I had the same misgivings about the still head when I started to
build one,and contacted the still designer(Bob Lennon) and he
explained it the open top, better than I could ever do, so here it
From the still designer "Stillmaker"
"Contrary to intuition, the condenser shell on the still is left
open to the
This is not a mistake, and to cap or seal the shell would cause the
pressures inside the still to rise to a dangerous level, and
would blow the thermometer/safety cap off the column.
And while it seems intuitive that the vapours would be lost to the
at this point, sometimes intuition can be misleading.
What really happens, if you take a closer look at the still
that a relatively large volume of hot saturated vapour is reduced to
small volume of a few drops of distillate as the vapour passes over
This reduction in volume causes a partial vacuum or lower pressure
point. When that happens, the outside atmosphere immediately rushes
fill the void. So in reality the flow goes from the outside
the still, and not the other way around.
Because of this, no vapours are lost to the atmosphere if the still
operated properly. However, that is not to say that you could not
the condenser capacity by applying excessive heat to the boiler."
End quote I hope that explains it OK