the lowest tubes at the front of the condenser,
reversing direction at the water boxes three times,
and leaving at the top of the tubes in the con-
denser. Each condenser has a pet cock for
venting entrained air and noncondensable gases.
The evaporator stages become larger in the
direction of reduced pressure. The feedwater loop
seals which extend from the bottom of evaporator
stage one through four are visible as cylinders.
An evaporator drain is located in the center of
the dished bottom of each loop seal. The flanged
brine outlet from the evaporator is at the bottom
of the fifth stage.
The distillate loop seal between the distillate
collection trough of one stage, and the condensers
of the following stages, also protrude below the
bottom of the evaporator.
If the salinity of the distillate reaches 0.065
epm per gallon, a warning device indicates the
high salinity. The salinity cell shutoff valves per-
mit withdrawal and descaling of the salinity cells
without securing the unit.
Although each stage condenser produces an
equal amount of distillate, the amount flowing
from each stage is larger than the preceding. Con-
sequently, the loop seal piping grows progressively
The total distillate production of the five
stages is withdrawn from the bottom of stage five
and pumped into the shell of the distillate cooler,
and on to the storage tanks.
The DISTILLATE COOLER is a heat
exchanger of the shell-and-tube type, in which the
heat of the hot distillate flowing around the tubes
is transferred by conduction to the cooler feed-
water flowing through the tubes.
Distillate flows into the shell space sur-
rounding the tubes through an inlet near the feed-
water outlet. The distillate is retained in the cooler
long enough to efficiently transfer its heat through
the tubes by vertically placed baffles, as it flows
from top to bottom of the cooler.
Thermometers are mounted on the inlet and
outlet piping of the cooler and on the feedwater
As the distillate leaves the cooler, it is pumped
to storage tanks, provided the salinity does not
exceed 0.065 epm per gallon. (If the salinity
exceeds 0.065 epm per gallon, a solenoid trip valve
operated by a salinity indicating cell, dumps the
Chapter 7AUXILIARY MACHINERY
distillate to the bilges or waste tank until the salin-
ity is again back to or below 0.065 epm per
Pet cocks are located on each end of the cooler
to bleed off any accumulation of air or non-
The FEEDWATER PREHEATER is a gas or
liquid heat exchanger of the shell-and-tube type,
similar in design to the distillate cooler. The
preheater is located in the feedwater line between
the condenser of the first evaporator stage and
the saltwater heater.
High pressure ships steam, first used by the
air ejectors to evacuate the stage evaporators, is
piped into the preheater shell. A series of five baf-
fles, spaced closely together in the top steam
outlet, reduce the velocity of the steam and let
the steam condense on the outside of the heat
Feedwater that has already been partially
heated in the tubes of the distillate cooler and the
five-stage condensers flows through the tubes of
the preheater via the front water box in a single
pass and acquires the heat of condensation of the
air ejector steam before leaving the preheater at
the rear water box outlet.
A salinity cell is set to energize at 0.10 epm.
It operates as a shutoff valve in the piping below
the condensate outlet to dump high salinity water
to the bilge or the drain tank. A 6-inch loop seal
in the condensate line ensures that the salinity cell
is submerged at all times.
A thermometer is located on the front of the
preheater, and a pet cock for venting is located
on the water box.
The SALT WATER HEATER is a gas or
liquid heat exchanger designed to raise the feed-
water temperature prior to its entrance into the
flash chamber of the first evaporator stage. The
saltwater heater is mounted on the operating end
of the evaporator and extends the full width of
the unit. Feedwater enters and leaves the heater
from the front water box after making four passes
through the heater.
Four thermometers are installed on the heater:
two to measure the feedwater inlet and outlet
temperatures; a third, mounted on the heater
shell, to measure the steam temperature sur-
rounding the tubes; and a fourth, mounted on top
of the heater shell, to measure the temperature