# Slide valves



## iceclimber (Aug 8, 2010)

When "inside slide valve operation" describes the valve gear, does that mean that the cylinder with piston is outside (side-frame) while the valve is inside (side-frame) or does it mean simply that the admission and exhaust ports are inside the slide valve gap as opposed to outside? So I guess it would be inside admission vs. outside admission?

Or do slide valves only have "inside admission" opposed to piston valves with "outside admission"? 

If by saying an engine has "inside slide valve operation" it means simply the latter, then I understand that. If it means the slide valves are inside the frame, are they being operated by eccentrics on one of the drivers? If so, is there a benefit of having it this way as opposed to having the valve chests and valves atop the cylinder? I know some engines even had the valves below the cylinders. 

I should also add, that in the description along with the note of "inside slide valve operation" is was also noted of having "outside" double acting cylinders, so I am thinking perhaps on this model the former is what was meant, that the slide valves/steam-chests are inside the side-frames. 

The more I think about it I can guess I am right in that the slip eccentric is operating the slide valves for setting forwards and reverse. Do I have that right?


----------



## Semper Vaporo (Jan 2, 2008)

Posted By iceclimber on 06 Apr 2011 04:00 PM 

 When "inside slide valve operation" describes the valve gear, does that mean that the cylinder with piston is outside (side-frame) while the valve is inside (side-frame) or does it mean simply that the admission and exhaust ports are inside the slide valve gap as opposed to outside?  So I guess it would be inside admission vs. outside admission?
 
Or do slide valves only have "inside admission" opposed to piston valves with "outside admission"? 
 
If by saying an engine has "inside slide valve operation" it means simply the latter, then I understand that.  If it means the slide valves are inside the frame, are they being operated by eccentrics on one of the drivers?  If so, is there a benefit of having it this way as opposed to having the valve chests and valves atop the cylinder?  I know some engines even had the valves below the cylinders. 
 
I should also add, that in the description along with the note of "inside slide valve operation" is was also noted of having "outside" double acting cylinders, so I am thinking perhaps on this model the former is what was meant, that the slide valves/steam-chests are inside the side-frames. 
 
The more I think about it I can guess I am right in that the slip eccentric is operating the slide valves for setting forwards and reverse.  Do I have that right?


----------



## Semper Vaporo (Jan 2, 2008)

Hmmm... typed a long answer and it dissappeared when I hit Submit... tried it again and it failed again... trying Quick Reply to see if that works!


----------



## Semper Vaporo (Jan 2, 2008)

Try the long answer in Quick Reply... dunno why the test doubled-up! Anyway... 

You might have to infer what is meant from the context of what you are reading... "Inside" and "Outside" valve gear may mean that the valve gear is between or outside of the frame of the engine. English and European practice was to have the whole engine contained within the frames and American practice was to have the whole engine outside the frames. 

Might also refer to some engines that had the steam chest offset from being directly above the power cylinder... some were tipped "inside" and some were tipped "outside" of the vertical axis. I can't remember which of the western U.S. narrow gauge lines had engines built in both of these configurations. 

As for "inside admission" slide valves... yes, there were some (real world) engines that attempted to use inside admission with slide valves. They had an entrapment mechanism that held the slider down against the valve seat/face to keep the steam pressure from lifting the silder off the seat, letting steam bypass the valve directly to the exhaust. This increased the friction and thus lost power in engines so equiped and quickly was abandond as a bad idea. 

Which engine are you refering to in your question?


----------



## iceclimber (Aug 8, 2010)

I read that info on the gauge 1 model company page for the description of the Britannia. I know it is slip eccentric design, so I was not sure if by saying "inside slide valve operation" they were meaning the valve chests were on the side of the cylinders inside the chassis or if it simply meant to explain that the slip eccentric was what changed the admission of the valves, but the valve chest was still atop the cylinder.


----------



## rbednarik (Jan 2, 2008)

It means what it says, the valve chests are mounted inside the frames, with the cylinders located outside the frames. This eliminates the use of rocker arms to drive outside valves and allows the Britannia to keep the prototypical (albeit non-functioning) looking valve gear on the outside, containing all the working bits of the valve gear inside. It is a often used practice by G1MRA builders and stems from British/European loading gauges necessitating the use of valve gear in between the frames, which does not always scale down well without adding significant cost and complexity to the R&D of the model. 

The usual practice is to have the port face either facing down or parallel to the frames, with the exhaust and entry ports on the side of the cylinder rather than the top, although the top can still be used, depending on the way the cylinders are mounted.


----------



## iceclimber (Aug 8, 2010)

I see, thanks for that explanation Ryan. 

As for another question pertaining to valve gear. I understand the basic premise of cross-porting on valve faces. I understand that it allows for the prototypical location of the radius rod in the expansion lever for forward, neutral and reverse. I also understand that while Aster makes use of cross porting on the engines with slide valves, Accucraft does not and so there are ways to "fix" this such as with the Daylight. For me, I don't think I would care much as only "I" would notice, while others looking at the engine are probably either going to be "wowed" by other things or they probably won't know much about how the prototype valve gear looked. 

However, what I don't quite understand is how this all is set up to begin with. If the radius rod's position is backwards, which requires the cross porting to allow for the opposite admission port to get steam while the valve opens that port up, why not build it so that it is backwards in the valve chest? It's hard to explain how I am thinking about it, but if the slide valve were to be positioned so that with the stroke of the piston, the radius rod would move in the proper way to begin with? Well, I doubt I am doing a whole lot of good explaining myself now, and I am probably confusing myself more as I type, so if anyone gets sort of what I am trying to say, good luck. Thanks.


----------



## iceclimber (Aug 8, 2010)

Did the K36 have "modified Walchearts gear" with the combination lever only linked at the bottom and top (including the radius rod and valve rod together in one link)? If so, is that why it can't be "notched" like the prototype could have?


----------



## rbednarik (Jan 2, 2008)

Jeremiah, 

-On the K-36 valve gear, yes, it follows the simplified method, with the radius rod, combination lever and valve spindle all sharing a common pivot point. All Accucraft engines that come from the factory to date with Walschaerts valve gear, with the exception of the Royal Hudson (which uses full walschaert gear), use the simplified valve gear. 

-Cross porting is necessary with Walschaerts to retain the correct position of the eccentric crank while making the radius rod run in the correct position on a (outside admission) slide valve model of a (inside admission) piston valved prototype. 
The geometry cannot be reversed within the valve chest without altering the external valve gear. The common and easy way to make the radius rod down for forward is to rotate the eccentric 180* towards the rear of the engine (turning a leading eccentric into a trailing one), which reverses the valve throw. Cross porting allows the valve gear to remain true to prototype, reversing the passages inside the cylinders to allow the use of slide valves on a model that was piston valved in full size. The only other way to accomplish this is to build the engine true to prototype, with piston valves and inside admission valve events.


----------



## Andre Anderson (Jan 3, 2008)

Jeremia,

On the real - full size locomotives the term inside admission and out side admission refer to where the steam is in the valve chest. The valve chest can be many places, on top, on bottom or inside the frame. Slide ors D valves are usually of the inside admission type, meaning that the live steam is inside the slide valve with the exhaust steam on the out side of the valve helping to seal the slide valve. The main reason that American have there valves on top of the piston is that real early in the game American Railroads figured out that it was much easier to work on the pistons, main rods, and valves if they were not hidden between the frames. Repairs in the field were much easier if you did not have to crawl under the thing and then up between the frames. On the early 4-4-0's the eccentrics that ran the valves were run off the front axle so they were fairly easy to get to.


Piston valves were usually out side admission because it was easier to build the chambers in to the piston valve casting. The exception to this rule were locomotives that had piston valves and retained their Stephenson Valve gear. I have seen in print that some people refer to K-27's as having both inside and outside admission piston valve gear with with Walschaerts motion, this is incorrect, they were all out side admission the only thing that was different was that on some the piston valve was inside of the center line of the piston and others had the piston valve out side of the center line of the piston.


On our models the manufacture may switch things around to make things simpler for manufacturing or assembly. While this does bother some of the people in the hobby, I myself don't worry about it, I am very happy that the locomotives that i have run as well as they do.


----------



## livesteam53 (Jan 4, 2008)

Myself, I never worry about it being exact. 

Of course I am not a Rivet counter. 

Hey as long as it looks like a real one and runs well I am Happy........


----------



## iceclimber (Aug 8, 2010)

That is true Mark. I guess right now, the only thing I can be is a rivet counter. Whenever I get an engine I am sure I will just enjoy running it. I have been reading through "a passion for steam" gaining a lot of head knowledge and then through pictures trying to see which locos have what. I thought the K36 had the modified or "simplified" walschearts gear, but wasn't sure as I didn't have the best picture. Thanks everyone. 

Ryan, that makes sense with the "cross-porting" to me.


----------



## rbednarik (Jan 2, 2008)

Andre,

As far as I know, the K-27's, like most others were inside admission, judging by their valve gear arrangement, but I could be mistaken (It's happened plenty before!). 

Outside admission piston valves on full scale locomotives was a rarity indeed since the steam placed a very heavy loading on the ends of the valve, which would cause ringland wear.

Referring to this photo:


----------



## Kovacjr (Jan 2, 2008)

I think the K27 were listed at inboard and outboard cylinders. As I think Accucraft made both versions. It pointed out the angle of the cylinder and the valvechest some were leaning In and some leaned out.


----------



## iceclimber (Aug 8, 2010)

Don't want to start a new thread, but I recently acquired some back issues of SITG mags. In one I have looked through, I noticed a great idea for the water sight glass. The author took a piece of brass, painted lines running diagonally across it and placed it behind the sight glass. It was suggested that it be cut in sort of an H pattern and the legs of the H would straddle the upper and lower piping heading back into the boiler. The water, when low will cause the lines to reverse their pattern near the water level. 

Has anyone here performed this modification? If so, did you use sheet brass or something else? How does it hold up over time? Is there a better way to fasten it? Well, thought it was a good suggestion anyways.


----------



## David Leech (Dec 9, 2008)

Jeremiah, 
Just like the real thing! 
Works very well. 
Up to you to find the best way for your locomotive. 
Even a vertical line will do - the water will magnify it, but the empty glass will not. 
All the best, 
David Leech, Delta, Canada


----------



## iceclimber (Aug 8, 2010)

David Thanks, 
I tried this with a piece of paper and a glass of water. It worked just like the article showed. So, yeah, finding the right look and material will be the key.


----------



## Semper Vaporo (Jan 2, 2008)

Posted By iceclimber on 08 Apr 2011 06:34 PM 
Don't want to start a new thread, but I recently acquired some back issues of SITG mags. In one I have looked through, I noticed a great idea for the water sight glass. The author took a piece of brass, painted lines running diagonally across it and placed it behind the sight glass. It was suggested that it be cut in sort of an H pattern and the legs of the H would straddle the upper and lower piping heading back into the boiler. The water, when low will cause the lines to reverse their pattern near the water level. 

Has anyone here performed this modification? If so, did you use sheet brass or something else? How does it hold up over time? Is there a better way to fasten it? Well, thought it was a good suggestion anyways. 

Yes, that was my article and I got the idea from Jan-Eric Nystrom of Helsinki, Finland in an article he wrote for Live Steam magazine. I tried to attribute the idea to him, but he defered to the fact that it has been done in full sized engines for almost as long as there have been sight-glasses.

I made mine from printer paper and it lasted a couple of seasons before it got all wrinkly, so I just made another one from paper... Paper is cheap and I can get a couple dozen on one sheet of paper... If I could manage to keep the sheet clean and neat for the time it takes the first one to wear out (and remember where I put it)!


----------



## iceclimber (Aug 8, 2010)

That was a good article Semper. I thought of using paper or a heavy card stock and using some tape over it, but I thought a nice thin sheet of brass or copper would look good and last longer like your article points out. So, if I can find something to cut a piece from, that is probably what I will use.


----------



## iceclimber (Aug 8, 2010)

Are most throttles "inside throttles" ? Or are they still making boilers which have the steam line going outside and underneath the boiler? By "they" I mostly mean commercially manufactured small scale live steam engines.


----------

