Statfold Barn Railway Mallet

Here is my photo of it taken in September 2002, at Jatibarang Sugar Mill, Java. The additional tender is used to carry bales of 'Bagasse', sugar cane waste, which is used to fire the locomotives.
As the calorific content of Bagasse is low, a continual feed into the firebox is necessary.

 

Sorry, the date should have read September 1992.

 

Presumably as a Mallet, this is a compound? What is the ratio of the cylinder sizes? Is the cut-off for the LP linked to the HP, independently variable or fixed?

 

I can answer some of this. I don't know the cylinder sizes but yes she is a compound. The Cut off positions are fixed together and controlled from a single wheel reverser ie both High and Low pressure units are in full for gear at the same time and link up by the same amount up to full reverse.

 

High Pressure Cylinders 30cm x 20cm

Low Pressure Cylinders 30cm x 30cm

 

She is also fitted with a simpleing valve which enables high pressure steam to be admitted to both sets of cylinders if required.

Ian

 

Thanks, so the ratio of HP/LP voume is 2.25:1 (assuming my maths are correct), which seems to be towards the lower end of such ratios. Intuitively, one would have thought that the LP cylinders would have a longer cut-off than the HP, on the basis that there is not much point in conserving the steam after it leaves the HP cylinders.

 

... and wouldn't running with a short LP cut-off choke the HP exhaust? Makes you wonder what the optimum LP cut-off would be, other than full gear? Unless there's an LP receiver in the line, which I doubt?

 

Yes, my thoughts too. I imagine the aversion to always having the LP engine in full gear is the potential effect on balancing the work of the two engines, bearing in mind it would still make sense to work the HP expansively.

 

The pipe feeding the LP cylinders acts as the receiver, the engine is not a Woolf compound. The valve gears should be linked so that both HP and LP sections produce an equal amount of output. You would want to keep the HP steam chest pressure as high as possible and have a period of admission long enough to minimise condensation. It would be interesting to do some testing on the engine in order to get the best out of it, it would also be interesting to know how the engine is being worked at present.

 

Agree one has to have a receiver for a Mallet, as the two engines are not necessarily in phase, but as you say, the connecting steam pipes achieve the same. Still trying to understand the principle here though. I believe there were/are compounds where the cut-off is fixed on the LP. For a Mallet, balancing does not seem to be a particular issue compared with, say, a two cylinder compound where a large twisting moment could be set up, so this may not be the best example. I can see that having independently variable gear may have been discouraged on the basis that it could not be assumed that the driver would use it properly, so wondering whether, where the valve gears were linked, if the rule of thumb was that they were linked at the same cut-off, on the basis that the cylinder volume ratios took care of the rest, or that the linkage was such that the LP cut-off tended to be longer for a given HP cut-off. Anyone know what the position is for the Midland Compound?

 

These theory on compounding are very sound and totally justified on a larger main line engine, but remember the context. This Mallet was built as a basic industrial loco to be used by less well educated operators with minimal maintenance. As for the Midland locos, the valve gears were fixed and If I remember correctly the starting high pressure steam to the low pressure cylinders was admited based on the position of the valve gear (IE in full forward/reverse) rather than by a manual control for the driver.

 

Yes, it's a bit off topic. Live steam was admitted to the LP cylinders on the Midland compound when the regulator was opened a small way. The passage to the LP cylinders was closed as the regulator was opened wider.

 

Get hold of a copy of "Compound Locomotives" by J.T. van Riemsdijk ISBN 0 906899 61 3 published by Atlantic. You will find a few errors but it is worth a read, try also "Advanced Steam Locomotive Development" by L.D. Porta, still in print and published by Camden Miniature Steam Services, then there is "La Locomotive a Vapeur" by Andre Chapelon. Reading up from what sources are available will explain the theory and go on to show how hard it was to apply in practice. There were very few really good compound expansion designs, but the same can be said about simple expansion types. To cover all the ins and outs would take too many key strokes to even think about!

Good Luck

 

Not convinced about van Riemsdijk, long on nice pictures but a bit short of some basic info, possibly because he tries to cover too many locos. I will try to get copies of the others.