Boiler water injection efficiency

[ChipsAhoy]

Has anyone done a study on the efficiency of the various methods of boiler water injection?
Seems to me everything on a steam locomotive is pointed towards producing steam used to provide locomotion. Therefore any use or leakage of steam not use for locomotion is wasted.
That being said.... of all the methods using steam for boiler feed... which uses steam most efficiently?
Axle pump, injector, simplex/duplex pumps?
I suspect (but i do not know) the axle pump waste less.
Thoughts? Facts? Experience?
Or is this an exercise in futility?

[ALCOSTEAM]

If all working in good shape its really hard to beat an axle pump. There is many an engine out there that guys can run all day and maybe not use an injector except if sitting long periods. Another good use is if you happen to get to a low water condition is an engine can be pulled or pushed by another and water can be fed into the boiler. You just really need a means of getting water into the boiler that doesn't need steam to function.
Two quality injectors and a properly sized axle pump would be my idea of the ideal set up, of course that is what is on many engines running today.

[DianneB]

In full-size practice, for both locomotive and traction, injectors won the feed water war and were universally used by the 1920s.

In stationary practice both injectors and duplex pumps were common though pumps were more expensive and required more maintenance. Pumps had the advantage be being reliably self-starting and could be used with 'automatic' water level control.

Models are a whole different story! Most everybody I know has an injector, many have axle pumps, and some have duplex pumps. Variety is the spice of life

[Asteamhead]

Hello,
Question was which method of feed water device is of the highest (thermal) effiency. In full size practice this was a feedwater pump in combination with an economizer like the Worthington SA or BL feedwater system. Next regarding the economy is a reliable injector due to it's using of 100 % of the injected steam to heat the cold water. An axle pump may be the most simple method to feed water to our model boilers. In case it is used without a (closed) economizer using exaust steam to heat the water (as it iscommon prctice), the thermal effiency will be poorer.
Open feedwater economizers as the SA or BL will ad undesired oil to the feed water, if there are no measures (filters). This had been a severe problem even in full size prcatice.
I recommend using 1 or 2 reliable injectors ("super scale!"), perhaps of different sizes. More fun makes useing a steam driven feedwater pump as shown in my thread "A 1239" in the Build log. A check of the Link - pump at 100 psi + made recently showed a feedwater volume of 13 gal (50 liters) per hour. It is working perfectly any time!
A duplex pump will work, too, of course.

Just my two cents
Asteamhead

[BClemens]

May I add to the original question...? Wouldn't the most reliable method and simplist as well be the use of a (with a backup) good quality and reliable injector to keep the water supply up in the boiler? Seems a mechanical (axle pump) or steam pump of any sort will suffer with long term reliability issues - being intricate mechanisms. The steam or mechanical pump method will also require some method of preheating the water before being forced into the boiler...an obstacle very conveniently eliminated by the operation of an injector. Now, the injector must have the ability or efficiency of design to work to put water in the boiler at about ~ 30% of boiler pressure. That will eliminate most all haphazardly manufactured injectors on the market today and will most certainly demand the use of mechanical pumping systems too as backup. Efficiency is surrounded by safety issues as most (hopefully all) live steamers will attest so two or even three means of water supply is not at all efficient - but safer - if they work.

There is much to be read about keeping a boiler supplied with water - and is probably a primary goal for safe operation of a steam boiler. Loss of fire is loss of steam pressure; reduced water supply is uncontrolled increase in pressure with catrastrophic results unless the boiler is built with a massive safety factor. This is much experience, much study along with safe working practices and precision - and luck should not be any sort of consideration. Someone here said recently that a steam locomotive is (not quoting) barely efficient at all so a model one is even worse for efficiency - so then build it with grand safety factors and a full understanding of what it is capable of.... as I'm telling myself again - and again.

Thanks for the oportunity for the 'question' - BC

[Crosshead4]

I would think that the steam driven water pumps (scale ones without a heater) would be the least efficient because the live steam used is exhausted to atmosphere. Injectors return most of that heat to the boiler.

[BClemens]

Injectors return most of that heat to the boiler.

If you think about the injector: "let's design a device with no moving parts that uses steam from a boiler to put water back into it". And as an added benefit, heat the water too. It is a very simple device that uses very simple physical concepts and conditions - but having all those 'complexities' of an injector work so well together - its existence is like a miraculous gift. Another miraculous gift...

BC

[Pontiacguy1]

On our models, I don't worry nearly as much with efficiency as I do with reliability. A small loss in thermal efficiency on our models will be unnoticeable, whereas on the full size with the thing running thousands of hours per year, it would be a big deal. When you run your locomotive dozens of hours per year, the efficiency really isn't that important as long as it can make enough steam to do the work it is being asked to do.

That being said, I think that a good axle pump is one of the most reliable pumping methods out there. Some say they are useless/worthless, but I know of too many of them that have been reliable for decades, and on many different locomotive sizes. The do not have that many intricate mechanisms, are actually quite simple, and most will last for decades with nothing more than lubricating a couple of times per day and the occasional change of the sealing o-ring. I also think that a good injector that is plumbed in properly and has a suction line strainer to keep debris out of it is an excellent method and probably the most thermally efficient in our scales.

Again, I go back to reliability, and that really means that you need to have more than one method. Some use a couple of injectors, I use an axle pump plus an injector. A good duplex pump will keep your water up and is interesting to watch run, however, a lot of those tend to be temperamental, and like was mentioned before, without a feedwater heater, I don't think they are too thermally efficient.

Just my two cents' worth: Worry more about reliability than efficiency.

[DianneB]

If you think about the injector: "let's design a device with no moving parts that uses steam from a boiler to put water back into it". And as an added benefit, heat the water too.

I have been a keen student of the physical sciences since childhood and I understand the principles on which an injector works, I can explain it, I can teach it, I can design it, but some small part of my mind still rails "Nothing can be 100% efficient - where's the waste? Where's the lost energy?!" (I know the lost energy is in heat but you can't see heat LOL!)

[pat1027]

It's the heat of vaporization. Once water reaches the boiling point it takes more energy to convert it from liquid to gas than it did to raise the temperature. The steam is giving up this energy to push the water into the boiler.

[Bill Shields]

giggle...what does EFFICIENCY have to do with enjoying our hobby?

if you want efficiency -> forget boiling water with coal....

this is all about having fun...

axle pumps are great and have a loco in my basement right now that has not had the pump open in 50 years and still has the original packing...

...but if you get stuck in traffic you need something else...

[pat1027]

From a practical prospective the difference in efficiency between pumps and injectors will be negligible. The enjoyment in the question comes from the discussion itself.