Porterbrook Cl.769 'Flex' trains from 319s, initially for Northern

edwin_m said:

The train would have to stop in the required distance with the maximum load that's physically possible, plus the extra weight of the diesel kit. By definition that needs better braking performance than a 319, though it may be comparable to the 170 which is a heavier body on a similar bogie. Being Northern I imagine a crush load would happen more often than intended.

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No it doesn’t. You are assuming the 319s braking performance is as bad as is permitted by the system. It almost certainly isn’t. Like car stopping distances, they will have a load of safety but,t in. And then some. I can stop from 60mph in just 30% of the required distance in one of my cars. Even my enormous 4*4 will stop in less than 36% of that distance (315ft).

I've had a look at my through the window photos from last night and they're not worth uploading. Suffice it to say there was ballast along the length of the vehicles and in the vestibules.

I also took a photo of inside the cab but that hasn't come out that well either, however something that might be of interest to some as I know there has been some discussion regarding top speed on diesel, the stated top speed as displayed in the cab is 100 mph. No differential stated between electric and diesel operation.

Justapunter said:

No it doesn’t. You are assuming the 319s braking performance is as bad as is permitted by the system. It almost certainly isn’t. Like car stopping distances, they will have a load of safety but,t in. And then some. I can stop from 60mph in just 30% of the required distance in one of my cars. Even my enormous 4*4 will stop in less than 36% of that distance (315ft).

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You're suggesting eroding the margin of safety on a 769 compared with a 319. Safety case for that should be interesting, especially during the period before the 319s go, when the same people will regularly be driving both units.

AM9 said:

Only the 319/4s were uprated yet the 319/0, 319/2 and 319/3 subclasses weigh the same as the 319/4s and have the same passenger crush load, then there must be some spare capacity on the uprated braking system, - presumably enough to accommodate the additional weight.

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Exactly what was upgraded? Possibly something to do with reliability of the brake system but I can't see one sub-class being updated to cope with a greater passenger load when if other sub-classes could equally well end up with a similar crush load. The only exception might be if the area taken up by seats was reduced, meaning more standing space so more total passenger load. But if that was the case then the increased load would also be possible as a 769, unless seats are being added back to reduce the passenger load. Perhaps this explains why the test unit has no seats?

edwin_m said:

Exactly what was upgraded? Possibly something to do with reliability of the brake system but I can't see one sub-class being updated to cope with a greater passenger load when if other sub-classes could equally well end up with a similar crush load. The only exception might be if the area taken up by seats was reduced, meaning more standing space so more total passenger load. But if that was the case then the increased load would also be possible as a 769, unless seats are being added back to reduce the passenger load. Perhaps this explains why the test unit has no seats?

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This:

• Emergency brake pressure increased to the +12% G standard, giving an extra 1 Bar brake cylinder pressure in emergency
• Emergency brake 'timeout' period reduced from 2 minutes to 20 seconds

The limits of emergency braking were increased, possibly because the 100+ mile runs from Bedford to Brighton requiring keeping to tight paths at high speeds, (slotted between more agile Electrostars) would be running the trains closer to their limits than the slow ambles around the Sutton loop and all shacks to Luton. Of course sometimes the wrong sub-class ends up on the more gruelling diagram but they would obviously still meet the minimum standard. The reduced timeout would be more valuable on the fast lines.

All the 319s used by Northern have had the 12%G emergency brake since they arrived up here.

AM9 said:

This:

• Emergency brake pressure increased to the +12% G standard, giving an extra 1 Bar brake cylinder pressure in emergency
• Emergency brake 'timeout' period reduced from 2 minutes to 20 seconds

The limits of emergency braking were increased, possibly because the 100+ mile runs from Bedford to Brighton requiring keeping to tight paths at high speeds, (slotted between more agile Electrostars) would be running the trains closer to their limits than the slow ambles around the Sutton loop and all shacks to Luton. Of course sometimes the wrong sub-class ends up on the more gruelling diagram but they would obviously still meet the minimum standard. The reduced timeout would be more valuable on the fast lines.

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I was involved with the decision process which agreed to upgrade emergency brakes to 12% back in 1994-ish, albeit only as a humble minute-taker. The reason was to give the drivers some extra braking power for SPAD mitigation, whereas previously the emergency brake was the same retardation as the service brake (but applied in a failsafe manner). The view from the people that should know was that it was quite easy to do on modern units, so I'm a bit surprised some 319s don't have it 25 years later.

The emergency brake rate wouldn't affect the journey time between Bedford and Brighton because it would only be used in emergency. Drivers would be expected to keep it in reserve for unforeseen events rather than changing their driving style because it was available. The shorter timeout would reduce delays on the occasions when an emergency stop happened in error, such as due to accidental release of the driver's safety device, so would help with service performance. It's possible that when they decided to change the timeout, they also decided (or were forced) to include the 12%g feature while they were making changes to the brake system.

The brakes would need at least some adjustment and possibly more major changes to maintain either the 9% service brake or the 12% emergency brake with a heavier train. As I posted above I very much doubt it would be allowed to deteriorate even if it remained within the required standard. They might have got away with less then 12%g if they'd started with trains that didn't have the 12%g mod, and then improved it as far as reasonably practicable with the extra weight. Adhesion isn't the ssue here as more weight allows the train to employ proportionately more retardation force for the same coefficient of wheel-rail friction. But the extra mass also requires proprtionately more retardation force in proportion to achieve the same deceleration, so the train mass cancels out. However the brakes would need to apply more force to the discs to achieve the greater retardation force, and also be capable of dissipating more kinetic energy as heat. The fact that full braking tests haven't been done until now suggests to me that there have been some problems achieving this - although I'm aware this is the third or fourth theory I've lobbed into this thread for delay to 769s!

Bertie the bus said:

I also took a photo of inside the cab but that hasn't come out that well either, however something that might be of interest to some as I know there has been some discussion regarding top speed on diesel, the stated top speed as displayed in the cab is 100 mph. No differential stated between electric and diesel operation.

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I'd have thought maximum operating speed is the same regardless of power source - it simply lacks the power to get there on diesel without help from a falling gradient.

Chris125 said:

I'd have thought maximum operating speed is the same regardless of power source - it simply lacks the power to get there on diesel without help from a falling gradient.

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Agreed

hwl said:

Agreed

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What size engines are in the 769 ' and how many?

Railperf said:

What size engines are in the 769 ' and how many?

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Two 390kW/530hp MAN D2876 diesels.

Looking at this from the other end the makers must be confident these trains basically "work" as the only reason to brake test is prior to main line running for mileage and training.

ac6000cw said:

Two 390kW/530hp MAN D2876 diesels.

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So about 80% of the 319's rating with about another 15% weight on non-driving axles.

About the same diesel power/weight ration as a 156.

AM9 said:

So about 80% of the 319's rating with about another 15% weight on non-driving axles

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On electric, I assume a 319/769 has a somewhat higher short-term rating? (which would make the difference between electric and diesel performance even more noticeable)

Chris125 said:

I'd have thought maximum operating speed is the same regardless of power source - it simply lacks the power to get there on diesel without help from a falling gradient.

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To be fair they also lack the power on AC to get to 100mph on other than a falling gradient. Some won't even get to 90mph on the totally flat Chat Moss route in the six miles between Newton le Willows station and Astley. The only tines you can ever get one to 100mph on Northern's routes is on the WCML on the falling gradient either side of Coppull between Wigan and Euxton - going towards Wigan if you're lucky and brave you might (but might not) get to 100mph for about ten seconds before having to brake for the 80 PSR before Wigan. Going towards Preston having stopped at Wigan NW you will only get to 100mph if kept fast line at Euxton.

ac6000cw said:

On electric, I assume a 319/769 has a somewhat higher short-term rating? (which would make the difference between electric and diesel performance even more noticeable)

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They're not powerful enough to need any short term rating like a loco might. There is no ammeter in the cab.

AM9 said:

So about 80% of the 319's rating with about another 15% weight on non-driving axles.

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You cannot equate the shaft power output of the diesel engines to the electrical power input to the traction motors. There are losses in the generators and traction controllers, plus some of the power is diverted to auxiliaries (heating, lighting, brake compressor etc.) Wabtec/Porterbrook have said that the available power on diesel is about 550kW, only 55% of that on AC or third rail.

See Post #2971.

Greybeard33 said:

You cannot equate the shaft power output of the diesel engines to the electrical power input to the traction motors. There are losses in the generators and traction controllers, plus some of the power is diverted to auxiliaries (heating, lighting, brake compressor etc.) Wabtec/Porterbrook have said that the available power on diesel is about 550kW, only 55% of that on AC or third rail.

See Post #2971.

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The power:weight being similar to a 156 is encouraging though - 156 can get well above 75mph if anyone lets them (or at least could when new).

Correct - in addition to the traction system, all train heating on 319s (and 769s) is electric directly off the 750v busline, they don't use waste engine heat like the majority of DMUs. The air compressor is also very power hungry, again running off the 750v busline and the lower voltage electrical systems (425v AC, 110v DC, 24v AC) are supplied by a motor alternator which runs off, guess what, the 750v busline.

The 110v DC control voltage alone on 769s will have been converted from ~900-1000v AC produced by the alternators on the new engines, rectified to 750v DC, through the smoothing choke, run the MA set to produce the 415v AC which is then stepped down and rectified again to 110v DC.

769s will not be electrically efficient machines.

The same 5Q01 Allerton – Preston and 5Q02 return ran again last night. RTT shows 5Q01 was cancelled at Springs Branch at 02:07 due to a problem with the traction equipment but 5Q02 departed Preston on time at 01:30. They can’t both have happened so I’m not sure what went on.

https://www.realtimetrains.co.uk/train/O37539/2019/09/04/advanced
https://www.realtimetrains.co.uk/train/K03536/2019/09/05/advanced

Llama said:

Correct - in addition to the traction system, all train heating on 319s (and 769s) is electric directly off the 750v busline, they don't use waste engine heat like the majority of DMUs. The air compressor is also very power hungry, again running off the 750v busline and the lower voltage electrical systems (425v AC, 110v DC, 24v AC) are supplied by a motor alternator which runs off, guess what, the 750v busline.

The 110v DC control voltage alone on 769s will have been converted from ~900-1000v AC produced by the alternators on the new engines, rectified to 750v DC, through the smoothing choke, run the MA set to produce the 415v AC which is then stepped down and rectified again to 110v DC.

769s will not be electrically efficient machines.

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With aircon the GWR ones will be even worse.

Bertie the bus said:

The same 5Q01 Allerton – Preston and 5Q02 return ran again last night. RTT shows 5Q01 was cancelled at Springs Branch at 02:07 due to a problem with the traction equipment but 5Q02 departed Preston on time at 01:30. They can’t both have happened so I’m not sure what went on.

https://www.realtimetrains.co.uk/train/O37539/2019/09/04/advanced
https://www.realtimetrains.co.uk/train/K03536/2019/09/05/advanced

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Could it be that a 319 was sent from Preston to tow the 769 back to Allerton in the original schedule?

Seems unlikely to be honest as they would need to get a crew to Preston to prep and drive the 319. Apparently there was a thunderbird ROG 37 at Warrington Bank Quay on Tuesday night, and last night it was supposed to head off to Derby. The path to Derby started at Crewe and there was also a VSTP light engine working from Allerton – Crewe, so what looks like happened is the 37 rescued it and took it to Allerton.

That, however, doesn’t explain the timings between Preston and Springs Branch but I suppose they could have been manually entered, though I don’t think I’ve seen ghost times at Preston before.

edwin_m said:

You're suggesting eroding the margin of safety on a 769 compared with a 319. Safety case for that should be interesting, especially during the period before the 319s go, when the same people will regularly be driving both units.

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but we (I) don't know how much safety it has built in, If it can stop easily, laden in a lot less than the set out braking distances, then it may well be fine. There comes a point when you are adding margin for the sake of it. It doesn't do anything.

Justapunter said:

but we (I) don't know how much safety it has built in, If it can stop easily, laden in a lot less than the set out braking distances, then it may well be fine. There comes a point when you are adding margin for the sake of it. It doesn't do anything.

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However you've probably got to do a lot of work to justify any worsening in any aspect of safety even if it's within standards. See level crossing risk assessments for example. There's always going to be a scenario where a few metres extra stopping distance makes the difference between hitting something or someone and stopping short. There's also the question of whether the 769s can meet the criteria for SP differential speeds, which I imagine they will encounter on their non-electrified routes and which require a certain level of braking peformance.

Bertie the bus said:

That, however, doesn’t explain the timings between Preston and Springs Branch but I suppose they could have been manually entered, though I don’t think I’ve seen ghost times at Preston before.

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The timings before Springs Branch were indeed entered manually, and I notice they have the "Terminated" marker set:

http://charlwoodhouse.co.uk/rail/liverail/train/16993004/05/09/19

AM9 said:

So about 80% of the 319's rating with about another 15% weight on non-driving axles.

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Only 80% of rated diesel engine output usually makes it to the rails. In that case diesel power at rail will probably be 60 to 65% of the electric power at rail under 25kV. 750v DC output has always been low too.

Railperf said:

Only 80% of rated diesel engine output usually makes it to the rails. In that case diesel power at rail will probably be 60 to 65% of the electric power at rail under 25kV. 750v DC output has always been low too.

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Given that they are being promoted for use on unelectrified (mainly branch) lines, the power deficit of the diesel configuiration should be manageable, and partly recoverable when under OLE. If by low DC output you mean that they are less powerful than under OLE, then that is more a shortcoming of 3rd rail DC electrification than the trains, - most 3rd rail trains are now running with maximum current caps enforced by software.

AM9 said:

Given that they are being promoted for use on unelectrified (mainly branch) lines, the power deficit of the diesel configuiration should be manageable, and partly recoverable when under OLE. If by low DC output you mean that they are less powerful than under OLE, then that is more a shortcoming of 3rd rail DC electrification than the trains, - most 3rd rail trains are now running with maximum current caps enforced by software.

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Yes the power to weight ratio is likely to be at current DMU levels - enough to maintain 60 to 70mph and probably reasonable acceleration..but nowhere near Class 755 levels of performance.

Out again tonight. Sure I’ve just gone past it at Edge Hill. Full of blue bags and orange jackets.

edwin_m said:

The power:weight being similar to a 156 is encouraging though - 156 can get well above 75mph if anyone lets them (or at least could when new).

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Yes, I chartered a brand new 156480 from Regional Railways for a Harrogate to Blackpool, Chester and return trip and we reached 88mph between Preston and Wigan. Harrogate-Leeds was completed in 19 minutes for 18 miles..