PRINCIPLES OF NAVAL ENGINEERING 



147.115 

 Figure 15-18.— Lobe pump (heliquad type). 



than gear teeth; as a rule, there are only two or 

 three lobes on each rotor. 



There are several different types of screw 

 pumps. The mainpointsof differencebetweenthe 

 various types are the number of intermeshing 

 screws and the pitch of the screws. A double- 

 screw low pitch pump is shown in figure 15-20, 

 and a triple-screw high-pitch pump in figure 

 15-21. Both of these pumps are widely used 

 aboard ship to pump fuel oil and lubricating oil. 

 In the double-screw pump, one rotor is driven by 

 the drive shaft and the other by a set of timing 

 gears. In the triple-screwpump, a central power 

 rotor meshes with two idler rotors. 



The rotating element in a rotating plunger 

 pump (fig. 15-22) is a plunger which is set off- 

 center on a drive shaft that is rotated by the 

 source of power. The plunger is driven up and 

 down and around the chamber by the rotation of 

 the shaft, in such away as to make a sliding seal 

 with the walls of the chamber. In moving, 

 the plunger alternately opens and closes a pas- 

 sage to the discharge. 



Because of its valveless construction, the ro- 

 tating plunger pump is suitable for pumping oil 

 that may contain sand or other sediment and for 

 pumping high viscosity liquids. The pump can 

 produce a very high suction lift. 



A moving vane pump (fig. 15-23) consists of 

 a cylindrically bored housing with a suction inlet 

 on one side and a discharge outlet on the other 



side; a cylindrically shaped rotor of smaller 

 diameter than the cylinder is driven about an axis 

 placed above the centerline of the cylinder in such 

 a way that the clearance between the rotor and the 

 cylinder is small at the top and at a maximum 

 value at the bottom. 



The rotor carries vanes which move in and out 

 as the rotor rotates, thus maintaining sealed 

 spaces between the rotor and the cylinder wall. 

 The vanes trap liquid on the suction side and 

 carry it to the discharge side; contraction of the 

 space expels the liquid into the discharge line. 

 The vanes may swing on pivots, as shown in the 

 illustration, or they may slide in slots in the 

 rotor. 



The moving vane type of pump is used for lu- 

 bricating oil service and transfer and, in general, 

 for handling light liquids of medium viscosity. 



An internal gear pump is shown in figure 15- 

 24. In the gear pumps previously described, the 

 teeth project radially outward from the center of 

 the gears. In an internal gear system, the teeth 

 of one gear project outward but the teeth of the 

 other project inward toward the center. In an in- 

 ternal gear pump, one gear stands inside the 

 other. 



A gear directly attached to the drive shaft of 

 the pump is set offcenter in a circular chamber 

 fitted around its circumference with the spurs 

 of an internal gear. The two gears mesh on one 

 side of the pump chamber, between the suction 

 and the discharge. On the opposite side of the 

 chamber a crescent-shaped form stands in the 

 space between the two gears in such a way that 

 a close clearance exists between each gear and 

 the crescent. 



The rotation of the central gear by the shaft 

 causes the outside gear to rotate, since the two 



147.116 



Figure 15-19.— Two-lobe pump. 



406 



