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> Now, how to regulate speed? You use a thing called the throttle. This is
> essentially a bar that, via linkages that adjust the valve gear(2),
> regulates the proportion of the total stroke cycle that steam is
> admitted to the cylinder. The longer, proportionally, that the steam is
> admitted, the more expansion you get and the more work done against the
> piston face. As work increases beyond that required to maintain steady
> state you get acceleration.
Sorry Larry, not true. The throttle controls the pressure in the steam chest
(Ideally), which controls the speed. (in fact, it does regulate pressure, but
also regulates volume) What you are suggesting is done on some engines
(corliss mill engines), but even then, it is not as a throttle, but as a means
of regulating power, not speed. The speed falls off, so the valves are held
open longer to allow less expansive working, with the valves being controlled
by the governer
> Now, actually it's not THAT simple. You have to take timing into
> account. There is another bar called the "reverse gear(1)" or "Johnson
> bar" that regulates WHEN in the cycle the steam is admitted. This is
> sometimes called the "cutoff". As the cycle speed increases you need to
> let the steam in earlier and earlier or it doesn't have time to expand.
> (this is analogous to advancing/retarding ignition timing in an otto or
> wankel cycle internal combustion engine).
The timing (valve gear) is more analgious to the gears on a car. It controls
the amount of power (vs the throttle, which controls speed). If you have a
very heavy train, and you need the power, you leave the engine 'notched' down
(Ie, full gear). This admits the full pressure to the cylinders for longer,
giving you more power (but less efficency). The thing is, is that if you are
in full gear, you are using more steam, likely more than the boiler can
produce...at least at speed. So, you notch up.
(btw, steam produces 0 hp at 0 mph, and more as you go faster...however, you
get max. torque at 0 rpm)
It's complicated, but simple at the same time. :)
> It's called the reverse gear because if you adjust it far enough you are
> admitting steam at the "wrong" point for forward travel which eventually
> slows the engine down, and if you leave it there, starts working the
> engine in reverse. Unlike an otto or wankel, a railway reciprocating
> steam engine is just as happy running in reverse as forward. It HAS to
> be, there is no transmission per se, the piston rod connects to the
> connecting rod at the main driver and there is no gearing to change
> direction of travel.
Ah, yes but no...a otto engine is reversable (at least, a diesel is) Diesels
are often reversable (at least, marine diesels are) We're stripping down a
250hp one right now in school.
James P
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Message has 2 Replies:
 | | Re: Engine Speed Regulation
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| Great detailed explanations! If I simplify things, the throttle on a steam engine controls Torque. To set a certain speed with a certain load, a certain torque is needed. The speed regulator (governor) is a device that controls the applied torque so (...) (25 years ago, 29-Oct-99, to lugnet.off-topic.geek, lugnet.trains)
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Message is in Reply To:
| | Re: Engine Speed Regulation
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| (...) Working from memory and I could be wrong. But I doubt it. Review. Reciprocating steam engines function by admitting pressurised steam into a chamber (the cylinder) where it expands, doing work against the walls. One of the walls (the piston (...) (25 years ago, 29-Oct-99, to lugnet.off-topic.geek, lugnet.trains)
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