The Home Machinist!

I am installing an axle pump on my 2-4-2 Columbia. Should I heat the water before it enters the boiler? If so, how.
Thank you
Tom

The best way is to put a series of water-filled tubes directly in front of the fire tubes in the smokebox. Many people will put a coil inside the perimeter of the smokebox, but this is not as effective at heating as from putting it where the combustion gases pass directly over them. If using coal for fuel, you will probably need to brush the fire tubes from the firebox end.

I've seen many people over the years, add a feed water heater, and a lot of builders don't mess with them ,?.....the effect on efficiency is negligible

OK, so why do you thing so many do it?

The feedwater heater mounted to the smokebox on my engine adds a tremendous amount of heat to the water prior to entering the boiler. It also reduces the "shock" to the boiler of adding cold water.

It also depends on how fast you are pumping through the smokebox coils, if you have an axle pump or steam pump and it's very slowly pumping, then you'll get a lot more heat transfer than if the water is moving through the coils faster.

Honestly though... very hard to beat a pair of reliable injectors...

For a smaller engine like that ( unless 3.75 scale?) The EE small or intermediate injectors would probably be a great fit.

thermal shock is not really a problem with our smaller boilers.

I have taken out (for others - maybe a dozen over 40 years) more feedwater heaters than I have installed on my own (none)..

they are more trouble than they are worth in the smaller scales...and marginal on bigger stuff.

Why do people put them in?

Well...it is a case of 'yes, they do add efficiency -> in theory'...but are they more trouble than they are worth?

once they get covered in grime and blasted by cinders, become pitted and leak and get in the way of keeping the smokebox clean...out they come....

no argument on injectors providing heated water...but the heat has to come from somewhere...

TANSTAAFL

Yes, the steam being used to run the injector..

Injectors are easily more efficient than a steam powered water pump with FWH.

I love watching steam pumps operate though, so cool! then axle pumps are great for when family or friends are running that don't feel as comfortable with injectors.

I added a feedwater heater to my locomotive because it was prototypical. the benefit was secondary. It has been on the engine for 30 years with no problems of leaks. It does have a drain on the bottom of the tank to dry it out after a days running. Does it work? The harder the locomotive works the hotter it gets just from the heat from the smokebox gases on its exposed part in the smokebox. I also have two injectors to add water to the boiler which are fun to use.

While temperature shock may not seem a problem on a small boiler, what is small? The money invested in the boiler on my engine was significant. There is lots of jewelry attached to that boiler. To replace that boiler would be a major expense and challenge..... So, I am a firm believer in preheat and pretreat that water. When water inters my boiler is by an injector or through the feedwater heater. So here is my vote to preheat! By the way....I would invite anyone to put their hand on my feedwater heater and still have a doubt to its efficiency.

No argument about water treatment.

I had a couple of pre-heating loop inside the smokebox of my 2-10-0. I ended up taking it out about 10 years ago. It started leaking, and I simply plugged the holes off and bypassed it. I honestly couldn't tell much difference in the way it ran and steamed. The axle pump ran through the smokebox pre-heater. I also have an injector. That's my experience with it on my own fairly large 1/8th scale steamer.

Main thing for me though, is simplicity on my steamers. If it is something that is likely to be finicky, touchy, or just plain-ol' quit working while I'm out running, then it won't be added, or will be dummied up. Ditto if it keeps me from doing cleaning or inspecting, and especially brushing the flues, since I burn coal. To each their own. I've seen some really nice feedwater heaters that seemed to work fairly well, and I've seen some that were definitely not worth the hassle, and in fact were detrimental to the performance of the locomotive because they interfered with other stuff. Nothing wrong with adding one, as long as it does it's job and stays out of the way otherwise.