First serious steam engine build.

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zimirken
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Re: First serious steam engine build.

Post by zimirken »

Disappointing but not unexpected results today.

My boiler came up to temp in about 10 minutes. Since it holds about 5 gallons or so of water, that means the heat flux was somewhere in the range of 40-50,000btu. This is just a ballpark figure, as I didn't measure temps, use a stopwatch, measure exact volume of water, and I'm sure my hair blower pushes a bit too much air. That's about the bare minimum for running the engine. I was hoping for more like 60-100k, but this will work for now. I don't know how efficient it is, I'll have to add a stack thermometer eventually. However, I made some tweaks to the steam blower, and now it works VERY well. Just a little crack on the needle valve and it makes a good draft. I can tell because when it's all set up right the acrid smell of rich burning propane goes away. I'd love to have one of those wideband oxygen sensors to tell me what kind of ratios I'm getting, but those are expensive. On the plus side the wood lagging seems to work well, as it's barely warm to the touch on the outside. I'll have to finish lagging it.

Anyways, on to the bad news. My little one cylinder engine just doesn't have enough torque to push me. It wants to, and I'm sure if I was running on rails instead of using rubber tires in the yard it would. My calculations show that I'm probably getting about 20-30 pounds force in tractive effort with the current setup and boiler pressure limits. I'm going to start by gearing it down. I'm going to switch from 13in tires on the back to the 10in tires that match the front. I'm also going to put a bigger rear sprocket on. Right now I have a 14/36 ratio, but I think I can bump it up to 40 or 45 teeth on the rear sprocket. I may also be able to remake my front sprocket to one with less teeth as well. It's going to be pretty slow, but I can live with that for now. I'd rather have a very slow steam car that works, as I can drive it around to renew my spirits after setbacks.

Simultaneously, I'm starting to plan the addition of a second cylinder to my engine. The design is almost done, as it's not much more than just duplicating the whole thing and redesigning the framing components. In theory I could even make a four cylinder engine this way if I really wanted to. This will also make it self starting, so no dead spots, which is good when it's a direct drive to the wheels.

Also, a bonus:
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Bill Shields
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Re: First serious steam engine build.

Post by Bill Shields »

that is a lot of heat into a cold boiler - really fast.....probably too much, but then I don't know the exact construction techniques / materials of your boiler.

nothing is lost by warming a cold boiler slowly....except a few minutes that can be used to 'oil around' and check that all is ready to go...

as for not being able to push you without extra gearing....not surprising
Too many things going on to bother listing them.
zimirken
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Re: First serious steam engine build.

Post by zimirken »

Well, I moved under power! For like 10 feet. I switched from a 12in wheel to a 10 in wheel, and changed the rear sprocket to 45 teeth, and it just barely has enough torque to carry me on nice level ground. It'll pull itself through the grass without me on it though. It would probably work fine if I had a 100 or 125psi boiler, but I'll work on that later this year.

So I'm going to build a little gearbox. I like the current ratio for high gear, so I'll try to keep the high gear near 1:1, especially when I add the second cylinder. The low gear I'll probably aim for a 2 or 3 ratio on top of the final drive ratio.
zimirken
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Re: First serious steam engine build.

Post by zimirken »

Update, I printed a small gearbox, but it didn't work out. I ran out of ball bearings so I just used plain bearings, and it was too much friction for my little baby flywheel to overcome without being already worn in. I ordered more ball bearings (10 for $10 on amazon, very nice), but I'm just going to focus on adding another cylinder to the engine. I already have the second cylinder and valve block made, and I'm working on the rest of it. The majority of the parts are just machined out of half inch aluminum plate, so they're pretty simple to crank out.

This is my favorite way to machine parts, cut them all out one by one from a plate:
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Also, my whistle just didn't want to work well, and I realized my length/diameter ratio was waaay off. I cut it shorter and it works much better now.
zimirken
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Re: First serious steam engine build.

Post by zimirken »

The 2nd cylinder is mostly complete, up to a running state. It seems to run much smoother than it did with one cylinder. For the frame I ended up getting some aluminum rods, machined them to length and put tapped holes in the ends. This seem to work really well, as the frame is very sturdy now. I just need to make the second exhaust manifold, and machine replacements for the two printed valve levers. I might try to make some sort of notched setup for the reversing lever, but I will try a pinch bolt based position lock first.

zimirken
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Re: First serious steam engine build.

Post by zimirken »

Well, the engine works great! It runs smoothly, it has enough power to pull me >50psi, the displacement lubricator works, I got a sick burn on my leg from the uninsulated steam pipe going to it, and the valve and piston seals are so good that I can turn off the throttle, wait like 30 seconds, and still get steam out of the cylinder drain valves and steam chest. It goes backwards and forwards equally well, the valves are timed well. I used a spring loaded pinch bolt in a slot on the reverser handle and that seems to hold position well. The hackworth slide rods are still stainless steel which is not compatible with linear ball bearings (the hard bearing balls quickly wear grooves in the rods), but I should be getting my 5mm hardened chromed rods in the mail this week. The aluminum eccentric straps ride smoothly on the PLA+ printed eccentric bearing surface, and they are working well even at high speeds. I made gaskets out of soda can 12 pack box cardboard, and they seem to work. Everything seems to be wearing in quite well.

Most of the rest of the car works too. The whistle is nice and loud now, the water gauge works, the hand and electric feed pump work, it steers fairly well, however...

My boiler is inadequate. Once I start moving pressure quickly starts to go down. I need way more surface area. I measured it and it only has about 1 square foot of heating surface. I added a grill temperature gauge to the stack and the exhaust temp is over the 700F max reading, so I have enough fire. So I'm going to either make a new boiler or add some forced circulation coils in the exhaust duct. I'm going to aim for at least 3-5 square feet of tubing surface area. That should be plenty, since monotubes and small diameter tubing coils only need ~2 sqft of surface area per BHP.

I did some mocking up with some copper tubing, and it's probably not going to be reasonable to add coils to the existing boiler. I could fab up a chamber on the exhaust outlet that has a stack of tubing in it, but at that point, it's turning into a band aid. I might as well redo it from the ground up. I've got a "camp stove" I made from a small propane tank last year, that is the perfect size to fit a coal fire or propane burner in the bottom, and plenty of copper coils in the top. I'll have to do some thinking.
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Bill Shields
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Re: First serious steam engine build.

Post by Bill Shields »

A propane tank is not suitable to use as the outer pressure shell for a boiler
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zimirken
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Re: First serious steam engine build.

Post by zimirken »

It's going to be the firebox and overall enclosure, not a pressure vessel.
Pontiacguy1
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Re: First serious steam engine build.

Post by Pontiacguy1 »

I think he's making a water tube boiler.
Is that what you have now?
And congratulations on building something that works! Success breed further success.

be careful with the boiler. There are a lot of designs out there and a lot of knowledge on how to properly build those designs. Take advantage of that and do not try to reinvent the wheel on this. Take advantage of other people's experience. Also, use good materials and building methods. Boilers are not the place to be messing around or trying to go cheap. Safety is the most important. One poster on here put it like this: "I sit behind this thing, with my legs spread!"
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Bill Shields
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Re: First serious steam engine build.

Post by Bill Shields »

i shudder when i see people rushing through things, get to the boiler and continue full speed ahead and the heck with <fill in the blanks...>

a square foot of heating surface is quite a bit...I don't think that I have a loco that has THAT MUCH (except my 1-1/2" scale)....

If you have a 700 F stack temperature, you are throwing a LOT OF HEAT out into global warming....

to say nothing of which => it appears you are in Michigan...where even small boiler rules are just to the left of draconian...and some would argue for very good reason...
Too many things going on to bother listing them.
pat1027
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Re: First serious steam engine build.

Post by pat1027 »

Bill Shields wrote: Tue Jun 28, 2022 1:49 pm it appears you are in Michigan...where even small boiler rules are just to the left of draconian...
Draconian meaning excessively harsh or severe?

Michigan's hobby boiler rules only apply to boilers on public display or use. The inspection procedure was drawn from what the Tri-State Locomotive Club and the Great Lakes Live Steamers were already doing. Basically a hydrostatic test followed by a saturation test to confirm the safety valves function. Probably the biggest headache would be providing design specifications and calculations get a state boiler number for a new boiler. Objections from the hobby have been the fees ($75) and that state inspectors only work week days. The rules do provide for clubs to perform the inspections and certify boilers but so far the clubs have left it to the state. Enforcement is based on complaints.
zimirken
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Re: First serious steam engine build.

Post by zimirken »

I remembered that I have access to an oxy-acetylene torch at work, which means I can easily do silver soldering now. I did some silver soldering a few years ago on some boiler fittings, and it was rather tedious with just a propane torch. Also, silver solder seems to be much cheaper now and available in store. I cut the top off my little tent stove and took some measurements and sketched up some ideas.
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It's 9in o.d., and ~8.5in i.d. at the weld seam. It's about 8in long from the grate up to the top where I cut it off. It's quite spacious in there.

I was thinking of lining the inside with 1/2in copper pipe soldered together in a zig zag to make a sort of "water wall". Using 6 inch long pieces and 1 regular and 1 street elbow, each vertical pipe is ~1.375in apart, which lets me fit about 16 around the circumfrence for about 1.5 square feet of heating surface. That's already halfway to my goal, at the cost of about $50 in copper pipe and elbows. Then, for the center, I'll probably make a pancake coil like I have previously.

I pulled this out of the last boiler I made a few years ago. The coil and the circulation pump worked perfectly, but there were other issues (like not having a viable path to an engine at the time) and I just lost interest.
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I made it using a 3d printed frame and tying it together with wire. I might try and reuse this coil, or make a new one. 20 feet of 1/4in tubing nets me about 1.3 square feet of surface area for like $12 in copper. 1/4in tubing is by far the best bang for my buck around here. Regardless of wether I use this coil, or make a new one, I'll be making a frame out of two steel plates with threaded rods welded on to mount the coils and the water wall.

For the circulation pump, I still have my original piston pump on a gear motor that worked pretty much perfectly. Except now it's upgraded with all aluminum parts, so there's no risk of heat warping the printed parts I originally used. How did I get away with using 3d printed parts on a pump that pumps boiler water? I used an idea that I saw online from a commercial boiler. They had a circulation pump made from a long tube with check valves on one end, and a motor operated rubber diaphragm on the other. The long tube kept the heat from reaching the diaphragm pump. I used about 4 feet of uninsulated copper tubing between the piston and the check valves, so the hot boiler water never reached the pump, and cold water just cycled back and forth inside the long tube.
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Oh, and I was bored and made a centrifugal pump to try as well. I was told that centrifugal pumps don't work very well at these scales as circulation pumps, but we will see. It pulls about 6 amps when trying to pump water against my finger on the outlet and applies a good bit of pressure. There is of course zero blade geometry optimization, but it's super easy to make a new impeller if this one shows promise. It should stand up to the pressure and temperature with two viton o rings for a shaft seal, but it may need a small fan on the back of the motor.
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Oh, and this is all exempt from the hobby boiler code anyways since it's on a moving vehicle that's not on rails, as confirmed with an email to the inspector a while ago.
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