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Re: digital steam engine indicator

Posted: Fri Apr 29, 2016 3:38 pm
by fredrosse
Liberty ship engines:
3 cylinders triple expansion 24.5 37 70 x 48 inches, 622mm 940mm 1776mm x 1220mm common stroke

And a very much larger marine engine, the triple expansion 5 cylinder recips of the Campania, 47 feet high, 165 PSIG
37 inch HP Bore x two cylinder, 79 inch IP bore, 98 inch x two cylinder LP bore, with 69 inch stroke. (940mm HP Bore, 2007 mm IP bore, 2489 mm LP bore, inch x 1753 mm common stroke). These engines were 15,500 IHP each @ 79 RPM, twin engine installation on an 1893 liner.

The most powerful marine reciprocating engines in steam I have found. Notice the size of the "power reverse" cylinders, needed to throw over the Stephenson Links for cutoff and forward/reverse control.

Re: digital steam engine indicator

Posted: Fri Apr 29, 2016 7:54 pm
by Mike Rometer
Looking at that got me thinking. Did anyone produce a compound engine with two highs feeding a large low?

Re: digital steam engine indicator

Posted: Sun May 01, 2016 1:23 am
by barts
Mike Rometer wrote:Looking at that got me thinking. Did anyone produce a compound engine with two highs feeding a large low?
I think they went the other way - one high, one intermediate, and two low pressure cylinders, since otherwise the pistons got too heavy and the castings were really awkward. The Titanic has such engines:

http://www.titanic-titanic.com/titanic_ ... room.shtml

- Bart

Re: digital steam engine indicator

Posted: Sun May 01, 2016 2:02 pm
by RGSP
Mike Rometer wrote:Looking at that got me thinking. Did anyone produce a compound engine with two highs feeding a large low?
I think one (or more) of the Webb compound locomotives on the LNWR may have been arranged that way. There's only room for one low pressure cylinder between the frames, an HP was put both sides for balance, from what I remember (and my memory is not perfect). Anyway, the driving axles were different for HP and LP, and were not coupled, and occasionally they could be seen with one set of wheels spinning uselessly forwards, and the other backwards.

Re: digital steam engine indicator

Posted: Sun May 01, 2016 7:56 pm
by Mike Rometer
I was thinking more marine than Loco, but I'd need to check on that about the Web Compound myself. Seems odd not to connect the two sets of drivers. I do remember they were "different:.

Re: digital steam engine indicator

Posted: Sun May 01, 2016 9:11 pm
by johngriffiths
Webb's compounds were known for not starting because of the axles not being coupled. Wise station masters would arrange for a shunter to be strategically place to offer a helping hand, such was the power and influence of Chief Mechanical Engineers in British railway companies. Now't to do with engine indicators this.

Seem to remember an earlier discussion on this forum concerning electronic engine indicators and in it I mentioned the late Robin Wallace Sims having made one for the SBA. The transducer volume needs to be quite small or it will effect the readings which is the trouble with trying to use one intended for a full size engine and there is the problem of fixing such a large object. A major problem is determining crank position, small engines do not have constant angular velocity and RWS was very surprised at how much variation there was. It is easy if it is built into the engine from new but a different matter entirely if the unit is intended to be used on a diversity of engines.

Go to it folks, enough skills here to design and make one.

Re: digital steam engine indicator

Posted: Mon May 30, 2016 6:20 pm
by Lopez Mike
More post hijacking but explain about the axles not being coupled? I have a partially machined 2-8-8-2 compound articulated locomotive in 1/8 scale. (Anyone want a project??) The front engine is the low pressure and the rear is high pressure and they run quite well independently. I suppose you might reverse one engine without reversing the other.

Perhaps a link to an explanation? My knowledge of railroad practice is rather parochial and stops pretty much at the borders of the U.S. sad to say.

Re: digital steam engine indicator

Posted: Mon May 30, 2016 11:31 pm
by ron parola
Eer, the HMS Campania engines pictured above DOES have 2 high pressure cylinders feeding an intermediate pressure cylinder. rp

Re: digital steam engine indicator

Posted: Tue May 31, 2016 9:04 am
by RGSP
Lopez Mike wrote:More post hijacking but explain about the axles not being coupled? I have a partially machined 2-8-8-2 compound articulated locomotive in 1/8 scale. (Anyone want a project??) The front engine is the low pressure and the rear is high pressure and they run quite well independently. I suppose you might reverse one engine without reversing the other.

Perhaps a link to an explanation? My knowledge of railroad practice is rather parochial and stops pretty much at the borders of the U.S. sad to say.
I'm not sure about the exact details here, and don't know of a link, but I THINK the low pressure cylinder & axle had some rather primitive form of valve gear, possibly a slip eccentric, which wasn't controllable from the cab, and just "followed" the high pressure axle. There was no simpling valve, so the high pressure axle usually dominated at starting. Sometimes it didn't though.

I've not seen it written down, but the problems MAY have occured if the high pressure axle stopped in a bad position for forward starting torque, and the driver had to "set back" a few inches.

Re: digital steam engine indicator

Posted: Tue May 31, 2016 3:29 pm
by Lopez Mike
Ah. Primodial stuff. There was a lot of that sort of thing tried out in the beginnings. Don't think I'll be encountering much of that soon.

As to digital indicators, the price of digital rotational sensors has plummeted. We use coarse versions of these every time we adjust the volume on a modern radio. The computer can easily know the crank angle as closely as needed.

Another issue is that all of the historical data is based on piston travel and connecting rod angularity was, I believed, quietly ignored. If we start recording pressure v.s. crank angle we will do well to be aware of this.

It is easy to correct for this in software if we know the connecting rod length but which data do we want and, as importantly, does it really make any practical difference?