4920 Dumbleton Hall

It is about 6024's alteration, but is described in the 6023 thread.

 

All those Plantagenets look the same to me ...

Tom

 

Thought I heard that 5972 had 'slimmed down' cylinders? Presumably in the cladding rather than the casting?

Will

 

Was that after it clouted the platform at Carlisle?

 

Here is a question, modified halls versus the standard halls what is the width over the cylinders

 

8' 11 1/4" for 49/59xx and 8' 11 1/8" for modified Halls so not a lot of difference unfortunately.
Ray.

 

Reducing the cylinder diameter would reduce the nominal TE but most of the time out on the main line you're notched up to some extent, and the available power depends primarily on how fast the boiler can produce steam. Working at a somewhat longer cutoff to compensate for reduced cylinder diameter would cause a small loss of efficiency, but probably hardly significant. The problem could be just how great a reduction of diameter would be needed, given the lower cylinder height. Might it be possible to raise the centre line a bit as well? That would require raising some of the valve gear including the rockers but would seem worth at least looking at.

 

Interesting that there is a width difference between the two hall classes, is that down to differences in frame thickness ?

With a black 5 being supposedly 8'8" wide over cylinders, i'm struggling to believe that a hall is only 1.5" wider per side than a black 5 considering how restricted a Hall's route availability is. If that was the case, reducing the height of the crinolines that the cladding and insulation would take you most of the way to getting one in gauge.

 

I'm struggling to understand how a Hall can be wider over the cylinders when their diameter is smaller than the Black 5's cylinders. The wheels are the same distance apart and so presumably are the big ends, and one would expect the cylinder's centre lines to be in line with the big ends. Or is it all more complicated?

 

Have you see size of the big ends on a Hall? Phwoar

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On the original Halls, like most of the other GW locos with 2 outside cylinders, the cylinders are cast in with half a smokebox saddle and are bolted in pairs to the ends of the mainframes. Extension frames are bolted in front of the cylinder/saddle assembly i.e they don't have continuous frames. The Modified Halls and Counties have continuous frames from front buffer beam to back dragbox with the cylinders bolted, separately, to the outside of the mainframes - like a Black5 etc.
ISTR that the main difference between the Hall and the Black 5 is that the 5's cylinders are not just slimmer but are pitched higher.... but I'd have to check!
Ray.

 

I believe that both Halls and Black 5s have 18½in diameter cylinders. On the Black 5, the cylinders spacing is just under 6ft 8in. Most large British outside cylinder locos were around the same figure. But on the GW outside 2-cylinder types, the spacing appears to have been 6ft 10in. Possibly this wide spacing was to allow for adequate sideways movement of the bogie frame, given the low position of the GW horizontal cylinders. The wide cylinder spacing may also have been a factor in Churchward's choice of the unusually long cylinder stroke of 30in, in order to compensate for the limitation on cylinder width resulting from the low horizontal placement.

A Hall is more than 3 inches wider over cylinders than a Black 5, of which 2 inches is explained above by the cylinder spacing, leaving another inch that must reflect differences in cylinder wall and cover-plate thickness. It is curious that all of the large 2-cyl GW engines have an overall width between 8ft 11in and 8ft 11½in, although the cylinders are a mix of 18in, 18½in and 19in. Did they use a common external casting but bore the cylinder insides to one of these 3 alternative diameters?

 

Acording to my information, a Hall and a Black 5 are both 18½" diameter.

I've never seen a cylinder with crinolines. The cladding is usually screwed directly to the cylinders where it is thickened to take the cylinder cover fixing studs.
Structure gauge is at its narrowest at platform height with is 3'-0" above rail level. Both Hall and Black 5 have 6ft driving wheels so platform height and axle centreline coincide. GWR locos generally had horizontal cylinders only marginally above axle centreline so the widest part of the cylinder coincides with the platform. Black 5's had cylinders inclined at 1 in 24 which put the widest part of the cylinder at some 3'-7" above rail level.

 

The tyres on GWR loco wheels were 0.5" wider than used on other railways according to Holcroft.

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Yes I've realised i didn't mean crinolines, but rather what i assume are the reinforcing strips at 90 degrees to the bore of the cylinder.

 

Thanks for the subsequent explanations. I stand corrected. I had assumed, without checking, that Stanier's design would have increased the diameter to make up for a reduction from the Swindon 30 inch stroke.

 

Good point about the reduced tractive effort from smaller cylinders but this could be ameliorated by redesigning the boiler - and obtaining the necessary
approvals - for 250 psi.

PS This might enable the new build Hawkesworth County to run at 250 psi. (I think this is probably the nearest to the original 280 psi that could be reasonably possible - for the full pressure it would probably mean a steel firebox and a smaller grate.)

 

The limiting factor for the County, ex 8F, firebox is the stay pitch. Without replacing almost every piece of plate to allow closer pitched stays I seriously doubt any boiler inspector or verification body would allow an increase beyond the designed pressure - 225 psi. For this very reason I've always felt that re-using the parts from the 8F was "penny wise and pound foolish".
I'm not sure why you think a new boiler designed for 250, or even 280 psi, would require "a steel firebox and a smaller grate" as the original was copper. Just wondering.
Cheers,
Ray.

 

If the hall diameter was reduced by 1" that would reduce TE by 11%, but only reduce width by 1" as the cylinder centre line would be the same. To get 2" reduce by 2" and you lose 20%.
The new cylinders on 6024 are slimmer because the ribs on the cylinder are thinner and the cover flange is narrower thus needing more studs of smaller diameter. The grade of cast iron is stronger to make this possible.
I can't see much chance of anyone going down the slim cylinders with a Hall route as the cost of mainline operation must make working with a class 5 and the possible payload difficult to make pay.
Rob

 

SR 'confirmed' that new owner is a certain Mr D Smith, albeit he has strenuously denied this.