Pumps rotary lobe

Rota.ry Lobe Pumps. Rotary lobe pumps are similar to gear pumps in principle. These pumps have an added advantage of noncontacting metal parts by use of external gears, which reduces the wear, but adds complexity. Low wear and improved shear characteristics make these pumps apphcable to the food industry, where cleanliness and absence of contamination are required. These pumps produce a strong pulsing flow that must be addressed. 

Liquid ring pumps, rotary lobe blowers and root pumps presently allow only small suction volumes, which lead to a large number of machines. At a suction pressure of 100 mbar the compression of 0.34 million mN would require, for example, about 60 liquid ring pumps. 

Figure 6-45. Cut-away view of internal assembly of rotary lobe vacuum pump. By permission, Tuthiii Corp., M.D. Pneumatics Division.

Figure 6-46A. Exploded view of rotary lobe gas pump with mechanical seals and pressure lubrication for bearings. By permission, Roots Division Dresser Industries, Inc.

A typical performance range of capacides of rotary lobe vacuum pumps is shown in Figures 6-48A, 6-48B and 6-48C. Another set of curves for rotary lobe pumps, shown in Figure 6-49, provides the brake horsepower, airflow at inlet (CFM) (referred to as their standard volume at 70°F and 29.92 inch Hg abs discharge pressure—essentially atmosphere), and the temperature rise through a non-cooled (no internal or external cooling) vacuum. All data... 

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Related Calculations. Use this procedure for any type of rotary pump—gear, lobe, screw, swinging-vane, sliding-vane, or shuttle-block—handling any clear, viscous liquid. Where the liquid is gas-free, apply only the viscosity correction. Where the liquid viscosity is less than 600 SSU but the liquid contains gas or air, apply the entrained or dissolved gas correction, or both corrections. 

Vacuum blowers (vacuum pumps) are used to draw waste nitrogen, carbon dioxide, and water vapor from the adsorber vessels during the evacuation step. There are two rotary-lobe blowers operating in series. They are positive displacement machines. A timing gear arrangement maintains the close tolerances that are essential for ef cient operation. 

With respect to the gear, rotary lobe or cog-wheel-type pumps they are not recommended for sensitive proteins, since high shear forces generated in the pump head, possibly in combinations with other factors such as air entrapment, can lead to protein aggregation and de-naturation. 

PUMP, ROTARY - A pump that moves fluid by positive displacement, using a system of rotating vanes, gears, or lobes. 

In the past, environmental problems associated with the commonly used pump fluids, namely water and oil, have led to the development of dry vacuum pumps that compress without contact. Rotary lobe and screw-type vacuum pumps (Fig. 5 and 6) are the types most commonly used for industrial applications. 

The rotary lobe vacuum pump (Fig. 5) is a single or multistage vacuum pump in which the gas is sucked into the cylinder gap as illustrated. 

Fig. 5 Section through a rotary lobe vacuum pump, Dr.-Ing. K. Busch GmbH...

The rotary lobes rotate in opposite directions. Each lobe has one or two teeth, the shape of which is such that the gap between the tooth and the second lobe and cylinder remains constantly narrow. As the lobes rotate in opposite directions, the teeth move together, roll over one another and then move apart. This cycle is repeated with every revolution of the shafts according to the number of teeth. The volume beneath the inlet to the cylinder increases until the next tooth moves past. Then the volume enclosed between the teeth of the lobe is pumped until it emerges opposite the second lobe. The gas is then compressed between two teeth of the two lobes until one lobe exposes the outlet slot in the cylinder cover and the gas is expelled. 

Dry Vacuum Pumps (DVPs) These use the operating principles of rotary-lobe roots blowers, claw compressors or screw compressors, and hence require electrical power. They run dry and hence at very high temperature due to the heat of compression. Usually,... 

Dry vacuum pumps Three-stage rotary-lobe 1.5 60-240... 

Positive-displacement compressors, such as rotary lobe, screw type, or sliding-vane types, pump a relatively constant volume of vapor against whatever back pressure (resistance to heat transfer) is developed by the eveporator. The mass flow rate depends upon the inlet vapor density. Rotary lobe compressors are used for compression ratios up to about 2.0, the compression ratio being limited by mechanical and thermal distortion of small clearances inside the machine. The efficiency of positive-displacement compressors is between 60 and 75%. 

The maximum Inlet capacity of a single-stage rotary lobe compressor is about 30,000 cubic feet per minute which is equivalent to 60,000 Ib/hr of water vapor at atmospheric pressure. Positive-displacement compressors pump against whatever resistance Is developed by the evaporator discharge pressures will increase and evaporator rate will remain relatively constant as the evaporator becomes fouled. Evaporator capacity may be varied when using positive-displacement compressors by ... 

Q. There are other types of vacuum pumps, seldom found in cleaning machines. A fifth type of pump is a dry pump, which can be a screw, scroll (high speed), or claw design. Booster pumps are also dry and a generally rotary lobe type. 

Rotary Pumps. Rotary pumps are characterized by a rotary movement types include screw, lobe, vane, and gear. Figures 5-16 and 5-17 illustrate rotary-type pumps. Rotary pumps displace liquid with gears, vanes, screws, or other rotating elements. The common thread between these two groups is the positive displacement action of the device. Centrifugal pumps are often mistakenly... 

Rotary lobe pumps are a special form of positive displacement pump. They feature two lobes (Figure 9-16) that rotate against each other like intermeshing gears. They are avail-... 

Rotary lobe slurry pumps are used with certain soft slurries with mild abrasion characteristics such as wastewater and sewage disposal, flotation slimes, digested scum, lime slurry in waste treatment plants. They are also used in food processing to move potato and starch pulp, mash, food paste, tomato paste, food wastes, and dairy waste and whey in milk processing. They are used in the paper industry to pump lime slurry and adhesives. They are used in the plastic recycling industry to pump plastic and Styrofoam cups. They are also used in the construction indnstiy for pumping bentonite siurries. clay slurries, and mud. 

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. 

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