Steam Dome Throttle

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daves1459
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Re: Steam Dome Throttle

Post by daves1459 »

Bill Shields wrote: Tue Jan 01, 2019 10:43 pm I use a tapered plug 'pull' throttle in several of my locos and find them very easy to operate...

You can also consider having a small orifice I the throttle to keep response under control.

My 1-1/2 camelback has a 3/16" hole from the throttle to the 2" diameter cylinders and 9" drivers...the tip of the throttle is a 1/8" nose that clears the orifice after you have the throttle about 1/2 way open.

It is very easy to start and you REALLY HAVE TO TRY to get the wheels to slip....as in whack pull the throttle COMPLETELY OPEN and be on wet rail.
,
You could start with a 1/4" orifice and put a tapered plug with a 3/16" (or so) nose on the end.

The advantage to this type of setup is that you can easily pull the throttle plug out of the back of the boiler and change the dimensions without ripping anything apart to play with dimensions.

I can send pictures / drawings if you like, but it doesn't take a rocket scientist to figure it out.

Of course, I designed everything around this setup...and if you already have a boiler without the back head fitting(s) to allow this, you may not be able to travel this road.
I didn't realize that there was any history with a tapered plug type throttle. I was obviously wrong.

Do I understand correctly that you were feeding a pair of 2" diameter cylinders through a 3/16" diameter hole at full throttle? I must say that sounds awful small. Obviously low speed control must have been very good. BUT, did you experience any speed or load resrictions, particularly any speed restrictions under a heavy load or long hill. My first live steamer project was a Little Engines 0-6-0 with a 2 1/4" bore and 7" drivers. The throttle was a 3/8" NPT ball valve. It was a full port vavle with I'd estimate a 3/8" bore. With that throttle wide open the cylinders would have limited speed/power on a long hill with a heavy load. None the less the tapered plug type of throttle has promise and I think I can squeeze one into my steam dome.

Dave
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Bill Shields
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Re: Steam Dome Throttle

Post by Bill Shields »

you are correct on the size....

loco runs just fine on any of the tracks where I run.

I do not pull long trains full of people...so that may be a concern, however....

you have to remember that you can get a LOT of steam at 1100 feet / second through a 3/16" hole...
Too many things going on to bother listing them.
Pontiacguy1
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Re: Steam Dome Throttle

Post by Pontiacguy1 »

I have a 2-10-0 that was built using LE 0-4-0/0-6-0 castings. The bore is 2 3/8" x 3" stroke. I use a 3/8" ball valve in the dome and have never had any issues with higher speeds and long hills, and I really do pull some heavy trains up long grades, and sometimes at higher speeds than I probably should. The locomotive is a very good performer, and doesn't feel restricted at all. My boiler is 10" diameter, with a 7"x12" grate size, and 3/4" copper flues. It may not be your throttle valve size, it may have been your boiler's steaming capacity. That happened quite frequently on full-size locomotives. The boiler wasn't able to keep up with the volume of steam required for heavy loads at higher speeds, thus many locomotives were limited to the speeds they could attain. That's what gave rise to the 'superpower' series of locomotives. I knew of one guy who had an 0-6-0 with an 8" boiler on it. He said it would steam fine and pull any load you wanted to as long as you didn't try to run it real fast. If you tried to run it at 7 or 8 MPH with a load, it wouldn't keep up and you'd lose pressure. Slow down a little bit and it was fine. The full-size never did go that fast, and weren't designed to. Not surprising to me that the model behaved in much the same manner.

I do agree that a 3/16" hole sounds awful small for a 2" bore cylinder, especially if you are working it hard up a grade. I bet it still has a lot of low-speed torque. Most likely, going up a grade with a big load, it would just slow down until it reached an equilibrium, then would hold that speed. With 9" drivers you'd likely still be moving pretty good.
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cbrew
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Re: Steam Dome Throttle

Post by cbrew »

Bill Shields wrote: Fri Jan 04, 2019 7:43 am you are correct on the size....

loco runs just fine on any of the tracks where I run.

I do not pull long trains full of people...so that may be a concern, however....

you have to remember that you can get a LOT of steam at 1100 feet / second through a 3/16" hole...
need to remember this is not a naturally aspirated engine relaying on a vacuum to move "gases" :D :wink: :lol:
Bill, what is the ID of the delivery lines?
on my allen, I went from 3/8 copper to 1/4 copper and saw zero change in performance and a drier stack
If it is not live steam. its not worth it.
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Bill Shields
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Re: Steam Dome Throttle

Post by Bill Shields »

3/8 od copper, but the hole through the cylinder block to the valve chest is maybe 1/4"...standard Allen size
Too many things going on to bother listing them.
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cbrew
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Re: Steam Dome Throttle

Post by cbrew »

ok, what made the decision easy for me is the use of 1/8 npt fitting feeding the cylinders.
If it is not live steam. its not worth it.
F Wright
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Re: Steam Dome Throttle

Post by F Wright »

F Wright
I Built and own "Trish", 1-1/2 inch NG (4-3/4" track) Mogul. It has a 1/2" ball valve for a throttle. This engine was finished in 2004 and has been running at the St. Croix RR ever since. I haven't had any trouble with this valve, It is a full flow, 400LB type for gas, water & oil. The linkage is some what different as the valve shaft and the actuating shaft don't line up, so there is a second bell crank, inside the steam dome and a link. The valve only opens about half way. I wrote an article about the engine in LSOR, July/August 2011, Two of the pictures show the outside bell crank if you look close. I'm sorry that I don't have any pictures of inside of the steam dome. Fred
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