5
Introduction
Barnstead electrically heated water stills are
available in four sizes; 1, 2, 5 and 10 gallons
per hour of distilled water. The distilled water
produced by the stills contains not more than
1.0 ppm total solids, with a pH value of 5.4 to
7.2 and an electrical resistance of not less than
300,000 ohms at 25°C when the stills are
operated on most potable water. The stills are
designed to use not more than 9 gallons of
cooling water and feedwater combined, for
each gallon of distilled water produced. The still
consists of: an evaporator with its heat supply,
a condenser, and devices to control the water
level and salt concentration in the evaporator, a
Q baffle for pyrogen removal and a low water
cutoff control. The operating characteristics for
each size still are shown in the Installation
Diagram.
Evaporator
Still evaporators are the vertical, cylindrical
double-wall type with air-insulating space. The
evaporators are built sufficiently high and wide
to provide ample vapor disengaging space and
operation at low velocity.
The evaporator shell is of polished stainless
steel. The inner shell (boiler) is fabricated of
copper, brass and bronze. The evaporator
cover is brass, finished in polished nickel and is
provided with a Q baffle. All surfaces that
contact the vapor and distillate are coated with
pure tin to prevent metallic contamination. A
water level sight glass is provided on all 5 and
10 gph stills.
