The concept of gear pump is very simple, that is, its most basic form is that the same size of two gears in a close-fitting rotation of the mutual engagement within the shell, the shell is similar to the internal "8" shape, two gears inside , The outer diameter of the gear and both sides of the shell with the close fit. The material from the extruder enters the middle of the two gears at the suction port and fills this space, moving along the housing as the teeth rotate, finally exiting when the two teeth mesh. In the jargon, a gear pump, also called a positive displacement device, is like a piston in a cylinder that is squeezed out mechanically as one tooth enters the fluid space of the other tooth. Because the fluid is incompressible, the liquid and the tooth can not occupy the same space at the same time, so the fluid is eliminated. As a result of the continuous meshing of the teeth, this phenomenon occurs continuously and thus provides a continuous discharge at the outlet of the pump, the same amount of discharge per revolution of the pump. As the drive shaft rotates uninterruptedly, the pump discharges the fluid without interruption. Pump flow directly with the pump speed. In fact, there is a small amount of fluid loss in the pump, which makes it impossible to achieve a pump operating efficiency of 100% because these fluids are used to lubricate both sides of the bearing and gear, and the pump body can never be gap-free Can not make the fluid 100% discharged from the outlet, so a small amount of fluid loss is inevitable. However, the pump can still run well and still achieve efficiencies of 93% to 98% for most extruded materials. For fluids with varying viscosity or density in the process, the pump will not be affected too much. If you have a damper, such as a screen or a restrictor on the side of the outlet, the pump will push fluid through them. If this damper changes at work, ie if the screen becomes dirty, clogged, or the backpressure of the restrictor is increased, the pump will still maintain a constant flow until the mechanical limit of the weakest part of the device is reached (Usually fitted with a torque limiter). There is actually a limit to the speed of a pump, which depends mainly on the process fluid. If the oil is delivered, the pump can rotate at a high speed, but when the fluid is a high viscosity polymer melt When the body, this limit will be significantly reduced. It is very important to push the highly viscous fluid into the two-tooth space on the side of the suction port. If this space is not full, the pump can not discharge the exact flow rate, so the PV value (pressure × flow rate) is another limiting factor, and Is a process variable Due to these limitations, gear pump manufacturers will offer a range of products, namely different sizes and displacements (quantities discharged per revolution). These pumps will be matched to the specific application process to optimize system capacity and price.
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