PRINCIPLES OF NAVAL ENGINEERING 



conditions of load. The discharge pressure of the 

 main feed pump is considerably higher than the 

 pressure carried in theboiler steam drum. Pro- 

 vision is made for the recirculation of water 

 from the main feed pump discharge back to the 

 deaerating feed tank, in order to protect the pump 

 from overheating at very low capacity. 



SAFETY AND CASUALTY CONTROL 



In the event of a casualty to a component part 

 of the propulsion plant, the principal doctrine to 

 be impressed upon operating personnel is the 

 prevention of additional or major casualties. 

 Under normal operating conditions, the safety of 

 personnel and machinery should be given first 

 consideration. Where practicable, the propulsion 

 plant should be kept in operation by means 

 of standby pumps, auxiliary machinery, and 

 piping systems. The important thing is to prevent 

 minor casualties from becoming major cas- 

 ualties, even if it means suspending the opera- 

 tion of the propulsion plant. It is better to stop 

 the main engines for a few minutes than to put 

 them completely out of commission, so that 

 major repairs are required to place them back 

 into operation. In case a casualty occurs, the of- 

 ficer or CPO in charge of the watch should be 

 notified as soon as possible; he in turn must 

 notify the OOD if there will be any effect on the 

 ship's speed or on the ability to answer bells. 



LOSS OF VACUUM 



The major causes of a loss of vacuum are: 

 excessive air leakage into the vacuum system, 

 improper functioning of the air- removal equip- 

 ment, improper drainage of condensate from the 

 condenser, insufficient flow of circulating water, 

 and high injection temperature. 



1. EXCESSIVE AIR LEAKAGE INTO THE 

 VACUUM SYSTEM may be caused by: 



a. Insufficient gland sealing steam. 



b. Vent valve on idle condensate pump 

 open. 



c. Loop- seal filling valve open. 



d. Bypass valve on drain tank open. 



e. Drain tank float valve stuck open. 



f. Taking make-up feed from empty feed 

 bottom. 



g. Leakage of flanges, fittings, or valve 

 stem packings under vacuum. 



2. IMPROPER FUNCTIONING OF THE AIR- 

 REMOVAL EQUIPMENT may be due to: 

 a. Insufficient steam to the air ejectors. 



b. Foreign matter lodged in the air ejec- 

 tor nozzle(s). 



c. Erosion of the air ejector nozzle, over 

 a period of time. 



3. IMPROPER DRAINAGE OF CONDEN- 

 SATE FROM THE CONDENSER may be 

 caused by: 



a. Low speed of condensate pump, indi- 

 cating malfunctioning of the pump's 

 speed-limiting governor. 



b. Condensate pump air-bound because 

 of the vent connection from the first 

 stage being closed or not opened wide, 



4. INSUFFICIENT FLOW OF CIRCULATING 

 WATER may be caused by: 



a. Improper adjustment of the overboard 

 discharge valve (the main injection 

 valve being wide open whenever the 

 condenser is under vacuum). 



b. Inadequate speed of the main circulat- 

 ing pump. 



c. Plugged tubes, resulting from mud, 

 shells, small fish, or kelp being 

 trapped against the injection strainer 

 bars or in the inlet water chest. 



d. Air trapped in condenser. 



5. HIGH INJECTION TEMPERATURE 



Basically, the injection temperature limits 

 the maximum vacuum (minimum absolute pres- 

 sure) obtainable in a specific plant, assuming the 

 condenser, associated equipment, and piping 

 under vacuum to be clean and properly operated. 



Whenever there is a loss of vaccum, the first 

 step in correcting the trouble is to locate the 

 cause of the casualty. The major possible causes 

 are so numerous that no attempt will be made to 

 list the proper action required for each one. The 

 required action may be very simple, such 

 as closing the loop seal filling valve, or it may 

 be much more complicated, such as leaning the 

 main condenser or replacing air ejector nozzles. 



SALT WATER LEAKAGE 

 INTO CONDENSER 



If a condenser salinity indicator shows a rise 

 in the chloride content, the source of the contam- 

 ination must be determined immediately. To lo- 

 cate these sources, test the fresh water from 

 different units in the system by checking the 

 proper salinity indicators (if installed) and by 



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