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Maybe one of you full-scale engineers can answer this--

When Sam Posey and I were "road testing" the Strasburg Railway's decapod a few years ago, Sam got to run the loco and was told by the hostler to open the dirfting valve (I think that's what it was) before opening the throttle. This was to ???avoid hydraulicing the drive pistons? I don't know, as I was merely the photographer.

Anyway, here on Maui, I've noticed the Sugar Cane Train, which stops right across the street from us, always seems to start up with that valve/device open, so it kinda sounds like, "Ssss, chuf, sss,chuf, sss, chuf..." until it gets up to speed. Is that what the engineer is doing?

I could post a streaming video if someone tells me how to get it on MLS.
 

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'Big Joe' at 4largescale.com is an engineer on Disneyland's RR and before that he was engineer at Knott's Berry farm's 122 year old narrow gauge C-19 engine........he has a lot of articles about 1:1 Steam on his web page and I'm sure he would be happy to answer your questions drop him an email, at [email][email protected][/email]
 

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I'm not 100% certain on the functioning of a "drifting valve" (perhaps using the cylinder's compression to help slow speed, as in putting a car in low gear downhill?), but the "hiss- chuff" you're seeing from the "Sugar Cane Train" when starting is most likely from the "cylinder cocks".:)  When a steam locomotive is first started, steam is admitted into one end of the cylinder through the throttle & valve gear.  If the cylinder is cold, the steam will condense back to water:confused:; at the other end of the piston's stroke, the valve gear now admits steam to the opposite end of the cylinder, pushing the piston back.  IF water (which is incompressible) from condensed steam has accumulated in that end of the cylinder, the cylinder head could be blown off /DesktopModules/NTForums/themes/mls/emoticons/crazy.gif as a result!  (Severely damaging the engine /DesktopModules/NTForums/themes/mls/emoticons/shocked.gif - & anyone near the cylinder head!/DesktopModules/NTForums/themes/mls/emoticons/cry.gif).  To prevent this nasty occurence, the cylinder cocks - small drain valves at each end of the cylinder, near the bottom, are opened when starting the locomotive; any accumulated water is now safely ejected from the cylinder /DesktopModules/NTForums/themes/mls/emoticons/blush.gif by the advancing piston.  This is the "hiss" you're hearing, usually accompanied by clouds of steam & water escaping from the cylinder ends (part of the "show"/DesktopModules/NTForums/themes/mls/emoticons/w00t.gif steam locos put on!).  Once all the water is ejected & the cylinders fully warmed up, the engineer closes the cylinder cocks to allow maximum steam pressure (& accompanying power) on the piston.

On model live steamers, we run into a similar situation, but the forces generated by our small boiler's aren't high enough to blow cylinder heads/DesktopModules/NTForums/themes/mls/emoticons/wow.gif; any compressed water in the cylinder will just keep the engine from running PERIOD!/DesktopModules/NTForums/themes/mls/emoticons/ermm.gif  I've dealt with this myself with my two Accucraft live-steamers, a 3-cylinder Shay & "Ruby"2-4-2 (the latter pretty close in outline to the "Sugar Cane Train 2-4-0's!:cool:).  In the case of small model loco's like these, we get the water out by alternately reversing the locomotive back-&-forth until the water is ejected (both from a drain on the bottom of the smokebox, & out the stack itself - usually accompanied by all sorts of burbling noises/DesktopModules/NTForums/themes/mls/emoticons/blink.gif & hot water splattering /DesktopModules/NTForums/themes/mls/emoticons/whistling.gif out the stack!  (You can see this in one of my live steam videos here):;)

www.youtube.com/watch 

By the way, I had a chance to read that Road-&-Track "road test" of Strasburg #90 a while back - HILARIOUS!!/DesktopModules/NTForums/themes/mls/emoticons/laugh.gif

I've also ridden the "Sugar Cane Train" myself on a trip to Maui @ 2 years ago - GREAT ride!/DesktopModules/NTForums/themes/mls/emoticons/w00t.gif

Tom
 

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By the description of the function I'm sure they're talking about the cylinder cocks. I've never heard the term "drifting valve" used before and I did my steam fireman training at Strasburg, but that's all I can imagine fits the description of how and when it was worked, although generally you want to open the cylinder cocks when slowing to a stop and leave them open until you are under way again.

I'm not aware of any special valve that uses steam back pressure to slow or stop the engine, but when I run the William Mason (1856 and no air brakes) I throw the reverser to the oposite of the direction we are traveling and give it a little throttle and that slows and stops the engine, but no special valves involved.
 

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I found this info via a Google search...

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

Another feature which plays a most important part in the successful operation of the articulated compound locomotive, and so should be clearly understood by the engineer, is the by-pass valves.

The purpose of these valves is to prevent the injurious effects which would otherwise result from the pumping action of the large low pressure pistons when the locomotive is drifting.

These valves are so designed that they automatically establish communication between the two ends of the cylinder, when the engine is running with the throttle closed, thus performing several important functions:

First, they prevent alternating vacuum and compression in the cylinders when the locomotive is drifting, thus insuring the free movement of the pistons.

Second, by permitting the circulation of the free air drawn into the cylinders through the vacuum-relief valves, they prevent this air from being overheated by the churning of the pistons and thus destroying the lubrication, when the locomotive is drifting down a long hill.

Third, by destroying the vacuum which, without them, would be formed by the large piston, they prevent the smoke and gases from the smoke box being sucked into the cylinder.

Fourth, they prevent excessive fanning of the fire from the pumping action of the large pistons when drifting
 

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Tom,

I tried to read the article on Strasburg #90. That link is the same as the Shay, chapter 1
 

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Discussion Starter #7
Once again, you guys amaze me with your knowledge. Thanks. I think Tom and others are right when they say it is the cylinder cocks. Dwight, who thinks like me (that's why I like him) mentions drifting valves, but that's another subject. BTW, the two Maui locos, Anaka & Myrtle, do a lot of that when they are on their way to the engine house and Y (newly-installed) that marks the line's terminus. From Kaanapali station north (to the end of the line) is downhill and you can hear the loco softly chuffing as it coasts home. Actually, what you really hear is the single piston air pump, which has a very pronounced, "Pam, pam, pam, pam."

On the subject of cyilnders seizing up, when we were running our circle track midget at Ascot Speedway in the late1970's, we got lazy after surface packing and didn't back off the cylinders (done by putting the car in gear, then rolling it backward to suck any unspent fuel from the cylinders). Big (and expensive) mistake! When the pushtruck gave us a shove, the pistons froze (methanol doesn't compress that easily either), there was a "bang," resulting in a broken connecting rod. No, I didn't drive the car (blue number 77, CRA and USAC registered). My brother-in-law did, because my wife wouldn't let the love of her life try to mess himself up in a midget or a sprint (we shared one of those). What we did is pay the bills. For both. :mad:
 

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We found out the hard way the effects of failing to open the cylinder cocks.... after a public outing of the deccapod at a local college, and several people had been allowed to "run" the engine..... we found the right cylinder had been stripped from the drive shaft.... i've just about got it repaired... 

The "drifting valve" is also often referred to as a "snifter" .... 

happy steaming...
 

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Discussion Starter #10
Dwight, I didn't mean to step on your toes. I don't know what the deice is called. No hard feeling, eh, bra?
 

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No problem Joe. I didn't take it that way (as you stepping on my toes). I was just clarifying why I posted what I did. Before you asked this question, I'd heard the name "drift valve" but I had no idea what it did either, and I figured others were also in tha same boat. :D Now thanks to Maurice, we also know what "Snifter valves" are for. ;)
 
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