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- 18

 

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Scraping the ice off by hand.

Shutting off the refrigeration for a time.

Defrosting by special heating batteries placed beside the evaporators.

Spraying evaporators with water.

Circulating warm outside air around the evaporators.

Defrosting with special brine heater.

Hot gas defrosting in systems with direct expansion.

 

III. .

 

1. Hot gas defrosting is used in refrigeration systems with direct expansion.

2. A brine heater is fitted in the case of indirect cooling with brine.

3. The brine is heated by electricity or steam.

4. The heat generated in the fan will be utilized for defrosting.

5. Special heating batteries use electricity, steam or hot water.

6. Scraping ice off by hand may notbe used for evaporators fitted with finned tubes, laminar fins, thin walled copper tubes.

7. The frost should be removed from tubes carefully.

8. The melt during the idle periods in the cold storage spaces.

9. In automatic plants refrigeration is shut off for a time when the ice will melt. in case of forced air circulation the fan should be kept running continuously.

 

- 19

 

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Refrigerant cylinder , continuous control , service valve , suction side of the compressor , charging pipe -, , shut off valve , to drive the air out , to fully tighten , gaseous refrigerant , gas bubble , sight glass - , remove the pipe () .

 

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1. The service valve is backseated against the rear outlet.

2. The charging pipe must be connected to the refrigerant cylinder.

 

- 20

 

3. The shut valve is opened to let the gas escape for a few seconds through the union at the compressor to drive the air out of the charging pipe.

4. Charging may continue with the compressor running.

5. Charging can be accelerated by placing the cylinder in a bucket of lukewarm water.

6. The sight glass shows how the process of charging is going on.

7. The charging pipe is removed at the and of charging before closing the junction opening.

 

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Loosen one of the units. Expel the air by degrees until it is all removed. Purging should be done.

 

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Evaporation pressure , low pressure section , compressor shaft seal , internal corrosion , machinery is operating , air collected in the receiver , , a state of equilibrium , pressure gauge , pressure corresponds to the temperature , air is present - , to remove the air , the top of the condenser , the air and refrigerant escape , by degrees , gradually , as indicated , the above mentioned , pressure differance , differance becomimg zero , loss of refrigerant , as low a temperature as possible .

- 21

 

II. . . that.

1. If the evaporation pressure is lower than the atmospheric pressure, air may be drawn into the system.

2. If the gauge shows a pressure higher than that of the cooling water, it means that the air is present.

 

III. . .

 

1. by removing the air from the system. . 2. By stopping the machine. . 3. by closing the out from the condenser. . 4. by allowing cooling water to flow. .

 

IV. .

 

1. Air may be drawn into the system when it is opened for repairs.

2. Yes, the air collects in the condenser and receiver.

3. If the gauge shows a pressure higher than that which corresponds to the temperature of the cooling water, there is air in the condenser.

4. The gauge shows pressure.

5. The unions should be loosen to remove the air. The air should be expelled by degrees because it is under high pressure.

6. Purging should be done at as low a temperature as possible.

7. There is loss of refrigerant during purging that is why it is done at as low temperature as possible.

 

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Steam turbine powered vessels , , diesel engine powered vessel , , engine room , to handle fresh water () , vertical shaft unit , centrifugal pump , rigid coupling , pump casing , split casing , two halves - , suction nozzle , discharge nozzle , disassembly of a pump , reassembly of a pump - , secured by means of studs , stuffing box , a good sign , entire rotating system , to prevent from seeping , slight clearance , discharge chamber - , grease lubricator , motor shaft end -, , operating features , power requirements - , motor rating , inlet nozzle , discharge nozzle .

 

- 3

 

3. , . .

1. What does the pump consist of?

2. What does the vertical shaft unit consist of?

3. What does the stationary part consist of?

4. What does the stuffing box consist of?

 

4. .

 

1. A rigid coupling connects the shaft to the motor.

2. A key secures (keys) the impeller into the shaft.

3. A bracket connects the motor to the pump.

4. A grease lubricator lubricates the guide bushing.

 

5. .

 

6. . .

 

1. Are the motors connected to the pumps by means of couplings. Yes, they are.

2. Are the pump casing halves connected by means of studs? Yes, they are.

3. Are the sleeve and shaft connected by means of bolts? Yes, they are.

4. Are cap nuts generally secured by means of the screw?

 

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8. Past Simple.

 

1. Did the screw secure the cap nut?

2. Did the bolt connect the sleeve and sleeve shaped shaft?

3. Did the liquid flow from the discharge chamber?

4. Did the seal ring adhere on the collar?

5. Did the packing gland press the packing tight?

 

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The vertical shaft unit consists of a one impeller centrifugal pump and of an electric motor connected to it through rigid coupling. , .

The motor is connected to the pump by means of connecting bracket. .

- 4

 

the two halves of which are connected by means of studs. .

the pump driver connecting bracket is flanged and secured by means of studs. .

The shaft is connected to the motor by means of rigid coupling. .

rigidly connected together by means of bolts. .

IV. .

 

1. The pump is fitted with a suction nozzle.

2. The pump casing is closed with a cover.

3. Impeller is keyed onto the shaft.

4. There are collars on the side of the impeller.

5. The shaft passes through the pump casing.

6. It is a good sign when drops of liquid seep through the packing.

7. The electric motor is connected to the pump by the coupling.

8. The shaft is protected from handled liquid.

 

V. :

1. The capacity of a centrifugal pump is 150 m3/hour.

2. Pumps are designed for sea and fresh water supply.

3. The pump casing is closed by a cover on the bottom.

4. Halves of a split pump are secured by means of bolts.

5. Drops of liquid can seep through the packing.

6. The clearance between the seals and a collar is very small.

7. Impeller is placed onto the shaft and is keyed.

8. The capacity of this pump is 14 HP at shaft rotation equal to 1400 revolutions per minute.

 

VI. . .

1. What is the most often used type of pumps in ships? it is a centrifugal pump.

2. Where are these pumps to be found? They are found in engine rooms.

3. What is the function of the pumps? They handle either salt water or fresh water.

* * *

1. What does the pump consist of? It consists of a one impeller centrifugal pump and of an electric motor.

2. By means of what are the two halves connected? They are connected by means of studs.

3. What is the stationary part fitted with?it is fitted with the suction and discharge nozzles.

* * *

1. Where is a stuffing box with packings formed? it is formed where the shaft passes through the pump casing.

2. How should these packings be pressed? they should not be pressed too tight.

3. Is it good when liquid seeps through the packings? it is not good, only a few drops are allowed to seep.

 

- 5

* * *

 

1. Is impeller keyed onto the shaft? Yes, it is.

2. By means of what is it fixed? It is fixed by means of shaft key.

3. How is the shaft protected against liquid? It is protected withtwo top and one bottom bushings.

 

* * *

 

1. Collars are on the sides of the impeller, aren't they? Yes, they are.

2. What is the clearance between these collars and seal rings? the clearance is very slight.

 

* * *

 

1. What lubricates packings? The liquid handled lubricates packings.

2. From where does this liquid flow? this liquid flow from the discharge chamber.

 

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Suction check valve , complete filling , discharge check valve , direction of rotation , operating requirements - , motor permissible rating , tightness of packing gland , to prevent harmful heating , pump output , switched off motor - .

 

3. .

 

1. Suction check valve and air vent valve should be open to fill the casing up.

2. You should close the air vent as soon as liquid flows out of it.

3. No, the discharge valve is opened.

4. An arrow shows the direction of rotation.

5. I must open the discharge valve slowly.

6. The motor rating is checked on ammeter.

7. Yes, the packing gland must be tightened slowly and slightly.

8. A few drops are allowed to seep through the gland to prevent harmful heating of packings and shaft.

9. The pump output is to be controlled by operating on the discharge valve.

10. The motor must be switched off, suction and discharge valves must be closed.

 

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