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GWR/WR 15xx Class (1948)


JimC

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I was mulling over the design of the (to me at least) strangely appealing 1948 15xx. It was a pure GWR design, and it appears from the NRM drawings list that it was actually on the drawing boards as early as 1944. As Cook tells us it was designed as a "24 hour shunter", not needing to be serviced over a pit: a worthy aim, but rendered largely obsolete by the early 350HP diesel shunters that were being introduced at the same time. I've seen an interesting comparison made between the GWR 0-6-0PTs and their theoretical equivalents on other lines, the Riddles Austerity/J94, the LMS Jinty and the USA tanks used on the Southern. The numbers indicate that the GWR locomotives have considerably greater boiler capacity than the others, but a similar tractive effort. A pure shunter doesn't really need much boiler capacity, since there is plenty of time for boiler pressure to recover, whereas a locomotive used for traffic work does need continuous steam, and 57s and 94s were regularly used on branch and even short trip main line services.

A flaw/feature in the 15xx design is commonly held to be the relatively short wheelbase, which is reported as rendering them somewhat unstable at speed, and it seems they rarely if ever undertook the traffic roles of other pannier tanks, although the survivor with the Severn Valley seems to do well enough at preserved line speeds. The actual wheelbase is 6ft 4in + 6ft 6in, 12ft 10in.  Its interesting to compare this with dedicated short wheelbase dock shunters, such as the  GWR 1361 and 1366 classes , 6ft + 5ft - 11ft,  , the USATC S100 at 5ft + 5ft for 10ft and the Riddles Austerity 5ft 9in + 5ft 3in for 11ft. The shortest wheelbase regular 0-6-0T on the GWR was the 850 class,  7ft 4in + 6ft 4in - 13ft 8in. The short wheelbase on the 15s is commonly held to be intended to improve their ability to traverse curves, and their work in Newport and on the Paddington ECS workings stated to support this. Its interesting that the wheelbase on the 15s is intermediate between the pure shunting types listed above and traffic locomotives such as the 850, and even more the other large pannier tanks, 94xx, 57xx and their 7ft 3in + 8ft 3in 15ft 6in wheelbase. As such it has occurred to me that the 15xx wheelbase might be for other reasons than curves. My theory is this: the 57 and 94 cylinders are set partially between the wheels, as is possible with inside cylinders. The big outside cylinders on the 15 can't be, so the leading wheels have to be set back relative to the smokebox in order to clear the cylinders. In addition, whereas on the inside cylinder locomotives the cylinders themselves brace the frame, on the 15xx there's a large structure between the cylinders to perform the same function. All this makes the locomotive heavy, and in particular front heavy.  This in turn means that the trailing wheels have to be set forward for the locomotive to balance. The 15 is heaviest on the leading wheels and lightest on the 3rd pair, whereas the 94 is opposite. It would be interesting to know what someone better versed than I on the subtleties of steam locomotive designs makes of that idea. 

 

Its often claimed that the 15xx was inspired by the S100/USATC 0-6-0T. The locomotives are indeed superficially similar, with prominent outside cylinders, outside walschaerts valve gear, external steam pipes, water tanks that do not flank the smokebox and no footplate. However this claim doesn't appear in any of the memoirs of contemporary GWR staff that I am familiar with.  Given the design aim declared by Cook, a 24 hour shunting locomotive that did not need to go over a pit for servicing, then when examined in detail the comparison is less certain. The design aim forces outside valve gear and outside cylinders. GWR practice was to use walschaerts gear on (their few) outside valve gear locomotives - notably the railmotors and the VOR 2-6-2Ts.  By this time external steam pipes were standard on GWR outside cylinder classes.  The S100, with its very short (10ft) wheelbase drives to and has the eccentric on the rearmost driving wheel. Apart from anything else there would be no room for the valve gear driving on the middle wheel. The 15xx, on the other hand, has 12ft 10in wheelbase, and a connecting rod driving the trailing wheels would be some 13ft 6in long.  The longest connecting rod on any of the Churchward standards was 10ft 8½ inches. I wonder if 13ft 6in would be practical.  Here's a list of similarities and differences.

Similarities

No footplate
Outside cylinders with prominent steam pipes

Outside Walschaerts gear

Wheel size 4'6 v 4'7.5

Differences

coal capacity (1 ton , 3.25 ton)

parallel/taper boiler

driven wheel

wheelbase (s100 as short as possible, 15xx longer)
boiler proportions (much bigger boiler on the 15xx)

 

All in all, I submit that there's a strong case to describe it as convergent evolution, rather than consider the 15xx to be a direct descendant of the S100. Arguably the only feature of the 15xx which may not be extrapolated from previous GWR practice is the absence of footplate. This could well be a weight saving feature, and in that respect we might also look at Bulleid's 1942 Q1 as an inspiration.

On the other hand the GWR drawing office must have had drawings for the S100 available, since the first weight diagram for the type at Swindon is dated July 1943. They may have been in service at WD sites adjacent to the GWR as early as 1942,  but RCTS states they were not used on GWR metals until June 1944. The first drawings at the NRM for what became the 15xx are dated February 1944. 

Edited by JimC
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I've also always been sceptical about promoting the idea of the need for short-wheelbase locos working the Paddington ECS duties, considering standard 15'6" wheelbase locos had been doing the job for yonks, and I think your 'weight balance' theory is far more plausible.

 

What was needed at Paddington was a strong/heavy ECS loco because of the gradient on the 'carriage flyover', and in that respect the 15xx was ideal, although it could be said the 94xx were perfectly adequate for the task, and they existed in plentiful numbers.

 

 

Edited by Miss Prism
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From a prep perspective 1501 wins hands down over a normally aspirated pannier. Everything including the axleboxes can be done from the outside; you just have to make sure the engine is set correctly to do it easily. The only thing you need to go underneath for is to check the springs. You could argue its better on a pit to do the two on the brake shaft, 

 

On the road the 15 has buckets of power and handles 8 with ease. You can clearly see they would have been good on the ECS's in and out of Paddington.  

 

Some might feel they waggle or are unstable, but to be honest the only time you see a waggle is if you pull it up too soon and at too slow a speed. Its more stable than a normal pannier. However the temperature in the box is noticeably higher. Quite a number call it a raging bull, 

 

I would be surprised if they ever got to more than 30 on those ECS's considering the weight of them. 

 

In short a great engine and a nice easy prep and disposal, with bags of power. 

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Thanks for that.

It would be interesting to hear a comparison with the USA/S100 and/or the Riddles Austerity from someone who has relevant experience. 

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It should be said that being piston valve means accelerating away and notching up are easier as you don't have to do the two handed shuffle as with a flat valve engine, ie blower on, regulator closed, move the pole, regulator open and blower shut. In first valve it can be possible to do it without totally shutting off, in second valve you have no chance. Every second the regulator is closed of course is loosing momentum. Whereas with 1501 you can notch up without having to shut off at all. 

 

the 94xx do have a slight edge on the 15xx in terms of power though and I can imagine they would be preferred for that bit extra they give.

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18 hours ago, Miss Prism said:

I've also always been sceptical about promoting the idea of the need for short-wheelbase locos working the Paddington ECS duties, considering standard 15'6" wheelbase locos had been doing the job for yonks, and I think your 'weight balance' theory is far more plausible.

 

What was needed at Paddington was a strong/heavy ECS loco because of the gradient on the 'carriage flyover', and in that respect the 15xx was ideal, although it could be said the 94xx were perfectly adequate for the task, and they existed in plentiful numbers.

 

 

However the 57XX, various versions, were equally capable on Old Oak Common - Paddington ECS trains - they were allowed 400 tons trailing between Old Oak Common and Kensington which was over a steeper rising gradient (1 in 61) approaching Viaduct Jcn than eitjher the Up (1 in 75) or Down (1 in 93). E&C Lines via the flyover between Old Oak East and Ladbroke Grove.  Very many years ago (obviously) I had a footplate trip on an 8750 on an Up ECs from OCC to Paddington with 13 Mk1s behind the engine and it went up the bank with no difficulty at all.  But of course the 57XX, 94XX, and 15XX were all Power Group C so not much in it in official terms.  incidentally (officially) speed on the E&C Lines was restricted to a maximum of 10mph although it was raised to 15 mph in the late 1960s.

 

I don't think there was any particular concern about short wheelbase locos for Paddington ECS work because there were no restrictions at all on where the 57XX/94XX could go at Old Oak and Paddington (apart from the need for ATC clip-up on the electrified lines to the suburban station.  So were the 15XX at Old Oak for ECS work because they happened to be 'more modern looking' harking back to the story of the emergence of the 94XX?  I wouldn't know and i doubt if anyone else does but equally there is no doubt they did good work there and the ease of oiling was no doubt popular with the Enginemen some of whom would have come off main line work fora a more sedate or less strenuous life (Paddngton ECS turns were for years the work on which Old Oak Drivers who had ageing or health problems were usually accommodated).  

 

As an aside in fact the only restriction in the immediate London area on 0-6-0Ts was the Guinness Sidings at Park Royal where in the 1950s 57XX and 94XX were not permitted.    

 

Photos also indicate that in South Wales 15XX were used to work freight trips which suggests that such work was not beyond their capabilities.

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An interesting vignette from the GWR Elist. Apparently on ECS workings the 15s didn't ingratiate themselves with the S&T department "because nearly every week it seemed one would take out a shunt signal somewhere between Paddington and OOC - and there was no room to move the signals, so the same ones got clobbered time and time again!"

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It occurred to me to draw a comparison between 94xx (above) and 15xx Chassis. They are sketched with the boiler in the same place. 
Note that the apparent disparity in size between the cylinders is because the 94 has slide valves between the cylinders, but the 15xx has piston valves above the cylinders. If I were to draw a plan view the 94 cylinders would look larger. Even so The difference in where the weight is is striking. I hadn't really appreciated, until I drew it like this, just how much weight there must be on the centre axle with the crank. It would be interesting to know the difference in weight between a crank axle and a plain one.  If anything, though, the drawing tends to confirm my supposition that the outside cylinder/walschaerts configuration was inherently front heavy. It would be interesting to compare with other designs. A quick browse of my 1957 Observer's Book suggests that other 0-6-0T with outside cylinders tend to have shorter overall wheelbases than the 15s.  Most are specifically described as dock tanks.



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