PRINCIPLES OF NAVAL ENGINEERING 



Hi 



ATMOSPHERIC 

 PRESSURE 



75.283 

 Figure 15-29.— Jet pump (ejector type). 



increases gradually beyond the chamber, in 

 order to decrease the velocity of the discharge 

 and thereby transform some of the velocity head 

 to pressure head. As the steam jet forces some 

 of the fluid from the chamber into the discharge 

 line, pressure in the chamber is lowered and the 

 pressure on the surface of the supply fluid forces 

 fluid up through the inlet, _D, into the chamber and 

 out through the discharge line. Thus the pumping 

 action is established. 



Jet pumps of the ejector type are occasionally 

 used aboard ship to pump small quantities of 

 drains overboard. Their primary use on naval 

 ships, however, is not in the pumping of water 

 but in the removal of air and other noncon- 

 densable gases from main and auxiliary con- 

 densers."^ 



An eductor is shown in figure 15-30. As may 

 be seen, the principle of operation is the same 

 as that just described for the ejector type of jet 

 pump; however, water is used instead of steam. 

 On naval ships, eductors are used to pump water 

 from bilges, to dewater compartments, and to 



supply a positive pressure head for pumps used 

 in firefighting. 



Pump Maintenance 



Pumps require a certain amount of routine 

 maintenance and, upon occasion, some repair 

 work. Pumps are so widely used for various 

 services in the Navy that it is necessary to con- 

 sult the manufacturer's technical manual for 

 details concerning the repair of a specific unit. 

 Routine maintenance, however, is performed in 

 accordance with the Planned Maintenance Sub- 

 system (3-M System) requirements. Figure 15- 

 31 illustrates the planned maintenance require- 

 ments for one type of turbine-driven main lube 

 oil pump. Similar requirements are established 

 for all pumps. 



Safety Precautions 



The following safety precautions must be ob- 

 served in connection witiithe operation of pumps: 



1. See that all relief valves are tested at the 

 appropriate intervals as required by the Plan- 

 ned Maintenance Subsystem. Be sure that relief 

 valves function at the designated pressure. 



2. Never attempt to jack over a pump by hand 

 while the throttle valve to the turbine is open or 

 the power is on. Never jack over a reciprocating 

 pump when the throttle valve or the exhaust 

 valve is open. 



Air ejector assemblies used on condensers are dis- 

 cussed in chapter 13 of this text. 



Figure 15-30.-Eductor. 



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