Friends models hudson

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Bill Shields
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Re: Friends models hudson

Post by Bill Shields »

:D

The combustion chamber and siphon tubes in the Langworthy design are (to me) just a copy of full size design for the sake of copying the design...not practical small boiler practice.
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kcameron
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Re: Friends models hudson

Post by kcameron »

What is meant by "l/d ratio"? Something about length and diameter I guess, but of what part? I've not run across it or just drawing a blank right now.
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Builder01
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Re: Friends models hudson

Post by Builder01 »

Hi Ken,

Yes, L/D is length to diameter of the flue tubes. Here's a site that I used to check the potential effectiveness of my boiler. Using the spread sheet, it actually made me reduce the size of my pistons to better match the boiler. This was also the advice from another fellow on an English ME site whom was familiar with my loco design. So, I followed it!

http://www.modeng.johnbaguley.info/Loco ... esign1.htm

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Berkman
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Re: Friends models hudson

Post by Berkman »

Now maybe adding a firebox arch would make sense and be a worthwhile addition, some also tout that adding a superheater makes more of a difference in the lower pressures of 3/4 scale than 1.5 scale.
James Powell
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Re: Friends models hudson

Post by James Powell »

Bill, 9/16 OD copper tubes- so something like .510 ID. Our experience with small tubes left a very bitter taste in our mouth- dad built the 2nd boiler for the roller with 3/8" tubes (as per LBSC in the 30's), and it was always a dog to steam. The Britannia boiler as drawn by LBSC steams like a witches caldron with U235 driving the reaction...basically regardless of the coal that it is burning. Whereas, my superheated Caribou is far more sensitive to coal quality- it will burn Quinsum, but not happily. It much prefers a diet of Pochahantas, of which I have about 50-100 lb left.

Berkman- the L/D ratios don't tell the whole story. As you get to smaller tubes (the 7/16 and 3/8") predicted results via renolds numbers stop having much value quickly due to buildup of soot. The soot size does NOT scale, it is basically a constant thickness. If you have a .375 tube, taking .010 out of it matters far more than if you have a .500 tube. That's why there can be some advantage to going to a combustion chamber earlier than you might think in a smaller (particularly 3 1/2", or 2 1/2" gauge) loco, so the L/D ratio stays low enough for "free" steaming, with enough small enough tubes to transfer heat effectively. It shouldn't matter as much as it appears it does, based on my experience.

If it was I designing a boiler for a Hudson in 3 1/2", I would look at a steel boiler. It depends on the water legs available- if you look at our Hudson, it probably had an oversized boiler (in that it had 3 rows of stays...), and I'm not sure on how much water leg it had. That being said, a copper boiler for a Hudson is going to run a fair amount of money for both the copper and the silver solder to put it together.

ImageHudson Sept 1989 by Peach James, on Flickr

_absolutely_ superheating makes a huge difference to the operation of the engine. Regardless of scale- because that is sensible heat that can be extracted by the engine ! If I was setting to design an engine, it would be superheated without any doubt. The only time we haven't is with an existing boiler where it can't be done. (so the roller is not superheated, as the block was designed/built as a steam jacketed block...and neither is my little wagon, as the boiler for that had no provision for a superheater ). If there is any rational way to get a superheater in the steam circuit, do so.

James
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Bill Shields
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Re: Friends models hudson

Post by Bill Shields »

I repeat my good experiences with 7/16 OD tubes and anthracite in this scale.

I have also had good experiences with 3/8 however you have to be picky regarding choice of anthracite.
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FKreider
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Re: Friends models hudson

Post by FKreider »

The very best 3/4" scale steamers I have ran so far have had 1/2" OD tubes in a 5" diameter boiler and 3/8" OD tubes in a 4" boiler. In both cases we are talking about Atlantics and 10-wheelers so not necessarily as long as a Hudson or Northern boiler.

I was also advised that depending on overall boiler length a combustion chamber can be helpful and is recommended in 3/4" scale. That being said I have never ran an engine with a combustion chamber so I cant really comment on the topic.
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LVRR2095
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Re: Friends models hudson

Post by LVRR2095 »

My LBSC Maisie has a combustion chamber and it steams like a witch.
Frank, next time I have it to the PVLS you are welcome to run it as much as you’d like.
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Jordanleeds
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Re: Friends models hudson

Post by Jordanleeds »

Combustion Chambers I can see make sense of an arch plate is used to lengthen the flame path and burn off the volatiles left but cross tubes and such do seem a complication too far that are likely nigh on impossible to repair if issues arise
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gwrdriver
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Re: Friends models hudson

Post by gwrdriver »

I've used cross tubes ("thermic siphons") in many small scale boilers to great advantage, but they are almost always a part of a center flue design where the flue itself can be made, checked, and pressure tested before being added to the shell for final soldering. And the siphon tubes are always of heavier gauge tube than is typical for flues. In general thermic siphons in such model boilers are a good thing. However, I would agree with Jordan that thermic siphons of the firebox type add construction complications and then potential problems which might not be justified by significantly improved steaming.

Thinking outside the Box . . .
There are less complicated and safer (in terms of potential for repairs) ways of increasing heated area and heat transmission in small boilers, even large small ones. One of those is to introduce heat sinks, and one of those which comes to mind is to extend the inside ends of firebox stays by a few diameters. You should never cut off stay ends dead flush anyway so extending the stay shank by a few diameters, although not to the extent used in a Porcupine boiler, will add metal in the gas path and increase heat transfer. This is a "free" improvement, in that it has virtually no added expense or potential for troubles aside from what's there anyway. This might not be workable depending upon your design. It could interfere with an arch if one is planned, but then a combination of extended stays and partial arch could be a winner. A clever boy could arrange for the extended stays, or a few of them, to be the supports for an arch.
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Jordanleeds
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Re: Friends models hudson

Post by Jordanleeds »

In full size practice the pins that support the arch are tapped onto the inner box between the stays and caulked in place.
Not sure using stays as heatskinks would be ideal considering they could easily burn away .
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Bill Shields
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Re: Friends models hudson

Post by Bill Shields »

Charlie Purinton used to run his firetubes out into the firebox over the coal fire.

Everyone said 'they will burn off'...but last time I saw him run one of those designs they seemed just fine.

he called it 'Purinton Arch'....
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