Gear pumps are driven by an independent motor, effectively blocking upstream pressure pulsations and flow fluctuations. Pressure pulsations at the gear pump outlet can be controlled to within 1%. Using a gear pump in an extrusion production line can increase flow output speed and reduce material shearing and residence time within the extruder.
External gear pumps are the most widely used type of gear pump; generally, the term "gear pump" usually refers to an external gear pump. Its structure, as shown in Figure 1, mainly consists of a driving gear, a driven gear, a pump body, a pump cover, and a safety valve. The sealed space formed by the pump body, pump cover, and gears constitutes the gear pump's working chamber. The shafts of the two gears are respectively mounted in bearing holes on the two pump covers. The driving gear shaft extends out of the pump body and is driven to rotate by the motor. External gear pumps are simple in structure, lightweight, low in cost, reliable in operation, and have a wide range of applications.
When the gear pump is working, the driving gear rotates with the motor, driving the driven gear to rotate as well. As the meshing teeth on one side of the suction chamber gradually separate, the volume of the suction chamber increases and the pressure decreases, drawing liquid from the suction pipe into the pump. The sucked liquid is then pushed into the discharge chamber by the gears within the tooth grooves in two separate paths. After entering the discharge chamber, the liquid is compressed by the continuous meshing of the two gear teeth and forced from the discharge chamber into the discharge pipe. The continuous rotation of the driving and driven gears allows the pump to continuously draw in and discharge liquid.
The pump body is equipped with a safety valve. When the discharge pressure exceeds the specified pressure, the pumped liquid automatically opens the safety valve, allowing the high-pressure liquid to return to the suction pipe.
An internal gear pump consists of a pair of meshing internal gears, a crescent-shaped component between them, and the pump casing. The crescent-shaped component separates the suction and discharge chambers. When the driving gear rotates, a partial vacuum is created where the gears disengage, drawing liquid into the pump and filling the spaces between the teeth in the suction chamber. The liquid then flows into the discharge chamber along the inner and outer sides of the crescent-shaped component in two separate paths. Where the teeth engage, the liquid between the teeth is compressed and sent into the discharge pipe. Gear pumps, besides being self-priming and having flow rate independent of discharge pressure, lack suction and discharge valves on the pump casing. They are characterized by simple structure, uniform flow, and reliable operation. However, they are inefficient, noisy, vibrating, and prone to wear. They are mainly used to transport various non-corrosive oils without solid particles and possessing lubricating properties, typically at temperatures not exceeding 70°C, such as lubricating oils and edible vegetable oils. Typical flow rates range from 0.045 to 30 mS/h, pressures from 0.7 to 20 MPa, and operating speeds from 1200 to 4000 r/min.
