More of those indirect-Walsch-in-forward-gear engines than I thought. How about a Toledo, Angola and Western 0-6-0? Other switchers too-- L&NE and CNJ 0-8-0, NH 3-cyl 0-8-0, C&O 0-10-0.
The PRR 2-8+8-0 and 2-8+8-2 were indirect; PRR's CC2 0-8+8-0 had indirect on the rear eng only, as did the first order of C&O 2-8+8-2s.
One of the best coverages of valve gear design was in the Bulletins of the Railway & Locomotive Historical Society back in the days when it was housed in the Baker Library. There were a lot of issues of the bulletin before that subject was exhausted. All steam engines of any application (not just railroads) resulted in serious interest in valve gear.
Nobullchitbids wrote:
"2. No one so far has mentioned the effect that superheating had on the problem. I've always been told that Stephenson only could be used with slide valves, which could not be used once superheating became the standard practice. This explains why Walschaerts took over at the turn of the last century even though it was invented half a century earlier."
With reference to point 2, I would suggest that there were additional issues, other than those already mentioned, which lead to the demise of the Stephenson valve gear for locomotives.
1- The Stephenson valve had relatively large sealing faces, and were generally designed for outside admission of steam which results in the steam acting on the outside of the valve, forcing the valve against the sealing faces of the cylinder block. Thus, as locomotives grew in size, so did the size of the valve and the area of the sealing / wear faces. Since these valves were normally operating in a horizontal direction on top of the cylinder block, the weight of the valve (which in the larger sizes can be considerable) is added to the downward force of the pressure of the steam acting on the back of the valve, thereby increasing the friction forces between valve and block. As the boiler working pressure is increased so too does the aforementioned friction forces, which further increases the wear rates and reduction in engine efficiency.
2- With all outside admission steam valves, there is the issue of being able to seal the valve rod against live steam loss through the gland as steam pressure increases.
3- Superheating reduces the lubricity of the steam significantly. The resulting dry steam can no longer provide lubrication of those large sealing faces of the Stephenson valve, which again increases energy losses due to friction and wear of the sealing faces.
4- The design of the Stephenson valve, in keeping the valve travel relatively short, results in long steam passages between the valve chest and the cylinder ports. As locomotive speed increased, those long steam passages became a liability in terms of getting live steam to the cylinder, and exhaust steam out of the cylinder, fast enough to meet the cylinder demand, thus limiting the maximum speed of the locomotive.
5- Changing to piston valves, and valve gear other than Stephenson, afforded the following advantages:
-Reduction in the size and weight of the valve, while also reducing the bearing / sealing surfaces and thus friction;
-Allowed for the use of inside admission steam which meant valve rod glands only had to seal against the much lower exhaust steam pressure;
-Allowed for reduced steam passage lengths between valve chest and cylinder, all of which improved the timing events and thus the speed and efficiency of the locomotive.
I would suggest that in addition to all the previous answers to the original question, the large number of different valve gears that were developed world wide was in large part due to people trying to improve the efficiency of the steam locomotive by better controlling the steam inlet and exhaust events.
As for the various rotary and poppet type valve systems developed, my understanding is that when used on locomotives the increase in engine efficiency achieved was not enough to offset the costs associated with their complexity and increased maintenance demands.
One of the more efficient reciprocating steam engine types was the Skinner Uniflow engines and their European counterparts. At least one RR company in the US and UK tested locomotives using the uniflow principal but again this type of engine was not adopted by railroads either, apparently due to the costs out-weighing the increased efficiencies obtained (or so I understand).
Seafarer
C&O used Unaflow engines in its last carferries. In addition to the efficiencies mentioned above, the low back pressure allowed for quick responses to reversals, an important factor while maneuvering into and out of the dock areas.
Paul Milenkovic The Walschaerts gear became popular when the locomotive designers and railroad maintenance people wanted to move the gear from inside the frames to the outside, where not only can railfans admire the valve gear in motion, but where it is easier to maintain and repair on later locomotive models where the space inside the frames becomes hard to get at.
The Walschaerts gear became popular when the locomotive designers and railroad maintenance people wanted to move the gear from inside the frames to the outside, where not only can railfans admire the valve gear in motion, but where it is easier to maintain and repair on later locomotive models where the space inside the frames becomes hard to get at.
I'm gonna guess that railfan admiration of valve gear in motion might not have been a design consideration.
Actually, I am in complete awe of those engineers who could dream up such complex "monkey motion" in the first place. In fact, I have nothing but admiration for anyone who seems to understand valve gear workings as you do. If I study steam locomotives for another 50 years, I might begin to follow it.
ChuckAllen, TX
lone geep I seen and heard of many different types of valve gear for steam locomotives, like Walschaerts, Baker, Southern, Etc. I know this is a silly question, but why are there so many types? Was some types of valve gear better for different jobs (Walschaerts for speed, Baker for switching, Etc)? Or was simply one type improving on the other?
I seen and heard of many different types of valve gear for steam locomotives, like Walschaerts, Baker, Southern, Etc. I know this is a silly question, but why are there so many types? Was some types of valve gear better for different jobs (Walschaerts for speed, Baker for switching, Etc)? Or was simply one type improving on the other?
Yet another simple question that turns out to be more complicated than we think!
Firelock76 A Southern engineer named WILLIAM SHERMAN Brown? He may have worked for the Southern, but you can bet he wasn't from the South!
A Southern engineer named WILLIAM SHERMAN Brown? He may have worked for the Southern, but you can bet he wasn't from the South!
Johnny
The engineering is to this layman incomprehensible. As a what if, would this valve system be of any value to enhancing the performance of a reciprocating steam locomotive?
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