Regulator/throttle.
It regulates the proportion of the piston stroke that recieves steam. Sure, on that first movement it can't limit the torque, but once there is a partial revolving of the wheels it definitely will limit the torque.
First, please don't middle post, it's worse than top posting.
Second, the regulator regulates that amount of steam admitted to the pistons, it doesn't regulate the proportion of the piston stroke that receives steam. That's done by the cut off.
-- Cheers Roger T.
Home of the Great Eastern Railway (Site now back up and working)
Read the sequence above - we were talking specifically about the valve motion.
The regulator can only limit the amount of steam admitted to the pistons over time, which is different to "the amount of steam admitted to the pistons" - it _throttles_ the flow of steam.
Regards, Greg.P.
On re-reading the above, several times, it seems you were referring to the valve gear and not the regulator. The "it" in your sentence could also refer to the regulator, hence my post.
-- Cheers Roger T.
Home of the Great Eastern Railway (Site now back up and working)
You're forgiven. :-)
Greg.P.
Yep, the throttle regulates the amount of steam to the cylinders by providing a restriction to the flow of steam. A smart engineer opens the trottle a little to get the engine started and shuts off that throttle if necessary to limit the power (torque) of the loco when starting as necessary to keep the wheels from slipping. The valve timing control (the Johnson bar) is generally in the "hole" or at the full limit to maximize the amount of timing as this is necessary to allow for the longest entrance of steam to the cylinders. As the loco starts moving, the dynamic of the cylinders moving allow for the low flow of steam from the throttle to keep the torque down to usable levels. As the torque requirements of the loco drop as the speed increases, the Johnson bar can be picked up from the end of it's travel and the steam allowed to expand in the cylinders rather than stay at the full pressure. At this point, the throttle can also be opened to the "balancing point" where the steam flow won't increase as the throttle is opened further (this is normal!) and the amount of steam admitted to the cylinders is controlled by the Johnson bar to control the speed. At this point, the closing of the throttle will indeed reduce the speed but generally isn't used as such for fine tuning speed as the loco is in it's efficiency region and responds only lightly to the throttle control. The major contol of speed at this time is just what the valve timing is and that isn't the throttle that controls that. Been there and done that with a real live steam loco and this was how it was taught to me. I've also done this with the small live steam engines and the owners of the locos have always been impressed that I was able to get the loco to performe much better than they could. You could also tell who had any idea of how to time a loco and did so with their loco. On several occasions, I've had the owner riding behind me on the tender ask me to slow down a bit as they felt that their loco would run out of steam quickly at that kind of speed.
-- Why isn't there an Ozone Hole at the NORTH Pole?
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.