Application of gear pump under special conditions In many applications, the pump is not simply to transport the water medium at room temperature and low pressure. Centrifugal pumps become ineffective as viscosity increases, and users need to consider using positive displacement pumps (PD pumps, or positive displacement pumps). When pressure needs to rise, some positive displacement pumps are unsustainable. When the temperature rises. Other pumps will also fail. So when you need more than 35 kg of pressure, or 300 degrees Celsius, or viscosity up to hundreds of thousands or millions of centipoises how to do? Maybe some pumps have been specifically designed or modified to meet one or both of these requirements, but what if the condition requires the pump to meet all these harsh conditions? This requires a high performance external gear pump designed for these harsh conditions. This pump can handle any or all of these conditions through specially engineered materials, clearances and designs. External gear pump has two same size gear shaft. The drive shaft connects the motor or reducer (via flexible coupling) and drives the other shaft. In heavy duty industrial gear pumps, the gears are usually one piece with the shaft and the journals have small tolerances. Gear shaft as a whole is to withstand high pressure, high viscosity under high torque load. The four journal bearings are dynamically supported and lubricate the bearings with pumped media. There are three common forms of gear: straight teeth, helical teeth and herringbone teeth. The three forms have their own advantages and disadvantages, have different applications. Straight teeth are the simplest form and are optimally used under high pressure conditions because there is no axial thrust and the delivery efficiency is high. Helical teeth have the least amount of pulsation during delivery and are quieter at higher speeds because the meshing of the teeth is gradual. However, due to the axial force, the selection of bearing material may result in limited pressure difference between inlet and outlet and lower viscosity. Because the axial force will push the gear to the bearing section and friction, so only choose the higher hardness of the bearing material or in the cross-section of the special design to cope with this axial thrust. Herringbone teeth are back to back helical forms that provide slightly lower pulsation than straight teeth, and axial forces can be balanced. However, the manufacturing cost is high, and assembly / disassembly is difficult because it must be installed in pairs. In high viscosity applications, liquids are easy to cure, or in very large pumps, which is a real drawback. External gear pump operation principle is very simple, the liquid into the suction side of the pump, the meshing interdental cavity inhalation, and then driven within the cavity between the teeth, along the outer edge of the gear shaft to reach the exit side. The re-engaged tooth pushes the liquid out of the hole into the back pressure. In theory, the nominal displacement of a positive displacement pump is independent of the pressure. However, volumetric failure or internal leakage is inherent in the form of positive displacement pumps. In order to achieve a high pressure differential and the required nominal flow rate, the gear pump must overcome this internal leakage. There are four kinds of internal leakage: 1: Between the gear journal and the bearing 2: Between the gear end face and the bearing face, 3: Between the tooth top and the pump housing, 4: Between the meshing teeth. In order to maximize the pressure bearing capacity of the pump, the clearance between these mating components must be as small as possible to limit internal leakage. However, just narrowing the gap is not as simple as it sounds, and other factors such as temperature, viscosity, and material selection must also be considered. Leakage from inside is not all bad. In gear pumps, some internal leakage is required to lubricate the internal passages and form a fluid film in the sliding bearings to dynamically support the gear shaft. The correct design should be, the internal leakage is 1-3% of the flow. Material selection is high temperature industrial pump selection is very important. Gear pumps are often used to deliver fluids that are highly corrosive, wear resistant or variable. Pump housing, shaft and bearing material must first match with the pumped liquid. Pump design becomes more complicated when extra heat is taken into account, even considering the thermal expansions of various materials. As mentioned earlier, the smaller the internal clearance, the better to achieve the highest pressure capability. Under high temperature conditions, the pump needs to expand within the existing clearance due to the thermal expansion of the part. This is beyond the usual considerations of most general purpose gear pump manufacturers. Over-estimating the material's thermal expansion can cause the pump's clearance to be too loose to produce the required pressure; underestimating the thermal expansion can cause the pump to lock when it reaches the process temperature. For this reason, pumps designed for high or low temperatures often do not function well at non-design temperatures.
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