Run out of steam pressure after 100 feet

[RET]

Hi,

When you were running under steam, did you ever move the Johnson bar back towards mid-gear (towards the middle of its travel)? Running with the bar all the way forward (or reverse) is very wasteful of steam because of the late cut off.

I expect to get a little flack on this, but (especially on level track as shown in the video), the proper way to run a locomotive is to open the throttle part way and then control the locomotive's speed by moving the Johnson bar back and forth as required between the center position and all the way forward (or reverse). To slow the engine down, or when descending a grade, you can even move the lever from forward into reverse where you are using steam pressure to oppose the motion of the pistons. Don't move the lever too far, or the wheels will start spinning backwards and they will lose their grip.

Some people like to hear a sharp bark in the exhaust (what they call "Stack Talk") but this happens because there is still significant steam pressure in the cylinders when the exhaust valve opens. This pressure can be used for performing additional work instead, but if this is done, the exhaust will be much quieter.

If everything is set just right, a 7 1/4" / 7 1/2" gauge locomotive will run on level track either forward or reverse in mid-gear. It won't have any power, but over about 5 miles an hour it WILL run! I have done it with a 7 1/4" Virginia (4-4-0) and it works. I didn't set the valve gear on the engine, that was done by someone who knew a lot more about these things than I do.

Just my two cents for what its worth.

Richard Trounce.

[NP317]

I agree with Richard.
I always "hook up" the Johnson bar after the locomotive is moving. It produces economical operation.
That's how I can get up the 2.5 mile 2%+ grade at Train Mountain pulling a load and hooked up 50%, and not need to stop and refill the tender with water.
It make a big difference in operation.
Of course, your valve gear needs to be in good condition with very little slop in the pins, to operate hooked up.
RussN

[Drprez]

Wow thank you everybody for all your replies!!

I did solve my firebox heat issue with the propane by adding a perforated piece of stainless steel plate about a quarter inch above my flames and they hold a ceramic grate 4x6 in and then on top of that I put ceramic biscuits just like used in a barbecue grill.

Ceramic grate

The propane hits the biscuits getting them red hot and they give off much more even constant heat.

So once I get moving the biscuits work just like coal continuing to radiate heat keeping the firebox hot and my boiler happy. It actually works very well.



I also have an arch that goes from the front to back with about a quarter inch opening on the top for the exhaust and it seem to be working fantastic.

Here is my arch and just below the firebox door is where my stainless piece sits to hold the ceramic

Arch looking from mud ring

Stainless piece

Arch curve

Here is the link for the grate.
https://smile.amazon.com/gp/aw/d/B0713X ... UTF8&psc=1

[Drprez]

My original video was played in reverse that is why the smoke is going in sorry about that.

So I worked on the valves I think I got it better here is it back on air testing it

https://drive.google.com/file/d/1Xfezxw ... p=drivesdk

[Drprez]

So here is an update Dec 31, 2019.

I did what RET Richard suggested and it worked great. Here are the steps I did from Richards suggestions.

"In that position, the slide valve should just crack open very briefly at the extremes of its travel. to achieve this, you may have to move the eccentrics forward or back on the axle and adjust other parts of the valve linkage. These adjustments are fiddly and take a while to get right. It is also important that you have the proper mindset when you are doing this. A lot of that comes with experience.

Work on one side of the locomotive at a time and if it helps, you can disconnect the valve gear temporarily on the other side. If you can set each side properly using this method, you will have an engine that will run in mid-gear when you are traveling over 5 miles an hour on level track. That is the goal you should aim for. You will also have a locomotive that doesn't waste steam.

The basic idea behind both the model and full size is that steam is under pressure in the boiler and by expanding in the cylinders does work. Ideally the pressure in the valve chest should be close to boiler pressure when the throttle is open. In operation, you should use the throttle to set the "power level" and then use the Johnson bar to control the speed by varying the cut off. When you are close to mid-gear, the admission of steam to the cylinders is cut off by the slide valve before the piston has traveled very far down the cylinder and the steam expands to supply a continuing but continually reducing pressure on the piston. By moving the Johnson bar away from its mid- position, you make the cut off later so the piston sees full pressure for a greater portion of its stroke thus giving more power. There are lots of other considerations like the fact that as steam does work its temperature decreases and some of it may condense in the cylinder, but this may be enough to get you started."

So The key was to do one side at a time get that side perfect then move to the other side not worrying about the other and that made it near perfect in forward and reverse. It took some time to dial in the valve on each side just right going through all 7 positions: Forward 1,2,3 Neutral, Reverse 1,2, 3.

Then what I did was make sure the driver was in dead forward check the valve then rotate the driver to have the shaft in the dead reverse position and check the valve the should be exactly the same amount open or covered if not you adjust to get them just right. it takes a while to do all of the positions but you have to I found as I got to the reverse the changes seemed tiny but had a big impact when i would go all the way to the 180 dirction ( so from full reverse to full forward on the jbar) the difference could be huge so the adjustments had to be ever so slight to get them in just right



Now I am in shock how smooth the drive wheels move and no hang or lag its great here is a link to the working video after all the work.

https://youtu.be/h3sQ8sKDxHI

happy new year

nick

[RET]

Hi Nick,

Good job, sounds perfect!

Because of thermal expansion, you might have to make a few minor tweaks when you run it on steam, but you have done a great job. Congratulations on sticking with it.

Now you know the satisfaction you get when you do something and it works just the way you think it should. That makes all the hard work worth while.

Just as a minor aside, if you get the valve chest surfaces flat enough, you can put things together without any gaskets and it will work just fine. You can do this by using either a surface plate or a piece of plate glass (a surface plate is better if you have one). Take a sheet of 400 grit polishing paper and lay it on the surface plate (higher numbers work better but take longer) with the abrasive side up. Use paper, not cloth, because the paper is thinner.

Make sure the polishing paper and the surface plate are both clean. Take the part and rub it on the polishing paper with a circular motion, switching from a clockwise to an anticlockwise motion and back again. Try to hold and guide the part as close to the surface plate as you can.

Check the flatness by catching a reflection off the surface of the part. As the operation progresses, you will see the surface become the same all over as the high spots disappear.

Just something else you learn with experience.

Richard Trounce.

[Drprez]

So the pictures were how they were I since took them, well my dad was visiting and said to use.a laping (sp) block? and then I was lost but my question you mentioned a surface plate?

I have a 1/4 thick flat stainless will that work?
Do you use water or do it dry? Or use a compound like toothpaste or baking soda?

I got 600, 800, 2000, 3000 grit from Home Depot so I will try them per your suggestion.

So next question how do you pack the rods so the packing seals but don’t hold the rod up? I have cotton with grafite stuff what’s the trick?

[Rwilliams]

Lapping will surely make the surface smooth. You want to fill all of the holes and ports with some silicone sealer and once it cures, slice off the excess with a sharp razor blade. This makes cleaning the lapping compound off the surface a dream.

Heavy and flat are the secrets to a good lapping plate. The stainless may be OK for the coarse level of material. I would look into some heavy thick 1/2 inch glass for the finer finishing compounds. A small cast iron lapping plate with some slots would also work well. I have actually made up specialty cast iron lapping plates for specific tasks in the past that worked really well for the special application. McMaster-Carr will sell you nice blocks of cast iron that can be custom sized for the job at hand. Cut some small 1/16 wide and deep slots giving some 5/16 squares on the business surface of the plate and grind or lap smooth against another plate.

The coarser level of compounds will need some heavy lube oil to provide sufficient mobility of the block on the surface to be lapped.

Finer lapping compounds will need thinner lubricants to work well. Often times WD-40 will work well for the finer grit levels.

Be sure to clean off the cast iron block and the lapping plate surface each time grit levels are changed.

Never lap a surface that is too dry.

The cast iron block surface will take longer than the brass valve to lap smooth.

Clean real well and assemble with some Antisieze grease to insure things work well at the beginning of the operation on steam.

[RET]

Hi Nick,

A lapping plate may or may not be truly flat depending on how it has been used or even how the surface was when the plate was new. It works by being soft enough that the grit in the compound embeds in the surface of the plate. For sealing without gaskets, it is the flatness that you need.

A surface plate has the high spots scraped away until everything is true. The classic way to make a surface plate is to start of with three flat plates and scrape each one to the other two using blue to mark the high spots. It is a long, slow process but you will wind up with a truly flat surface if you know what you are doing. What I described is simple and it works, just be careful to keep the surface plate clean and don't let any of the abrasive get on or stay on the plate. You need to protect its surface so you don't destroy the finish and flatness. These days, most glass sheet is made by the float process, so a thick piece (1/2" or thicker) should be good enough for the purpose.

For you, the easiest rod seal would be graphite packing ("O" rings also work well, but you have to disassemble things to replace them). A plumber would either have some, or be able to tell you where to get it. The size doesn't really matter, you just unbraid some of it to get the size you need. Because of the graphite, it has a grey appearance somewhat like lead. Unscrew the packing nut and coil some in the space under the nut. If you want to be meticulous and for bigger glands, you are supposed to use diagonal cuts and wrap each piece around the rod making sure that the diagonal joins in the graphite don't line up. Sliding the gland nut back in place compresses the packing and makes the seal.

Once you know how, most of this stuff is pretty easy. It isn't rocket science, just common sense. The important thing is to have fun with it.

Richard Trounce.

[Drprez]

Ok so on the lapping plate are you using a computer or are you using fine grit sand paper on the plate? Where do I get the compound if it is not paper?


Thanks for the info on the graphite packing I got some but the piston shafts are so tiny I can barely fit any in the cap but I guess that all I can do

[Rwilliams]

Lapping compound is usually obtained in a metal can not unlike paint would be found in. There are various grades/grit sizes from coarse to superfine mixed with thick to thin oils to work well as a lubricant on the lapping plate. Quality lapping compounds can be found on the McMaster-Carr website catalog. Depending on the condition of the surfaces to be lapped, I often will start with a estimate of what I need to start with. Rust pitting can be deeper that it first appears. Often times my first grit will be some 120 or 150 grit just to see how things clean up and go up in number to 180 if possible or down to 100 grit depending on what is revealed after a few minutes of lapping.

Depending on the amount of surface roughness of your parts, one will start with the desired grit size on the plate and move the part or plate in a figure 8 motion to help equalize the wear and keep the surface level. Slow and easy is the best option with even pressure at all times. (With a lapping table, one often has the luxury of small weights to keep the parts flat on the table and speed the coarse lapping operation.) Once the entire surface has an even finish, clean off all the lapping compound from the part and plate. Apply the next finer grit size of compound to the plate/part and do the same thing over again. Lapping is a slow task, but results in a super smooth surface. For most steam valve work, 600 or 800 grit will be more than sufficient for your needs.

You might even want to investigate some YouTube video offerings on lapping surfaces flat for a better idea of what you are getting into.

You want a smooth even surface with no scratches or tool marks that could result in steam leaks.

[Drprez]

Thank you! So some
Say use glass some say use iron. Is one better then the other? Is there a minimum thickness of the glass or metal to use as a plate?? Or is it a go with what works as I find it kinda thing?

So I got 120, 600, 800 compound ordered. So the the theory is get both surfaces perfectly smooth so not to have to use and seal or gasket but simply the screws will be enough for the seal?

Why is that better than a gasket? Over time will the lapped pieces leak or no unlike a gasket that eventually will?