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In a vacuum oil filter, the gear oil pump serves as an oil discharge pump to remove the oil that has been purified in the vacuum separation tank from the tank; to do this, it must overcome the suction force of the vacuum. The noise generated by the gear oil pump is the main source of noise in the vacuum oil filter. Analyzing the causes of noise generated by gear pumps and controlling that noise will help improve the quality of vacuum oil filters. Reasons for noise generated by gear oil pumps. The main reasons for noise generation in gear pumps are as follows: (1) Oil trapping causes pressure surges or cavitation, which leads to noise; (2) Due to errors in gear manufacturing, when the gears mesh with each other, the teeth may experience sudden loading forces that cause vibration and thus noise; (3) Fluctuations in flow rate result in pressure fluctuations, which generate noise; (4) Noise can be caused by poor bearing precision or improper installation, as well as friction between the side plates and the sides of the gears. The most important ones are reasons (1) and (2), especially as the oil trapping phenomenon has the greatest impact on noise. Schematic diagram of the oil trapping phenomenon in gear pumps. To ensure smooth operation during gear meshing, the overlap coefficient must be greater than 1; as a result, two pairs of teeth are in contact at the same time. This creates an oil-trapped volume between these two pairs of gears, which cannot allow oil to flow out or in. It represents the variation pattern of the oil trapping volume. When the oil-trapping volume changes from large to small (with a change amount of Ah), the internal pressure rises, resulting in shock and vibration; when the oil-trapping volume changes from small to large (with a change amount of AF2), the internal pressure decreases, creating a vacuum that leads to cavitation. This is what is known as the oil trapping phenomenon. To address the noise caused by oil trapping, an effective measure is to machine relief grooves on the side plates. The principle behind this is as follows: when the volume of oil trapped decreases, the relief grooves allow it to communicate with the pressure chamber, thereby allowing the oil to be discharged; when the volume of oil trapped increases, the relief grooves enable it to communicate with the suction chamber, allowing oil to be drawn in. This approach helps to prevent oil trapping from occurring. If the unloading groove is designed accurately, noise can be reduced by about 7 dB(A). Analysis and countermeasures for gear oil pump noise faults: For a fully developed gear pump, its relief groove has been machined, and the precision of its gear teeth, bearings, as well as the accuracy of its installation have all been determined. Gear pumps can still generate significant noise at times, especially those used as oil discharge pumps in vacuum oil filters. Because to remove the oil from the vacuum tank, it is necessary to overcome the suction force of the vacuum, which makes it more difficult for the gear pump to discharge the oil; if not handled properly, this can result in significant noise. When the gear pump in a vacuum oil filter generates excessive noise, the causes can be identified and countermeasures taken from the following aspects: (1) Local blockage in the oil suction pipeline or filter ahead of the gear pump. At this point, it can be seen from the oil pipe that very little oil is being drawn in; insufficient oil intake can lead to dry grinding and cavitation, resulting in loud noises. It is necessary to identify the source of the blockage and remove any dirt so as to ensure smooth oil absorption. (2) Air is drawn into the suction line before the gear oil pump. At this point, bubbles can be seen in the oil suction pipe, and bubbles are also visible in the oil being discharged; air intake by the gear pump causes cavitation noise. The key areas to check are various valves before the pump, the sealing rings on the pump’s oil inlet flange, and the self-tightening skeleton oil seal of the pump; these issues should be resolved quickly once they are identified. (3) The flow area of the oil inlet filter is too small. If the flow area of the oil inlet filter is too small, it will also result in insufficient oil being drawn in, leading to dry grinding and cavitation, as well as loud noises. The solution is to replace it with a filter of equivalent flow area. (4) The pump speed is too high. Each gear pump has a recommended optimal operating speed; if the speed is increased in an attempt to boost flow rate, the vibration caused by tooth engagement will intensify, and the pump’s ability to draw in oil will be reduced, resulting in a sharp increase in noise levels. When this occurs, the speed should be reduced promptly. (5) The pump shaft and the motor shaft are not aligned. Gear pumps require the use of shaft sleeves or elastic couplings for transmission; if the two shafts are not aligned, it will lead to increased vibration during operation. When gear pumps are subjected to alternating loads, noise levels rise significantly, and they need to be reassembled. Maintain concentricity.