Author Topic: Popular Mechanics Boiler  (Read 29784 times)

Offline vtsteam

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Popular Mechanics Boiler
« on: July 18, 2014, 10:11:47 PM »
I decided to take a detour before going farther on flash boilers and make a little boiler I've always been curious about. It was featured as a project in a 1963 Popular Mechanics magazine, and more recently there was a U-Tube video of one:

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #1 on: July 18, 2014, 10:39:26 PM »
I had most of the materials to make it on hand. Nothing is particularly difficult about the construction, except the original safety valve. This was shown in rather vague detail. And the builder in the Youtube video substituted what looks like a commercial valve.

I have one I can use as well, but I was curious about building the version on the plans. It looked to me like it wouldn't work mechanically, so I figured I'd try to build it to see, and then substitute the purchased safety when ready to actually steam.

So I built the thing today and I was right. It can't possibly work as designed. I kind of wonder how many original readers attempted it and found it was whacked!

Sorry I don't have any photos until tomorrow, but to describe it, it's a weight and lever relief valve, that uses the head and smooth shank portion of a #8 wood screw as the lifting plug. This fits into a hole in the boiler pipe with "only 1 or 2 thousandths" clearance. This in turn is soldered to a pivoting lever arm, which gets a 1 ounce weight on the end.

Well, of course, there is no way the plug can lift without jamming, since it's solidly fixed to the lever, rather than pivoted.

This failed device got me curious about safety valves, and though I have a ton of reading material about making them in Model Engineer, and many books, I also like to work out simple calculators for myself.

I had a question about what the pop off pressure of this particular valve would be (if it had been workable), so I decided to write a simple spreadsheet calculator (attached below). 

A #8 wood screw has a .164" diameter shank, so I used that in the spreadsheet, along with other plan dimensions.

(to be continued)

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #2 on: July 19, 2014, 08:27:00 PM »
Here's a the relief valve. Notice it says to solder the lever to the valve. Actually the arrow makes it almost look like the valve is soldered shut! Also note no dimensions for the lever other then overall length. And the width is indicated at 1/8", which also can't be correct. The weight is also specified as 1/2" brass rod -- well maybe that's depth but not the rod diameter!

Whoever the draftsman was for this project must have come in to work bleary-eyed the morning after, Maybe the copy editor had joined him!

« Last Edit: January 12, 2018, 10:14:04 PM by vtsteam »
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Steve
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #3 on: July 19, 2014, 09:13:08 PM »
Here's the first trial fit. Nothing has been screwed down yet. The relief valve is immovable as specified (silver soldered to the lever arm and set in a hole with .001" clearance.) I didn't actually use a wood screw, instead I turned a valve from brass stock.




Later in the day I unsoldered the parts, and re-grooved the valve. It now lifts the lever freely, though there is no yoke to capture it if it lifts too high, and the part could be lost.

Using the spreadsheet I wrote earlier, I was able to calculate the the pop off pressure of the design as drawn was probably under 10 PSI.
« Last Edit: January 12, 2018, 10:14:40 PM by vtsteam »
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #4 on: July 19, 2014, 09:29:02 PM »
I don't particularly like the hole in the pipe body being the valve seat, and the sub 10 psi relief is lower than I'd like. That is with the 1 ounce weight out at the furthest notch. The only solution is more weight, or a smaller hole. More weight starts to get cumbersome -- it might contact the boiler side.

I decided I'd prefer .125" to the .164" present bore . so I started to make a replacement screw-in valve seat of brass. I can then drill out the present valve hole, tap and mount the seat. The seat was threaded for 1/8" pipe taper.




« Last Edit: January 12, 2018, 10:15:35 PM by vtsteam »
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #5 on: July 19, 2014, 10:00:51 PM »
I've just watched the video again, and though the dial face is very blurry, I was able to make out in a still frame that the gauge is a 0 to 30 PSI model, and that he's running 10 PSI in the video, though he has a different relief valve.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #6 on: July 20, 2014, 06:32:48 PM »
Here's a commercial ball and spring relief valve -- larger than needed for this particular boiler, but typical in design. In this case the spring is located in a housing above the ball. I like that particular feature.

« Last Edit: January 12, 2018, 10:16:32 PM by vtsteam »
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #7 on: July 20, 2014, 06:44:53 PM »
Here's a classic style small boiler steam relief valve. It's the valve actually used on Polly by Tubal Cain -- David Stilldrillin recently featured one of these engines here on MM:



This one requires a bronze ball and hand wound bronze wire spring. The ball is drilled and tapped to accept a guide rod. A cupped square hole washer is also required. The valve spring is located in the boiler, rather than externally.

These details make it seem difficult to me to build. I have no idea where I'd find bronze balls or wire, or how I would drill and tap the ball, and I don't like the idea of the spring being in the boiler as much as outside. Nevertheless I'm sure these give satisfaction -- just not what I'm favoring right now.
« Last Edit: January 12, 2018, 10:18:07 PM by vtsteam »
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Offline S. Heslop

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Re: Popular Mechanics Boiler
« Reply #8 on: July 20, 2014, 07:14:06 PM »
If the ball is guided by a rod, then wouldn't just a regular cone/ taper turned on the lathe work instead? It does seem weird to use a ball.

Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #9 on: July 20, 2014, 07:42:28 PM »
Hi Simon, a ball tends to be self centering, is easy to make a seat for (via light impact), and is considered to have less likelihood of jamming. You can buy balls ready made, high precision, and polished. Stainless is common, bronze isn't -- at least here.

So I was thinking this morning of how to use a stainless ball, in an external relief valve, that is a lever-weight type, instead of spring loaded, and one that doesn't require drilling a guide rod.

I kinda like the look of the lever type, and it's easy to change the relief cutoff pressure. Plus it's unusual.

Here's my present mockup cleaned up and with a weight installed using the Popular Mechanics lever valve design (sans solder) -- and it now works freely, and could probably be used as is.




But I'm still interested in making a valve of my own design, so I've been experimenting today with fabrication.

« Last Edit: January 12, 2018, 10:19:46 PM by vtsteam »
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #10 on: July 20, 2014, 07:57:37 PM »
So today I was thinking about how to solder a stainless steel ball to a guide piece, without getting silver solder on the working valve portion of the ball. We're talking about a 5/32" diameter ball (4mm).

I didn't have much faith that I could manage a strong butt joint to thin wire, or keep the solder masked properly.

Then I thought of a possible way to do it with strip brass, so had to try an experiment:

Spotting with 1/8" drill -- new valve seat also shown:

« Last Edit: January 12, 2018, 10:20:55 PM by vtsteam »
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #11 on: July 20, 2014, 08:02:48 PM »
The ball in place. The real question was whether I could solder something this small without getting solder in the wrong place.

« Last Edit: January 12, 2018, 10:21:39 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #12 on: July 20, 2014, 08:09:59 PM »
The setup for soldering. Flux paste and a tiny sliver of silver solder. I decided to heat from the bottom, as I was sure my torch would blow these bits right off the brass strip:

« Last Edit: January 12, 2018, 10:22:17 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #13 on: July 20, 2014, 08:20:35 PM »
It worked!  :ddb:

I did have to steer the silver with a tiny bit of wire because the flux boiled and moved it away from the ball. But it did work.

Here's a close-up outside in stronger light:

« Last Edit: January 12, 2018, 10:22:54 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #14 on: July 20, 2014, 08:23:59 PM »
« Last Edit: January 12, 2018, 10:23:38 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #15 on: July 20, 2014, 08:28:32 PM »
And how the valve would go together:



« Last Edit: January 12, 2018, 10:24:18 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #16 on: July 20, 2014, 08:51:39 PM »
I'm waiting for gauges to arrive, since I want to hydrostatic test the boiler, check the pop off of any relief valve used, And will also have a gauge attached when working. I'm hoping to be able to run 20 lbs pressure with this boiler.

From a little Internet research, 2" electrically welded steel pipe -- sch 40 -- has a working rating of 1500 psi.

It is pierced and tapped however in this design which would reduce that, and the sch 40 CI pipe caps have a working rating of only 150 psi.

So what I'd like to do is hydrostatic test the finished boiler to 150 psi and hold for a half hour. That should give me a reasonable degree of confidence for 20 PSI in use.

One aspect of this boiler that I do like quite a bit is the ability to remove the caps and inspect and clean it periodically. And the ability to replace the copper water tubes easily.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Popular Mechanics Boiler
« Reply #17 on: July 21, 2014, 02:32:54 AM »
Steve
To limit where silver solder flows to make critical or neat joints use Tippex type writer correction fluid. The solder will not wet where the chalky deposit is left
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #18 on: July 21, 2014, 06:25:27 PM »
I'll remember that, Andrew. I guess that must be the same thing as WhiteOut here.

Today was Fun With Sheet Metal Day! I managed only one small cut on the back of the thumb.....I did everything with snips and a couple of pieces of angle iron clamped in the vise by way of a bending brake. The boiler base came together surprisingly well, for me. I have hardly ever worked in the stuff, and this was pretty heavy gauge metal I had lying out back. A good day!  :beer:

« Last Edit: January 12, 2018, 10:26:03 PM by vtsteam »
I love it when a Plan B comes together!
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #19 on: July 21, 2014, 08:23:14 PM »
« Last Edit: January 12, 2018, 10:26:48 PM by vtsteam »
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Offline tom osselton

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Re: Popular Mechanics Boiler
« Reply #20 on: July 21, 2014, 11:18:37 PM »
Well done the only thing with that ball is it won't be able to self adjust I'd rather have the ball being pushed into place.

Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #21 on: July 21, 2014, 11:31:41 PM »
Not sure what you mean Tom.

I haven't built it yet. the ball and strip was just a soldering experiment.
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Offline vtsteam

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Re: Popular Mechanics Boiler
« Reply #22 on: July 22, 2014, 07:43:57 AM »
re. self adjusting:

A ball will tend to center (within limits) in a hole if the ball isn't constrained.

In a ball and hole valve, lack of constraint means play in whatever type of linkage there is connected to the ball. If there is no play, the ball is constrained.

However, the play is not only the means by which a ball will center, but also creates the need for self-centering in the first place. If a ball is perfectly aligned with a seat and the linkage has no play, the valve will be centered when closed

Play (or clearance) is necessary in a vertical ball and stem type steam safety valve, because the valve stem must be free to slide in the tube, despite corrosion, heating effects, lapses in lubrication, etc. Clearance can't be overly restricted. Therefore the ball needs to have a range of movement to self align. And in an internal valve of this sort, steam must also be able to pass alongside the valve stem. An external vertical tube ball type is somewhat better, but the ball must have a restricted clearance range in the tube, which amounts to the same thing.

In a lever type external ball valve any play will be located in the pivot. The circumferential play can be taken up by guides near the ball. Some clearance is necessary there, just as in the vertical tube and rod types. The radial distance is well constrained in this type of valve, but not absolutely so. The pivot will have a tiny amount of play. And to the extent that there is play, there is also the ability of the ball to self-align provided that any misalignment is less than the degree of play available for self-alignment.

Where there isn't enough play to overcome misalignment the ball will enter the hole off center. This will allow the valve to leak, but won't interfere with the safety of the valve. Generally ball valves are "set" by tapping in place to slightly form the seat, in which case the seat forms to the ball and corrects a minor misalignment, and sets a very slight taper in the seat. The same thing is done with a stem and ball valve.

If grossly misaligned, tapping in place won't work. Example: in a stem and ball type valve, If the stem is attached off center to the ball, it won't work. The solution is in carefully centering the stem when attaching to the ball, Likewise for a lever system it consists in properly aligning the lever when building.

Both systems have the same requirements for initial alignment, and both can use the advantage of self centering to a small degree.


« Last Edit: July 22, 2014, 08:54:31 AM by vtsteam »
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Offline spuddevans

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Re: Popular Mechanics Boiler
« Reply #23 on: July 22, 2014, 10:43:30 AM »
It's coming along well Steve  :thumbup:

Tim
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Offline tom osselton

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Re: Popular Mechanics Boiler
« Reply #24 on: July 22, 2014, 04:35:22 PM »
I meant  more along the lines of the comercial one where the ball gets inserted against the seat with a spring used for tension mind you a rod could be used to push the ball instead of the spring so you could use the weighted arm instead of the spring that way would prevent misalignment better.