Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



38.115X 

 Figure 15-36, —Rotating assembly for three- 

 stage vertical propeller-type blower. 



casing. Thepart of the casing near the propellers 

 is made in sections and is also split vertically 

 to allow removal of the three propellers when 

 necessary. The lower part of the casing, below 

 the air duct, houses the turbine. The lower part 

 of the turbine casing is welded to the oil reser- 

 voir structure. 



Although all vertical propeller blowers op- 

 erate on the same principle, and although they 

 may look very much the same from the outside, 

 they are not identical in all details. Perhaps 

 the major differences to be found among verti- 

 cal forced draft blowers are in connection with 

 the lubrication systems. Some of these differ- 

 ences are noted in the following section. 



Blower Lubrication 



Because forced draft blowers must operate 

 at very high speeds, correct lubrication of the 

 bearings is absolutely essential. A complete 

 pressure lubrication system for supplying oil 

 to the bearings is an . integral part of every 

 forced draft blower. Most forced draft blowers 

 have two radial bearings and one thrust bearing; 

 however, some blowers have two turbine bear- 

 ings, two fan bearings, and a thrust bearing. 



The lubrication system for a horizontal 

 forced draft blower includes a pump, an oil filter, 

 an oil cooler, a filling connection, relief valves, 

 oil level indicators, thermometers, pressure 

 gages, oil sight flow indicators, and the neces- 

 sary piping. The pump is usually turned by the 

 forced draft blower shaft but is geared down to 

 about one-fourth the speed of the turbine. The 

 lube oil is pumped from the oil reservoir, through 

 the oil filter and the oil cooler, to the bear- 

 ings. Oil then drains back to the reservoir by 

 gravity. 



Simple gear pumps were used in the lube 

 oil systems of older horizontal blowers such as 

 those found on DD 445 and DD 692 classes of 

 destroyers. These pumps were not completely 

 satisfactory for this use, since a simple gear 

 pump does not supply oil to the bearings when 

 the blower is turning in the wrong direction. 

 This is a serious disadvantage in forced draft 

 blower installations because of the possibility 

 that idle blowers may be rotated in reverse 

 when automatic shutters fail to close. To pre- 

 vent damage to the bearings from this cause, 

 the simple gear pumps in some horizontal 

 blowers were replaced by a special type of gear 

 pump that continues to pump oil, without change 

 in the direction of oil flow, when the direction 

 of blower rotation is reversed. This alteration 

 has been accomplished on many ships that have 

 horizontal forced draft blowers. 



Some vertical blowers are fitted with a gear 

 pump and alubrication system which is generally 

 similar to that just described for horizontal 

 blowers. However, most vertical blowers have 

 quite different lubrication systems. 



One type of lubrication system used on some 

 vertical forced draft blowers is shown in figure 

 15-37. In this system, the gear pump is re- 

 placed by a centrifugal pump and a helical- 

 groove viscosity pump. The centrifugal pump 

 impeller is on the lower end of the main shaft, 

 just below the lower main bearing. The vis- 

 cosity pump (also called a friction pump) is on 

 the shaft, just above the centrifugal pump im- 

 peller, inside the lower part of the main bear- 

 ing. As the main shaft turns, lubricating oil 

 goes to the lower bearingandfrom there, by way 

 of the hollow shaft, to the upper bearing. In 

 addition, part of the oil is pumped directly to 

 the upper bearing through an external supply 

 line. The oil is returned from the upper bear- 

 ing to the oil reservoir through an external 

 return line. 



In this system, the lubricating oil does not 

 go through the oil strainer or the oil filter on 

 its way to the bearings. Instead, oil from the 

 reservoir is constantly being circulated through 

 an external filter and an external cooler and 

 then back to the reservoir. 



The viscosity pump is needed in this system 

 because the pumping action of the centrifugal 

 pump impeller is dependent upon the rpm of the 

 shaft. At low speeds, the centrifugal pump can- 

 not develop enough oil pressure to adequately 

 lubricate the bearings. At high speeds, the 

 centrifugal pump alone would develop more oil 



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