Performance of "lumbering" Cl 40s and other early BR diesels

The Crab said:

I think it was running down the level of water ("mortgaging" the boiler) in order to keep the pressure up for a short period.

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I think that's right, yes. Essentially shutting the firebox door and not shovelling coal in nor operating the injectors.

The Crab said:

I think it was running down the level of water ("mortgaging" the boiler) in order to keep the pressure up for a short period.

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This was fine when climbing steeply uphill, as the water level would rise anyway at the back of the loco over the firebox (the important place) so it was straightforward to let it fall a bit. Mortgaging the boiler is actually using it as a power reservoir, consuming steam more rapidly than it is being generated.

This was however a nightmare on Dainton bank, west of Newton Abbot, where the top of the 1 in 36 up is immediately followed by 1 in 36 down to Totnes, something you don't get on the Lickey or elsewhere steep. Thank you Brunel! As a result you needed to come over the top with sufficient water level not to cause a problem as you tip over the top. The difference in water levels is 6" or more at the back of the boiler. I believe when the Britannias first came along, which had longer boilers than anything the GWR ever had, apart from The Great Bear (which was not allowed down to Plymouth) there was more than one case of a blown fusible plug at that point as a result.

Grierson the GWR chief civil engineer came up with a plan for deviation lines to overcome the issues of the South Devon banks, and it was put to the GW board for approval, all part of the many cut off main lines built 1900-10 on the GW. Churchward, who had a long-running disagreement with Grierson (Nock called it a feud), told the board he was able to design locomotives which could handle the banks for far less capital expenditure than the new lines and tunnels required. And so we are where we are there today.

Taunton said:

This was fine when climbing steeply uphill, as the water level would rise anyway at the back of the loco over the firebox (the important place) so it was straightforward to let it fall a bit. Mortgaging the boiler is actually using it as a power reservoir, consuming steam more rapidly than it is being generated.

This was however a nightmare on Dainton bank, west of Newton Abbot, where the top of the 1 in 36 up is immediately followed by 1 in 36 down to Totnes. Thank you Brunel! As a result you needed to come over the top with sufficient water level not to cause a problem as you tip over the top. The difference in levels is 6" or more at the back of the boiler. I believe when the Britannias first came along, which had longer boilers than anything the GWR ever had, apart from The Great Bear (which was not allowed down to Plymouth) there was more than one case of a blown fusible plug at that point as a result.

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I can only imagine the level of skill drivers and firemen needed to use to get over those gradients safety and on time.

AndrewE said:

....................Cowley, were the diesel-hydraulics physically C-Cs, , i.e geared to lock the axles in synch, or did the oil go through each "traction motor" in series? I'll have to go and do some digging!

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each bogie had all wheels linked by shafts and gears -i.e. locked
in addition on the two single-engined classes, the two bogies were locked as well, there doesn't appear to have been the equivalent of a slipping differential

randyrippley said:

in addition on the two single-engined classes, the two bogies were locked as well, there doesn't appear to have been the equivalent of a slipping differential

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This appears correct. Warships certainly could slip just one bogie (always the front one) and race one of the engines when starting a heavy train from Taunton in the pouring rain (probably where a D63xx had stood previously and leaked its lubricating oil!). Hymeks did not.

A 9F never suffered from having a long coupled wheelbase physically locked and which had to revolve exactly the same.

This was the issue with the Westerns I was thinking of:

"The most serious continual problem with the class was the design fault mismatch between the Maybach MD655 engines and the Voith L630rV three speed hydraulic transmissions. The top gear ratio in the transmission was too high for the torque characteristics of the engine: the result was that a single locomotive could struggle to reach its claimed 90 mph (145 km/h) top speed in the absence of down grades, more so when work-weary and due for overhaul."

hexagon789 said:

"The most serious continual problem with the class was the design fault mismatch between the Maybach MD655 engines and the Voith L630rV three speed hydraulic transmissions. The top gear ratio in the transmission was too high for the torque characteristics of the engine: the result was that a single locomotive could struggle to reach its claimed 90 mph (145 km/h) top speed in the absence of down grades, more so when work-weary and due for overhaul."

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There was a subset of Westerns that, somehow, had identified well-matched engines and transmissions. I don't know why whatever they had could not be applied to all. They were known as the "Golden Westerns" because they were first selected to handle the Golden Hind day return business service from Plymouth to Paddington and back. You tended to get them on the Cornish Riviera as well.

There was another golden Western, D1015 Western Champion, which from new and for a few years afterwards was in a gold livery. Unfortunately not kept as clean as it should have been, and it rather deteriorated to a brownish hue over time. Eventually repainted maroon. It was regarded as a bit of a special loco on the Western, it was this loco that hauled the ecs of Churchill's funeral train from Oxfordshire back to London.

Taunton said:

There was a subset of Westerns that, somehow, had identified well-matched engines and transmissions. I don't know why whatever they had could not be applied to all. They were known as the "Golden Westerns" because they were first selected to handle the Golden Hind day return business service from Plymouth to Paddington and back. You tended to get them on the Cornish Riviera as well.

There was another golden Western, D1015 Western Champion, which from new and for a few years afterwards was in a gold livery. Unfortunately not kept as clean as it should have been, and it rather deteriorated to a brownish hue over time. Eventually repainted maroon. It was regarded as a bit of a special loco on the Western, it was this loco that hauled the ecs of Churchill's funeral train from Oxfordshire back to London.

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Interesting, are these the ones that were often timed at a ton or more?

AndrewE said:

We're not talking about thermal efficiency here, nor the manpower needs or relative manpower or preparation times of the different technologies, which are all well-recognised. "Slow and lumbering" is only about acceleration or top speed, and edwin-m is agreeing that a loco with electric transmission has to be notched back as the speed falls, handicapping it on a n adverse gradient. ....

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But the power delivered is still fairly constant, in fact it may increase. The reason for notching back is the increase in amperage going through the traction motors, not because the power out put is dropping.

randyrippley said:

Better way to look at that is engineers trained on steam were trying to work on diesel engines and transmissions with minimal training, shortage of parts, and in converted unsuitable steam sheds. I read somewhere that one of the commonest causes of failure of the early hydraulics was steam engine soot in the transmission fluid due to an inability to maintain cleanliness standards
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You may or may not be correct in some of your assumptions stated here at some times - but no, in the case when the men were talking to me, I don't believe any of those conditions you mention applied. This conversation was from 40 years ago, so of course, I can't go back and examine their every word - but the gist of it was they simply thought Cl 52s were complicated to work on and cramped compared to a Cl 47.

I have to say, I was suprised to hear them say this. But say it they did.

70014IronDuke said:

But the power delivered is still fairly constant, in fact it may increase. The reason for notching back is the increase in amperage going through the traction motors, not because the power out put is dropping.

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The tractive effort may be constant or increasing as the speed reduces, but the power will be constant or reducing. Power is tractive effort multipled by speed.

AndrewE said:

that a loco with electric transmission has to be notched back as the speed falls, handicapping it on a n adverse gradient.

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Only if speed falls significantly, a driver told me that in Class 47s you can get away on full power without overloading the traction motors but you need to make sure you don't keep this up for too long. The only other time I can think of when you notch back on a Diesel-electric is when you come up to point where the Field Diverts come in. On 47s this happens 3 times as the loco accelerates up to maximum speed and is the reason why the DBSOs had a field light so the driver knew when to notch up the power controller.

On the subject of class 40's I thought I'd mention (because I haven't seen it elsewhere here) East Lancashire Railway have a class 40 Anniversary event advertised 13th 14th 15th April for those that might be interested.
The advert says at least 5 attending.