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["WILLIAM JONES" <billj AT harborside.com>]

I've mentioned all these devices, so we might as well make it official.
1.   The Spiral Manometer
Also called the Wirtz pump or Belcher pump, it just consists of a spiral of 
hose submerged partly in water, so that the plane of the spiral is held 
vertical.  At the wide end of the spiral there's usually a little jug that 
allows it to collect water each time the hose dips under the water.  This 
plug of water moves along as the spiral turns, forcing the air collected 
between dips into smaller and smaller spaces, and also sucking in a new dose 
of air with each revolution.
The Spiral Manometer allows us to turn motion into pressurized air and water. 
 They are easily separated by gravity.  Few people can make a cylinder/piston 
combo to do the same thing, but any child can make a Spiral Manometer!
The Spiral Manometer concept can be reversed to turn pressurized water or air 
into motion (as in the proposed Wirtz bike), but it has to fed air and water 
alternately, which requires a little extra hardware.
2.   Displacement Pumps
The Stauffer pump is one type of displacement pump.  Basically compressed air 
is used to pump water, and the meniscus where the two come together serves as 
a perfectly fine piston, as long as it remains level.
It's quite possible to do the opposite, to use pressurized water to compress 
air.  Later I'll be talking about the details of using a hydraulic ram to 
compress air to higher pressures than is practical with a Spiral Manometer.
3.   Buoyancy Engines
I first started wondering about this when I took my basketball into the pool 
when I was a kid.  I mistakenly let it go right under my face, and it hit me 
hard right in the nose.  Everyone has seen a Buoyancy Engine in action, right 
down at the pet shop.  The "bubble wheel" that's so commonplace is yet so 
poorly appreciated.  It requires very little pressure to force the air to 
such a shallow depth.  Once in place, the air (and thus energy) is stored 
more-or-less permanently in place.  It can be made to produce any desired 
level of torque, just by making the the float larger.  But like the Spiral 
Manometer, it must never be made to run fast.
Buoyancy Engines come in two types.  The bubble wheel is an "open-float" 
Buoyancy Engine, since it just jettisons the charge of air with each 
revolution.  The new heat engine I've been talking about is a "closed-float" 
Buoyancy Engine, since the air is reabsorbed back into the blackbottle.