Rotary lobe positive displacement pump for viscous and solids-laden transfer

01

Size by displacement per revolution, speed and pressure

Alfa Laval's OptiLobe leaflet lists ten pump heads from 0.06 L/rev (model 12, 25 mm ports) to 1.72 L/rev (model 53, 100 mm ports), each rated for 8 bar (115 psi) differential pressure, with maximum speed of 1,000 rpm up to model 43 and 750 rpm for models 52 and 53. It gives a maximum temperature of 266 °F and flow up to 383 US gal/min for the range. [1]

Editorial calculation: theoretical flow is displacement × speed. The model 53 at 750 rpm gives 1.72 × 750 = 1,290 L/min, or about 77 m³/h; the model 33 (0.40 L/rev) at 500 rpm gives 200 L/min, or 12 m³/h. Real delivery is lower by the internal slip at your viscosity and pressure, so ask the supplier for a curve at your duty. [1]

ACE's product page states that its flow table is measured on water, that speed is set between 200 and 900 rpm with a variable-speed motor or frequency converter, and that motor power must be increased for high-viscosity liquids. ACE claims its pumps can move products up to 1,000,000 cP. [2]

Give the supplier the product, its viscosity at pumping temperature (and whether it thins under shear), density, solids size and content, required flow range, suction and discharge pipework with static heads, temperature, CIP or SIP needs and the duty cycle.

02

Protect against hard solids, wear and pipe friction

LobePro applies its rotary lobe pumps to wastewater sludge at flows up to 2,000 gpm and pressures up to 150 psi once hard solids over 1/8 in (3 mm) and grit have been removed; where such solids are consistently present it suggests an in-line grinder, filter or knock-out tank. It states that pump speed affects wear exponentially and that lobe tip speed is the best measure of speed for wear. [3]

LobePro states the pumps can self-prime with swan-necked suction and discharge fittings, with suction lift depending on speed, viscosity and specific gravity. It warns that pipe friction losses for some sludges exceed those for water and asks for head calculations that allow for this; it notes that the EPA friction curve it reproduces is a rough guideline only for pipe velocities of 2.5–8 ft/s, and that restarting a line shut down for over a day can need unusually high pressure. [3]

Editorial calculation: 2,000 gpm is about 454 m³/h and 150 psi about 10.3 bar, against 77 m³/h and 8 bar for the largest OptiLobe head, so hygienic food heads and sludge heads cover different duty ranges. [3] [1]

03

Choose rotor form, seals and materials

ACE lists four rotor forms: single-lobe for products with large solid particles, butterfly rotors for fillings and viscous products with solids, three-lobe rotors for general viscous transfer, and multi-lobe rotors, which it says improve delivery but can break the product. Options include 304 or 316L stainless steel, drives from 0.55 to 55 kW, 110–600 V, heating jackets and trolleys. [2]

The OptiLobe head is 316L with EPDM or FPM product elastomers, a single carbon/stainless-steel shaft seal (single-flush option at a maximum flush pressure of 7 psi and 8 gph), duplex stainless shafts and a front-loading seal that can be changed without disturbing pipework. Alfa Laval states the range is EHEDG-certified as CIP cleanable and conforms to 3-A. [1]

04

Sanitary lobe pumps for food and cosmetics, and heavy-duty units for sludge

Listings range from sanitary lobe pumps with a choice of rotor forms for food and cosmetics to heavy-duty lobe pumps for wastewater sludge.

05

Pump head, rotor form, timing gearbox, shaft seals, variable-speed drive and inlet protection

06

Displacement, speed, differential pressure, viscosity and port size for a rotary lobe pump

Flow follows displacement per revolution times speed, for example 0.06 to 1.72 L/rev across the OptiLobe heads, so ask for the curve at your viscosity rather than water flow. [1]

07

Send the product, duty and pipework data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Product: [name; viscosity at temperature; density; shear sensitivity]
Solids: [size; content; hardness]
Duty: [flow range; differential pressure; temperature; hours per day]
Pipework: [suction and discharge sizes; lengths; static heads]
Hygiene: [CIP/SIP; finish; seal flush]
Drive: [power; voltage; VFD]

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