The concept of the gear pump is very simple, that is, its basic form is that two gears of the same size rotate in mesh with each other in a close-fitting housing. The inside of the housing resembles an “8” shape with two gears inside. The outer diameter of the gear and both sides are in close cooperation with the housing. The material from the extruder enters the middle of the two gears at the suction inlet, fills this space, moves along the housing as the teeth rotate, and finally exits when the two teeth mesh.

In terms of terminology, a gear pump is also called a positive displacement device, that is, like a piston in a cylinder, when a tooth enters the fluid space of another tooth, the liquid is mechanically squeezed out. Because the liquid is incompressible, the liquid and the teeth cannot occupy the same space at the same time, so that the liquid is eliminated. Due to the constant meshing of the teeth, this phenomenon occurs continuously, thus providing a continuous discharge at the outlet of the pump. The amount of discharge is the same for each rotation of the pump. With the uninterrupted rotation of the drive shaft, the pump also discharges fluid without interruption. The flow of the pump is directly related to the speed of the pump.

In fact, there is a small amount of fluid loss in the pump, which makes the pump operating efficiency can not reach 100%, because these fluids are used to lubricate the bearings and gear sides, and the pump body can never be no clearance fit, so The fluid cannot be discharged 100% from the outlet, so a small amount of fluid loss is inevitable. However, the pump can still operate well. For most extruded materials, it can still achieve 93% to 98% efficiency. For fluids with varying viscosities or densities in the process, this pump will not be affected much. If there is a damper, such as a strainer or a restrictor on the discharge side, the pump will push fluid through them. If this damper changes during operation, ie if the filter becomes dirty, clogged, or the back pressure of the limiter increases, the pump will still maintain a constant flow until the mechanical limit of the weakest part of the device is reached (usually equipped with a torque limiter).

The speed of a pump is actually limited. It depends on the process fluid. If the oil is conveyed, the pump can rotate at a very high speed, but when the fluid is a high-viscosity polymer melt. In physical terms, this restriction 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 inlet. If this space is not full, the pump cannot discharge the accurate flow, so the PV value (pressure×flow rate) is another limiting factor, and Is a process variable. Due to these restrictions, gear pump manufacturers will offer a range of products, namely different specifications and displacements (volumes discharged per revolution). These pumps will work with specific application processes to optimize system capabilities and prices.

The gear and shaft of the PEP-II pump are all integrated, and the hardened whole process is used to obtain a longer working life. The “D” type bearing incorporates a forced lubrication mechanism that allows the polymer to pass over the bearing surface and return to the inlet side of the pump to ensure effective lubrication of the rotating shaft. This feature reduces the possibility of polymer retention and degradation. The precision-machined pump body can precisely match the "D" type bearing with the gear shaft to ensure that the gear shaft is not eccentric to prevent gear wear. The Parkool seal structure and the PTFE lip seal together form a water-cooled seal. This seal does not actually touch the surface of the shaft. Its sealing principle is to cool the polymer to a semi-molten state and form a self-sealing seal. A Rheoseal seal can also be used, which has a reverse spiral groove on the inner surface of the shaft seal, allowing the polymer to be back pressed back into the inlet. For ease of installation, the manufacturer has designed an annular bolt mounting surface to mate with the flange mounting of other equipment, which makes the manufacturing of the cylindrical flange easier.

The PEP-II gear pump is equipped with a heating element that matches the specifications of the pump and is available as an option for the user. This ensures rapid heating and heat control. Unlike heating in the body of the pump, damage to these components is limited to one plate, independent of the entire pump. The gear pump is driven by an independent motor that effectively blocks upstream pressure pulsations and flow fluctuations. The pressure pulsation at the outlet of the gear pump can be controlled within 1%. Using a gear pump on the extrusion line can increase the flow output speed, reduce the shear and dwell time of the material in the extruder, reduce the extrusion temperature and pressure pulsation to improve productivity and product quality.