Smokebox Throttle Valves
Smokebox Throttle Valves
I searched throught he archives on throttle valves and got some good information but many of the posts are conflicting. Here is my problem. I have a 4-8-4 1-1/2" scale loco with 3" diam pistons and a 4" stroke. Yes, they are fairly large for that scale but made it as close to the real one as possible. I use 1/2" copper pipe to feed the cylinders. My throttle is a SS ball valve that is fire rated$$. With my background in automobiles and motorcycles, I also machined all the passages for a smooth and obstruction free path. I think I did too good of a job because I can only open the valve a fraction (and I mean a fraction) like one notch. Any more and that thing will scare the pants off you. Many of you suggest a gate valve, others a ball valve and both say the response is great. I have to change out the ball valve as I have minimal control. What whould you guys suggest I use (i.e. gate valve, poppet valve, etc.)? I even thought of artificially restricting the steam pipes to the cylinders to 1/4" to give me more control of the steam going to the cylinders. I want something that I can move a few notches and still not have it take off like a bat out of hell. A 45-90 degree movement would also be needed.
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Bill Shields
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Throttle valves
Ball valves are not designed to throttle, just on / off, hence they tend to be sudden.
This doesn't mean they don't work well for many, just that is not what they are designed for.
Where are you going to mount the valve?
Gates really aren't designed to throttle either, but they work well for many people, not so for others.
A lot has to do with the linkage the valve is connected to.
If you set the linkage up to slowly open the valve and forget about getting it 100% open, your response will be much better.
If you actually do the calculations of the amount of steam that has to go through the pipes to fill the cylinders at normal running speeds, a restriction down to 1/8" diameter actually won't make any noticible difference, unless you run this loco REALLY FAST.
Consider (remember) that steam travels at the SPEED OF SOUND. At 1 atmos, that is 1100 feet / second. At 100 psi, its quite a bit faster.
I run my loco on a 1/4" pipe with a 1/8" orifice and a taper pull pin as the throttle.
Response is good, never been starved.
This doesn't mean they don't work well for many, just that is not what they are designed for.
Where are you going to mount the valve?
Gates really aren't designed to throttle either, but they work well for many people, not so for others.
A lot has to do with the linkage the valve is connected to.
If you set the linkage up to slowly open the valve and forget about getting it 100% open, your response will be much better.
If you actually do the calculations of the amount of steam that has to go through the pipes to fill the cylinders at normal running speeds, a restriction down to 1/8" diameter actually won't make any noticible difference, unless you run this loco REALLY FAST.
Consider (remember) that steam travels at the SPEED OF SOUND. At 1 atmos, that is 1100 feet / second. At 100 psi, its quite a bit faster.
I run my loco on a 1/4" pipe with a 1/8" orifice and a taper pull pin as the throttle.
Response is good, never been starved.
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Russ Hanscom
- Posts: 1955
- Joined: Wed Mar 15, 2006 11:10 pm
- Location: Farmington, NM
One other thing to consider would be a ball with a contoured port. Some control valves are built like ball valves except the port is Vee shaped on one end; the sharpness of the Vee determines the flow characteristics as the valve is just starting to open.
If you can lay your hands on a ball of the same size to rework ,or even make a press-in plug for the valve you have, you could make order of magnitude changes in the flow characteristics. The Vee does not even have to have straight sides.
Try a search for Vee ball and control valves.
If you can lay your hands on a ball of the same size to rework ,or even make a press-in plug for the valve you have, you could make order of magnitude changes in the flow characteristics. The Vee does not even have to have straight sides.
Try a search for Vee ball and control valves.
my new engine is also 3 X 4 and i use 3/8" pipe for the plumbing. i use a 3/8" pipe thread ball valve with a 3/8" dia. hole in the ball. i have no problem with the throttle. it starts real smooth and at wide open will reach a speed where i want to slow it down. i have 3/8" pipe for the exhaust too with a .400" blast nozzle.
hope that helps,
fred v
hope that helps,
fred v
Dan,
Sounds like you finally got the GS running. Be careful when you paint it red and orange, it may go even faster. A friend actually bushed his cylinders down to reduce the power in his big Mikado. I am not sure how much reduction he made but it made quite a difference.
Russ,
The idea of a contoured ball valve sounds like a great way to go to help control the steam flow to the cylinders. I was not aware of this type of option in ball valves. Where would one start looking for this type of valve?
Robert
Sounds like you finally got the GS running. Be careful when you paint it red and orange, it may go even faster. A friend actually bushed his cylinders down to reduce the power in his big Mikado. I am not sure how much reduction he made but it made quite a difference.
Russ,
The idea of a contoured ball valve sounds like a great way to go to help control the steam flow to the cylinders. I was not aware of this type of option in ball valves. Where would one start looking for this type of valve?
Robert
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Bill Shields
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V-Ball
Good luck finding one of those Russ described critters in our sizes.
They are usually limited to much larger diameters and pressures for industrial applications, usually things like hydrocarbon or high pressure water service. The last one I saw was 24" in diameter and good for 3000 PSI..but then all we had was big stuff..
However, Triad makes them smaller - hang on to your wallet
http://www.triadprocess.com/adwordsB.cf ... medium=cpc
You could make one if you wanted to go to the trouble, but if you get it wrong, you run the risk of tearing up the seats and having a leaker....nothing like a runaway loco to get your attention...quickly
In the long run, it's probably easer to go with something a bit more purpose-made for our application.
Dave swears by his quick opening gate valve, and if it works in that application with the correct linkage then...why reinvent the wheel? Although your linkage may not have enough throw to work his recommended type of valve.
Unless you are like me and really enjoy swimming upstream..
They are usually limited to much larger diameters and pressures for industrial applications, usually things like hydrocarbon or high pressure water service. The last one I saw was 24" in diameter and good for 3000 PSI..but then all we had was big stuff..
However, Triad makes them smaller - hang on to your wallet
http://www.triadprocess.com/adwordsB.cf ... medium=cpc
You could make one if you wanted to go to the trouble, but if you get it wrong, you run the risk of tearing up the seats and having a leaker....nothing like a runaway loco to get your attention...quickly
In the long run, it's probably easer to go with something a bit more purpose-made for our application.
Dave swears by his quick opening gate valve, and if it works in that application with the correct linkage then...why reinvent the wheel? Although your linkage may not have enough throw to work his recommended type of valve.
Unless you are like me and really enjoy swimming upstream..
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Russ Hanscom
- Posts: 1955
- Joined: Wed Mar 15, 2006 11:10 pm
- Location: Farmington, NM
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timmy wheeler
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Greg_Lewis
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In Joe Nelson's book So You Want to Build A Live Steam Locomotive, Chet Peterson describes a smokebox throttle that is operationally the same as a ball valve. The hole in the valve plug is only 7/16 dia. I don't know if this is what he used on his Northern but the small aperture is food for thought.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Here is a poppet style throttle valve that is in a pile of stuff in the shop. close to protoype design and function of the late super power era.
i dont know any history about it, or if it worked. one clue may be that it is not on a locomotive. but i feel with a little design and thought, one could make a very usefull throttle out of this design. the boiler presure holds the tappets closed but for raising by the cam. maybe having 4 smaller valves raising in a spread sequence , 90 deg of lever to all 4 are open might make a decent valve with good control . definetely would have to be shielded.
i dont know any history about it, or if it worked. one clue may be that it is not on a locomotive. but i feel with a little design and thought, one could make a very usefull throttle out of this design. the boiler presure holds the tappets closed but for raising by the cam. maybe having 4 smaller valves raising in a spread sequence , 90 deg of lever to all 4 are open might make a decent valve with good control . definetely would have to be shielded.
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