There is a small amount of fluid loss in the gear pump, which makes the pump's operating efficiency unable to reach 100%, because these fluids are used to lubricate the bearings and both sides of the gear, and the pump body can never fit without clearance, so fluid cannot be used. 100% is discharged from the outlet, so a small amount of fluid loss is inevitable. However, the gear pump can still run well, and for most extruded materials, it can still reach an efficiency of 93% to 98%.
In terms of terminology, a gear pumps is also called a positive displacement device, which is like a piston in a cylinder. When one tooth enters the fluid space of another tooth, the liquid is mechanically squeezed out. Because the liquid is incompressible, the liquid and the tooth cannot occupy the same space at the same time, so that the liquid is eliminated. Due to the continuous meshing of the teeth, this phenomenon occurs continuously, and thus a continuous discharge amount is provided at the outlet of the pump. The discharge amount is the same for each revolution of the pump. With the uninterrupted rotation of the drive shaft, the pump continuously discharges fluid. The flow rate of the pump is directly related to the speed of the pump.
For fluids whose viscosity or density changes during the process, this pump will not be affected too much. If there is a damper, such as a strainer or a restrictor on the discharge port side, the pump will push fluid through them. If this damper changes during operation, that is, if the filter screen becomes dirty, clogged, or the back pressure of the limiter increases, the gear pump will still maintain a constant flow rate until it reaches the weakest part of the device. Limit (usually equipped with a torque limiter).
There is actually a limit to the speed of a pump, which is mainly determined by the process fluid. If the transmission is oil, the gear pump can rotate at a very high speed, but when the fluid is a high-viscosity polymer When melted, this limit will be greatly reduced.
It is very important to push the high-viscosity fluid into the two-tooth space on the side of the suction port. If this space is not filled, the pump will not be able to discharge the accurate flow rate, so the PV value (pressure × flow rate) is another limiting factor, and It is a process variable. Due to these limitations, gear pump manufacturers will provide a series of products, namely different specifications and displacement (amount discharged per revolution). These pumps will be matched with specific application processes to optimize system capacity and price.
