Rotary Lobe Pump Rotors: How Tri-Lobe, Bi-Lobe and Acteon Differ, and How to Choose

A rotary lobe pump is a positive-displacement rotary pump: two lobe-shaped rotors rotate synchronously in opposite directions via a timing gearbox. The two rotors do not touch each other but maintain a very small clearance, so there is no mechanical wear between the lobes and no lubrication is required inside the pump chamber. With each rotation, liquid is “metered” within the cavities between the rotor lobes and the chamber wall, then discharged through the outlet.

The number of lobes on a rotor changes how fluid is metered and displaced. The more lobes a rotor has, the smaller each cavity becomes, and the more discharge strokes occur per revolution — resulting in smoother, more uniform flow, but with less clearance for solid particles. Conversely, a rotor with fewer lobes provides larger cavities, accommodating larger particles and thicker fluids, at the cost of slightly higher flow pulsation. This is precisely why OMAC offers multiple rotor types to match each fluid type.

The tri-lobe rotor has 3 lobes, so each revolution creates more displacement strokes, delivering uniform, low-pulsation, low-vibration flow. Shear forces acting on the fluid are also gentler, preserving the structure of shear-sensitive products such as cream, sauce, yogurt, cosmetic cream, or emulsions. This is the common choice when the primary requirement is post-pump product quality and stable metering.

Tri-lobe is suitable when: the fluid has a structure that must be preserved, smooth flow is needed for precise metering, or pressure and flow rate requirements are steady and continuous. Tri-lobe can still handle small, fine solid particles, but for larger particles, bi-lobe should be considered.

The bi-lobe rotor has only 2 lobes, so each metering cavity is considerably larger. The larger cavity allows solid particles, fruit pieces, meat chunks, or highly viscous fluids to pass through with minimal crushing. In return, because there are fewer discharge strokes per revolution, flow pulsation may be slightly higher than with tri-lobe — typically acceptable in applications transferring thick or coarsely structured fluids.

Bi-lobe is suitable when: pumping fluids containing particles or chunks that must retain their shape, fluids with high viscosity, or when priority is given to open pump cavities to reduce blockage risk. OMAC’s monobloc BE series uses bi-lobe rotors and can handle solid particles approximately 10–19 mm in size, a typical example of the large-cavity design approach.

In addition to tri-lobe and bi-lobe, OMAC also offers the Acteon rotor — a specially designed rotor for specific operating requirements where the two standard types are not fully optimised. Selecting Acteon is typically tied to particular fluid conditions; it is advisable to discuss the details with a technical engineer to determine the rotor configuration suited to your fluid.

Regarding material, rotors are manufactured from AISI 316L stainless steel to meet hygienic requirements for food, chemicals, and cosmetics. When the fluid is abrasive, the rotor can be fitted with an elastomer coating to protect the surface and reduce wear. Whether tri-lobe, bi-lobe, or Acteon, both rotors rotate synchronously and do not contact each other, so no metal particles are generated to contaminate the product. The main wear components of the pump are the mechanical seal and rotor clearances, not the contact surfaces between lobe faces.

Start by describing the fluid using four questions: does the fluid have a structure that must be preserved (cream, sauce, yogurt); does it contain particles or chunks, and what size; what is the viscosity level; and is the fluid abrasive. From there, tri-lobe is oriented toward smooth fluids requiring gentle flow, bi-lobe toward thick or chunky fluids, and elastomer-coated rotors are for abrasive fluids. Acteon is the option when operating conditions are particularly specific.

Rotor geometry is only one piece of the puzzle. You also need to select the pump series suited to your hygienic requirements (3-A, EHEDG, ATEX), the seal type, and the CIP/SIP configuration. Send your fluid specifications to receive full configuration guidance.