It seems that a lot of steamers used walshaerts to the end of steam, despite the proliferation of other types after 1900.

Was there any valve gear that was the "best"? I remember reading somewhere that the MO-PAc refitted a Pacific (6000, 600?) with rotary cam poppet valves and could get the same performance at speed as a Mountain but that maintenance killed it.

Why did some roads go for Baker later on? Did walshaerts survive as "good enough" but familiar technology, or did it have some inherent advantages over newcomers? I seem to recall hearing that in high peed applications, certain parts tended to get hammered.

Superheater@rrmail.com

> That's high speed applications, not what I wrote!!!!

Superheater@rrmail.com

Walschaerts evolved when engines got too big to use Stephenson - the weights of the duplicated and heavier seperate forward and reverse gears couldn't be conveniently operated and contributed a lot of moving weight under the boiler.

Walschaerts is easier to maintain because you don't have to climb under the engine to maintain it, but harder because valve setting requires blacksmithing the rods to different lengths. Taking up the wear in the shoes and wedges can set it out of time.

Baker doesn't have the link machining difficulties Walschaerts has, pretty much all pins and bushings.

Best? Won't go there......lots of dependence on the situation and people involved. Glovers built a few engines with Smith gear - a semibaker type based on oscillating levers in a yoke outside the frame - for Haitian American Sugar co. Haitian mechanics could easily maintain this gear without pits and heavy tooling. In the 1940's they recieved an order for new parts for the Stephenson gear on these engines. A frenchman had taken over as master mechanic for the sugar company and didn't understand or like the esthetics of the outside valve gear, and retrofitted what he was comfortable with.

Dave

Since its valve events were about as could as could be attined without resorting to poppet timing, the only drawback I have ever heard attributable to Baker was its tendancy to require more power at higher speeds, upwards of 100 hp per set at high speed. But in my poor old simple Texas brain, that should have been more than made up for in ease of maintenence (an overhaul just involves bushings and bearings), and a common parts inventory for several sizes and classes of power. Anything to keep out of a satanicically nasty pit wrestling Link Motion.............

lorija799@aol.com

There were advantages to just about every type of valve gear invented, but it seems there was no clearly "best" valve gear.

The Mopac steamer in question was a 4-6-2 fitted with Franklin O-C (oscillating cam) poppet valves. Trains magazine did a big article on it many years ago. The article did not say that it had significant maintenance problems. Poppets are generally acknowledged to give the best valve events as the intake and exhaust timing can be completely separated. They give large valve openings and can work well with very hot steam. Their drawback is that they are relatively delicate and require extremely precise machining of the parts. They are also more prone to steam leakage than well-designed piston valves due to distortion of the valve seats under pressure and heat.

The main difference between Baker and Walschaerts was that Baker eliminated sliding wear points (all motion was rotary) which made for simpler maintenance- just replace pins and bushings. It also allowed the use of needle roller bearings which gave extremely long life between shoppings. The geometry of Baker supposedly made it easier to design for long valve travel, which was a significant benefit on later steam locomotives. The main drawback to Baker is that it was a proprietary system- it was patented by the Baker-Pilliod Company and had to be bought from them. Some railroads probably stayed away from it just because of this.

It is interesting to note that the ACE 3000, the modern steam locomotive project that was attempted in the early 80's, was going to use Walschaerts valve gear and piston valves. The design team, headed by Argentinian steam engineer L. D. Porta, concluded that this setup was the best that could be devised.

Good Steaming,
Hugh Odom

> It seems that a lot of steamers used
> walshaerts to the end of steam, despite the
> proliferation of other types after 1900.

> Was there any valve gear that was the
> "best"? I remember reading
> somewhere that the MO-PAc refitted a Pacific
> (6000, 600?) with rotary cam poppet valves
> and could get the same performance at speed
> as a Mountain but that maintenance killed
> it.

> Why did some roads go for Baker later on?
> Did walshaerts survive as "good
> enough" but familiar technology, or did
> it have some inherent advantages over
> newcomers? I seem to recall hearing that in
> high peed applications, certain parts tended
> to get hammered.


The Ultimate Steam Page
whodom@awod.com

Couldn't let this go by without mentioning Southern valve gear. The three large EBT locomotives have this gear. It is actually pretty simple and seems to work quite well. By having a horizontally mounted stationary link in which the link block travels, the "slip wear" associated with Walschaerts is eliminated. The horizontal position of the link block determines the middle pivot point of the eccentric rod which imparts a vertical motion to a bell crank that operates the valve.

My experience with Baker is that it works, but personally it seems like the long way around the mulberry bush. Talked to a Rio Grande engineer who, upon seeing the Baker gear on our locomotive insisted on seeing me so he could tell me what a piece of junk it is. He had bad experiences with it on large articulateds in Utah. Said it never stayed in time.

A comment in "Apex of the Atlantics" made by someone involved in designing the E-6 (can't remember who), to paraphrase: The only thing you can count on with Stephenson gear is that when you have all those parts bolted together and they start flailing around, something is going to come loose. I certainly thought about that a number of times at 60 mph with 7002 and 1223. The only real advantage I see to Stephenson is the variable lead which is a pretty neat by-product of the design. I have often wondered whether it was intentional. I tend to think not. Anybody know?

Walschaerts is certainly a beautiful gear, but given a choice I might choose Southern based on simplicity and wear. Haven't timed Southern so this is not a totally informed choice.


linnwm@supernet.com

Linn:

Southern valve gear does have its advantages. The only drawbacks I have ever heard to it (from another article in Trains- maybe be Ed King?) were that it is difficult to arrange for long valve travel, and that the timing is affected by the locomotive suspension. When a Southern equipped engine goes through a curve at speed, causing the weight to shift to one side of the engine and compress the springs on that side, the engine will go slightly out of square.

L. D. Porta has actually panned on using Southern valve gear on several modern locomotives that have been proposed- one being the ACE 6000 2-10-2 that was proposed in ~1983 as an interim locomotive to be built prior to the ACE 3000, with all it's modern gadgetry. Most recently, he has worked to design a class of all-new switching steam locomotives for Cuba, which would be 3-cylinder compound 0-6-2T's, using Southern valve gear. Using Southern allows the valve motion for the center cylinder to be located mostly outside the drivers. The detailed design for the engines is evidently complete, but their chief proponent in Cuba recently died, and the general downturn in the sugar industry in Cuba is probably killing the need for new engines.

Also note the post by Dave regarding Smith valve gear. It is very similar to Southern (the actual motion of the gear is the same), except that the stationary curved slot is replaced by a pinned lever and some additional brackets. It has been applied to a few live steamers because it is extremely easy to fabricate.

Good Steaming,
Hugh Odom

> Couldn't let this go by without mentioning
> Southern valve gear. The three large EBT
> locomotives have this gear. It is actually
> pretty simple and seems to work quite well.
> By having a horizontally mounted stationary
> link in which the link block travels, the
> "slip wear" associated with
> Walschaerts is eliminated. The horizontal
> position of the link block determines the
> middle pivot point of the eccentric rod
> which imparts a vertical motion to a bell
> crank that operates the valve.

> My experience with Baker is that it works,
> but personally it seems like the long way
> around the mulberry bush. Talked to a Rio
> Grande engineer who, upon seeing the Baker
> gear on our locomotive insisted on seeing me
> so he could tell me what a piece of junk it
> is. He had bad experiences with it on large
> articulateds in Utah. Said it never stayed
> in time.

> A comment in "Apex of the
> Atlantics" made by someone involved in
> designing the E-6 (can't remember who), to
> paraphrase: The only thing you can count on
> with Stephenson gear is that when you have
> all those parts bolted together and they
> start flailing around, something is going to
> come loose. I certainly thought about that a
> number of times at 60 mph with 7002 and
> 1223. The only real advantage I see to
> Stephenson is the variable lead which is a
> pretty neat by-product of the design. I have
> often wondered whether it was intentional. I
> tend to think not. Anybody know?

> Walschaerts is certainly a beautiful gear,
> but given a choice I might choose Southern
> based on simplicity and wear. Haven't timed
> Southern so this is not a totally informed
> choice.


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whodom@awod.com