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8
OPERATION OF THE
MODEL X-1 DISTILLING UNIT
 
A. GENERAL PRINCIPLES
 
8A1. Heat supply. Heat is supplied to the unit two ways: one, by the work done by the compressor in compressing the steam, and the other by means of the electric heaters. The heat supplied by the electric heaters is proportional to the number of heaters turned on and can be varied at will by the operator. The energy supplied by the compressor cannot be changed at will by the operator. It depends on several conditions and changes as the conditions change. As the compressor discharge pressure increases, the energy input from the compressor increases. As the speed changes, the energy input changes. At a higher speed the compressor delivers more energy. However, only a small part of this increased energy, due to the increase in the compressor speed, is actually available because all the operating conditions change accordingly.

The heat supply is affected by the formation of scale. If the condition of scaling in the evaporator remained constant, the operation would be simple. But the scale accumulates on the boiling surfaces as operation continues, and decreases the heat transfer through the walls of the tubes between liquid and vapor. Normally a certain amount of the heat can be transferred; it remains in the compressed steam discharged from the compressor. The compressor discharge pressure therefore rises; which means that there is an increase in the heat input from the compressor.

8A2. Feed rate. The matter of feed rate is very important, and must be thoroughly understood in order to operate the unit correctly. The amount of heat which the feed can pick up depends on the rate at which it flows through the tubes of the heat exchanger and the steam chest of the evaporator. If the feed rate is slow, the water picks up more heat during that passage because it is longer in contact with the hot tubes. If the feed rate is fast, the water picks up less heat, for it has less time to do so.

  Experience has shown that with this type of unit a minimum feed rate of 70 gph is necessary in order that the rate of scale formation may be kept low. The unit is designed, therefore, so that sufficient heat is supplied to maintain vaporization of the feed, normally at a minimum feed rate of 70 gph with a compressor speed of about 2,000 rpm. If the total heat supply decreases, so that boiling is stopped, it is possible to restart the boiling by slowing the feed rate. This, however, causes a material increase in the rate of scale formation and a high degree of salinity in the distiller. Lowering the feed rate under 70 gph is therefore not permissible, except perhaps in an emergency, and then only for a short period.

If the heat input to the unit drops, the proper remedy is to increase the heat input by turning on more electric heaters.

8A3. Heat loss. Heat is lost from the unit through the insulation and in the hot condensate and overflow streams. The condensate is at a constant temperature. Its rate of flow depends on the compressor speed and will be substantially constant at a given compressor speed. Hence the heat loss in the condensate stream is substantially constant. The overflow is also at a constant temperature, but its rate of flow depends on the feed rate. The heat loss in the overflow stream accordingly varies directly with the overflow rate or the feed rate.

8A4. Heat balance. If more heat is being supplied to the distiller than is required to balance the losses, more atmospheric pressure steam than the compressor requires will be generated. This will tend to build up a pressure above the feed in the evaporator and will cause the manometer pressure to rise. Increasing the feed rate will give more brine overflow, increase the heat loss, and make the manometer pressure stop rising and come down. Turning off the electric heaters would have the

 
(46)

same effect in balancing the heat input against the losses.

NOTE. In this discussion, where ever reference is made to manometer pressure rising and falling is to be understood that some installations are fitted with a compound gage instead of a manometer. The pressure gage will register the same rise and fall in the vapor pressure as the manometer.

Should the heat losses be more than the energy input, an insufficient amount of atmospheric pressure steam will be generated. A partial vacuum will be produced in the vapor separator, that is, the pressure above the feed will decrease slightly and the reading in the manometer will fall. To correct this, the feed rate must be reduced or more electric heaters turned on.

This unit is operated and kept in balance solely by adjusting the feed rate and number of electric heaters in use, resulting in a sufficient amount of feed and a constant pressure level in the manometer.

The heat balance of the unit is very sensitive. All changes made in the operating conditions must be small and must be made slowly.

8A5. Automatic operation. The vapor compression distilling unit operates best when all conditions remain constant. If the voltage varies, the speed of the compressor and the corresponding output of the condensate change. This varying condition necessitates constant changes in feed rate or number of electric heaters used to keep the unit in perfect balance. With the old type installation (units employing a manometer instead of a pressure gage), under the above conditions, or in a heavy sea, the unit should be balanced with a manometer reading of plus 2 to 4 inches. The operator then has merely to check the manometer pressure and make a slight adjustment, if necessary, to the flow control valve every 15-30 minutes when transferring condensate from the test tanks to storage.

Under normal conditions, and in a moderate sea, when the voltage is constant, the unit may be balanced so that the manometer pressure is between plus 2 inches and minus 4 inches.

Changes in air pressure inside the submarine will also have an upsetting effect on the heat balance of the unit. On the fleet type submarine this was not a serious problem because there were

  rarely any sudden or considerable pressure variations.

With the advent of the snorkel, varying hull pressures became an important consideration because air pressure changes while snorkeling sometimes are frequent and of sufficient magnitude to destroy the balance of an operating distilling plant. Since it is often necessary to run the distillers while snorkeling, conversion kits were supplied to the snorkel equipped submarines for installation on the distilling units. (See Figure 6-4.)

In this conversion, the manometer is eliminated and in its place a compound gage and pressure-static switch are installed. The gage serves the same purpose as the manometer, and the pressure actuated switch controls four of the eight heaters automatically to compensate for pressure fluctuations inside the hull.

The vent from the vapor separator to the atmosphere has been sealed off, and the pressure-static switch is set so that the pressure in the vapor space of the evaporator is maintained at between six and twelve inches of water. The entrainment separated from the vapor in the vapor separator runs into a seal cup inside the unit and flows away with the brine.

A stop valve has been installed in the evaporator level safety overflow line. This valve, when shut, prevents fluctuations in hull air pressure from being communicated to the interior of the evaporator through the brine overflow tube and funnel. The valve may be open or closed depending on the operation of the plant. It should be shut while snorkeling, but during such operations as acid cleaning or flushing it should be open because of the possibility of the normal brine piping becoming clogged at the heat exchanger. Usually the valve is opened when securing the plant, prior to flushing and left open until the units have been filled when placing the plant in operation (valve in question is valve "B" in Figure 6-4).

This conversion has largely overcome the problems caused by varying conditions and makes the operation of the distilling plants semi-automatic.

8A6. Continuous operation. For continuous operation, the unit should be secured every 24 hours and the oil levels in the compressor checked. It may be restarted immediately. If the unit is

 
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shut down more often, check the oil levels in the compressor before every start. Add oil when necessary.

A low feed pump discharge pressure indicates a dirty feed strainer. In such a case, switch to the other strainer and clean the dirty one. The strainers are located between the pump discharge and the gage.

8A7. Belts. As the belts wear and become loose, the variable pitch sheave on the compressor motor pulley must be tightened to take up excess slack in the belt. This increases the diameter of the pulley section in which the belts ride and gives a higher compressor speed. The maximum allowable speed of the compressor is limited only by the allowable motor overload. The speed of the compressor

  should not be such that the motor current exceeds 1.2 times its rated number of amperes as indicated on the motor nameplate.

8A8. Emergency operating. In an emergency, the unit may be operated longer than 500 hours without cleaning. However, when the compressor motor is overloaded by 20 percent as indicated by the ammeter, the unit must be secured and cleaned. Further operation may burn out the motor.

8A9. Distilling fresh water. Operating the unit on distilled fresh water for the last 10 to 20 hours from port, will tend to reduce the scale formation and will extend appreciably the number of hours between cleanings. The unit should be operated on fresh water in the same manner as it is on sea water.

 
B. STARTING THE MODEL X-1 DISTILLING UNIT
 
8B1. Starting routine. The following directions are for the Model X-1 (or Model AAA--1) distilling unit equipped with a G.M. 3 lobe helical compressor. Instructions for starting units converted for snorkel operation will be described in Section 8F.

a. Turn on the main power switch.

b. Line up the valves in the feed, condensate, brine overflow and vent lines.

c. Start the feed pump. Check the feed pressure gage, venting the feed pump if necessary. The minimum feed pressure is 25 pounds.

d. Open the feed flow control valve and observe the flow in the feed rotameter; adjust the feed so as to have a flow of 90 gph.

e. When the flow begins in the brine overflow rotameter, secure the flow control valve and the feed pump.

f. Turn on the electric heater switches, checking the ammeter as each switch is turned on.

CAUTION. The electric heaters will burn out unless covered with water. Do not turn on the electric heaters without first filling the unit with water, as evidenced by a flow in the brine overflow rotameter.

g. Check the following in preparation for starting the compressor motor

Bypass valve. The bypass valve must always be fully open when the compressor is started.

  Belts. Belts must have slack. Belts that are too tight will cause the compressor to bind and will overload the motor.

Desuperheater water. Check the water level in the tank. The tank should be at least half full.

Oil levels in compressor. Compressor oil levels must be midway in the sight glasses when the compressor is not running.

CAUTION. Use only Navy No. 9370 or SAE 40 oil in the compressor. Rheostat. Motors must always be started at the lowest speed with the rheostat all the way to the left.

h. Start the compressor motor 2 hours after turning on the, electric heaters.

CAUTION. Check motor ampere reading. If it is greater than 1.2 times the rated motor current as indicated on the motor nameplate, secure the compressor motor and wait an additional 10 minutes before starting.

i. Start the desuperheater drip at a very rapid rate.

CAUTION. Use only distilled water for the desuperheater drip.

j. Admit some water to the manometer through the fill valve at the bottom shortly after starting the compressor.

NOTE. The unit may still be taking in air through the manometer and will draw up the water. However, in a short time the water will return and the unit will stop taking air.

 
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k. When the manometer seals, add enough water to completely fill the large outer tube. The water level in the outer tube will now be at zero.

NOTE. Two indications that the unit has reached the point where feed must be added are (1) a drop in the compressor pressure, and (2) an overflow of water through the overflow rotameter. The pressure drop is caused by the manometer sealing itself and stopping the compressor from drawing in air. The overflow is caused by the boiling over of water from the steam chest. This overflow will stop as soon as the excess water has boiled over.

l. Set the compressor speed at approximately 2,000 rpm. Note the ammeter while adjusting the compressor speed. Do not exceed 1.2 times the rated motor amperes as indicated on the motor nameplate. If a tachometer is not available, adjust the motor speed to produce 45- to 50-gph condensate rate.

m. When the manometer reads plus 2 inches (the level in the inside tube 2 inches above the level in the outer tube), start the feed pump and adjust the flow control valve to give a 5-gph flow in the feed rotameter.

n. When the manometer reads plus 4 inches, set the feed rate at 10 gph.

NOTE. When the manometer does not rise to a plus 4 inches reading with this feed rate, or if the manometer goes up very slowly, trouble or unusual conditions are indicated. Read the instructions for starting the unit with low voltage or low compressor speed and proceed accordingly. See Section 8E3.

o. When the manometer reads plus 6 inches, set the feed rate at 15 gph.

NOTE. If, in actual operation, the manometer overflows when the above rates of feed are added it may be necessary to increase the amounts to as much as 10, 20, and 30 gph when the manometer reads plus 2, 4, and 6.

p. When the manometer level starts to go above a plus 6 inches reading with a 15-gph feed rate, vent the steam trap and start closing the bypass valve slowly, keeping the manometer above plus 3 inches and keeping the compressor discharge pressure below 6 pounds.

q. When the bypass valve is entirely closed, increase the feed rate 10 to 20 gph at intervals not to

  exceed 30 seconds as indicated by the manometer level, until the feed rate is about 70 gph.

The unit is now operating and making condensate, but it will require a slight adjustment of the feed rate during the next 2 hours to achieve a balance. The balance will be indicated by the pressure level in the manometer.

NOTE. Do not increase the feed rate when the manometer is on the minus side or falling.

r. Balance the unit by adjusting the flow control valve to obtain about 70-gph minimum feed rate, and use enough electric heaters so that the manometer will balance and remain constant at a point between plus 2 inches and minus 4 inches.

s. Adjust the desuperheater drip to give a minimum compressor pressure. Increasing the number of drops per minute lowers the pressure up to a certain point where a further increase in the desuperheater drip will cause the pressure to increase. The desuperheater drip should be kept adjusted to give this low point of compressor pressure. As the evaporator scales up, a faster drip rate will be required. A dirty evaporator will require a small steady stream in the drip sight glass.

t. Operating details:

To increase the overflow-increase the feed.

To decrease overflow-decrease the feed.

To make the manometer rise-turn on the electric heaters or reduce the feed rate.

To make the manometer fall-increase the feed rate or turn off the electric heaters.

To increase the condensate rate-increase the compressor speed.

To reduce the condensate rate-reduce the compressor speed.

CAUTION. The maximum compressor speed is limited only by the allowable motor overload. The normal speed is 2,000 rpm, and this is the preferred speed since it is the rated rpm for the installation. Conditions may arise when it may be necessary to increase or reduce the condensate rate by varying the compressor speed. Keep the desuperheater drip adjusted to give a minimum compressor pressure. In a heavy sea or when the voltage is fluctuating, operate the unit to balance the manometer between plus 2 inches and plus 4 inches.

 
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CAUTION. Should the unit lose heat and take in air through the manometer, open the bypass valve immediately and proceed from Step n to restart the unit.

8B2. Watch readings and log. The following are the recommended hourly watch readings: time; hours run since last cleaning; compressor pressure; compressor rpm; feed rate; overflow rate; gallons of condensate distilled; feed pressure; manometer

  reading; number of heaters on; volts; amperes; condensate salinity; fill desuperheater tank; time distillation started; and time unit secured.

Record the data from the first run of the new unit or units under the headings given above.

A log book should be kept on the distilling unit and the above data recorded at least every 50 hours. It should also be recorded just prior to and immediately after every cleaning.

 
C. OPERATION OF THE MOTOR
 
8C1. 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 started 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 in 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.

 
D. STOPPING
 
8D1. Stopping routine.

1. Fill the desuperheater tank.

2. Turn off the electric heaters.

3. Open the bypass valve.

4. Stop the compressor motor.

5. Secure the desuperheater drip.

6. Open the flow control valve to feed 70 gph and continue feeding for 15 minutes or longer. The longer the flushing, the more effective will

  be the reduction of scale formation. For longer flushing, note the overflow rate and set the feed rate equal to the overflow rotameter reading.

7. Secure the flow control valve and feed pump.

8. Secure the sea chest valves.

9. Pull the main electrical switch.

CAUTION. The unit must at all times be left full of water.

 
E. OPERATING DIFFICULTIES
 
8B1. Rise of pressure in the Model X-1 unit. A clean unit will operate with a compressor discharge pressure of about 3 pounds. The compressor   pressure will rise slowly as scale accumulates on the heating surfaces in the evaporator. This rise should be about 1/10 of a pound or less
 
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for every 24 hours of operation. If the compressor pressure rises more rapidly than this, improper operation or trouble is indicated. If the rise is only a few tenths of a pound, it is probably due to improper operation. The hourly watch readings for the past 24 hours operation should be checked. A feed rate below the minimum will cause the pressure to increase more rapidly. If all electric heaters are not in use and the feed rate is low, turn on additional electric heaters and increase the feed rate.

While starting the unit, the compressor pressure will be unaffected by the scale condition of the evaporator tubes. When the compressor is first started (2 hours after starting the heaters) the pressure will be about 3 1/2 pounds with the bypass fully open. As steam is generated by the electric heaters, the pressure will slowly fall to about 1 1/2 pounds by the time the manometer is at plus 6 inches, and it will be time to close the bypass valve (about 10 minutes after starting the compressor). As the bypass valve is closed, the compressor pressure rises. With the bypass valve fully closed the compressor pressure will be about 1/2 pound above the normal operating pressure existing immediately prior to the last time it was secured. (The scale condition of the tubes determines the normal operating pressure.) The compressor pressure will drop back to normal during the 30 minutes required to balance the unit after closing the bypass valve.

Operating difficulties usually encountered with this unit are discussed in Sections 8E2 through 8E8. Each section lists the difficulty, the probable causes, and the detection and remedy far each difficulty.

8E2. High compressor pressure. The probable causes of high compression pressure are scaled tubes in the evaporator; the evaporator boiled partially dry; a condensate buildup in the steam chest caused by the steam trap being air bound or improperly installed, the steam trap stuck closed, a plugged air vent orifice, or a restriction or closed valve in the condensate line; or an air buildup in the steam chest caused by a plugged, restricted, or excessively small steam chest air orifice, a restricted vent line, an air leak in the evaporator or excessive air in the feed.

The detection of each of these possible causes and the remedy for each, are as follows:

  a. Scaled tubes in evaporator. After an extended period of operation, scale will gradually build up on the tubes, The compressor pressure should increase about 1/10 of a pound or less during 24 hours of operation due to the accumulation of scale on the inside of the tubes in the evaporator. If the compressor discharge pressure rises more rapidly than this, improper operation or trouble is indicated.

b. Evaporator boiled partially dry. If the level of the salt water inside the tubes is too low, heat cannot be transferred effectively and the compressor pressure rises.

Low water inside the tubes is the most frequent cause of compressor pressure going above 6 pounds when closing the bypass valve. The manometer will usually be rising rapidly and may even go over plus 10 inches. Stop closing the bypass valve at 6 pounds and increase the feed rate to 60 gph.

NOTE. If the pressure starts to fall, low water is indicated. Continue closing the bypass valve as the pressure falls and resume normal operation. If increasing the feed rate as described above fails to cause compressor pressure to fall, the water level is not too low. Proceed as follows to determine the trouble:

c. Condensate buildup in the steam chest. Condensate is normally taken from the steam chest as it is formed. If the flow of condensate is restricted, it builds up in the bottom of the steam chest, blanks off part of the tubes, reduces the effective surface, and causes the compressor pressure to increase. Only a small amount of condensate is made before the bypass valve is closed. However, as soon as the bypass is completely closed, the unit is making condensate at rated capacity. Condensate buildup is the next most probable cause of a high pressure on starting.

If the condensate is building up in the evaporator, the manometer will react normally while the unit is being started until after the bypass valve is closed. From this point on, the manometer will tend to fall as the feed rate is increased and it will be impossible to bring the feed rate up even to the normal condensate rate without the manometer falling to a minus 10-inch reading and taking in air. Upon closing the bypass valve, the compressor discharge pressure will be only slightly above normal, but will increase at the rate of 3 pounds in 30 minutes. The condensate buildup

 
51

will also cause a steady, small stream of water to be discharged from the open vent pipe out of the bottom of the exchanger.

Check as follows for the cause of the condensate buildup: Vent the steam trap for about a minute until water or steam appears. If steam is discharged, the condensate is probably not building up in the steam chest. Check other causes of high pressure. If water is vented from the steam trap, the condensate may be building up in the steam chest. Check the condensate rate by breaking the line to test tanks or by opening the sample cock on the cold side of the heat exchanger. If the condensate rate is low or zero for the given compressor speed, something is wrong with the mechanism of the steam trap. Secure the unit and inspect the mechanism steam trap. Check to see that the condensate line is open and not restricted.

d. Air buildup in the steam chest. The steam chest air vent orifice is of such size (3/64-inch for X-1 units) that all of the air normally dissolved in the sea water will be continually vented from the steam chest. Accumulation of air in the steam chest will blank off some of the tubes, reduce the effective surface, and cause the compressor discharge pressure to increase.

e. Plugged, restricted, or too small steam chest air vent orifice or a restricted vent line. If the vent orifice or vent line is entirely plugged or restricted, the manometer will tend to seal a little sooner than normal, but will react entirely normally from that point on. The compressor discharge pressure will be substantially above normal as soon as the bypass valve is closed, The unit will otherwise be normal in appearance and operation with the exception of the compressor discharge which will continue to rise at about the rate of 2 pounds in 30 minutes after the bypass valve is closed. If the vent orifice is only partially plugged or too small, the compressor discharge pressure will not rise so fast and may stop rising. The unit will operate normally except that a higher pressure may exist than the scale or compressor speed will indicate. Place a cup of water over the open end of the vent pipe at the bottom of the heat exchanger and look for air bubbles. Air bubbles indicate that the vent line or orifice is not entirely plugged. If entirely plugged, check the valves in the vent line. Secure the unit and inspect the vent orifice.

  f. Air leak into the evaporator. When the unit is operating with the manometer on the minus side. any leak in the atmospheric pressure or compressor suction part of the evaporator will let air into the unit. The steam chest orifice will not vent this extra air and the compressor discharge pressure increases proportionally to the amount of air leakage. If the manometer is on the plus side, no air can leak into the unit; instead, steam will leak out.

If an air leak is suspected, start the unit in the usual manner, keeping the manometer always on the plus side. After the unit is in operation, test for an air leak as follows: Balance the unit with the manometer at about plus 4 inches and note the compressor discharge pressure. Increase the feed or secure heaters to balance the unit with a minus 6-inch to 8-inch manometer reading. Note the compressor discharge pressure. Balance the unit with the manometer at about plus 4 inches and note the compressor discharge pressure. If the compressor discharge pressure rises with a minus manometer, but returns to normal with a plus manometer, the unit has an air leak. Operate the unit with the manometer at about plus 4 inches or 6 inches and look at the following points for leakage of steam:

1. Loose glass in sight drip valve.

2. Loose connection between the drip valve and compressor.

3. Drip valve open and desuperheater tank dry.

4. Loose packing nut or worn rubber washers in the manometer.

5. Leak in the bypass valve packing nut.

6. The check valve after the manometer may be stuck open or worn out.

7. Loose packing glands on compressor. Loose compressor glands usually leak steam even with minus manometer, but may possibly let air leak in on a few compressors.

8. Gasket joints leaking at

(a) manhole cover
(b) top joint of evaporator shell
(c) bypass valve flange
(d) center joint of evaporator shell
(e) compressor base
(f) compressor top

g. Excessive air in feed. Check the feed rotameter for large bubbles of air. As soon as the air is eliminated from the feed the compressor pressure will return to normal.

 
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8E3. Minimum feed rate and manometer sealing difficulty. Sometimes the unit while in operation does of take the minimum feed rate specified without the manometer falling to minus 10 inches, or while starting, the manometer takes unusually long to seal and rises very slowly or not at all, even with a small flow of feed. These difficulties are probably caused by too large a steam chest orifice; a steam leak at the compressor glands or elsewhere; low compressor speed; low heater volts or burned out heaters; or the steam trap being stuck open.

The detection of these possible causes and the remedy for each, are as follows:

When the feed rate to balance the unit (a manometer reading between plus 2 inches and minus 4 inches) with all the electric heaters on, is below the minimum feed rate specified, the heat losses are excessive or the energy input insufficient.

a. Steam leak at the compressor glands or elsewhere. The usual source of excessive heat losses is a steam leak at the compressor glands or elsewhere. Even a small steam leak can cause a high loss of heat and must be corrected. The following conditions will give an insufficient energy input:

1. Burned out or shorted electric heaters or a blown heater fuse. To determine while operating the unit whether an electric heater is defective, turn each switch off, then on. Note the change in the ammeter reading. Fix or replace the heater at once.

2. On installations (submarines particularly) where the back pressure on the condensate is low, a stuck open steam trap will cause excessive heat loss and the manometer will be very erratic. Starting will be very difficult.

b. Low compressor speed or low heater voltage. With a scaled evaporator, the compressor pressure will be high, so that the unit will operate satisfactorily at low compressor speeds or with low heater voltage. A clean unit has the minimum compressor pressure and energy input. With a low compressor speed or low heater voltage, it may be impossible to maintain the minimum feed rate specified. Of course, if compressor speed is low the condensate rate will be low and the minimum feed rate required is 1.4 times the actual condensate rate. If the heater voltage is low and it is impossible to increase it, the unit may be operated at a reduced feed rate until sufficient scale

  has been formed in the evaporator. This will increase the energy input to the compressor and allow the minimum feed rate to be maintained. Operation at a feed rate below 1.4 times the condensate rate should be kept to a minimum and avoided if at all possible.

When the manometer takes unusually long to seal or will not rise readily to plus 6 inches with the feed rates as specified in starting Steps m, n, and o, under Section 8B1, check for excessive heat loss in the manner described above. Inspect the steam chest air vent orifice and check the compressor speed and heater voltage. Correct the excessive loss if any, or proceed as follows to start the unit if the manometer continues to rise slowly.

c. Starting procedure for low compressor speed or low, heater voltage.

1. Turn on the main electrical switch.

2. Line up the valves in the feed, condensate, brine overflow and vent lines.

3. Start the feed pump. Check the feed pressure gage, venting the feed pump if necessary. The minimum feed pressure is 25 pounds.

4. Open the feed flow control valve and observe the flow in the feed rotameter; adjust the feed so as to have a flow of 90 gph.

5. When the flow begins in the brine overflow rotameter, secure the flow control valve and the feed pump.

6. Turn on the electric heater switches, checking the ammeter as each switch is turned on.

CAUTION. The electric heaters burn out unless covered with water. Do not turn on the electric heaters without first filling the unit with water, as evidenced by a flow in the brine overflow rotameter.

7. Check the following in preparation for starting the compressor motor:

Bypass valve. The bypass valve must always be fully open when the compressor is started.

Belts. Belts must have slack. Belts that are too tight will cause the compressor to bind and will overload the motor.

Desuperheater water. Check the water level in the tank. The tank should be at least half full.

Oil levels in compressor. Compressor oil levels must be midway in the sight glasses when the ship is on an even keel and the compressor is not running.

CAUTION. Use only Navy No. 9370 or SAE 40 oil in the compressor.

 
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Rheostat. Motors must always be started at the lowest speed with the rheostat all the way to the left.

8. Start the compressor motor 2 hours after turning on the electric heaters.

CAUTION. Check motor ampere reading. If it is greater than 1.2 times the rated motor current as indicated on the motor nameplate, secure the compressor motor and wait an additional 10 minutes before starting.

9. Start the desuperheater drip at a very rapid rate.

CAUTION. Use only distilled water for the desuperheater drip.

10. Admit some water to the manometer through the fill valve at the bottom shortly after starting the compressor.

NOTE. The unit may still be taking in air through the manometer and will draw up the water. However, in a short time the water will return and the unit will stop taking air.

11. When the manometer seals, add enough water to completely fill the large outer tube. The water level in the outer tube will now be at zero.

NOTE. Two indications that the unit has reached the point where feed must be added are (1) a drop in the compressor pressure, and (2) an overflow of water through the overflow rotameter. The pressure drop is caused by the manometer sealing itself and stopping the compressor from drawing in air. The overflow is caused by the boiling over of water from the steam chest. This overflow will stop as soon as the excess water has boiled over.

12. When the manometer reads plus 2 inches, start the feed pump and open the feed valve to give 5 to 8 gph or less flow in the feed rotameter.

13. When the manometer reads plus 5 inches, vent the steam trap and start closing the bypass valve, keeping the manometer above minus 2 inches and the compressor pressure below 6 pounds.

14. As soon as the bypass valve is entirely closed, start increasing the feed rate 5 to 10 gph every half minute or less, as indicated by the manometer level, until the feed rate is about 60 gph.

15. Determine the condensate rate, if at low compressor speed, and maintain the minimum feed rate of 1.4 times the condensate rate.

16. Proceed to balance the unit as described in Step p under Section 8B1. For the first 3 or 4 hours of operation of a new or clean unit, at low

  compressor speed or heater voltage, it will probably be impossible to maintain the feed rate above 60 gph.

8E4. Low flow in feed rotameter. Sometimes with the flow control valve fully open and the feed pump running, the flow in the feed rotameter is low. Some of the possible causes of this difficulty are an air bound feed pump; dirty strainers on the feed pump discharge; clogged strainer on the feed pump suction; clogged or dirty flour control valve; dirty heat exchanger or scaled feed piping between the exchanger and the evaporator; or a nonfunctioning water regulating valve.

The detection of these possible causes and the remedy for each, are as follows:

a. Feed pump air bound. Open the vent valve on the feed pump and be certain that all the air is expelled.

b. Dirty strainers on the feed pump discharge. One strainer should be used at a time. Change to the second strainer, remove the cap on the first strainer and clean the screen.

c. Clogged Macomb type strainer on suction. Examine the strainer on the suction to the feed pump and clean it if necessary. Be sure to vent all air from this strainer.

d. Flow control valve clogged or dirty. Remove the valve bonnet and examine the valve. Clean if necessary.

e. Dirty heat exchanger. The heat exchanger tubes and piping between exchanger and evaporator will gradually become scaled. When the scale deposit is too great, the flow to the unit will be restricted. When this condition is reached, remove the end covers and follow the cleaning instructions.

f. Water regulating valve not functioning. Remove the cap on the top of the valve and clean out the valve. Flush water through the valve with the cap out. Replace the cap and operate the valve. If the valve cannot be made to function, remove it from the line and connect the feed pump directly to the flow control valve, regulating the feed to the unit by hand. Have the water regulating valve overhauled at a naval shipyard or tender.

8E5. Low flow in brine overflow rotameter. The probable causes of this low flow are a closed valve in the overflow line; a scaled overflow pipe; or a dirty heat exchanger.

 
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The detection of these possible causes and the remedy for each, are as follows:

a. Valve closed in overflow line. Check all valves in the overflow line, making certain that they are open.

b. Overflow pipe scaled. After an extended period of operation, the overflow pipe from the evaporator to the brine overflow pump and heat exchanger becomes scaled. Disassemble this pipe and clean it according to the instructions given.

8E6. Salt in condensate. Salt may accumulate in the condensate because of a salt leak in the exchanger; worn fiber bushings on the exchanger tubes or a salt leak in the exchanger; or because of a salt leak in the evaporator caused by too high a water level in the evaporator, a restriction in the vent line or a tube leak in the evaporator.

The detection of these possible causes and the remedy for each, are as follows:

When the condensate in the test tanks shows salt, check the salinity of the condensate between the evaporator and the exchanger and check the salinity of the water in the desuperheater tank. If the desuperheater tank has high salinity, secure the drip to the compressor and check the salinity of the condensate before and after the exchanger every 5 minutes.

a. Salt leak in exchanger and worn fiber bushings. With no desuperheater drip, the salinity of the condensate should be satisfactory before the exchanger but should be high after the exchanger. Secure the unit, remove the covers on the exchanger, and look for leaks around the tubes and bushings. The exchanger is full of condensate and any leak usually shows up as soon as the covers are removed. However, if no leaks show up, place small pipe sleeves over the studs and tighten the units securely. Put 10 to 15 pounds of air or water pressure on the condensate, and check the tubes and bushings again for leaks. Replace any leaky tubes using new fiber and metallic bushings. If a bushing leaks, remove the bushings from the lower three rows of the exchanger tubes and repack with new fiber and metallic bushings. It is not improbable that the unit will make distilled water even though the fiber bushing has worn out. In this case, the condensate is leaking into the feed. Check the condensate rate, and check the salinity of the condensate drawn from the exchanger while the unit is not running. If a bushing has gone, the

  condensate rate will be low and will be salty when the unit first starts distilling.

IMPORTANT. Experience shows that the bushings on the hot feed and brine tubes will wear out after about 1,500 to 2,000 hours' operation. Replace fiber and metallic bushings on the lower four rows of the feed and overflow tubes after every 1,500 hours of operation on the heat exchanger. Completely repack the entire exchanger (feed, 3/4-inch tubes, and condensate, 1 1/4-inch tubes) after every 3,000 hours of operation on the heat exchanger.

b. Salt leak in evaporator. 1. The water level may be too high in the evaporator because of a restricted overflow line on surface craft, or a restricted safety overflow vent line on submarines. If the overflow line becomes restricted, sea water will build up in the evaporator. When the level approaches the vapor separator baffles, excessive entrainment will be carried over and will cause the condensate to be salty. The flow out of the vent from the exchanger will be a steady stream. Also, the overflow rotameter will read lower than normally for a given feed rate. If the safety overflow line on submarines is kept open, a sea water buildup in the evaporator is impossible.

2. Restriction in vent line. If the vent line is restricted or has a seal, entrainment will not be vented from the vapor separator and may buildup, causing salt to be carried over into the condensate. Check the vent line for a seal or restrictions.

3. Tube leak in evaporator. If the leak is only a small one, the unit will probably make good condensate, but salt water will leak into the steam chest when the unit is not in operation. If the leak is a large one, the condensate will be salty during operation. Remove the manhole cover, fill the evaporator to the level of the funnel, and start the compressor. Close the bypass valve to obtain a 5-pound discharge pressure and look for air bubbles. Replace or reroll the leaky tube.

8E7. Noisy compressor. A noisy compressor may be caused by insufficient or too low viscosity oil; tight belts; or worn gears or bushings.

The detection of these possible causes and the remedy for each, are as follows:

a. Insufficient or too low viscosity oil. Check the level of oil in the oil sight glasses when the compressor is not running and add sufficient oil

 
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to show about halfway in the glasses. Use only Navy Symbol 1150 or SAE 70 oil in Roots-Connersville compressors. Use only SAE 40 or Navy Symbol 9370 oil in General Motors compressors. Lower viscosity oil than specified will hasten the wearing of the gears.

b. Tight belts. The belts between the motor and the compressor must be adjusted so that the belts will bow out about an inch when the compressor is running. Belts that are too tight will cause the compressor to bind. Adjustment may be made with the variable pitch drive on the motor.

c. Worn gears or bearings. Worn gears or bearings should be replaced by a naval shipyard or tender.

8E8. Excessive compressor motor current. This high current may be caused by belts that are too tight, compressor packing that is too tight, or by a worn compressor.

The detection of these possible causes and the remedy for each, are as follows:

a. Too-tight belts. Adjust the belts with variable pitch drive so that the belts will bow about an inch on the slack side during operation.

b. Compressor packing too tight. Loosen the packing gland and allow the compressor to operate until the steam blows out of each gland. Tighten the glands evenly and only to a point where steam does not leak.

c. Worn compressor. Have the compressor changed as soon as possible.

8E9. Low feed rate. Sometimes the feed rate to the balance unit is below the minimum when all

  the electric heaters are being used. This condition may be caused by a steam trap being stuck open, a dirty heat exchanger, leaky compressor packing glands, electric heaters not all operating, or insufficient compressor speed.

The detection of these possible causes and the remedy for each, are as follows:

a. Steam trap stuck open. Shut down the unit, remove the flanged cover on the trap, and check to see that the mechanism moves freely.

b. Dirty heat exchanger. Clean the heat exchanger as directed in the section on cleaning.

e. Leaky compressor packing glands. Tighten the packing glands carefully until no steam leaks. Pull down slowly until steam just stops leaking, otherwise the packing will be too tight. Change the packing when necessary.

d. Electric heaters not all operating. The operation of the electric heaters may be noted by snapping the heater switches on and off, one at a time, and observing the ammeter readings. If the ammeter readings do not change in accordance with the heater requirements when operating a particular switch, a fuse may be out, the wiring require testing, or a heater must be changed.

e. Insufficient compressor speed. On d.c. units, speed up the compressor with the field rheostat. On a.c. units expand the variable pitch drive as much as possible on the motor without having the belts too tight. If the compressor speed is still too low, follow the operating instructions for low compressor speed.

 
F. DISTILLING UNITS WITH SNORKEL CONVERSIONS OPERATING INSTRUCTIONS
 
8F1. These instructions and starting procedures approximate the procedures outlined for the Model X-1 (AAA-1) before their conversion.

STARTING:

IMPORTANT: Before starting unit, pump bilges so that hot pipes connecting heat exchanger and evaporator are not submerged. During operation keep bilge low enough to keep these lines out of the water.

1. Turn on the main electrical switch.

2. Check the valves in the feed line so that there will be an unrestricted flow of water.

3. Start the feed pump. Check the feed pressure gage, venting the feed pump if necessary.

  4. Open the feed flow-control valve and observe the flow in the feed rotameter.

5. Check the valves in the brine overflow line so that there will be an unrestricted flow of water and observe the brine overflow rotameter.

6. Vent overflow lines at high points for entrapped air. If during operation with a feed rate below 90 gph overflow comes out safety vent, vent high points on overflow line. When the flow begins in the brine overflow rotameter, secure the flow control valve and the feed pump. (UNIT IS NOW FILLED WITH WATER.)

7. Turn on all manual and automatic control electric heater switches, checking ammeter as each switch is turned on.

 
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CAUTION. The electric heaters will burn out unless covered with water. Do not turn on electric heaters without first filling the unit with water as evidenced by a flow in the brine overflow rotameter.

8. Check the valves in the condensate line so that there will be an unrestricted flow of water.

9. Check the following in preparation to starting the compressor motor:

a. Bypass valve. The bypass valve must be fully open when the compressor is started.

b. Belts. Belts must have slack. Excessively tight belts will cause the compressor to bind and will overload the motor.

c. Oil level in compressor. Compressor oil levels must be midway in the glasses when the ship is on an even keel and the compressor is not running.

CAUTION. Use only Navy Symbol 9370 or SAE 40 oil in the compressor.

d. Rheostat. Motors must always be started at the lowest speed with the rheostat all the way to the left.

10. Start the compressor motor when pressure switches cut out the automatic heaters about one and one-half hours after turning on the electric heaters.

CAUTION. Check compressor motor amperage. If more than 1.2 times rated motor current as shown on the motor nameplate, secure motor and wait an additional 10 minutes before starting. Allowance must be made for the current drawn by the heaters.

11. Start the desuperheater drip at a very rapid rate.

CAUTION. Use only distilled water for the desuperheater drip.

12. Set the compressor speed at about 2,000 rpm. Note the ammeter while adjusting the compressor speed. Do not increase speed so that ammeter reading of motor current will exceed 1.2 times rated motor current as shown on motor nameplate. If tachometer is not available adjust compressor speed to give about 45 gph of condensate.

13. When the gage shows between 2 inches and 4 inches pressure, start the feed pump and adjust flow control valve to give 5 gph flow in the feed rotameter.

14. When the gage reading reaches 4 inches pressure set the feed rate at 10 gph. IMPORTANT:

  If gage will not rise to 4 inches reading with 5 gph, feed rate, or rises slowly, trouble or unusual conditions are indicated. Read instructions for starting unit with low voltage or low compressor speed and proceed accordingly. Section 8F2.

15. When gage reaches 6 inches pressure, increase the feed rate to 15 gph.

16. As the pressure starts to go above 6 inches with a feed rate of 15 gph, start closing the bypass valve slowly, keeping the gage reading on the pressure side and the compressor discharge pressure below 6 pounds.

17. When the bypass valve is entirely closed, increase the feed rate by 15 to 20 gph at intervals not to exceed 30 seconds, until the feed rate is about 70 gph (see note). The unit is now operating and making condensate, but will require a slight adjustment of the feed rate during the next 30 minutes to balance the unit as indicated by the gage.

NOTE. DO NOT INCREASE FEED RATE WHEN THE GAGE READS ON THE VACUUM SIDE AND FALLING.

18. Balance the unit by adjusting the flow-control valve for a 70 gph minimum feed rate. Then, depending on feed water temperature keep as many heaters going as is necessary to hold the gage reading between 6 inches and 12 inches pressure.

(NOTE. For full operating efficiency during high voltage of battery charge, increase feed slightly. This will also tend to keep compressor pressure normal.)

Under most conditions, the two switches (four heaters) that operate automatically will be sufficient to maintain this pressure. However, if feed water is very warm, only one switch (two heaters) in automatic operation might be necessary, or if feed water is extremely cold, the manual switched heaters on continuously, might be necessary to maintain the 6 inches to 12 inches pressure reading.

19. Adjust the desuperheater drip to give a minimum compressor pressure.

20. OPERATING DETAILS.

To increase overflow-increase feed.

To decrease overflow-decrease feed.

To make gage pressure rise-turn on electric heaters or reduce feed.

To make gage pressure fall-turn off electric heaters or increase feed.

 
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To increase condensate rate increase compressor speed.

To reduce condensate rate-decrease compressor speed.

CAUTION. Maximum speed of compressor is limited only by allowable motor overload. At no time increase compressor speed overload to more than 1.2 times the rated amperage. Keep the desuperheater drip adjusted to give a minimum compressor pressure. In a heavy sea, or when voltage is fluctuating because of high speed operations on battery, operate the unit to balance the gage pressure at 6 inches to 12 inches.

CAUTION. Should the unit lose heat and the gage indicate a vacuum, open the bypass valve immediately and proceed from step 15 to restart unit.

8F2. Starting procedures for low compressor speed or low heater voltage.

Follow starting procedure, steps 1 through 12, and proceed as follows for steps 13 through 17.

  13. When gage reads 2 inches pressure, start feed pump and open feed valve to give 5 to 8 gph in feed rotameter.

14. When gage reads 5 inches pressure, vent steam trap. Start closing bypass, keeping gage reading above 2 inches vacuum.

15. When bypass valve is entirely closed, increase feed rate by 5 to 10 gph about every 30 seconds, until feed rate is about 60 gph. (See note below.)

The unit is now operating and making condensate.

NOTE. Do not increase feed rate when gage indicates a vacuum and falling.

16. Determine condensate rate, if compressor speed is low, and maintain minimum feed rate of 1.4 times condensate rate.

17. Proceed to balance units as from step 18. For the first three or four hours operations of a new or clean unit at low compressor speed or heater voltage it will probably be impossible to maintain feed rate above 60 gph.

 
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