BR Double blastpipes

I am interested in the upgrades to draughting of various locomotives by BR by installing double blastpipes in the 1950s. Can anyone confirm the diameters of the single and double blastpipes fitted to the following locomotives?
GWR Castle 4-6-0: single double
GWR King 4-6-0: single double
BR Standard 4-6-0 Class 4MT: single double
BR Standard 2-10-0 Class 9F: single double
Regards,
Alasdair

 

I take it that you are talking about the diameter at the top of the blastpipe caps?
Castle single ? double 3-7/8"
King single ? double 4"
Std 4 4-6-0 single 4-5/8" double 3-3/4"
Std 9 2-10-0 single 5-3/8" double 4"

 

That's interesting! The commonplace view is that the double blastpipes were based on the Dean Goods; clearly not.

 

The double blast pipe caps are all of Swindon design to drawing No. SL/SW 1310.

 

By the end of their lives the Dean Goods had received many upgrades, and IIRC I've seen a drawing suggesting the draughting was last changed in the late 30s or early 40s, so it was probably Swindon state of the art for that period, and very likely bore little or no resemblance to what they had when new. Its therefore not impossible that the dimensions on a 1940s designed Dean Goods blastpipe were much the same as those for a double blastpipe on something larger.

 

If I remember correctly, the only use of The Dean Goods arrangement doubled was for BR Duke of Gloucester. It wasn't used for any other double chimneyed loco.

 

Interesting figures!

It appears that:
(i) the double chimneys fitted to the King, 9F and Duke of Gloucester were all the same size (4"),
(ii) the double chimney fitted to the Castle class was larger (3.875") than that on the Royal Scot class (3.75")
(iii) the double chimney fitted to the BS Standard 4MT was the same size (3.75") as that on the Royal Scot class

Comments
(a) the fact that the Duke of Gloucester had the same size double blastpipe as the less powerful Class 9F is more evidence that the Duke's blastpipes were undersized - and the double blastpipe fitted to the King class may also have been undersized;
(b) in view of the success of installations (ii) and (iii), the double blastpipes fitted to Royal Scots may also have been undersized.

Regards,

Alasdair

 

One wonders what Sam Ell would say about your comments.

 

It's not a question of blast nozzle sizes. It is an assessment also of the distance of the blast nozzle to 'choke' dimension, and the diameter of the 'choke' and design of the petticoat pipe and bottom flare, and the 'L' length above the choke to chimney top and the diverging taper above the choke.

Sam Ell sort of perfected things for the GWR and BR(Western Region). Somewhere I have The Dean Goods test report on the Swindon test plant; and there is photographic evidence of this. As JimC alludes to this would have been later versions of The Dean Goods of which I also have the drawings for. "Courier" on here provided the missing bit of the jigsaw puzzle that model engineers already knew but was apparently not available to Jos Koopmans when he wrote his book and was rather dismissive of Sam Ell.

I don't think that the GWR double chimneyed locos owed anything to the rather late testing of The Dean Goods on the Swindon test plant, and the Castles and Kings went through various alterations with draughting as both single chimney and double chimney arrangements.

The classic case via Sam Ell is the GWR Manor alteration (and I have the details somewhere) where basically the blast nozzle was reduced without really altering anything else and at the expense of increased back pressure that didn't arguably materialise.

The GWR Castles and Kings were quite different with their long bending exhaust passages and pipes, and squat single chimneys originally. And not all ended up with double chimneys anyway.

Cheers,
Julian

 

Of the Sam Ell GWR Manor alteration I've found my notes from when the late Bob Youldon sent me the test report:-

"AREA 5 1/8" dia = 20.629 " square
4 5/8" dia = 16.8 " square
Reduction of 18.56% in area "

I can't vouch for my maths, but a 1/2" reduction in the blast nozzle diameter was a significant throttling of the exhaust. And that's basically what Sam Ell did to improve the performance of the Manors. My assumption is that Sam Ell did a bit of a very cheap alteration without altering anything else, and got away with it.

But there we are.

 

I was thinking of making much the same point. The BR test report on re-drafting the Jubilees is interesting as it includes the mods to the single chimney version (apparently broadly similar to the BR Standard Class 5) and an experimental double chimney version, with diagrams and dimensions of all three. The re-drafted single chimney version actually had a larger diameter blastpipe than the standard version (and changes to just about everything else to do with the chimney) and both it and the double chimney increased the front end limit to steam production to more than 25,000lb/hr from less than 21,000lb/hr, although the greater potential abiliity to handle inferior fuel was arguably as important.

 

Dear Julian,

I appreciate that locomotive draughting is a complex issue and blastpipe size is not the only factor involved. However, generally, the more steam the boiler produces the larger the blastpipe(s) needs to be. It would certainly be interesting to know what Sam Ell's comments would have been about the differences noted.

It is interesting that the blastpipes fitted in the very successful BR Standard Class 4MT upgrade were the same size as those in the Class 7P Royal Scot - and that the blastpipes fitted in the successful Castle class upgrade were larger than those in the Royal Scot. Was the Royal Scot draughting arrangement, which dated from the 1940s before Rugby testing station was available, not fully optimised?

Likewise,when the double chimney draughting systems for the Class 9F, King Class and Duke of Gloucester were being designed, the time and resources available for further steam locomotive development in BR were limited, so maybe it is no surprise that, despite their differences in design, number of cylinders and potential power output, 'one size fits all' double blastpipes were fitted to all three. The double chimney Kings appear to have been a success but the Duke of Gloucester suffered from poor draughting, only fully solved in restoration by a new Kylchap system. It is interesting to speculate what differences there might have been between the chimneys, blastpipes etc. fitted to these three locomotives if resources had been available in the 1950s to fully optimise their designs.

Regards,

Alasdair

 

The major problem with 71000 was that the damper apertures in the original ashpan were much smaller than what was shown on the ashpan drawing. This led to 71000 being a very poor steamer in BR days. In preservation this was corrected. The addition of the Kylchap improved things even further.

 

Royal Scot 46165 spent 6 months at Rugby Testing Station in 1955/56. There were modifications made, but it is doubtful that more than a few Scots received these modifications.

 

This has always intrigued me. I have a digital copy of the Swindon report and it is, as would be expected, extremely thorough examining everything in amazing detail, including the specific resistance of the locomotive and coaching stock isolated from each other. There are charts and graphs in their dozens, even hundreds, measuring everything including air flow at multiple points in the draughting system. I struggle to see how someone of Sammy Ell's expertise would have missed something so basic as this, either by visual observation or by data on the graphs displaying lower than expected gas flow or higher than expected vacuum in the system.

 

I have similar thoughts, but it is a fact that the damper apertures were wrong.

 

Agreed! But whether or not they were so wrong to cause all those problems . . .

Edit: Do we know how many ashpans 71000 had in its BR life? Although possible, I wouldn't be surprised if it hadn't needed at least one renewal.

 

Wasn't the brick arch installed in the wrong place and at the wrong angle too?