Gallery, Projects and General > Project Logs
Popular Mechanics Boiler
vtsteam:
Thanks Pekka!
By the way, the copper coils now go into the pipe body, not the end caps, now. I think it's an improvement to the design.
re. corrosion:
Galvanic corrosion can happen over time between dissimilar metals, and how fast depends on the water quality and metals involved. Welded or brazed tanks and fittings can allow this to happen out of sight. I read a recent account online of a model locomotive boiler that had passed club pressure tests for years, yet the owner found he could poke a screwdriver through the boiler wall in the last inspection, due to internal corrosion out of sight.
I would say that this little boiler has 4 very good qualities in that regard that I've come to appreciate as I've worked with and thought about what I originally considered to be a "crude" design:
1.) The boiler is WAY over built. The walls are .154" steel, and the end caps considerably thicker cast iron. There's a lot of material that would have to be eroded away to be able to stick a screwdriver through it from the outside.
2.) The end caps can be removed for direct inspection of the entire interior No need to also poke around with a screwdriver outside. Any wasting away or corrosion products at fittings would be immediately evident on inspection.
3.) There are NO welded or brazed boiler joints for hidden corrosion to occur in.
4.) All parts of the boiler are removable and replaceable, the fitting seats and threads can be inspected easily. All fittings can be removed in ten minutes time with 4 wrenches. Every part could even be replaced once a year if desired for a very small total cost. A new boiler body itself is just another $8 pipe nipple with a few tapped holes in it.
I think the key to lifetime longevity re. preventing corrosion with this one would be to make sure it is dry when not being used -- which is fairly easy with such a small boiler with a big fill plug removed and a little warming from a propane torch before putting away.
I think it's a very different case from larger traditionally constructed live steam boilers, or home made compressed air tanks, for that matter.
I'm very impressed with the concept of this small boiler, though not with the execution in the original design. The safety valve was unworkable as shown, and the fittings seated in the pipe ends discouraged inspection and sealing if there was a leak. There was no pressure gauge indicated and there was no accompanying article on building and using a hydrostatic test pump, which I think is essential for initial and periodic testing. Remedy these things, and I think the design has a lot of advantages.
awemawson:
Steve, presumably the boiler (and hence the screwed end cap joints) go above 100 C as it contains water / steam under pressure. What are you using as your sealing compound on the threads? Many proprietary ones top out at 100 C. I suppose Teflon tape is an option that will take the temperature, but I have an abiding loathing for it and use one of the Locitite thread sealers these days for oils, air and gas - but they fall off at about 100
vtsteam:
Well I'm not happy with that one aspect either,Andrew -- I'd prefer a non-PTFE compound, but they are all the fashion these days -- at least in the hardware stores I have locally. So yes I used some Teflon tape and also some teflon containing paste.
Why I don't like or want PTFE:
True it can withstand more than 100C by quite a lot, but if you exceed its breakdown temperature (over 250C -- say the boiler running dry) it is hazardous stuff. I'm scrupulous to remove any of it showing beyond any fitting in the firebox.
Fitting threads themselves are shielded from direct flame and are technically water cooled to a little above the boiling water temperature (@20 psi in this case). But still, I don't like using it at all.
If anyone here knows of better alternatives, I'd appreciate hearing them. I'd be happy to remove the present stuff.
I have read in older references that sal amonniac was used to induce a quick rust seal for pinhole leaks in steel pipe joints -- but I do wonder how easy the end cap fittings would be able to be removed afterwards.
Also in older references for model boilers, I've read of using just old thickened paint -- but ditto on removal for that. Of course I don't really know how hard it would be to actually break the joints free with either, after a year,
And also Andrew -- even if a paint or other sealant broke down with heat -- the residue might still seal the joint.
I don't know -- this is definitely an area that could use improvement, and all suggestions welcome.
ps. of course there are many proprietary "boiler seal" and treatment products on the market for hydronic heating and steam heating, and also automotive radiator stop-leak products. These could be added after assembly. But being proprietary, I kind of wonder what I'd be getting with something like that. Could be fine or could be downright evil stuff.
vtsteam:
Here are a couple photos. Pump parts:
The plunger was 3/8" cold rolled rod that just coincidentally fit the 1/4" brass pipe nipple used for the pump body. No machining necessary.
I turned a groove at the end and added an O-ring.
I also changed the cap, originally from brass scrap, to a simple pipe cap, drilled to .375" and some cotton string added for packing.
vtsteam:
And here's the pump assembled and painted:
ps. re. the plunger -- I'm going to make another of stainless steel -- just found an SS bolt to turn down for the replacement at the hardware store.
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