PRR Duplexes and Experimental Engines ( S1, S2, T1, Q1, V1 etc.)

[BaltACD]

https://www.youtube.com/watch?v=2RusRdlE-gg

[Overmod]

That video has some of the most splendid video quality I've ever seen in a YouTube video -- even before we consider the subject matter.  It's well worth watching, and I think we should encourage his 'channel' with likes and subscribes.

[Backshop]

You do know that was CGI?

[BaltACD]

Backshop

You do know that was CGI?

CGI can illustrate things that no longer exist as well as things that only exist in the mind of the creator.

[CSSHEGEWISCH]

BaltACD

 

Backshop

You do know that was CGI?

 

 

CGI can illustrate things that no longer exist as well as things that only exist in the mind of the creator.

 

It would be interesting to see some of the more outlandish proposals that were never built but turned up in Wiener's "Articulated Locomotives".

[Overmod]

Backshop

You do know that was CGI?

I was referring to the video clips at the beginning.  The MSTS was typical 2011 quality, no more, no less.

An actual render in modern CGI would be much closer to 'photorealism', both in ray-tracing lighting effects and resolution.  See the 3D derived-pointcloud models that were produced for the T1 Trust about a half-decade ago, but in color...

[Flintlock76]

Backshop

You do know that was CGI?

 

I enjoyed the video!  Authentic footage where available (and the rendition was excellent) and CGI where needed.  A pretty good balance and a great end product.

I definately gave it a "Like!"

[BaltACD]

Question - On compound non-mallet engines.  Are the low pressure cylinders quartered on the same phase as the high pressure cylinders?

[CSSHEGEWISCH]

BaltACD

Question - On compound non-mallet engines.  Are the low pressure cylinders quartered on the same phase as the high pressure cylinders?

 

It would have to be that way on Vauclain compounds and probably that way on cross compounds and D&H 1403.

[Overmod]

Thing is that it would require 180-degree opposition on each side to get the engine to balance, and that is manifestly not true of a Vauclain compound (I presume you mean type 1, with the high-pressure and low-pressure cylinders outside, driving on a common crosshead).  There are illustrations on the Web of the special piston valve and convoluted port and passage arrangement that is at the heart of this method of compounding, and although the porting and operation are complex to analyze, the system was certainly capable of developing near- if not actual world's-fastest speeds in the early 1890s.

I think the inside connections on a Cole balanced compound are quartered at something like 135 degrees relative  to the (quartered) outside.  Early compounds did not use the analogy to loop scavenging to lower effective HP backpressure going into the receiver, and I'd think dynamic balance would be a more important concern that equalizing MEP... especially with the actual condensation of LP steam in the receiver and then during expansion in the LP cylinders, which was often far more abysmal than manufacturers and designers seem to have realized.

The 'answer' of course can be seen first in effective steam-streamlined passages and superheating in modern compounds, and then in the 'booster valve' applied to some of the N&W Y-class engines (which of course were only circumstantially and accidentally 'in pnase' HP to LP).  I still have no hard information on whether the LP reheat 'superheater' on 160 A1 was actually useful or not.  In my opinion the 'best' approach is still that proposed by Chapelon, which is like a modulated version of the booster valve: high-pressure saturated or superheated steam is preferentially injected into the receiver at acceptable determined HP back-pressure excursion, so that not only the MEP but the instantaneous pressure on the LP pistons over the effective range of their stroke 'matches' what the HP cylinders are producing.  That does not require that the HP and LP be co-phased at all; in fact my RSR engine design phases the front and rear soft-conjugated engines (via a detent) at 135 relative (both engines being simple 2-cylinder DA in quarter) so that there are eight controlled power impulses per revolution for the engine as a whole, which also should help eliminate objectional high-speed surge effects.

[timz]

BaltACD

On compound non-mallet engines.  Are the low pressure cylinders quartered on the same phase as the high pressure cylinders?

Guess a four-cylinder would always have the low-pressure 180 degrees from the high pressure on that side, wouldn't it? And the left and right sides the usual 90 degrees apart. Presumably that's why the main-driver counterweight is at the bottom on this 4-6-0

https://babel.hathitrust.org/cgi/pt?id=uva.x002211444&view=1up&seq=604&size=125

Next question: what was more common, four cylinders all driving one axle or low-pressure driving the lead axle and high-pressure the second?

[Overmod]

Look up 'Plancher System' for a different approach to four-cylinder compounding (e.g. the early Italian cab-forward 4-6-0 design)

The de Glehn-du Bousquet design, one of the more successful compounds, had the HP drive on the main with a conventional axle and the LP on a cranked leading driver axle.  Four sets of valve gear with the LP fully adjustable separate from the HP -- a reason the French called engine-drivers 'mecaniciens'.

Most of the balanced compounds (such as Cole and Vauclain type 2, the latter being the "Baldwin balance compounding' applied to the New Haven engines) had a cranked main-driver axle and all four mains bore on the same driver pair -- in other words, not divided-drive.

An interesting type that you'd think couldn't work all that well was the von Borries, which is a normal quartered 2-cylinder DA... run as a compound with HP on one side, LP on the other, and asymmetrical counterbalancing.  The original PRR T1, with the 84" drivers, was made this way and there is a photograph of it at high speed with a considerable train -- the trick was that the two sides had separate cutoff so it was relatively easy to adjust running balance at a given throttle opening and HP cutoff.

[thomas81z]

I have read & reread this thread since 2018 & it still blows my mind well from what i understand , wow just wow . thank you guys so much for deep diving for us that arent as knowledgeable  on this subject