Discussion in 'Steam Traction' started by aron33, May 22, 2016.
.... and allows for more expansive running, plus of course, commonality with the A1 boiler.
I thought that the 4700 was going to re-use a Hall/28XX boiler/firebox to save the expense of building a new 47xx boiler/firebox..
Isnt there a high degree of similarity with the castle boiler and so tooling to create one would be seen as a worthwhile investment ?
The 4700 firebox is similar to a Castle one, and the 4700 barrel is similar to a shorter King barrel (in both cases vice versa of course) but how much can be usefully transferred is debatable. The 4700 project has put on line their plans for how they intend to integrate a 2800 cylinder block with the larger radius 4700 smoke box, so I don't think they are going the Std 1 route.
Suppose. Fitting a No 1 matched Smokebox saddle would preclude the use of a larger boiler/ smoke box, but it would still be possible to fit a larger (oversize) smoke box to a std no1 boiler and still use it whilst waiting for a larger boiler to happen...
As I understand it (and I am a contributor to the 47xx project), that option has been proposed as an interim step while the finance for the new boiler is generated. I need to be convinced that it is the best way forward personally.
There is of course precedent as the first of the class was put into traffic with a No1 boiler when first built. As Churchward had suspected, this proved that the No1 was not quite big enough for that application and the replacement No7, that was already on the drawing board, was soon substituted and used for the remainder of the class.
The original intent was to use the No7 on what ultimately became the Castles but it came out to heavy - so the boiler eventually used was something of a compromise.
I need convincing too: it would be fine if fully repaired and certficated Std 1 boilers grew on trees and were readily available, but as they aren't... It would be very nice for the GWS to have a spare Std 1 boiler so they could rotate boilers round the fleet but it doesn't feel like the best use of available cash and effort to overhaul the ex 2861 boiler when it comes off the Saint.
Does lead me to one thought though: that I wonder if they considered fitting Std 8 boilers to the 47s when new boilers were required in 1955.
I rather suspect that if the 4700 is completed with the No 1 boiler the momentum will be lost and the No 7 will always remain just an aspiration.
Surely not. Think of a 47 and we automatically picture it with a no. 7 boiler. I can't believe the GWS would consider that with a no. 1 boiler the resurrected 47XX would be "job done".
But aren't they using a bodged up LMS 8F boiler?
Big difference here. The County will have a part LMS 8F boiler which will look identical to an original County boiler. If the 47xx had a standard no. 1 boiler, it would just look like a big wheeled 28xx, nothing like a 47xx, as we know it.
Basically agree, but the first 4700 did run for a while with a Standard 1 boiler because the Standard 7 wasn't ready. In this form there was a spectacularly long smokebox.
"Not ready" always sounds a little odd to me, but on reflection my guess is they were trying to design a boiler using the Great Bear flanging blocks that could be used on a Star and Saint chassis and get within the weight limits. Weight studies exist of a Std 7 boiler on Star and Saint chassis, and in both cases they are a ton too heavy on the middle driving wheels. Which brings us full circle back to the County which, by using the 8F flanging blocks which were intermediate in size, could be regarded as an enlarged boiler on a Saint chassis . Les Summers, in his book 'Swindon Steam', talks the reader through the development of the County design using various surviving weight studies. Its maybe surprising that a Castle boiler wasn't considered, but perhaps that had been rejected in previous studies that haven't survived.
The strongest argument in favour of the Std1 boiler is that it would preclude anyone wanting to paint the poor thing in BR bl**dy lined black.
For interest, here's a sketch of the original 4700 with the Std1 against the class as it ended up. The Std 1 boiler version does lack the sheer brute muscle of the final design. Note that the Std 1 sketch was very quickly worked up this morning, its not going to be that accurate.
On the subject of accuracy, I worked this up from the weight diagram in Russell, and I was puzzled because the cab seemed shorter than the cab on the later diagrams, but the wheelbase dimensions were identical. Then I remembered I do have a full GA drawing of the Std1 version, and compared. And yes, the cab drawn in the weight diagram was a good 6 inches too short, had the wrong cab steps and some other changes. Presumably the weight diagram was drawn up as a weight study in the early stages , and when the design was changed they didn't bother to redraw the weight diagram but simply corrected the dimensions.
Jim, I also noticed the difference in how the whistle steam pipe is shaped on both boilers: the Std1 version has the pipe bent up at a 90-degree angle, whilst the final design had the pipe angled down and sits on top of the firebox.
4700both by aron33 posted Apr 30, 2017 at 5:19 PM
I wouldn't take that as gospel mate, I did knock that sketch together quickly by just copying the boiler for a 28xx drawing, repositioning and extending the smokebox. . And in any case I shouldn't be surprised if that sort of thing varied between locos and over lifetimes. I have a whole library of standard components drawn, but its hard work trying to find a decent reference for every little detail of how they were installed.
I think you are underestimating the psychology of fundraising. Once a project looks "finished", it becomes very hard to raise funds for, even if there is still in reality more work to be done. I'd agree with the point made by others - if a loco emerges with a 28xx boiler but carrying number in the 47xx series, the majority of people who wanted to see a 47xx will think "job done" and move on to the next idea, leaving the task of raising funds for a new No. 7 boiler much harder.
As I understand it, refurbishing one of the existing no.1 boilers for 4709 rather than building a no.7 from scratch will save a lot of money, and the no.1 is to be disguised by larger cladding to look like a no.7. As long as the loco only toddles up and down at Didcot, having the smaller boiler really won't matter at all. If they take it on preserved lines it will have comparable power to a Hall, which should be plenty. It won't even be too serious if they take it main line, merely reducing the allowable loadings a bit. And building a no.7 at some future date remains possible, however likely or unlikely.
It's a bit different with the County, where so much of the 8F boiler is being replaced by new material that there can be only a minimal cost saving in exchange for the limitation on performance from the lower pressure. Slightly increased cylinder bores and slightly larger wheels than a Hall's will mean much the same TE, and the boiler is a bit bigger than a no.1, so the available power will be a bit more than a Hall's but still giving a reduction from the power of the original Counties at 250 psi and a larger reduction from the Counties as originally designed and built to work at 280 psi.
Halls have 6'-0" dia wheels. Counties have 6'-3" dia wheels.
I have to say I do struggle a bit with this 'building the next in line of the class' or 'replica' when they are not actually a replica as such.
Indeed, as I realised a few minutes ago, so I've edited my post accordingly.
Separate names with a comma.