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Popular Mechanics Boiler
vtsteam:
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.
vtsteam:
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.
vtsteam:
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.
S. Heslop:
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.
vtsteam:
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.
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