Mk3 loco-hauled - why only 110mph?

[nightstar.train]

This is something i've wondered about. Why are Mk3a and 3b stock restricted to 110mph, whilst their Mk3 HST brethren are allowed at 125mph? As i understand it the only difference is the wiring in them, they are structurally the same. Is it just because they only had 110mph engines, and if so why haven't they been upped to run behind class 67s?

 

BTW i am talking about everyday running, not special exemptions for testing or what have you.

[Fat Controller]

It's not directly to do with the wiring, but because of the system of brake actuation (not sure if it's a variant/development of electro-pneumatic braking), which applies and releases the brakes within an entire HST set at once, rather than the lag one gets between the application of the brakes to individual vehicles. On the basis that 'The ability to stop gives the right to speed' this means that HSTs are allowed a higher maximum top speed, as they can stop more quickly.

[Bob Reid]

It's not directly to do with the wiring, but because of the system of brake actuation (not sure if it's a variant/development of electro-pneumatic braking), which applies and releases the brakes within an entire HST set at once, rather than the lag one gets between the application of the brakes to individual vehicles. On the basis that 'The ability to stop gives the right to speed' this means that HSTs are allowed a higher maximum top speed, as they can stop more quickly.

 

More like an Electronic version than EP, though the principles the same - each Power Car is equipped with a Davies & Metcalfe E70 electronic Brake Controller which through application valves on each power car (and the associated train wires), applies and releases the brakes simultaneously from each end, basically for the same length of train at a faster rate than a conventional loco-hauled set - we are talking fractions of a second difference in lag for either type however on an HST it's sufficient enough to reduce the stopping distance at maximum speed quite considerably!

 

Aside from all that, both the Loco-Hauled and HST Mark 3s were originally designed to operate at 125mph!

[The Fatadder]

If I remember rightly the 67s ride quality is so bad at 125mph they wouldnt want to use them at that speed anyway.

[45125]

The brakes are applied from both ends of an HST, therefore speeding up the brake application. The E70/DW2 can only release the brake from the end the set is being driven from. There is nothing to stop a loco hauled MKIII from doing 125 if you can apply the brake from both ends, remember the prototype HST used loco hauled vehicles.

 

The E70 is technically an EP brake uses EP valves to apply and release the brake, they are just controlled via electronics, the card receives inputs from three brake wires and send an output to the respective valve dependent upon what a transducer in the control chamber is seeing. The Westinghouse system,DW2 is all EP valve controlled.

[Bob Reid]

I'll need to stop using that invisible ink

[mr45144]

Is there not also the factor that, once you get above 110mph, the unions require a second man in the cab so the extra speed wasn't worth the candle.

 

Kev

[Fat Controller]

Is there not also the factor that, once you get above 110mph, the unions require a second man in the cab so the extra speed wasn't worth the candle.

 

Kev

No- that stopped ages ago.

[Pennine MC]

Possibly a red herring, but werent the cl. 87s and the WCML timetables upgraded to 110mph scheduling at around the time these vehicles were introduced? (or was it t'other way round, the scheduled speed was simply a result of the braking capability )

[great central]

Many of the 'new' cross-country HST trailers were modified from hauled stock, and presumably and rated at 125mph, not an expert on the goings-on of these things.

[nightstar.train]

Thats all v intresting, thanks all. So now my next question is, how are the Mk4 coaches braked, as these are 125mph and designed for 140mph. Do they have more powerful brakes? And if the Mk3 brakes are applied electronically, how come they are only applied from the loco end in a loco hauled set? Surely if its electronic they should all come on at the same time (give or take a micro-second).

[Fat Controller]

Thats all v intresting, thanks all. So now my next question is, how are the Mk4 coaches braked, as these are 125mph and designed for 140mph. Do they have more powerful brakes? And if the Mk3 brakes are applied electronically, how come they are only applied from the loco end in a loco hauled set? Surely if its electronic they should all come on at the same time (give or take a micro-second).

The Mk4 stock was designed to do 140 mph under what was effectively '5-aspect' signalling- there was intended to be a flashing green aspect as well as the normal 4. This would have increased the braking distance, which is the governing factor for the speed, by 25%. In the end, it was decided that signalling sighting at 140 mph was not certain enough, and that this speed would only be permitted with some form of cab-signalling.

As to the difference in HST vice loco-hauled performance- it's because part of the electronic system is in the trailing HST cab, and so the brakes are applied from both ends simultaneously (or at least as close as makes no difference outside the field of particle physics...). The Mark 3 loco-hauled stock was designed to be hauled (DVTs arrived later), and the trains included Mark 1 stock- gangwayed brakes were used as no Mark 3 Brake vehicles were built- so it wasn't thought necessary for the stock to be 125 mph-capable. It might have been possible to retro-fit the stock once DVTs became available, but there probably wasn't enough spare stock to enable whole rakes to be taken out of service to be fitted. It only became feasible to fit the equipment once the stock had been displaced by the Pendelios, by which time it wasn't seen as a priority. It's one of these cases of 'If only we'd thought of that' or 'we should have employed a Systems Engineer' which bedevil so much of industry. Mind you- the converse situation of specifying and fitting equipment which is rarely if ever used can also be problematic...What you really need is a reliable crystal ball, and an unlimited budget!

[iploffy]

A further thought or two. When I went to work for Inter-City the class 90's were being introduced these loco's had a maximum speed of 110mph obviously this could only be used with a set of Mk3's but if I remember correctly there was a small valve called a DW3 in a DVT just underneith the cooker next to the drivers cab door, It was left to the driver if he wanted to leave it in or isolate it, but when you rode in the DVT cab you could hear the brakes applying and releasing via this valve and the braking was superior. As to the second point the infastructure was not equiped to cater for higher speeds and in the latter years of BR couldn't put up with higher speeds due to restrictions on the amount of money that was spent on it, pity as the ride in a Mk3 was good but when you passed another train at full pelt everthing on your table flew off.

 

Ian

[Bob Reid]

The Mark 3 loco-hauled stock was designed to be hauled (DVTs arrived later), and the trains included Mark 1 stock- gangwayed brakes were used as no Mark 3 Brake vehicles were built- so it wasn't thought necessary for the stock to be 140 mph-capable. It might have been possible to retro-fit the stock once DVTs became available, but there probably wasn't enough spare stock to enable whole rakes to be taken out of service to be fitted. It only became feasible to fit the equipment once the stock had been displaced by the Pendelios, by which time it wasn't seen as a priority. It's one of these cases of 'If only we'd thought of that' or 'we should have employed a Systems Engineer' which bedevil so much of industry. Mind you- the converse situation of specifying and fitting equipment which is rarely if ever used can also be problematic...What you really need is a reliable crystal ball, and an unlimited budget!

 

Why would it have been 140mph? They were designed for 125mph though (as a result of being "hauled" restricted to 110mph. 140mph only ever became a consideration (and then for Mark 4 stock, on the advent of the IC225 project). Why would BR have considered retro-fitting the Mark 3s for 140mph, when there were no locomotives, nor any plans or funding to produce any 140mph capable locomotives after the Class 91s?

 

You say it wasn't a priority? As far as I'm aware (certainly within INTERCITY) it was never considered let alone a priority, as the next step would have been the Mark Vs - I'm not disputing it ever happened however I certainly don't ever remember a "if only we'd though of that' moment or 'we should have employed a Systems Engineer', in respect of the Mark III stock - Why on earth would they?. The Mark IIIs were well designed and executed and their length in service has proven that time and time again. BR was already full of capable engineers - and a had plenty of competent and active Systems Engineers. The only thing BR lacked was a cohesive plan for the progressive replacement of rolling stock, such as had existed up until the end of Mark III construction, which would have course have necessitated a government that wasn't intent on running BR down.

[Fat Controller]

Why would it have been 140mph? They were designed for 125mph though (as a result of being "hauled" restricted to 110mph. 140mph only ever became a consideration (and then for Mark 4 stock, on the advent of the IC225 project). Why would BR have considered retro-fitting the Mark 3s for 140mph, when there were no locomotives, nor any plans or funding to produce any 140mph capable locomotives after the Class 91s?

 

You say it wasn't a priority? As far as I'm aware (certainly within INTERCITY) it was never considered let alone a priority, as the next step would have been the Mark Vs - I'm not disputing it ever happened however I certainly don't ever remember a "if only we'd though of that' moment or 'we should have employed a Systems Engineer', in respect of the Mark III stock - Why on earth would they?. The Mark IIIs were well designed and executed and their length in service has proven that time and time again. BR was already full of capable engineers - and a had plenty of competent and active Systems Engineers. The only thing BR lacked was a cohesive plan for the progressive replacement of rolling stock, such as had existed up until the end of Mark III construction, which would have course have necessitated a government that wasn't intent on running BR down.

Sorry- finger error- I meant 125 mph. I had been up since 03:30......

[Bob Reid]

Sorry- finger error- I meant 125 mph. I had been up since 03:30......

 

Crikey Brian you've knocked me off my rant there!

[nightstar.train]

Okay i think i get it now. The coaches are air braked and the engine supplies the air for it. In an HST it is supplied by 2 engines from both ends, so brakes twice as fast. But the loco-hauled only has one engine at the front (or back). The coaches them selves don't have electric brakes. Is this correct?

[Bob Reid]

Okay i think i get it now. The coaches are air braked and the engine supplies the air for it. In an HST it is supplied by 2 engines from both ends, so brakes twice as fast. But the loco-hauled only has one engine at the front (or back). The coaches them selves don't have electric brakes. Is this correct?

 

Not really - the signal that causes each coach to apply or release the brakes individually is provided by altering the pressure in the Auto-Air Brake Pipe throughout the train. Sticking to application of the brakes, on conventional loco-hauled air braked stock, this alteration to the AABP is done by reducing the air pressure from the (leading) locomotive. In the case of the HST however, whilst the reduction in pressure is still initiated at the leading Power Car under the control of the driver it is also automatically reduced via an electric signal at the rear Power Car as well. This reduction in pressure from both ends at once, increases the speed at which each coach is signalled to apply the brakes, and proportionally reduces the distance required to reduce the speed of the train or bring the whole lot to a stand. No electronics are involved in the braking system of the Mark III stock, being entirely controlled by air pressure, the Power Cars however use an electrical system to communicate the position of the brake controller (and hence the application of the brakes) from the front to the rear PC.

 

[Edit] Thinking of a more basic analogy - if the speed (and hence the rate) of brake application was dependant on letting water out of a 600ft long pipe what would the effect of letting the water out of both ends of the pipe at the same time be as opposed to just one of them?

[Fat Controller]

To give some idea of the effect of an Electro-Pneumatic control system on maximum speeds, due to braking distances:-

The trains I work with have a normal service maximum of 140 kph with EP available on all 28 vehicles.

If 3 wagons have the EP isolated, and only have the normal air brake working, then the permitted speed is reduced by 10%.

If more than 3 vehicles have EP isolated, or there is a problem with the control gear for the EP on the loco, then the train may run at 100 kph maximum. In practice, this means you sideline the train as soon as possible, as you start get knock-on delays to other services.

A colleague went over to Red Team as a driver-leader, having spent more than ten years driving Shuttles. As part of his conversion course to driving on a 'real railway', he drove the 'Jumbo Train' from Westbury to Acton, at a maximum speed of less than 80 kph. He called me later to say that even that seemed too fast, as the brakes seemed to take an eternity to apply (as he's an ex-Para, with a colourful command of English, I've paraphrased that last bit...)

[The Stationmaster]

To give some idea of the effect of an Electro-Pneumatic control system on maximum speeds, due to braking distances:-

The trains I work with have a normal service maximum of 140 kph with EP available on all 28 vehicles.

If 3 wagons have the EP isolated, and only have the normal air brake working, then the permitted speed is reduced by 10%.

If more than 3 vehicles have EP isolated, or there is a problem with the control gear for the EP on the loco, then the train may run at 100 kph maximum. In practice, this means you sideline the train as soon as possible, as you start get knock-on delays to other services.

A colleague went over to Red Team as a driver-leader, having spent more than ten years driving Shuttles. As part of his conversion course to driving on a 'real railway', he drove the 'Jumbo Train' from Westbury to Acton, at a maximum speed of less than 80 kph. He called me later to say that even that seemed too fast, as the brakes seemed to take an eternity to apply (as he's an ex-Para, with a colourful command of English, I've paraphrased that last bit...)

 

But I bet the bit that really got him was how long it takes for the brakes to release - that is not so much in the way of fun without very careful handling.

 

When we carried out the (not exactly successful) 'giant' train trial with Class 59s back in the early 1990s the brake application and release issue was one of the biggest concerns. I suggested that Yeoman should try to borrow an end-of-train monitoring unit from EMD but the US folk weren't keen on the idea although Derby did rig up some sort of flow meter on the mid-train helper to at least give the Driver and Inspector on that a better idea of what was going on in the Brake Pipe.

 

But in the end it was the brake release rate which was at the root of the problem that brought things to an end because - puttng it simply - the brakes at the back end of the train hadn't released by the time power was being applied at the front end to get it up a short stretch of 1 in 78, so something broke, and that was the end of that

[nightstar.train]

Not really - the signal that causes each coach to apply or release the brakes individually is provided by altering the pressure in the Auto-Air Brake Pipe throughout the train. Sticking to application of the brakes, on conventional loco-hauled air braked stock, this alteration to the AABP is done by reducing the air pressure from the (leading) locomotive. In the case of the HST however, whilst the reduction in pressure is still initiated at the leading Power Car under the control of the driver it is also automatically reduced via an electric signal at the rear Power Car as well. This reduction in pressure from both ends at once, increases the speed at which each coach is signalled to apply the brakes, and proportionally reduces the distance required to reduce the speed of the train or bring the whole lot to a stand. No electronics are involved in the braking system of the Mark III stock, being entirely controlled by air pressure, the Power Cars however use an electrical system to communicate the position of the brake controller (and hence the application of the brakes) from the front to the rear PC.

 

[Edit] Thinking of a more basic analogy - if the speed (and hence the rate) of brake application was dependant on letting water out of a 600ft long pipe what would the effect of letting the water out of both ends of the pipe at the same time be as opposed to just one of them?

 

Thanks, thats all clear now. I was just getting confused as to how the actual brakes on the carriages work. I assume then that this system is fail safe and if the train splits in the middle the AABP loses pressure and the whole train stops PDQ.

So do the Mk4s have a different system, or does the Mk4 DVT also apply the brakes? As these are allowed to do 125mph with normal signalling. Great shame that they will be replaced before the cab signalling arrives that would allow operation at their design speed of 140.

 

So Fat Contoller do you drive 'Le Shuttle' (or whatever its called at the moment)? Cool.

[Bricky89]

Thanks, thats all clear now. I was just getting confused as to how the actual brakes on the carriages work. I assume then that this system is fail safe and if the train splits in the middle the AABP loses pressure and the whole train stops PDQ.

So do the Mk4s have a different system, or does the Mk4 DVT also apply the brakes? As these are allowed to do 125mph with normal signalling. Great shame that they will be replaced before the cab signalling arrives that would allow operation at their design speed of 140.

 

So Fat Contoller do you drive 'Le Shuttle' (or whatever its called at the moment)? Cool.

 

Just too pick you up on something, there are some sections of the East Coast Mainline which the Mk4 sets with 91's operate upto 140mph, not entirely sure of the sections though but there isn't that many.

[The Stationmaster]

Just too pick you up on something, there are some sections of the East Coast Mainline which the Mk4 sets with 91's operate upto 140mph, not entirely sure of the sections though but there isn't that many.

 

Like none at all, unless 'something' has happpened very recently

[Adrian Wintle]

Thanks, thats all clear now. I was just getting confused as to how the actual brakes on the carriages work. I assume then that this system is fail safe and if the train splits in the middle the AABP loses pressure and the whole train stops PDQ.

So do the Mk4s have a different system, or does the Mk4 DVT also apply the brakes? As these are allowed to do 125mph with normal signalling. Great shame that they will be replaced before the cab signalling arrives that would allow operation at their design speed of 140.

 

So Fat Contoller do you drive 'Le Shuttle' (or whatever its called at the moment)? Cool.

 

If I understand Brian's post above, the 140mph limit for the Mk4/IC225 would have been primarily from having an extra block between trains (5-aspect signals). Presumably they would also have had the double control of the brakes like the HSTs (to give 125mph on 4-aspect signalling?), but the acceleration from 125mph to 140mph would have been from adding an extra block of headway between trains.

 

Adrian

[The Stationmaster]

If I understand Brian's post above, the 140mph limit for the Mk4/IC225 would have been primarily from having an extra block between trains (5-aspect signals). Presumably they would also have had the double control of the brakes like the HSTs (to give 125mph on 4-aspect signalling?), but the acceleration from 125mph to 140mph would have been from adding an extra block of headway between trains.

 

Adrian

 

The extra braking distance required to stop from 140 mph was to have been achieved by adding a 5th signal aspect (flashing green) and I believe some signals can still actually show that aspect but for a variety of reasons the idea was never taken up (cost possibly being one?).