Thank you so much for the information. Very interesting. So it appears in the lower paragraphs the engineer had to at least somewhat control the wagner? Whereas in the upper portion of reading that it seems to be more automatic.

The locomotives I've been around were smallish and basically just had check valves mounted on cylinder block somewhere to break the vacuum, then when drifting the normal throttle was slightly opened to give enough steam for lube and compression padding.

Looking at the recent 611 photos is also appears to have the "third cylinder" similar to the 1309. Wonder if this is a similar device to those on the ATSF.

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Did some looking around for Wagner bypass valves.

https://www.nwhs.org/qna/BypassValves.html

As applied on the ATSF:

http://sfrhms.org/Reviews/HO/Steam/3800/Drift.htm

Note that the indicated 'vent' in the NWHS page is precisely where the bushing for the two curved pipes is located, a further guide as to what their purpose is.

At one time I had an actual detail drawing of one of the ATSF Wagner valves, and posted it in several threads here and on the Trains Magazine forums. I cannot find a copy now, and encourage anyone here either to find the source on the Web or link to one of those prior posts to get the image over here for discussion.

The spring in these valves is notable for having very, very many terms, so its effective rate doesn't change with the degree the valve heads move. I repeat that I'd like to see careful detail pictures from the 3751 and 2926 groups of the valve and its bushing, together with any technical material or records they may have on the devices or the company that made them.

There are a few pictures here
http://www.nmslrhs.org/Photos/2010/09-04/index.html

"No, it is really necessary. Either you do this, or you have a cold air drifting valve on the valve chest. Without either one, not only do you suck in grit, but depending on the valve setting, you get really rough compression resistance when rolling."

In the really old days a skilled engineer would know when to open the cylinder cocks to drain moisture out of the cylinders and/or release the compression forces from the cylinder when no steam was supplied. Cylinder cocks could be opened when drifting downgrade to release the vacuum condition.

The engineer could use the compression forces from the cylinders as a sort of "dynamic brake", but I don't think that was a common practice.

The modern "Jake Brake" on a semi truck in the US does exactly that, it uses the compression forces from the engine cylinders to slow down the axles of the truck directly through the transmission.

The drifting valves removed some of that task from the locomotive engineers list of things to pay attention too.

With a drifting valve the engineer only had to be concerned about "draining" water from the cylinders after the loco was stopped. The drifting valve "automatically" took care of the vacuum conditions inside the cylinder/valves when no power (steam) was applied.

Just my understanding of how these things worked. Would be interested to learn when the first drifting valves were installed ? Probably in the 1880's (just a guess).

Cylinder drains don't allow enough flow to fully release the pressure. That is why the engine still moves when they are open. Without a drifting valve, the engine will behave as I describe, even with the drains open. Especially at high speed.

Are we confusing drifting valves with simple snifters? The two are very different......

We shouldn't be. A drifting valve involves steam, a snifter valve air.

Neither should be confused with a bypass valve, which involves adding neither but just allowing 'what is there' to shuttle between ends of the cylinder with neither fresh steam nor fresh air necessarily involved.

Jeeze, the railroads ran steam locos for 150 years and here we are discussing how it was at all possible without a drifting valve ???

My opinion is the drifting valve was a "later" improvement to the basic steam engine design. I think the basic steam loco with a skilled operator could move a train full of "stuff" without a drifting valve.

Adding drifting valves just made the engineers job a bit easier. And it reduced wear and tear on the moving "bits".

If anyone has a strong case that it is impossible to move a railroad steam locomotive without a drifting valve I would like to learn from it.

Well, yes, you are absolutely right. I/we have been mixing them together.

The snifter lets in cold air. The drifter lets air/steam shuttle fore and aft in the cylinder, as the item in the photo would do.

One of these two is necessary.

If an engine is fitted with drifters, will it also have snifters?

I did not think it would take long for the peanut gallery sarcasm to start.

Drifting valves of any kind on conventional recip steam are something of a refined luxury -- the 'default' downhill operation simply involves the engineer cracking the throttle enough to relieve the vacuum, usually gauged by seeing visible flow at open cylinder cocks. Only when water and maintenance become of great importance to railroads will you see special equipment for this provided.

What we are discussing in this thread is something considered NOT a luxury, the provision of drifting bypass in the LP cylinders of a good-sized Mallet compound. It is difficult to arrange 'vacuum-breaking' steam flow through the receiver to these with the throttle closed to where drifting would not be 'powered' on the HP engine, and I doubt if manipulating the intercepting valve to 'shoot' a proportion of HP steam to do that job makes any real sense. In any case, as noted, opening the cylinder cocks to atmosphere may not flow enough air for full vacuum-breaking at expected road speed downhill on cylinders this large. Hence the provision of a device that does this, essentially servo-controlled from the LP engine steam-chest pressure.

I believe some of the Catskill Archive material covers this in 'from the factory' detail.

"I did not think it would take long for the peanut gallery sarcasm to start."

Speaking from the peanut gallery (thank you very much for the disrespect, I hope to have the pleasure of returning the favor in the future).....

To review this topic; First question was "what's that gizmo", first answer was "it's a drifting valve", followed by comments that a drifting valve is essential for a steam loco to operate.....

I opined that a drifting valve was NOT essential for a "generic" steam loco to operate and that a skilled loco engineer could operate a loco just fine without a drifting valve....

I further opened the alleged educational discussion with open questions about when drifting valves were first employed on US railroads....

Hoping to widen the discussion about the absolute necessity of drifting valves we get from you a Phd dissertation about how nobody with any level of skill at all could operate the mallet locomotive in question without a complex drifting valve....

From the Peanut Gallery..... (obscenity deleted).....

When Mr. Ellsworth has actually operated the locomotive in question he is again encouraged to explain his procedures in detail..... And then he can tell us all how he was involved in the original design of that loco and all the other steam locos that operated in the US for a hundred years....

Connection to an earlier thread on drifting, including discussion of Wagner valves.

viewtopic.php?f=1&t=33596

You seem to want to persist in misunderstanding the difference between a bypass valve on a Mallet and drifting procedure for regular steam engines. I still don't see where that comes from, or why you feel it's ridiculous or pointless to have the former. Your argument over operating practice would be better referred to the engineers who originally specified the bypass valves for those engines (and there must have been some justification to retain them all the way up to the literal end of steam-locomotive production in America).

I do apologize for the 'peanut gallery' remark, but I was nettled by the repeated assumption backed by what I still think is insufficient recognition of the technology.

BTW: it was interesting to re-read the older thread (which contains the drawing I was talking about!) as it contains some fairly ghastly misinformation from me. The Wagner throttle (which Porta misspells) dates from near the turn of the century, and is interesting for being an early kind of fluidic amplifier many years before those became a refined topic of engineering interest. This (as I recall) has little to do with the Wagner who formed the company making the drifting valves ... I did go through to trace the corporate history but don't remember it now without notes. I would be surprised not to see them in at least one of the contemporary Locomotive Cyclopedias.

Meanwhile, it turns out that the 'best' Romanization for the Trofimov valves is the one that Meiningen in East Germany, who first took up the specific form of these valves and subsequently modified them slightly to help with the jingling and bangs, etc. when operating, chose to use. They are improved in part by incorporating small pistons that engage bores in the floating heads near the stops that keep the heads located under steam; this cushions both the engagement and any tendency for the heads to 'walk' against the stops on the valve spindle (this should be little, because of the sealing between the piston-valve rings and bore, but is apparently enough to cause mechanical interference in the older or 'license-built' versions of the arrangement.

For an older version of the idea, which has an interesting if somewhat politically-charged history, look up Nicolai valves (and their subsequent German 'equivalent'. I find it interesting to compare their detail design with that for the Trofimov valves, particularly as pressure and degree of superheat began to increase in locomotive practice.

My apologies again to M. Austin, with whom I had far less actual controversy than the record in that old thread would indicate.