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　　Working Principle of Gear Oil Pump and Working Principle Diagram of Gear Oil Pump

　　I. Structure of Gear Oil Pump

　　The working mechanism of gear oil pump is a pair of meshing gears. According to the meshing characteristics, gear pump can be divided into external meshing and internal meshing, as shown in Figure 7-8. Gear pump teeth have involute teeth and arc cycloid teeth.

　　II. Working Principle of Gear Oil Pump

　　The working principle of gear oil pump is that gears mesh with each other, and the working volume changes during the meshing process to convey liquid. The working volume is composed of the grooves of pump body, side cover and teeth. The meshing area divides the space into suction cavity and discharge cavity. When a pair of teeth rotate in the graphical direction, the gear teeth located in the suction chamber gradually withdraw from meshing, so that the volume of the suction chamber increases gradually, the pressure decreases, and the liquid enters the suction chamber along the pipeline, and fills the volume between the teeth. When the gear rotates, the liquid entering the suction chamber is brought to the discharge chamber. Because the meshing of gears occupies the volume between the gears, the volume of the discharge chamber becomes smaller and the liquid is discharged. Therefore, gear oil pump is a kind of volume pump. Its characteristics are: basically independent of discharge pressure, fluctuating flow and pressure, no inlet and outlet valves, simple structure, easy manufacture, easy maintenance, reliable operation, and even flow than reciprocating pumps. In order to prevent the blockage of the discharge pipe and other reasons, the discharge pressure is too high and accidents occur. A safety valve is installed on the pump housing. When the discharge pressure is too high, the high-pressure liquid opens the safety valve, so that part of the liquid flows back from the channel to the suction port, so as to reduce the outlet pressure and play a protective role. The safety pressure can be adjusted by changing the spring force by adjusting the helix. In order to ensure the motion balance between the continuous transmission of liquid and the meshing teeth, it is necessary to require the first pair of teeth to engage before they are detached. Therefore, a part of the liquid is trapped in the closed volume formed between the two meshing lines and the two end caps. This volume is called "closed volume". When the closed volume changes from large to small, it is trapped in the closed volume. The liquid is squeezed and the pressure rises sharply. As a result, the trapped liquid is forced out of all the leakable slots. At this time, the gear and bearing are subjected to great pulsed radial force, the power loss increases, and the wear is aggravated. When the closed volume increases from small to large, the pressure of the remaining trapped liquid decreases, forming a local vacuum, which causes the gas dissolved in the liquid to precipitate or the liquid itself to gasify to form cavitation, and causes the pump to produce vibration and noise. This phenomenon is called the liquid diagram phenomenon. The phenomenon of liquid trapping is harmful to the working performance and service life of gear oil pump. Gear pump is suitable for high viscous liquids without solid impurities. If the liquid contains impurities, screw pump or pneumatic diaphragm pump is recommended. In order to eliminate the phenomenon of trapping liquid, unloading measures such as unloading trough and unloading hole can be taken to connect the closed volume with oil suction or pressure chamber. Because there are high pressure chamber and low pressure chamber in the pump, there is leakage problem. In order to ensure sealing, appropriate clearance should be selected. If the clearance is large, the leakage will increase, but it is not easy to jam, and the mechanical efficiency is high. In the axial and radial clearances, the axial clearance is the main one. Generally, the radial clearance should be in the range of 0.04-0.lOmm and 0.10-0.1mm. Because of the large clearance and sealing area of gear oil pump, the sealing performance is not as good as that of reciprocating pump, and the pressure that can be achieved is also lower. The quality of manufacturing and assembling of gear pump has a great influence on the performance.