[VAC] Pressurized tanks

[K C <silvertrailer@xxxxxxxxx>]

Circular tanks are lighter in weight and stronger for
their volume then other shapes. Using them with a
pressurized sytem  then goes well with airstream
engineering esthetic.   Only spheres provide a more
efficient  shape.  Hot water tanks are cylinders for
good reasons.  I believe 
pressurized system was dropped because of cost. A good
air pump costs a lot more than a good water pump. A
good air pump for domestic water use must be able to
compress air without spitting lubricate
into the water tank.  This is not an easy thing to do
economically.