PRINCIPLES OF NAVAL ENGINEERING 



UPPER BEARING 



OIL GUARD 



OIL TO 



UPPER BEARING 



PRESSURE - 



GAGE 



TACHOMETER 



CENTRIFUGAL 

 PUMP IMPELLER 



^OIL 

 RESERVOIR 

 THERMOMETER 



38.116 

 Figure 15-37. — Lubrication system with hollow- 

 shaft oil supply and external oil supply for 

 vertical forced draft blower. 



pressure than is needed for lubrication, and the 

 excessive pressure would tend to cause flood- 

 ing of the bearings and loss of oil from the 

 lubrication system. The viscosity pump, which 

 is nothing more than a shallow helical thread 

 or groove on the lower part of the shaft, helps 

 to assure sufficient lubrication at low speeds 

 and to prevent the development of excessive oil 

 pressures at high speeds. 



The hollow-shaft type of lubrication system 

 just described is still found on some vertical 

 forced draft blowers. The newest vertical 

 blowers, however, do not use a hollow shaft to 

 supply oil to the upper bearings. Instead, oil is 

 pumped to the bearings through an external 

 supply line, passing through an oil filter and an 

 oil cooler on the way to the bearings. Most of 

 these newer vertical blowers have a gear pump 

 and an additional hand pump that is used to 

 establish initial lubrication when the blower is 

 being started. Some of the newer vertical 

 blowers have a centrifugal pump and a viscosity 



pump of the type shown in figure 15-36; but these 

 blowers, like the other newer ones, have a com- 

 pletely external oil supply to the bearings in- 

 stead of a hollow-shaft arrangement. 



One feature of some of the newer vertical 

 blowers is an anti-rotation device on the shaft 

 of the lubricating pump. This device prevents 

 windmilling of the blower in a reverse direction 

 in the event of leakage through the automatic 

 shutters. The anti-rotation device is continuous- 

 ly lubricated through a series of passageways 

 which trap some of the leakage from the thrust 

 bearing. 



Control of Blower Speed 



Forced draft blowers are manually controlled 

 on all naval ships except those that have auto- 

 matic combustion control systems for the boil- 

 ers. Speed-limiting governors (discussed in 

 chapter 16 of this text) are fitted to all forced 

 draft blowers, but they function merely as safety 

 devices to prevent the turbine from exceeding 

 the maximum safe operating speed; the speed- 

 limiting governors do not have any control over 

 the turbine at ordinary operating speeds. 



Manual control of blower speed is achieved 

 by a valve arrangement that controls the amount 

 of steam admitted to the turbines. In some 

 blowers a full head of steam is admitted to the 

 steam chest; steam is then admitted to the tur- 

 bine by means of a manually operated lever or 

 handwheel that controls four nozzle valves. The 

 lever or handwheel may be connected by link- 

 age for remote operation. The four valves are 

 so arranged that they open in sequence, rather 

 than all at the same time. The position of the 

 manually operated lever or handwheel deter- 

 mines the number of valves that will open, and 

 thus controls the amount of steam that will be 

 admitted to the driving turbine. The steam chest 

 nozzle valve shafts of all blowers serving one 

 boiler are mechanically coupled so as to pro- 

 vide for synchronized operation of the blowers. 

 If only one blower is to be operated, the root 

 valve of the nonoperating blower must remain 

 closed so that steam will not be admitted to the 

 line. 



In other installations, a throttle valve is used 

 to control the admission of steam to the steam 

 chest. From the steam chest, the steam enters 

 the turbine casing through fixed nozzles rather 

 than through nozzle valves. Varying the opening 

 of the throttle valve varies the steam pressure 

 to the steam chest and thus varies the speed of 



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