34046 Braunton

Any of You B'lleidophiles Know what the Nozzle diameter on a WC/BB lemaitre is ?

 

2.75 inches diameter x 5.

 

I'm nicking that to describe the Southern mob in future

 

Then I guess I am a B'lleidophile and a one of the Southern Mobs!! Or just call me 'Mr Bulleid'....

 

I doubt supporters of the P class locos would approve of similar descriptions

 

Yes, two separate sets, but probably with a large intersection

 

2.75 inches ?that is a lot of blast tip area ... is that the size of the hole or the size of the bit of metal with the hole in . is it the same as the MN'S ?

 

I can confirm that all drawings have the holes marked 2.75 inches dia, the Merchant Navys are the same, giving an area of 29.68 sq in - if my maths is correct!

 

DL Bradley gives five nozzles of 2.625" for a Merchant Navy, situated 15.625" below boiler centre line and discharging through a 25" choke.

I'm only skim-reading and can't find an equivalent figure for a WC/BB, but the fact that he doesn't explicitly mention a different dimension might suggest the proportions are the same?

Tom

 

But is the nozzle parallel / cylindrical internally or is like a venturi with a choke point somewhere below the tip, which would be of a smaller diameter?

For interest, from the DoG website ...... The total area of the plain blastpipe nozzles of No 71000, at 25sq in, was less than either the five-nozzle unit of the 'Merchant Navy' at 27.5 sq in, or the twin-cloverleaf pattern of the 'A2' Kylchap blastpipe at 29.5 sq in.

 

162cm Sq ? I work that back to 2 x 4 inch ' Nozzles' on ex works 71000, same as a 9f? which is acceptable......for a 9f (or a clan....)

 

The bores on the blast pipe cap for the Bulleids are 2-3/4" dia at the bottom and 2-5/8"dia at the top.

 

Yes, my error, I was reading the measurements off the blast pipe drawings instead of the one for the cap!

 

How does it work Vic....?
Ah dunnoh, but it does.

 

in AE Durrant's book "Swindon Apprentice" he writes:

"Always eager to learn new techniques, I was most interested to discover how Bulleid's modified Lemaitre exhaust varied according to locomotive size, and extracted the relevant drawings for study. [he was seconded to Ashford at the time]. To my amazement they were all virtually the same, five jets of 2 5/8 inches diameter on closely similar pitch circle. Only much later did the significance of this emerge. The original design was probably prepared for the 'Nelsons' and worked well. On the Schools, it was really too big, which is why no definitive results were obtained in its favour. When these same sized jets were applied to the far larger 'Merchant Navy' class, they created too much back pressure, as confirmed with the tested high fuel consumption, but also created so much draught that the boilers were unbeatable! By coincidence the identical arrangement on the smaller Pacifics provided a less extravagant draught and back pressure, giving them their popular acceptance. It seems amazing that the jet and chimney dimensions were not varied according to locomotive size, this being one of those little mysteries which make locomotive history so rewarding."

 

So there you have it, if you have a MN it might benefit from a renozzling ( is that a word ?)
Will keep a look out for that book.

 

If what Mr.Durrant said is correct, why weren't the draughting arrangements modified during the rebuilding process?

 

Apparently there was a proposal from Swindon test plant to modify the draughting of the rebuilds, with the nozzles opened up to around 30sq in and the petticoats modified to be longer with a tighter choke. My reference (Rogers, Bulleid Pacifics at Work) doesn't say whether this only applied to the MNs, or all the Pacifics . Nothing to do with efficiency though, they'd been asked to suggest a way of curbing the extravagant fire throwing of the rebuilds, although apparently the probability of fuel savings was noted. But by then it was 1961, and nothing was done about it. I'm sure I once read (rough quote): 'Anyone who thought the Bulleids threw a lot of sparks from the chimney hadn't seen a Nelson at night.'

 

It is rather curious after reading that interesting quote, certainly chimney and blastpipe dimensions can make a big difference, especially since Bulleid would have been aware of the difference the double Kylchap made on Gresley Pacifics.