Homestead mailing list

[Bill Jones <billj AT harborside.com>]

Despite my rush to complete the porch before the change of seasons, I 
just had to take a moment to write about my latest idea.  I figured I 
could afford to share this with the world, since no one will ever 
attempt to market it, as it's sixteen feet tall.  In order to get the 
liquid propellant to flow back to the reservoir, I had to stack all the 
stages vertically, and two stages require some height in their own 
right.  So here goes...

I call it a buoyant bladder vapor engine (BBVE).  It uses a bare minimum 
of high-tech materials, no force over 100 pounds, no pressures over 
aquarium pump levels, and no temperatures over that of hot water.  It 
assumes that you already have a tank of hot water produced from a solar 
water heater somewhere on the second floor (great for a gravity-fed hot 
shower at the end of the day).

The journey begins as a drop of fluorocarbon propellant seeps through 
the control valve, passing first through a check valve.  Because the 
boiler pressure is only around 2-3 PSI, I was able to do away with the 
boiler feed pump and replace it by an in-line five-foot tall thin column 
of liquid propellant that provides pressure through gravity alone.  The 
drop of propellant enters the "boiler" (a black metal tube illuminated 
by a solar reflector, ideally encased in a glass or clear plastic 
sheath) and vaporizes at only about 120F.  Vapor passes through a 
"slobber box" (a wide spot in the line where foaming occurs, to ensure 
that only gas travels upward) and past a pressure gauge and pressure 
relief valves.  The vapor flows up about 12 feet through a black tube 
that's kept in its own narrow solar oven (one rib of Suntuf glued onto a 
black metal sheet) so the vapor doesn't cool.

The heart of the system uses a buoyant bladder to lift a lever arm, and 
the force is transferred to the well pump handle via a pulley system.  
Vapor is injected into a bladder immersed in hot water (so the vaporized 
propellant doesn't start to cool).  Leverage converts the 10-20 pounds 
of buoyant force into almost 100 pounds of force pulling upward on a 
wire.  A 3-way valve changes position when the bladder floats to the top 
of its range, causing vapor to exit the bladder.  It must exit from the 
bottom of the water tank, because there could be a problem if vapor 
starts to cool prematurely.  Water pressure on the collapsing bladder 
drives the exhaust downward into the condenser, where copper coils 
wrapped in wet cloth are shaded in the breeze, and the condensed 
propellant flows back into the reservoir.

If you think about it, this differs from a conventional steam engine in 
one major way.  The amount of force generated doesn't depend on the 
pressure of the vapor!  It just takes enough pressure to fill the 
submerged bladder, and the amount of buoyant force is proportional to 
the size of the bladder.  The temperature required to attain this 
pressure for our fluorocarbon propellant is only around 140F.

Certainly there's a way to produce rotary motion using an old shot 
engine to convert the force, maybe with two floats opposing each other.  
I came up with this idea when I realized that I could never succeed by 
injecting propellant directly into cylinders, since tiny bubbles of 
propellant would lodge in the oil and eventually expensive propellant 
would leak out through the oil pan.  Here's the cosmic part.  When I was 
a kid a took a balloon in the pool with me one day, and marvelled at the 
steady buoyant force and the apparently high terminal velocity (never 
reached in my dad's six-foot deep pool).  I remember wondering whether 
buoyancy could ever be used to drive an engine.  The nice thing about it 
is that its totally low-tech, requiring only one little valve, some 
plastic bags, and some expensive propellant (as any vapor engine would).

Bill