Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGsupply a positive pressure head for pumps usedin firefighting.Pump MaintenanceHiATMOSPHERICPRESSUREPumps require a certain amount of routinemaintenance and, upon occasion, some repairwork. Pumps are so widely used for variousservices in the Navy that it is necessary to consultthe manufacturer's technical manual fordetails concerning the repair of a specific unit.Routine maintenance, however, is performed inaccordance with the Planned Maintenance Subsystem(3-M System) requirements. Figure 15-31 illustrates the planned maintenance requirementsfor one type of turbine-driven main lubeoil pump. Similar requirements are establishedfor all pumps.Safety PrecautionsThe following safety precautions must be observedin connection witiithe operation of pumps:Figure 15-29.— Jet pump (ejector type).75.283increases gradually beyond the chamber, inorder to decrease the velocity of the dischargeand thereby transform some of the velocity headto pressure head. As the steam jet forces someof the fluid from the chamber into the dischargeline, pressure in the chamber is lowered and thepressure on the surface of the supply fluid forcesfluid up through the inlet, _D, into the chamber andout through the discharge line. Thus the pumpingaction is established.Jet pumps of the ejector type are occasionallyused aboard ship to pump small quantities ofdrains overboard. Their primary use on navalships, however, is not in the pumping of waterbut in the removal of air and other noncondensablegases from main and auxiliary condensers."^An eductor is shown in figure 15-30. As maybe seen, the principle of operation is the sameas that just described for the ejector type of jetpump; however, water is used instead of steam.On naval ships, eductors are used to pump waterfrom bilges, to dewater compartments, and to1. See that all relief valves are tested at theappropriate intervals as required by the PlannedMaintenance Subsystem. Be sure that reliefvalves function at the designated pressure.2. Never attempt to jack over a pump by handwhile the throttle valve to the turbine is open orthe power is on. Never jack over a reciprocatingpump when the throttle valve or the exhaustvalve is open.Air ejector assemblies used on condensers are discussedin chapter 13 of this text. Figure 15-30.-Eductor. 47.48412