Keep lobes in mind

Understand why and when to consider these positive-displacement pumps.

By John Hall, Viking Pump, Inc.

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direction of flow

Yes

Model dependent

No

Model dependent

Yes

Run dry capability

Excellent

Poor

Excellent

Excellent

Good (material dependent)

Handling of thin to thick liquids

Excellent

Excellent

Very good

Excellent

Excellent

Cleanability

Excellent

Very good

Good

Good

Good

Pressure capabilities

To 400 psi

To >1,000 psi

(multistages for higher pressure)

Limited to plant air pressure, usually 100 psi

To [greater than symbol]>1000 psi

 

Internal gear

to 280 psi External gear

to >1,000 psi

Abrasive liquid handling

Good

Very good

Very good

Good

Very good

Metering capability

Excellent

Excellent

Poor

Excellent

Excellent


The table compares several types of PD pumps by some usual selection criteria. These comparisons are based on common types of pumps, and some models by specific manufacturers may vary from these generalizations.

Initial costs for lobe pumps can be higher than for some other PD units, because lobe pumps must include timing gears and typically do not operate at motor speeds (except for smaller sizes) and thus require either a gear reducer, gear motor, or belt- or variable-speed drive. Their high efficiency and low maintenance offset the initial costs, however, to achieve very reasonable life-cycle costs.

Lobe pump capacities range from 0.01 to more than 1,000 gpm (0.02 to >227 m3/hr). Units can handle viscosities from 28 to 2,000,000 SSU (1 to 440,000 cSt) and frequently deal with temperatures up to 400°F (204°C). Jackets can be provided for heating or cooling. Material options range from Alloy C to Type 316 stainless steel to cast iron. Because they are PD pumps, lobe units require some form of pressure relief, either integral to the pump or mounted on the discharge line.

 

Catalyst feed application
Figure 6
Figure 6. This 6-in. industrial lobe pump handles 100-cSt catalyst solution at 220 gpm and 200 psi.


Problem solvers
Lobe pumps frequently offer solutions for process applications that have caused plant engineers and operators headaches. Before selecting a lobe pump, however, users should understand how the pumps compare to kinetic and other PD technologies, and their benefits and tradeoffs. Additionally, to ensure getting the sought-after performance, users need to be aware of the variety of lobe pump designs available, particularly in the areas of lobe forms, shaft support and shaft sealing.

John Hall is product manager for Viking Pump, Inc., Cedar Falls, Iowa. E-mail him at jhall@idexcorp.com.

 

Some suitable services

Examples of materials and processes for which lobe pumps commonly are chosen include:

Shear sensitive materials
fats, greases and oleo-chemicals
monomers and polymers
natural and synthetic rubber latexes and slurries
cellulose acetate
adhesives and sealants

detergents, lotions and creams
sugars and starches
water-treatment polymers (polyelectrolytes)
flavors and fragrances
clay slurries
gels
emulsions, suspensions and foam solutions
explosives

Other materials
inks, dyes, pigment slurries and paints
crude oils and oil sludges
fermentation mashes
waxes
chemical slurries

Processes
batch operations where solvent flush or steam cleaning is needed
processing units requiring frequent cleaning
liquid terminals and tank farms where reversing of flow direction is necessary to eliminate a second pump or for line stripping
liquid/liquid separation processes (e.g., ultrafiltration, centrifugation, coalescence and oil/water separation)
volumetric filling operations
base chemical transfer and ingredient metering
recirculation loops


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