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Rotary Pumps
Published in J. T. McGuire, Pumps for Chemical Processing, 2020
Figure 7.28 shows a three-lobe pump and the product flow through it. In principle the lobe pump is similar to the external gear pump; liquid flows into the region created as the counter-rotating lobes “unmesh,” “displacement volumes” are formed between the surfaces of each lobe and the casing, and the liquid is displaced by “meshing” of the lobes. The detail differences are two. First, the lobe forms in use, one, two, and three lobe with one rare, are not capable of driving each other, so must be “timed” with separate gears. The lobe pumps produced for chemical processing have their timing gears removed from the pumped liquid [7.14, 7.15], and thus are externally timed. Second, the relatively large “displacement volumes” enable large solids (nonabrasive) to be handled. They also tend to keep liquid velocities and shear low, making the pump type suitable for high viscosity, shear-sensitive liquids.
Hydraulic Power Generation
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
There are many different types of gear pumps other than the spur gear pump. A few commonly seen examples are lobe, gerotor, and screw pumps. A lobe pump is a rotary, external-gear pump and operates in a similar way to a conventional external gear pump. The major difference is that both lobes are driven externally so that they do not actually contact each other and are therefore much quieter than a conventional gear pump in operation. Another noticeable difference is that a lobe pump generally produces greater pulsation on the discharge flow due to the smaller number of teeth than a conventional gear pump. A gerotor pump is a rotary, internal-lobe pump and operates similarly to a conventional internal gear pump. In a typical gerotor pump, the inner rotor does mesh with the outer rotor to drive the pumping operation. Normally, the outer rotor has one more tooth than the inner one, and the pump displacement is determined by the space formed by the extra tooth in the outer rotor. A screw pump is an axial-flow gear pump. A typical screw pump consists of three screws, with a central-drive rotor meshing with two idler rotors inside a closed-fitting housing with no metal-to-metal contact. In the pumping process, the inlet flow is pushed uniformly through a screw pump axially in the direction of the drive rotor. Because the fluid delivered by the screw pumps does not rotate, and the rotors work like endless pistons that continuously move forward, it results in no pulsations at any speed of motor operation. These features make a screw pump operate very quietly and efficiently.
Mitigation of radial exciting force of rotary lobe pump by gradually varied gap
Published in Engineering Applications of Computational Fluid Mechanics, 2018
Yi-Bin Li, Dong-Sheng Guo, Xiao-Bin Li
Rotary lobe pump is a positive displacement pump, one of rotary volumetric pumps, widely used in chemical, food, and pharmaceutical industries (Dickenson, 1995). The rotary lobe pump takes the advantage of its simplicity of high flow rate, components and low maintenance costs, etc. In the working process of the rotary lobe pump, the volume of the suction and drainage cavity will change periodically with the rotation of the transmission shaft. The operating mechanism of the rotary lobe pump determines that it generates flow and pressure pulsation in the operation. As the fluid pressure at the pump outlet fluctuates, the radial exciting force also shows a periodic change, exerting an alternating load on the drive shaft. As a result, the service lifespan of the drive shaft is reduced, so that all components of the entire system will cause serious damage. Therefore, how to reduce the flow fluctuation and pressure pulsation at outlet of the rotary lobe pump, so as to improve the stability of the whole system, becomes an important issue.