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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
 
4B1. Starting

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 strainer.

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.

 
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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 compressor motor.

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 setting.

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 control.

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.

 
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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 reasonably constant.

 
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

 
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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
 
4E1. Stopping.

a. Heaters. Cut off all heaters.

b. Motor. Stop the motor.

c. Bypass. Open the bypass valve.

d. Desuperheater. Shut off the desuperheater drip.

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 operations.

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.

 
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