OPERATION OF THE
MODEL S DISTILLING UNIT
A. PRIMARY OPERATIONS|
4A1. Checking the oil levels in the compressor.
The proper oil for use in the distilling unit compressor is Navy Symbol 1150 or SAE 70 for the
Roots-Connersville type and SAE 40 or Navy
Symbol 9370 for the General Motors type. The
oil levels in each compartment should be individually set after installation is completed. Pour
approximately 2/3 of a quart of oil into the front
oil compartment (pulley end) and mark the level
on the sight glass. Pour approximately 1 1/3
quarts of oil into the gear end (opposite end from
pulley) and mark the level on the glass (the levels
should stabilize about one-half full in the sight
glasses). Never use oil lighter than Navy Symbol
1150 in the Roots-Connersville compressor. The
oil levels in the compressor are critical and should
be kept as near as possible to the level indicated
by the above procedure.
The oil level in the gage glasses will not read
correctly during operation, due to the violent agitation in the oil compartments. The oil level
should be checked at least once every 24 hours of
continuous service by stopping the unit and noting
the level after about a 20-minute rest. If the level
is below the mark on the gage glass, add sufficient
oil to raise the level and then start operating.
4A2. Checking the tightness of belts. Belts may
be tightened by adjusting the variable pitch sheave
attached to the motor. Loosen the belt adjustment screws in this sheave and turn the adjustable
part of the pulley with a spanner wrench until
the belts are at proper tension. Belts, while running, should bow out about an inch on the slack
side from a straight line between the faces of the
pulleys. If the belts are pulled up too tightly
they may distort the compressor and cause the
impellers to bind. Suitable wrenches will be
found in the distilling unit spare parts box.
B. STARTING OPERATIONS|
a. Feed. Start the feed pump and open the
main supply valve on the feed line.
b. Strainers. Check the valves on the strainer
manifold to be sure the flow is open through one
c. Overflow. Open the feed valve and allow the
unit to fill to the proper level with water as evidenced by flow through the overflow cup. Adjust
the feed valve to determine the normal operating
setting. Note the setting and feed pressure for
future use. Shut the feed valve. The flow to the
unit during operation is approximately 60 gallons
per hour and the flow control valve setting will
depend on the pressure in the feed line. With a
given pressure to the feed line, the condition of the
strainers will also change the valve setting. To
determine the normal operating setting of the flow
control valve, allow water to flow through the unit
after filling and adjust the valve so that the flow
through the weir will be exactly at 50 gph.
d. Heaters. Turn on the main switch (if provided), then snap on the 4 heater switches, one at
a time. Observe the ammeter readings as each
switch is turned on to insure that all heaters and
switches are working properly.
CAUTION. Heaters are designed to operate
only while they are submerged and will burn out
unless covered with water. Do not turn the heaters on at anytime unless the unit is full of water as
evidenced by a flow through the weir.
e. Bypass. Open the bypass valve on top of the
unit and turn the field rheostat counterclockwise
all the away to the left (lowest speed).
f. Motor. About 30 minutes after starting the
electric heaters start the vapor compressor motor.
CAUTION. Always start the motor at the
lowest speed and with the bypass valve fully open.
g. Desuperheater. Start the desuperheater drip
at about 200 drops per minute, after starting the
h. Feed valve. When a surge occurs in the
overflow cup, start the feed pump and open the
feed valve to one-third of the normal operating
setting. As soon as the bypass is shut, open the
feed valve immediately to the normal operating
i. Bypass. Shut the bypass slowly when steam
begins coming out of the vent pipe and the vent
thermometer reading increases rapidly. Never
allow the compressor discharge pressure to rise
above 6.5 psi. With a clean unit, while distilling,
the discharge pressure will be 3 to 4 psi with the
bypass valve shut. At the time that the compressor is first started the water in the distilling unit
is not at its boiling point. With no steam supplied, the compressor will take in air through the
vent pipe and discharge it through the condensate
pipe. Steam will gradually form and displace
the air. In 60 to 90 minutes, the water in the unit
will boil violently, supplying more than enough
steam for the compressor. The first indication of
this boiling will be a sudden flow in the weir, even
over the top of the tube. A few seconds later the
vent temperature will rise rapidly and steam will
appear at the vent. The pressure gage will fall
about a pound from the reading indicated before
the unit started to distill. Now shut the bypass
valve slowly, allowing 30 seconds to 1 minute to
close it completely.
j. Vent thermometer. Check the temperature
of the vent thermometer after about 3 minutes of
operation, during which time steam will be escaping from the vent. The thermometer should read
212 degrees F. The thermometer sometimes gets out of
adjustment during shipment. It should read 212 degrees
F. when the vent first starts steaming. If necessary, the thermometer should be adjusted as follows: Unscrew the front cover; hold the spindle
with a screwdriver; move the pointer with a finger
so that the reading will be 212 degrees F. when free;
replace the cover.
k. Heaters. The temperature of the feed water
and the amount of scale present will determine
how many heaters must be used. After the initial
surge through the overflow weir cup, the amount
of overflow will drop off. Adjustment of the feed
valve must be made to obtain a minimum overflow
of 20 gph (indicated by the overflow level in the
weir). All heater switches must normally be left
on to maintain steady operation with this rate of
overflow from a clean unit. A high rate of overflow will retard scaling of the heating surfaces.
When an overflow rate of about 30 gph can be
maintained, some of the heaters may be turned off.
1. Adjustment of feed rate. During the adjustment of the feed rate to the unit, the vent
will stop steaming and the vent thermometer will
drop below 212 degrees F. When this takes place, reduce
the feed rate about 1/20 of a turn on the flow valve
CAUTION. Make all changes in the feed rate
slowly. If the thermometer reading continues to
drop, reduce the feed rate still further by slow
adjustment of the feed valve at about 5-minute
intervals until the thermometer reading remains
steady. The rate of drop should not be over 3 degrees
to 5 degrees F. per minute.
Control of the temperature of the vent thermometer is essential, otherwise the unit will take
in too much air through the vent, build up a high
pressure on the compression side, and shut down.
During the adjusting operation, the pressure on
the compressor gage may go up 3/4 of a pound
above normal. If this happens, additional heater
switches should be turned on until normal pressure returns and steam issues at the vent. The
additional heaters may then be turned off and
adjustments of feed rate continued. A flow
through the weir must always be maintained and
if it slackens below the required amount, the flow
rate should be gradually increased.
CAUTION. The weir tube reading is affected
for 3 to 5 minutes by any change. Always wait
for at least 3 minutes after any change before
reading the weir tube.
m. Desirable feed rate. A feed rate corresponding to an overflow of 30 gallons per hour with a
slight trace of steam coming from the vent pipe,
and a vent temperature reading 200 degrees to 212 degrees F.
may be considered good operation. The adjustment period usually requires about 30 minutes.
C. OPERATIONS WHILE RUNNING|
4C1. Means of controlling. Control of the distillation process during operation is effected
chiefly by means of the vent thermometer and the
weir. The weir reading indicates directly the rate
of overflow and indirectly the feed rate, the latter
being the factor which is to be controlled. After
the distiller is in full operation, attention need be
given only to these two controls and the pressure gage.
4C2. Operation of the vent thermometer. The
unit is usually quite stable with a constant vent
temperature between 200 degrees F. and 212 degrees F. The
vent temperature should be read at least every 30
minutes. If it has fallen below 200 degrees F. the feed
rate should be cut very slightly; if it is up to 212 degrees
F. and steaming excessively at the vent, the feed
rate should be increased slightly. The distilled
water drip for desuperheating in the compressor
should be checked from time to time to maintain
about 200 drops per minute.
A falling reading on the vent thermometer
shows that the unit is losing heat. If this is accompanied by a pulsation on the ammeter of several amperes, and the discharge pressure gage
fluctuates more than 1/2 pound, the unit is taking
air through the vent pipe. To remedy this condition turn on an additional heater switch, reduce
the feed rate slightly, then turn off the extra heater
switch. Repeat this remedy if necessary.
After the unit has been run continuously for a
period of 4 or 5 hours without any change in power
or feed conditions, a slight amount of excess heat
may be available as indicated by the appearance
of steam discharging at the vent, and the vent
thermometer rising to approximately 212 degrees F. It
is advisable to compensate for this excessive heat
by gradually increasing the feed rate until only
a slight feather of steam remains at the vent and
the vent thermometer falls a little below 212 degrees F.
Should the unit lose too much heat, the vent temperature will fall considerably below 212 degrees F. and
air will be taken in through the vent. Under this
condition the compressor discharge pressure will
rise rapidly due to overload, and the relief valve
on the head plate of the unit will blow steam. If
this happens, the bypass valve should be immediately opened wide and the unit treated as if it
were being started.
When the operators are familiar with the behavior of the indicating instruments, they should
anticipate changes in the heat balance and make
corrections accordingly. The unit will operate
over several hours after adjustments without need
of changing the rate of feed or cutting the heater
switches in or out if the power conditions remain
D. OPERATION OF THE MOTOR|
4D1. Operating the motor. The feed pressure
and motor speed should remain substantially constant to obtain the best operation. If the line
voltage varies, the speed of the compressor and the
corresponding output of the distilling unit may be
somewhat increased or decreased by turning the
field rheostat to change the speed of the motor.
Operation of the controller is obtained by pressing the start button. The motor is started through
two steps of starting resistors, and acceleration is
controlled by the action of series relays. The
relays are adjusted to close the accelerating contactors on successive current inrushes and at 30
amperes decreasing current. An electrical interlock on the final accelerating contactor opens the
coil circuit to the first accelerating contactor which
remains open during the running period.
Low voltage protection is provided and, in the
event of voltage failure, the equipment can be
restarted when the voltage has been restored to
the line by pressing the start button. Stopping
of the motor is effected by pressing the stop button.
The operation of the controller is subject at all
times to the operation of the overload relay, which
opens the circuit to the main line contactor on
excessive overloads. After the overload relay has
tripped, it will reset automatically, but it is necessary to press the start button to restart the motor.
Speed adjustment above or below normal is obtained by inserting a rheostat in the shunt field
circuit and varying the resistance.
The operation of the motor should be continuously observed during the first few hours of
operation, noting the condition of the bearings, commutator, and other parts, and observing the temperature and balance of the motor.
The heat balance of the distilling system is
sensitive and all changes in the operating conditions should be made slowly.
E. STOPPING OPERATIONS|
a. Heaters. Cut off all heaters.
b. Motor. Stop the motor.
c. Bypass. Open the bypass valve.
d. Desuperheater. Shut off the desuperheater
e. Feed. Continue feeding for 11/2 to 2 hours.
This continued feed is for flushing the tubes. The
flow during this flushing should be through the
full slot in the weir. After flushing, close the
feed valve and secure the feed pump.
f. Desuperheater tank. Fill the desuperheater
supply tank with distilled water before discharging the condensate receivers.
4E2. Retarding scale formation. Scale will gradually accumulate on the heating surfaces during
normal operation. When the unit is shut down
from time to time, it must be left filled with sea
water, as the cold sea water exerts a solvent action
on the scale.
F. HULL PRESSURE CHANGES|
4F1. Variation of hull pressure. Under ordinary
conditions the unit may be operated equally as
well under the water as on the surface. When
running submerged on the ship's main motors, the
load variation will influence the line voltage, and
the motor speed should be adjusted as well as possible with the field rheostat to maintain a constant
output of distilled water.
Increase in the hull pressure will increase the
pressure readings on the compressor gage and
raise the boiling point of the sea water in the distilling unit. Additional electric heaters should
be turned on to compensate for the additional heat
required when the hull pressure increases. A reduction in the air pressure within the hull will
tend to make the distilling unit discharge steam
at the vent.
A rapid rise in pressure within the hull will
make it impossible to increase the heat sufficiently
to maintain operations. The unit will take in air
at the vent and cease to operate. When this difficulty occurs, the bypass valve should be opened
immediately and the unit treated as in starting
Changes in hull pressure will occur for a variety
of reasons. Such changes may occur after venting the negative tank; after firing a torpedo;
when running on the engines on the surface; and
on opening and closing the air lock doors. (For
effect of snorkel operations, see Section 8A5.)
To help alleviate these conditions, a water
seal or damper is attached to the vent. The construction and operation of this vent damper are
described in Section 3A14.
G. OPERATING WITH FRESH WATER|
4G1. Distilling fresh water. To distill fresh water
taken aboard from an outside source, or sea water
distilled only once, the following variation in
operation should be followed:
a. Vapor pressure. The compressor pressure
will be about 1/2 pound lower, that is, about 2 1/2 to
3 1/2 psi with a clean unit. The reason for this is
that the feed water is fresh, and therefore its normal condensation point does not need to be raised.
The heat put into the vapor by compression in this
case is used to balance the heat loss through the
insulation, the condensate, and the brine overflow.
See Section 2A2.
b. Overflow. The rate of overflow may be reduced from one-quarter to one-half that required
for sea water distillation.
c. Heaters. Under these conditions, after the
bypass valve is shut, fewer heaters maybe used.