Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



38.112X 

 Figure 15-33.— Horizontal propeller-type blower 

 (view II). 



merges into the disciiarge duct, and the discharge 

 duct is joined to the boiler casing. Diffuser vanes 

 are installed justinfrontof the blower to prevent 

 rotation of the air stream as it leaves the blower. 

 Additional divisions in the curving sections of the 

 discharge duct also help to control the flow of air. 



The shaft that carried both the propeller and 

 the turbine is a single forging. The propeller is 

 keyed to the shaft and held to the tapered end of 

 the shaft by a nut and cotter pin. The entire as- 

 sembly is supported by two main bearings, one 

 on each sideof the turbine wheel, outside the tur- 

 bine casing. The main bearing at the governor 

 end is locatedinthegovernor housing, which also 

 contains the thrust bearing. The speed- limiting 

 governor spindle and the lubricating oil pump 

 shaft are driven by the main shaft of the blower, 

 through a reduction gear. 



High powered two- stage or three- stage ver- 

 tical propeller- type blowers are installed in re- 

 cent combatant ships. One kind of three- stage 

 vertical propeller-type blower is shown in fig- 

 ures 15-34 and 15-35. Figure 15-36 shows the 

 rotating assembly of the same blower. As may 

 be seen, there are three propellers at the fan 

 end. Each propeller consists of a solid forged 

 disk to which are attached a number of forged 

 blades. The blades have bulb- shaped roots that 

 are entered in grooves machined across the hub; 

 the blades are kept firmly in place by locking 

 devices. Each propeller disk is keyed to the shaft 

 and secured by locking devices. 



38.113X 



Figure 15-34. — External view of three-stage 

 vertical propeller-type blower. 



The driving turbine is a velocity- compounded 

 impulse turbine (Curtis stage) with two rows of 

 moving blades. The turbine wheel is keyed to the 

 shaft. The lower face of the turbine wheel bears 

 against a shoulder on the shaft; a nut screwed 

 onto the shaft presses against the upper face of 

 the turbine wheel. 



The entire rotating assembly is supported by 

 two main bearings. One bearing is just below the 

 propellers and one is just above the thrust bear- 

 ing in the oil reservoir. 



The blower casing is built up of welded plates. 

 From the upper flange down to a little below the 

 lowest propeller, the casing is cylindrical in 

 shape. The shape of the casing changes from cyl- 

 indrical to cone-shaped and then to square; the 

 discharge opening of the blower casing is rectan- 

 gular in shape. Guide vanes in the casing control 

 the flow of air and also serve to stiffen the 



415 



