at a time on shed and between duties.

 

Certain TnT operations were designed to have both locos powering with the Edinburgh - Glasgow using class 27 locos being one of them.  The specially converted class 27/1 and 27/2 locos (one of each was required per train) used through wiring so that one could control the other.  

 

In more recent times through-wired control of a remote loco has been possible using TDM (Time Division Multiplex) which sent packets of information through the RCH (Railway Clearing House) jumper cables originally used for carriage lighting IIRC.  While more often used for push-pull in conjunction with a DVT this system meant the loco could be anywhere in the train and again IIRC more than one loco could be controlled.  This is pretty much the HST arrangement as I understand it.  For a short time you could find WCML trains with a DVT leading the seated coaches, then a loco and then some Motorail vans. That avoided some fussy shunt moves if nothing else.

 

The Southern Region had its own system using the 27-way control jumper which again was designed to enable a loco to be controlled remotely when propelling a train.  It worked equally well however with TnT locos and with a single loco mid-train as sometimes happened on the mixed-traction Waterloo - Southampton / Salisbury combined trains.  These should have been formed 33/1-8TC-4Vep but sometimes had the loco amidships.  

Edited June 17, 2018 by Gwiwer

[big jim]

Our test trains are top and tail using blue star jumpers, with those in both the locos power up when the lead one takes power, if I don’t want one of the locos to power up I can turn the control switch to off in that loco, also shutting the white ‘control air’ cock on the bufferbeam that will prevent the loco taking power

 

67s use AAR cables, thebonly odd thing about those is when you shut them down at the end of the day the stop button will only shut down the lead loco, you have to go to the rear to shut down the rear one

 

If like last night I had Top and tail locos without jumper cables or main reservoir pipe then the rear loco has to be left running and manned as it won’t maintain its main res and I wouldn’t know if it had caught fire!

 

Regards Lag when shutting/powering if you shut off too quick the rear loco can give you a little shove, particularly with a 37 DBSO combo (obviously driving from the dbso), Top and tail 37s aren’t too bad, HSTs can give you a bit of a shove if you shut off too quickly too

[leopardml2341]

There are different systems in use or having been used.

 

 

 

Certain TnT operations were designed to have both locos powering with the Edinburgh - Glasgow using class 27 locos being one of them.  The specially converted class 27/1 and 27/2 locos (one of each was required per train) used through wiring so that one could control the other.  

 

This is pretty much the HST arrangement as I understand it.  

 

1. Details of current and erstwhile mw systems can be found here:

 

https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://www.rssb.co.uk/rgs/reldocs/sd001%2520iss%25202.pdf&ved=2ahUKEwiLwpb53NvbAhVKIcAKHZ3ODE8QFjAAegQIABAB&usg=AOvVaw05bN3yYzmETHve0lwixvQ1

 

2. Please refer post #5 for info regarding the Class 27 push pull operations

 

3. HSTs do not use TDM, a 36 way through wiring system is used which allows discrete 'notched' engine control at idle and then 3 increases; also described in linked document.

 

Hope that clarifies.

[leopardml2341]

67s use AAR cables, thebonly odd thing about those is when you shut them down at the end of the day the stop button will only shut down the lead loco, you have to go to the rear to shut down the rear one

 

Same applies to class 67 and DVT iirc, and probably class 68 and DVT too - though I haven't had the benefit of working with Class 68 electrical schemes (yet!).

[newbryford]

.  According to some sources the same thinking applied to leaving first generation DMUs idling for hours at a time on shed and between duties.

 

 

 I thought that locos/DMUs were left idling because the batteries couldn't be trusted to re-start the morning after.........

 

Cheers,

Mick

[leopardml2341]

Also, running diesel engines under no load for extended periods glazes the bores which is not good

Edited June 17, 2018 by leopardml2341

[DCB]

Also, running diesel engines under no load for extended periods glazes the bores which is not good

Stopping, cooling down and starting and warming up does more harm Surely heaters to keep the cooling system warm should be do able.. Kenlowe used to do one for car engines so your car was warm when you started it in the morning, (You probably had to bump start it as it flattened the battery)    I think the WR Hydraulics were hot start and had to be pre heated before starting and when they were not it caused issues.

[leopardml2341]

Surely heaters to keep the cooling system warm should be do able..

They are, Webasto Thermo 300 used as pre and boost heaters on many 15x DMUs.

Edited June 17, 2018 by leopardml2341

[Rugd1022]

When top 'n' tailing with 66s I always leave the rear one running. We do quite a lot of it on T3 jobs and once inside the possession often have to swap ends straight away in order to get the train positioned correctly, worrying about whether it'll start or not isn't exactly ideal and could lead to a job overrunning or even cancelled. Even in the Summer months the cabs can be very cold at night so it's always worthwhile keeping as much heat on the go as possible.

 

When we top 'n' tail with the HOBC the rear loco is always booked to be manned, in which case both drivers communicate via back to back radio. The rear driver usually sits in the rear most cab with the controls set up to push in reverse when required, mostly for the gradients and it's easy to do it smoothly if the rear man signs the road too, it's pretty much becomes second nature this way. Sometimes it's quite entertaining sitting watching the generous amounts of clag wafting backwards over your head as you power up then shut off as you breast the summit!

Edited June 18, 2018 by Rugd1022

[Davexoc]

They were definitely trialled for summer Saturday Skegness services in 2005, but in the end EMT opted to use spare HSTs.

Found a picture, 31602 accelerating hard out of Sleaford at the back of the trial run, load 7 with 31454 up front.

 

 

Dave

[russ p]

Found a picture, 31602 accelerating hard out of Sleaford at the back of the trial run, load 7 with 31454 up front.

 

31602k.JPG

 

 

 

Dave

I'd think throttle response with seven coaches would be pretty awful I've driven test trains with six on and that was bad enough.

I reckon with seven or more the best way of driving it would be open the power controller go on holiday for two weeks and when when you get back they might have started to rev up!

[leopardml2341]

Those coaches are referred to in the RSSB publication, linked earlier

[frobisher]

1. Details of current and erstwhile mw systems can be found here:

 

https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://www.rssb.co.uk/rgs/reldocs/sd001%20iss%202.pdf&ved=2ahUKEwiLwpb53NvbAhVKIcAKHZ3ODE8QFjAAegQIABAB&usg=AOvVaw05bN3yYzmETHve0lwixvQ1

Cheers for that

 

Practically speaking, the coaching stock that is through wired with Blue Star has a straight 27-way cable run (no intervening electrics), correct? The same would be true of AAR wired stock also? If so, does this mean that with suitable adaptors at each end of the rake, Blue Star stock could be used with AAR equipped loco(s)/driving trailer setups and vice versa or is this a case of never the twain shall meet..?