Pumps/pumping lobe rotor

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Rotary pumps forcibly transfer liquid through the action of rotating gears, lobes, vanes, screws etc, which operate inside a rigid container. Normally, pumping rates are varied by changing the rotational speed of the rotor. Rotary pumps do not require valves in order to operate. 

FIGURE 9-6. Rotor or Lobe Pump Cross Section Outlet... 

Figure 7.19. Some rotary positive displacement compressors, (a) A two-lobe blower, (b) Performance of a two-lobe blower (Rools-Connersville Co.), (c) A screw pump with one power and two idle rotors (Kristal and Annett, 1940). (d) Performance of 3.5" screw pump handling oils at 1150 rpm against 325 psig (Kristal and Annett, 1940). (e) Principle of the liquid ring seal compressor (Nash Engineering Co.). (0 A sliding vane blower (Beaeh-Russ Co.).

Rotary screw (moyno) pumps Stator has one more lobe/screw than the rotor reduce rpm for abrasives starting torque = 4 X initial torque. If particles are present, try to minimize the abrasion by using viscosity > 5000 mPa.s. Backflow or slip is reduced as viscosity increases. NPSH problems are usually not important except for suction lift, pumping from a vacuum and fluid vapor pressures of > 15 kPa. 

Figure 14c Lobe pump with single-, tvriiw, and tri-rotor, [B]...

Circumferential piston pump (figure 14d) is very similar to the lobe pump. Instead of lobe, its rotor has arc shaped pistons or rotor wings. As lobe pump, it requires timing gears to operate and its major application is in food processing, but unlike lobe pump, its slippage is less. Maximum pumping rate is 600 gpm, and maximum pressure to 500 psi. 

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