Gallery, Projects and General > Project Logs
Popular Mechanics Boiler
vtsteam:
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:
vtsteam:
And finally, where I left off today -- the pump body and cylinder and attached check valve:
vtsteam:
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. :bang: :bang: :bang:
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. :hammer:
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. :hammer: :hammer: :hammer:
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! :ddb:
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! :med:
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. :beer:
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.
--- Quote from: vtsteam on July 30, 2014, 08:12:13 PM ---... Nevertheless I had fun pumping up the boiler with cold water and setting different pressures with it and watching it blow.
--- End quote ---
So, it was like watching paint to dry :lol:
Pekka
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