One or Two throttles?

[galaxy]

On the big articulated steam locomotives was there one or two throttle levers for the engines?

I know some recycled the steam from the rear engine driver wheels into the front engine driver wheels before chuffing it out. Was there then one throttle to control both engines?

And on the ones with separate steam supply to each of the engines was there two throttles?

[%-)]

[tomikawaTT]

On the big articulated steam locomotives was there one or two throttle levers for the engines?

I know some recycled the steam from the rear engine driver wheels into the front engine driver wheels before chuffing it out. Was there then one throttle to control both engines?

And on the ones with separate steam supply to each of the engines was there two throttles?

[%-)]

The big simple articulated locos have one throttle and one power reverse, because both engines have equal requirements for steam and cutoff settings. The engineer didn’t run a single engine, he ran both at once.

The big compound articulateds also had a single throttle and a single reverse system. To start, high pressure steam would be passed through a reducing valve to the low pressure cylinders. At a speed of somewhere between 4 and 10 mph, that valve would close and the low pressure cylinders would run on the exhaust from the high pressure cylinders. The later N&W 2-8-8-2s had another valve which the engineer could use to give the low pressure cylinders a shot of high pressure steam when needed - not exactly a separate throttle, just a ‘booster.’

OTOH, compound locomotives in France were equipped with separate throttles and separately-adjustable reverse gear. The French locomotive engineers were, “Works trained,” so they were able to coordinate the two separate sets of controls for optimum efficiency - at least, that was the theory.

Chuck

[SFbrkmn]

The only stupid questions are the one’s never asked.

[galaxy]

Thanks Chuck.

I suspected one throttle, but have seen videos of articulateds with the two sets of engine wheels slipping at different rates.

I wondered if that was because they just worked that way (the accidental spinning as can happen with one set of wheels), or if two throttles were being opened at slightly different times, resulting in the slipping of each engine’s wheels separately.

[CSSHEGEWISCH]

As far as I know, both simple and compound articulateds had only one throttle. However, compound articulateds also had a starting valve which allowed steam to be admitted to the low pressure cylinders directly from the boiler. This was necessary just to get the train moving since it would normally take a few rotations of the drivers before any meaningful amount of steam got from the high pressure cylinders to the low pressure cylinders.

[tomikawaTT]

Thanks Chuck.

I suspected one throttle, but have seen videos of articulateds with the two sets of engine wheels slipping at different rates.

I wondered if that was because they just worked that way (the accidental spinning as can happen with one set of wheels), or if two throttles were being opened at slightly different times, resulting in the slipping of each engine’s wheels separately.

Simple articulateds would have each engine slip in response to what was going on under that particular set of wheels. The slippage was independent of the other engine. (While not an articulated, the PRR T1 4-4-4-4 duplex was infamously slippery - too much cylinder diameter for the combination of other factors that determine tractive effort.)

Compounds would do what I refer to as ‘trip and slip’ If one engine slipped, the steam pressure across the other engine would increase and then IT would slip. That would decrease the steam pressure across the slipping engine, so it would stop slipping. If conditions were right, the two engines would alternately slip and grip until the sand got under the wheels and put a stop to it.

The N&W ended up loading the front engines of the later Y-class 2-8-8-2s with lead (14 tons, IIRC) to reduce their tendency to slip. They still used LOTS of sand on their many upgrades.

Chuck