Principles of naval engineering - Historic Naval Ships Association

Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS38.112XFigure 15-33.— Horizontal propeller-type blower(view II).merges into the disciiarge duct, and the dischargeduct is joined to the boiler casing. Diffuser vanesare installed justinfrontof the blower to preventrotation of the air stream as it leaves the blower.Additional divisions in the curving sections of thedischarge duct also help to control the flow of air.The shaft that carried both the propeller andthe turbine is a single forging. The propeller iskeyed to the shaft and held to the tapered end ofthe shaft by a nut and cotter pin. The entire assemblyis supported by two main bearings, oneon each sideof the turbine wheel, outside the turbinecasing. The main bearing at the governorend is locatedinthegovernor housing, which alsocontainsthe thrust bearing. The speed- limitinggovernor spindle and the lubricating oil pumpshaft are driven by the main shaft of the blower,through a reduction gear.High powered two- stage or three- stage verticalpropeller- type blowers are installed in recentcombatant ships. One kind of three- stagevertical propeller-type blower is shown in figures15-34 and 15-35. Figure 15-36 shows therotating assembly of the same blower. As maybe seen, there are three propellers at the fanend. Each propeller consists of a solid forgeddisk to which are attached a number of forgedblades. The blades have bulb- shaped roots thatare entered in grooves machined across the hub;the blades are kept firmly in place by lockingdevices. Each propeller disk is keyed to the shaftand secured by locking devices.38.113XFigure 15-34. — External view of three-stagevertical propeller-type blower.The driving turbine is a velocity- compoundedimpulse turbine (Curtis stage) with two rows ofmoving blades. The turbine wheel is keyed to theshaft. The lower face of the turbine wheel bearsagainst a shoulder on the shaft; a nut screwedonto the shaft presses against the upper face ofthe turbine wheel.The entire rotating assembly is supported bytwo main bearings. One bearing is just below thepropellers and one is just above the thrust bearingin the oil reservoir.The blower casing is built up of welded plates.From the upper flange down to a little below thelowest propeller, the casing is cylindrical inshape. The shape of the casing changes from cylindricalto cone-shaped and then to square; thedischarge opening of the blower casing is rectangularin shape. Guide vanes in the casing controlthe flow of air and also serve to stiffen the415