Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



HELICAL GEAR 



INTAKE 



147,114 



Figure 15-17.— Helical gear pump. 



herringbone gear pump; and the discharge flow 

 is, accordingly, even smoother. Since the dis- 

 charge flow is smooth in the helical gear pump, 

 the gears can be designed with a small number 

 of teeth, thus allowing increased capacity without 

 sacrificing smoothness of flow. 



The pumping gears in this type of pump are 

 driven by set of timing and driving gears, which 

 also function to maintain the required close 

 clearances while preventing actual metal-to- 

 metal contact between the pumping gears. As a 

 matter of fact, metallic contact between the teeth 

 of the pumping gears would provide a tighter seal 

 against slippage; but it would cause rapid wear 

 of the teeth because foreign matter in the pumped 

 liquid would be present on the contact surfaces. 



Roller bearings atbothendsof the gear shafts 

 maintain proper alignment and thus minimize 

 friction losses in the transmission of power. 

 Stuffing boxes are used to prevent leakage at the 

 shafts. 



The helical gear pump is used to pump non- 

 viscous liquids and light oils at high speeds and 

 to pump viscous liquids at lower speeds. 



Figures 15-18 and 15-19 illustrate twotypes 

 of lobe pumps. Although these pumps look some- 

 what like gear pumps, they are not true gear 

 pumps because the rotary elements are not capa- 

 ble of driving each other. One rotor is powered 

 by the drive shaft; the other is driven by a set of 

 timing gears. The lobes are considerably larger 



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