The problem is that, if I recall correctly, all three axles are rod-driven from the same cylinders.
Lionel Wiener had these problems and worse when attempting to classify articulated power (which he extended to locomotives with deployable powered booster axles, something as yet to enter this chat). We might gainfully look to him for some sense in working this out.
Isn't 809 a B1A?
For the top one, not 4-2-2, but how about 0-4-2-2-0?
So what do we call this little beauty then? 4-2-2 implies two driving wheels, not six, and is clearly wrong. There Goes The System.
This is a Belgian Type #3, No 809. Ten of these were built in 1874 for use on the Luxembourg line, which limited axle loading to 14 tonnes. An extra carrying wheel with lateral play was therefore inserted ahead of the rear driver.The true connoisseur will note that the extra wheel has been interlinked with the spring balancing of the main wheels. There is a sledge brake between the leading and middle drivers.
The UIC System copes rather better. This is based on the German system, and works thus:
Unpowered axles get a simple number: 1,2,3...
Coupled driving axles get a letter: A, B, C... A = one driving axle, B= 2, C= 3 etc.
Trucks, bogies get a ': 1' = two-wheel truck, 2' = 4-wheel bogie.
Individually driven axles get a o: Bo = two driven axles, Co = three driven axles, etc.
Articulated bits go in brackets: (2'C)C2' is a Mallet articulated Challenger.
There are often often odd letters and figures after the main wheel arrangement:h means Superheated Steamn means Saturated (ie unsuperheated) Steamv means CompoundTurb means Turbine (tricky one, that)t means Tank locomotiveA number following n or v is the Number of Cylinders
Thus n2T means a tank engine with no superheater and two cylinders.
No 809 above is therefore a B2A. This is more informative, but doesn't tell you that all the powered axles are coupled together.
Hey, mister, that's me up on the smokebox..."
That's M. Petiet on the right.
Eight of these duplex-drive engines were built, which proved to be eight too many.
The number on the smokebox is "441". (white figures on black ground)
THE LOCOMOTIVEThe idea behind the Locomotive Petiet A111A was to double the output of a Crampton-type locomotive, but without coupling together two driving axles. Apparently at the time coupling rods were not considered strong enough to handle high speeds. Hence there are independent driving wheels and cylinders at each end, while the smaller wheels in the middle just carry part of the weight. The amount of this weight available for adhesion must have been limited.
The long drum on top of the boiler is a steam dryer, not a feed heater, which accounts for the presence on top of it of a little box that presumably holds the regulator, just behind the forward sand container. The chimney runs through the dryer, and exhausts just ahead of the cab. There is swivelling cover for this chimney; this was known in French practice as the capuchon (cap) and was used as a draught damper as well as to keep the rain out.There was no feedwater heater and no injectors. The boiler was fed by a pump powered from one of the driving axles.
The two big square boxes are clearly for sand, and there seems to be no steam-dome as such, the dryer presumably rendering this redundant. From the regulator box a large pipe appears to feed steam to the forward cylinders. Behind this a conical thingy holds two Salter safety valves.The name of the railway "Nord" can be read at the rear.
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