In industrial fluid conveying scenarios, flow stability serves as one of the core indicators for evaluating pump performance, which directly affects the process accuracy and operational efficiency of production lines. As a typical type of positive displacement pump, the flow characteristics of rotary lobe pumps are a key focus for equipment selection and daily operation & maintenance.

- Bonve Pump Cam-style Twin Rotary Lobe Pump -

In terms of working principles, rotary lobe pumps essentially fall into the category of positive displacement pumps. Under theoretical conditions, the output flow rate is solely determined by the working chamber volume and operating speed, and has no direct correlation with discharge pressure, medium temperature, viscosity and other parameters. When the rotational speed per minute of the equipment is fixed, the theoretical conveying capacity per unit time remains constant — this is the most essential flow characteristic of positive displacement pumps.

However, the actual flow rate of rotary lobe pumps can never reach the theoretically calculated value in practical operation. The fundamental reason lies in that zero-clearance fit cannot be achieved for physical equipment. In an ideal state, if the fitting clearances between rotors, pump cavities, end covers and paired rotors are zero, the volumetric efficiency of the equipment can reach 100%, yet such a state is impossible to realize in practical application. To prevent rotor jamming, thermal expansion and seizure during operation, reasonable operating clearances must be reserved in the design phase. In accordance with material properties and process requirements, the industry generally controls the operating clearance around rotors within the range of 0.08mm to 0.30mm. This standard not only ensures stable and safe equipment operation, but also adapts to process requirements such as CIP hot cleaning.

The existence of clearances means that medium physical properties and system pressure will directly impact the actual flow performance. The higher the medium viscosity, the less internal backflow occurs through the clearances, and the lower the flow loss, while the corresponding equipment discharge pressure will rise simultaneously. Therefore, when conveying high-viscosity media, the operating speed of the equipment is usually reduced, and a power configuration with low speed and high torque is adopted. This measure helps cut down output pressure and energy loss, and guarantees the safe operation of the equipment.

On the contrary, when conveying low-viscosity media, the fitting clearances will cause more prominent internal backflow, resulting in a fixed proportional deviation between the actual flow rate and the theoretical value. The higher the discharge pressure, the greater the flow loss caused by backflow. When the pressure reaches a specific threshold, the flow rate may even drop to zero. Changes in medium temperature will also indirectly affect flow stability: temperature variation alters medium viscosity, and triggers thermal expansion and contraction of components to change the size of clearances.

For this reason, pump selection for rotary lobe pumps cannot merely refer to theoretical flow rate parameters. It is necessary to combine working conditions including the viscosity, temperature of conveyed media and system discharge pressure, so as to match suitable rotational speed, power and reduction gears. Accurate matching of working condition parameters is the fundamental prerequisite to achieve qualified flow rate and stable equipment operation. Only in this way can the output flow rate of the equipment steadily meet the requirements of actual production processes.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

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