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This is an idea I got from Paul Lather that he did to his Berk. On my AC11SS (Super Steam) I had previously eliminated the superheaters when I did my 101 mods before DH09. This weekend I put them back in as feed water heaters. The heaters are plumbed in between the axle pump and boiler check valve. Average running steam prussure use to be 40psig, and now is 60psig for the same load and throttle setting.

 

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Dave
Interesting that the saturated steam,given the temperature drop during the run back to the axle line(assuming unwrapped), along witha mixture of H2O from tender would have that much temperature variant from the stock water input into the boiler. We have seen similiar results from heating the gas tank using a globe valve (thus warning tank and keep water warm in the tender) allowing increased BTU output thus more steam therefore higher and more consistant steam pressure. Both ways seem to increase by 50% the CF's capacity to make steam and keep it consistantly higher.
If you get a chance, it would be a good reference point with a photo of the setup on the water line going to the boiler regards the 2 superheater tubes and the axle pump.
 

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Hi Dave,
I was just looking in "The Steam Locomotive" Ralph P. Johnson M.E. 1942, and there is on page 332 a table of locomotive efficiencies for two 4-8-4 types. The efficiency for the boiler superheater and the feed water heater are listed in separate columns.

For most of the cases the feed water heater is adding more efficiency than the superheater. In the ones where the superheater adds more it is by a smaller margin. The full size data looks like to me that if you have to choose only one or the other that the feed water heater is a better bang for the buck.

Dan
 

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Dan,

Thanks for the confirmation! My feeling is that the feed water heater is a much better value than a superheater. In a sense, I have a flash boiler feeding the main boiler. I was worried that the axle pump wouldn't like this mod, but I was wrong. The hand pump is now spongy under fire, and sometimes I can hear rasberries in the boiler. Someday my meth GS4 may get the superheater replace with a feed water heater.
 

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Charles,

This pic is the best I have to show the plumbing.

The red knob is the tender water heater. This use to be the auxillary throttle but now controls steam from the top of the boiler and is teed into the return water line.

The blue knob is the axle pump bypass. It now has a mini goodall valve in the boiler. The line closest to the boiler is the feed from the feed water heater. Inlet connection for the feed water heater is below the burners.

 

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Dave,

I was thinking of the same idea on my K28 but using a steam heated tank in place of one of the air tanks on the running boards. I sketched a few ideas but in the end I used the blowdown pipe with a valve on it to heat the tender thus preheating the water being pumped in and also keeping the gas at a stable pressure. Funny to see steam flow from the holes in the tender on a cold day.

Being on the that you did it on the cabfoward you are basically routing an additional loop where as I would of had almost 3' of extra piping to loop in the smokebox.

Also do you find that it fires better by sealing up the lower holes on the smokebox?

Jay
 

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Well guys, I guess it depends on design and purpose along with interpretation. Other references for these two applications with different purposes state that a feedwater heat could improve efficiency by 10-15% (for Dan-Eugene Huddleston: reference Uncle Sam Locomotives pg.28) where as superheater tubes had an efficiency increase up to 30% better utilization of coal/water (pg. 65 LOCOMOTIVE BOILERS AND ENGINES LLEWELLYN V. LUDY, M.E.).

Dave
Thanks, so it seems that design will prevent feedback into the axle pump that would cause a "vapor lock" preventing axle pump water flow from the tender(as many of us have had happen when the clack valve goes south). So, you have duel heating sources both in tender for the water bath and the superheater "feedwater heat".

The other factor as I understand is that you can effectively utilize the "SS" due to cylinder size increase thus able to bypass superheating the cylinders.

Really appreciate your insights and developments.
 

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Charles,
Ludy was a professor at the University if Wisconsin and Johnson was the chief engineer at the Baldwin Locomotive Works. A lot of this stuff is like apples and oranges, but the tests I cited were on the same locomotive and done in the same way and time. The types and sizes of both types of equipment have to be factored in for any meaningful conclusion.

Thanks for the reference. If you get a chance could you give me the reference for the critical crack length article in Model Engineering?
 

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Jay,

I played with restricting the holes in the bottom of the smokebox. It is possible to have too much restricting. There needs to be enough openings for the exhaust from the burners to get out. I just keep guessing until I find what works for each engine.

On the subject of fuel tanks close to the boiler vs in the tender with heat, my Amerigul has the tank in the cab. I am planning to build a tank for the tender and heating the water. At steam ups with a lot of wind, my steam heated fueled engines performed better than the ones with the tank in the cab. Using steam to heater the tender also gives you better control of the fuel temp/pressure. On the end of my tubes in the tender I install a piece of foam rubber to act as a rasberry muffler.
 

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Dan
One can reach a reasonable conclusion based on "real practice". In most cases, smaller engines benefited from the lesser drop in steam pressure due to effective heating of the feed water, while larger engines had the same marked increase through superheaters versus saturated steam, while in later years, the modern choice was to utilize both.


Yes, apples to oranges when it comes to the gauge one CF to which the above data really has no relevance. Even with the case that Dave presents, his CF is different from our CF so to reach the conclusion that feedwater heater would be a better application than the superheater is a bit flawed. A study could only be done usign a control group of two identical stock locomotives, then applying "Hottman feedwater heater" to one loco and more efficent superheaters to the other, and measure the efficency of both through both the Johnson formulas as well as others. That would be the true way for a reasonable conclusion whether the efficiency is greater one way or the other.
 

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Dan,

A couple items of my "SS" program that you would appreciate was to change the axle pump stroke from 12mm to 7mm, and retaper the bypass needle to double the resolution. In the cab picture you will see a blue and a white line on the control knob. The white line at 12 o'clock is off, and the blue line at 12 o'clock is the running setting. I also got rid of the humps on the feed side to the axle pump. Most of what the axle pump puts out goes into the boiler. Concerning the feed water heater mod, this is a good thing. I think that with a 12mm stroke too much steam heat could get to the fuel tank. So far the boiler has never run low, or has the engine shot water out the exhaust during 1.5 hour runs. Compared to other CFs I've run, I am content with not superheating my steam oil and heating the feed water. I am so pleased I have started waxing (Meguiar's Quik Detailer) my AC11SS.
 

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Dave
We share that concern: "I am content with not superheating my steam oil " that is why we put deadleg lubicators for each engine thus not cooking steam oil as per OEM design. Also allows better oil feed to each engine at the cylinders.

The concept of preheat is a good one. Might be able to do this via a extended run of water pipe from axle pump in and around the backhead area of the boiler or along the boiler between the shell then into the check valve to the boiler. Another option is the tried and true, 2 for 1 method of heating the tender water via globe valve. To enhance the effect is to pinch the end of the pipe (not all the way closed) in the tender for a slow release thus creating a steam pipe heater in the tender: warms the water keeping gas flow "charged up" along with warm water to the axle pump into boiler.
 

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Dave,
I think that the idea is brilliant. I agree that what you have is really a flash boiler in the feed water loop. You did not mention if you are adding water to the tender during your 1.5 hour run, which would cool down the tender tank.

I think that you are right that it is essential to reduce the pump stroke, so nearly all the water is going into the boiler not the tank. I am surprised on how close you came to the exact stroke length, because there is not much difference between shut off and running on the bypass control knob.

Just as in full size practice, the game is to capture the heat before it leaves the stack. The feed water is traveling at a slower rate than the steam would be in the old superheater pipe, and it is able to absorb more of the heat that would otherwise be lost up the stack.

Oh yeah I feel like the dumb kid in class, because I have no idea what CF stands for. I am sure that it is not corn flakes.
 

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Mr Rowe'
If you were out on the open sea in the center of the ship and the cabin was at the front, it would be a (CF) Cab Forward. HUH?? I think it means the same on a locomotive. Your Daylight is a CR, Cab rearward.
 

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Dan,

I top off the tender about every 10-15 minutes and cover the top of the hand pump. I keep the tender heater valve (red knob) open a little extra so that when I top off the tender water I'm cooling it down to where it should be. I have also found that if I run the tender lower level, it is harder to keep the fuel pressure up.

On the axle pump stroke, I was going back and forth on making a 6mm of 8mm eccentric. After a pack of smokes and a couple glasses of wine, I called it a draw at 7mm. Ther was no calculating, just a lucky guess. The main reason I decreased the stroke was to give the rigid engine more leverage and run less lumpy. All I use the hand pump for is priming the axle pump.

Don't feel like the dumb kid in class, I keep getting all confused on which end is which. Cliff said it best, talk in terms of "cab end" and "tender end". Everytime I see "CF"" I think of cough syrup.
 

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Dave, just hope Accucraft doesn't decide to produce an Erie Triplex. You might have to increase the wine budget.

Larry
 

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Now I know what you have been so 'busy' doing.
 

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For most of the cases the feed water heater is adding more efficiency than the superheater.


I take a guess this is because we don't run as much at expansion than in 1:1 practice.
 

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Dave,

Thank you for the series of AC-11 threads. Beautiful and creative work. The concept for using a tee into the axle pump bypass return line for the tender heater is innovative. On a CF it would avoid running another long line.

I love cab forwards and enjoy seeing how they can be modified for the next level of performance. At this point I can't wait to see the next run of S/N 52 at ECLSTS.

Best regards,

Alan

PS I really like the headlight you did on the SS --- and the XDH09 train number boards!
 
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