Paul of Covington BigJim: "Improved" meant that the locos were equiped with the "External Reducing Valve" and booster." By "booster" are you referring to the injection of some high-pressure, high-temp steam into the low-pressure steam? The Y's never had booster engines, did they? Or is this something else?
BigJim:
"Improved" meant that the locos were equiped with the "External Reducing Valve" and booster."
By "booster" are you referring to the injection of some high-pressure, high-temp steam into the low-pressure steam? The Y's never had booster engines, did they? Or is this something else?
This sounds more like you're asking about a starting valve, which performed that function to aid in starting a train from a standstill.
Paul of Covington By "booster" are you referring to the injection of some high-pressure, high-temp steam into the low-pressure steam? The Y's never had booster engines, did they? Or is this something else?
Compounds are designed so that, ideally, the torque produced by the HP engine and that produced by the LP engine are either roughly equal or proportional to the relative adhesion limits of the two engines. In practice, effects such as heat loss result in the LP engine developing substantially less than expected. The booster valve 'boosts' the power of the LP engine by adding an amount of live steam that brings the average pressure at either the receiver or the LP steam chests up to 'spec' -- or, if a bit more power is desired, beyond that... but not up to the 'full pressure' used when the conventional simpling valve is used.
As noted, the way the N&W had this set up, the power from the forward (LP) engine was higher enough that a bit of ballasting could provide a higher effective TE at the speeds where the booster was found most effective (IIRC from Rails Remembered vol 3 this was around 26mph).
Another way, in principle, that the 'boosting' can be done is to modulate steam into the LP chests more directly, so that not only the average pressure but the developed torque relative to stroke are similar between the HP and LP engines. This (in theory) allows the LP engine to be balanced accurately, and the engine to work compound to a higher speed. While it might be uneconomical to work even an 'improved' Y6b as fast as 40-45 mph (assuming you could get it that fast without bad riding), a modulated-admission locomotive -- with, perhaps, the slight additional improvements of having its forward engine hinged only in the horizontal plane, as the Alco Challengers were famously built (and, before them, the class A, although not nearly enough has been made about that point...) and being given better leading and trailing trucks (the class A's arrangement would probably do) -- could be made to run as fast as the steam mass flow from the boiler would permit. In my opinion, it would certainly have been practical to run such a locomotive at typical N&W fast-freight speeds on the flat, greatly expanding the range of the Y class (and incidentally taking advantage of the relatively high weight on drivers and short length for developed power of the 2-8-8-2 wheel arrangement.
[To an extent, of course, the external 'booster' valve would permit much of the same effect, and I personally suspect that any Ys which were actually run to high speed would have been 'improved' locomotives run by men who understood precisely how to use the improvement.]
CSSHEGEWISCH Paul of Covington BigJim: "Improved" meant that the locos were equiped with the "External Reducing Valve" and booster." By "booster" are you referring to the injection of some high-pressure, high-temp steam into the low-pressure steam? The Y's never had booster engines, did they? Or is this something else? This sounds more like you're asking about a starting valve, which performed that function to aid in starting a train from a standstill.
I think that would be the function of the intercepting/reducing valve. I remember reading (it may have been in something written by (horrors!) LaMessena.) that they added this feature that injected a small amount of high-pressure steam into the low-pressure side to boost power to the low-pressure cylinders. This could be done after it was running in compound mode.
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Thanks, Overmod. I was still making my last response when you entered yours.
Paul,Yes, the so-called "Booster" allowed a bit of live steam to enter the reciever pipe while still working in compound. It is not so much the pressure, but, the added heat that made the difference. This all worked through the reducing valve, which was now located outside of its previous location in the high pressure cylinder saddle to a position over top of the right high pressure cylinder. It is easily seen in photos of the right of the locomotives.
All steam to the low pressure cylinders was either routed through the reducing valve or from the HP exhaust to the reviever pipe going to the LP cylinders. The full 300 psi steam never went to the LP cylinders. The reducing valve regulated the steam pressure down to a value that would give the LP cylinders roughly the same power as the HP cylinders. I don't have the exact figure at my finger tips, but, I am thinking that it wouldn't be more than 115 - 120 psi.
FWIW, an engineer that I worked with when asked, said that 63mph was about as fast as you wanted to run one. After that, things started to get a little shakey.
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Thanks, BigJim. And I'm wondering under what circumstances someone ran a Y at 63 mph. I think of them as low-speed tractors that could out-pull anybody else.
Well, some engineers on the Shenandoah Valley and Bristol line knew how to let 'em roll.
BigJim Well, some engineers on the Shenandoah Valley and Bristol line knew how to let 'em roll.
I wonder what the M/W department thought of those engineers.
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