Popular Mechanics Boiler

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Turning done:

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Then back in the mill to add some wrench flats. I got to use one of my mill holders for my mill sharpening sander project to act as an indexing block while milling the valve here:

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Valve body done. After this photo I set the valve in the bench vise, dropped the ball in place and, with a drift, gave it a light tap to seat it.

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The brazing rod fit well and trapped the ball with just the right amount of play.

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I threaded both ends 1/8" NPT pipe thread. Then it was time to seal the pin.

The check valve outside on a fire brick, ready to silver braze the pin in place:

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Brazed:

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And done. It works great -- at least blowing through it. It seems quite free in the open direction, and instantly seals in the other. Horizontal orientation doesn't bother it. Quite happy with this result!

[tom osselton]

Looks good well done!

[vtsteam]

Thanks Tom!

Today I started work on the pump base valve. First I drilled through 1/8":

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Then I drilled 7/32" for the stainless ball, as done yesterday. And after, opened out to tap size for 1/8" pipe thread:

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Then I turned the base upside up, and drilled for the retaining pin and a hole to connect the valve passages with the pump cylinder:

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I''m going to use a 1/4" brass pipe nipple as the pump cylinder. I cut the threads off one end and turned a small step in the end:

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The pieces of the pump base -- I faced a small recess in the base to fit the step in the pump cylinder.

I had to offset the cylinder slightly to clear the retaining pin:

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The pieces together and ready to silver braze:

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Brazing complete:

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I found an odd bunch of scrapped hex fittings in my nail keg o'brass, so I drilled one out as the pump cap, and tapped it to fit the 1/4" pipe nipple threads:

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And finally, where I left off today -- the pump body and cylinder and attached check valve:

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I finished up the pump with linkages and handle the last couple days. No photos yet -- maybe tomorrow. After a little fiddling tracking down connection leaks it worked perfectly today easily building up 150 lbs of pressure when tested with a few strokes. I didn't try more, since that was all I needed for testing the PM boiler, though I'm sure it could go to considerably higher. Handle pressure was light even at 150 PSI.

With the new pump working, I attached the pump to the PM boiler filled the system with cold water and applied pressure. Unfortunately the  original style safety valve leaked at any measurable pressure. I tried lapping the seat with valve grinding compound, but it just wouldn't hold. That was okay, because I really wanted to make a ball valve along the lines I'd experimented with earlier. I didn't like the PM valve design from the start. I'm sure it would release, the problem is it leaks when closed.

Since I was binning the old valve, I decided I could just drill out the valve seat, tap for a screw in seat, and then put a pipe plug in there so I could test the rest of the boiler. So I emptied the boiler, removed all fitings, and spent a few minutes drilling and tapping. I reconnected everything and was gratified to see the gauge needle move steadily upwards. This time I was able to pump to my target of 150 pounds, but the boiler slowly leaked through the threads of the two pipe caps on the ends.

I wasn't able to hold pressure for long, but there were no other leaks through any of the smaller brass fittings -- only  the two pipe caps leaked along the threads. I saw no structural problems, but I wasn't able to give the boiler a steady half hour test at 150 lbs, which is what I want to do. (My intended max working pressure is only 20 lbs, so this represents a large factor of safety.)

Now with plumbing normally you'd just tighten leaking pipe caps to get rid of the leaks. But here's the rub with this project -- it just isn't possible on the Popular Mechanics boiler design.      

The reason is there is a coiled water tube under the boiler, and their fittings are tapped into the underside of the caps. Therefore, tightening the caps  rotates the coils in relation to the fittings on the top of the boiler which are tapped into the pipe. Well, unless you could do a full turn to tighten. I couldn't. The most I could manage even with an extension on the pipe wrench was 3/4 turn. 

Then while trying to tighten the second cap, the pipe slipped in the pipe vice, and the jaws ruined one of the tapped holes in the top of the boiler. 

So I realized, the boiler had to be scrapped. Even if I had managed a full turn on both caps, the boiler would have ended up shorter, and would no longer fit the base I made for it. A lot of work went into fitting the boiler exactly to the top of that base. 

I guess the only good part today is I know how I can now improve the design.Obviously the water tube coil fittings should go into the pipe body of the boiler, as they do on the top. Not the into pipe caps. The caps can then be tightened at any time and also easily removed for inspecting or cleaning the boiler, without disturbing any of the smaller fittings.

As it was before, if the boiler was taken apart for inspection, chances are the caps would have had to be screwed on tighter -- and the same positional problem would have arisen. I think one of the really nice features of this boiler is the ability to open it up -- and in fact disassemble it completely.

Problems? The boiler may have to be longer to fit the same length of copper tube underneath (although, I may be able to coil it differently and get the same heating surface on the same length boiler-- I have to think about that) . However a couple inches longer boiler wouldn't be a big problem, other than having to make a new base for it.  Stresses and material strength would be about the same as long as the diameter and construction is maintained.

The basic good news today was that none of the tapped fittings leaked and all stood up to 150 lbs for as long as I could hold it. I pumped up several tmes. That's where my main concern was in the PM design. I'd still like to do a half hour test with the finished boiler, but I have more confidence now that these fittings tapped into the steel pipe will be fine for the working pressure I have in mind.

Anyway, that's today's results. A couple steps back, but I think I see the way forward. Just a lot of work to have to repeat.

Basically I have a new pump. But not a boiler.

[vtsteam]

Today was the opposite of yesterday! 

I woke up at 4 A.M. with a sudden realization that I could save the boiler if I just drilled out the bashed 1/8" pipe thread hole to fit 1/4" pipe. Duh!!! I guess I was just tired and disappointed yesterday not to have thought of it.

So I went to town, bought two more pipe caps, and screwed them on. I re-drilled and tapped the bad hole and installed a pipe plug temporarily. With the new caps screwed tight with pipe compound the boiler still fit the sheet metal base. Yessss!

I looked at the old copper coil and realized I had stretched it out to fit the first boiler, all I had to do was compress the coils a little, and put two new flare fittings into the bottom of the boiler pipe to fit. The coil length would remain unchanged. Wooohoo!

So, I connected up the hand pump and pressurized the new rig to 150 pounds, and it slowly dropped -- over maybe 5 minutes. I tightened up the copper coil nuts and the next reading stayed over 100 pounds for 5 minutes. The pipe caps leaked a drop every half minute or so, but it was lunch time so I left it at that. Byt the time I got back the leak had stopped and the gauge needle was stationary at 50 lbs.

I pumped it up again and saw that now only one pipe cap was leaking an occasional drop, So I let it drop over another 20 minutes figuring the leaks would probably self seal at this rate, and indeed they did. I was finally able to do my 150 lb test with the needle stationary and no leaks for a timed half hour. Yahooey!   

Finally I dug out my commercial safety valve -- it had a 1/4" base which fit the new tapped hole. Basically I now had a boiler AND a pump, unlike the day before.

The valve was set for 100 psi,  unfortunately and I need one for 20 psi. so it wasn't usable today. It is an internal spring and ball type, and though adjustable, would really need a new spring to bring it down to the low range. Nevertheless I had fun pumping up the boiler with cold water and setting different pressures with it and watching it blow.

Sorry no pics today either -- tomorrow for sure. 

[PekkaNF]

Nice thing you didn't need to go back further. but I agree. Design could have been different.

About the design. I once used one fire extinguisher cylinder for a pressure tank of a compressor. I tought I was smart, drilled hole on the shell and hard soldered a fitting for a water cock. It corroded in ten years. Maybe having fittings on the cap will give there some extra material? I was thinkking of suggesting using T-unions on both ends and shortening the middle part, but looks would be very different. T-unions are pretty stong and they would allow easy internal inspection without upsetting coil fitting.

... Nevertheless I had fun pumping up the boiler with cold water and setting different pressures with it and watching it blow.

So, it was like watching paint to dry

Pekka

[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.