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|  MIL-D-18641F(SH)
3.1431 Scale preventive compound Connections shall be provided for introduction of scale
prevention compound into the salt water feed stream.
3.14.32 Proportioning pump. A proportioning pump and supply tank, in accordance with
MIL-P-21397, shall be furnished for introduction of the scale preventive compound.
.3..1.4.32.1 _Flow meter. A flow meter of design, materials, and measurement range for usc with
either feed treatment addition or on-line citric acid cleaning, shall be furnished.
3.15 Evaporators for type I, submerged tube type low pressure steam operated or type V heat
reovery units.
3.15.1 Cleaning and descaling. The tubes and tube nests shall be arranged as to be readily
removable and easily accessible for cleaning, descaling and repairs; and so that cleaning and
descaling can be accomplished with the removal of the least possible number of fittings and
connections.
3.15.2 Tubes. Two steam passes (type 1) or water passes (type V) shall be provided, The
tubes shall be so arranged that none of the heating surfaces will be exposed above the normal
working water level. The evaporator tubes may be straight and expanded into tube sheets at each
end or may be U-bent tubes expanded into an inlet/outlet tube sheet.
3.15.3 Scale preventive compound. The piping system of the distilling unit shall be provided
with a connection for injection of a scale preventing compound, so located that the compound will
pass through the tubes of all salt water feed heaters and all of the compound will pass into the
first effect evaporator shell with the feed.
3.15.4 Sump space An adequate sump space underneath the tubes shall be provided for scale
to lodge. A flat removable rover shall be provided so that the sump may be cleaned without
removing the tube nest.
3.15.5 Baffles. Baffles for suppression of wash and for moisture separation shall be fitted
over the tube nest as necessary to meet the requirements of 3.13.1.
3.15.6 Heating surface The ratio of heating surface of tubes to the disengaging surface (water
surface) shall not exceed 14.5 (type I).
3.15.7 Shell. The shell of each evaporator effect shall be fitted with two sight glasses located
just above the working water level.
3.15.8 Air vents and valves Each tube nest shall be provided with adequate air vents, and
valves shall be provided for regulation thereof.
3.15.9 Strainers. Strainers shall be provided in the evaporator shells or in the integral piping
of the distillation unit for the brine overboard pump suction and for the evaporator feed between
effects. Access shall be provided for cleaning any strainer installed inside the shell.
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