Basically, yes*. A single screw reverser permits independent working of the low and high pressure valve gears. Both valve gears could also be manipulated at the same time. It's a rather ingenious device that permits this. There are two regulators**, one supplies live steam directly to the H.P. valve chest, the other bypasses the H.P. side of things and allows steam into the reciever (effectively the steam chest for the low pressure cylinder). Finally, there's a pneumatically operated set of valves that permit the exhaust steam of the H.P. cylinders to escape directly in the blastpipe rather than feed the L.P. cylinders; in together with the L.P. regulator this effectively turns the engine into a four-cylinder simple expansion locomotive. As I gather it, there's five modes of operation being:
- Compound is the normal way of doing things.
- Simple permits easier starting, as when in compound, the reciever pressure only starts to rise after a few revolutions of the wheels, and those small H.P. cylinders won't start a train for you.
- Reinforced Compounding is effectively the same as working the engine as a compound, but letting a bit of extra steam into the reciever by means of the L.P. regulator. Incidentally, the reciever had its' own safety valve set at 6 atmospheres; presumably to prevent an uneven distribution of work.
- And finally there's two breakdown modes, where you'd work the engine with either the H.P. or L.P. side isolated. No good at all but it'll sort of get you to the next loop.
If I haven't gone insane yet, I shall soon
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* But not the only one. The vast majority of express locos built in France after this one seem to be some variety of this idea.
** So regulator implies a long metal lever, which some of 'em have, but very often the L.P. regulator is just a valve with a handwheel, much like a injector steam valve.