Could Jubilees have performed as well on the Cheltenham Flyer as Castles?

[jjb1970]

I like the GWR 4-6-0 locomotives because all of them were very elegant looking designs, and GWR livery was rather nice. As steam locomotives went the GWR also seemed to be rather good at designing and building them.

 

I'm only familiar with marine and power plant steam systems, but efficiency demands high superheat temperatures, which is then associated with high steam pressure, and ultimately going supercritical. And systems can get rather complex with reheat between turbine stages and various regen and waste heat recovery arrangements. However, power is really down to the evaporation rate (how much steam the boiler can deliver), and the evaporation rate is a function of how much energy you put into the boiler, or in other words how much fuel along with the air needed for combustion. On large boilers that's not a problem but manual firing with a shovel does introduce limitations. And the parasitic loads of steam plant are very high, not just FD fans but feed pumps, ID fans, fuel handling if combusting coal or biomass. We're talking motors rated in MW, not KW, in maritime applications the feed pumps tended to be turbo-feed pumps with smaller electrical units for start up.

[LMS2968]

There are limits imposed on a locomotive steam plant that are not necessarily there with a a marine or land-based system. Steam pressure with a conventional fire tube boiler is realistically limited to about 300 p.s.i., 350 if you want to push your luck; not so with water tube boilers. With a turbine, the lubrication system can be kept well away from the steam circuit so steam temperature can go as high as you can get it; this isn't so in a reciprocating engine where cylinders and valves are in need of an oil feed and in direct contact with the steam. The effect on the oil (carbonisation) requires a limit on the steam temperature lower than theoretically desirable.

[rogerzilla]

There's the rub.  GWR used comparatively low superheat, something Stanier took with him to the LMS but was quickly corrected when his first design was seriously indifferent. 

 

Churchward wasn't a fan of much superheat and Collett continued the same design principles of high boiler pressures but low superheat.   It wasn't until Hawksworth that GWR superheating temperatures caught up with the other railways.

 

The thing is, GWR engines worked well and used less coal, regardless of the failure to truly embrace superheating.  Welsh coal and really good valve events hid a multitude of sins.

[62613]

12 hours ago, rogerzilla said:

There's the rub.  GWR used comparatively low superheat, something Stanier took with him to the LMS but was quickly corrected when his first design was seriously indifferent. 

 

Churchward wasn't a fan of much superheat and Collett continued the same design principles of high boiler pressures but low superheat.   It wasn't until Hawksworth that GWR superheating temperatures caught up with the other railways.

 

The thing is, GWR engines worked well and used less coal, regardless of the failure to truly embrace superheating.  Welsh coal and really good valve events hid a multitude of sins.

Yes, just enough superheat to prevent the steam reaching its saturation temperature when the piston reaches the exhaust port opening point, I think

[The Stationmaster]

18 hours ago, rogerzilla said:

There's the rub.  GWR used comparatively low superheat, something Stanier took with him to the LMS but was quickly corrected when his first design was seriously indifferent. 

 

Churchward wasn't a fan of much superheat and Collett continued the same design principles of high boiler pressures but low superheat.   It wasn't until Hawksworth that GWR superheating temperatures caught up with the other railways.

 

The thing is, GWR engines worked well and used less coal, regardless of the failure to truly embrace superheating.  Welsh coal and really good valve events hid a multitude of sins.

Churchward did investigate higher siuperheat tempreratures but then j kept away from them for very good reasons.  The problem was lubrication and without the right sort of oils and really good, reliable, mechanical lubricators high temperature superheat  presented a number of problems especially in the valves and pistons where lack of efficient lubrication led to excessive wear and broken piston rings.

 

It is possible of course that Churchward's very reliable hydrostatic lubrication system might also have not worked so well with higher temperature superheat.  And of course when Western engines finally progressed to much higher superheat temperatures mechanical lubricators followed very quickly in their stead

 

l

[rodent279]

This was in the early 1900's, when quality coal was cheap, easily available, and the manpower to shovel it was the same.

I think GJC's argument was along the lines of "what's the point in higher degrees of superheat to save a few tons of coal, when the side effect is thinner oil (because of the heat), leading to increased oil consumption, increased cylinder and valve wear, increased risk of piston ring failure, and increased levels of carbonisation, necessitating more frequent de-coking".

At the time, given the primitive oil technology of the day, he was probably right.

[Compound2632]

40 minutes ago, The Stationmaster said:

It is possible of course that Churchward's very reliable hydrostatic lubrication system might also have not worked so well with higher temperature superheat.  And of course when Western engines finally progressed to much higher superheat temperatures mechanical lubricators followed very quickly in their stead

 

Mechanical lubricator of 1912, as used on superheated locomotives:

 

 

[Embedded link to scan of Midland Railway Study Centre item 26470.] 

 

R.M. Deeley wrote the textbook on lubrication, so it was a subject well-understood in the Derby LDO.

Edited April 2, 2023 by Compound2632
grammar tidy

[LMS2968]

That appears to be the same one as used on the LMS right to the end, and possibly on the BR Standards too.

[JimC]

On 28/03/2023 at 07:13, rogerzilla said:

2. SR happily sent Lord Nelson drawings, and parts of the firebox design were used.  Holcroft said it was more than that, Cox said that was all.

 

On 28/03/2023 at 07:32, LMS2968 said:

The LN and Scot fireboxes show similarities in profile but are very different in end view. Eric Langridge, a draughtsman at Derby, a was equally adamant that the Scot owed nothing to the LN design.

I think if you give a talented design team a set of drawings to use as inspiration/guide  they use the information as inspiration and influence without actually tracing individual parts. It doesn't bear thinking what the morale situation must have been in the LMS design office when the senior management delivered such a massive vote of no confidence in their own people as they did when rejecting an in progress in house design in favour of external contractors. It's little wonder everyone has their own spin on it.

 

It seems to me that another way of interpreting the Jubilee/high superheat thing is to note that Churchward's boilers with moderate superheat worked just fine, even on exchanges with LMS and LNER using local coal. If the jubilee boiler couldn't steam with moderate superheat but the Castle boiler could, does that indicate that there was something not quite right about the Jubilee boiler and/or draughting?

[LMS2968]

23 minutes ago, JimC said:

It seems to me that another way of interpreting the Jubilee/high superheat thing is to note that Churchward's boilers with moderate superheat worked just fine, even on exchanges with LMS and LNER using local coal. If the jubilee boiler couldn't steam with moderate superheat but the Castle boiler could, does that indicate that there was something not quite right about the Jubilee boiler and/or draughting?

If you read Arthur Cook's Raising Steam on the LMS (1999) RCTS ISBN 0 901115 85 1, he goes into it very thoroughly. Basically, the boiler ratios were all over the place; the LMS D.O. was convinced that low resistance to gas flow gave better steaming and the tubes were simply too large in diameter for the boiler's length. That was probably the main issue but it wasn't the only one, and addressing any single one didn't necessarily provide an improvement, so that particular correction might then be abandoned. The final solution therefore took time to find. A.J. Powell in Stanier 4-6-0s at Work (1983) Ian Allan ISBN 0 7110 1342 X lists no less than seventeen variations of the Class 3A boiler. And even then, it wasn't the most reliable of steam raisers.