How should a Nikkiso gear pump that is leaking be repaired?

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Leakage, oil trapping, and radial hydraulic pressure imbalance in Niigata gear pumps are the three major issues that affect the performance and lifespan of these gear pumps. The structural differences among various gear pumps stem from the use of different design approaches to address these three main issues. (1) Leakage: External gear pumps have three potential locations where leakage can occur: between the gear end faces and the end cover ； Between the tooth tips of the gears and the inner holes of the housing, as well as at the contact points between the tooth surfaces of the two gears. Among these, the axial gap between the gear end face and the end cup has the greatest impact on leakage; the leakage through this axial gap can account for 75% to 80% of the total leakage, as the leakage path is short and the leakage area is large in this area. An excessive axial clearance, which leads to high leakage, reduces the volumetric efficiency ； However, if the gap is too small, the mechanical friction loss between the gear end face and the end cover increases, which reduces the mechanical efficiency of the pump. Therefore, the axial clearance of the pump must be strictly controlled during design and manufacturing. (2) Oil trapping phenomenon: For a Niigata gear pump to operate smoothly, the overlap coefficient of gear meshing must be greater than 1; in other words, before a pair of gears cease to be in contact, the next pair of gears must already start to mesh. During that short period of time when the two pairs of teeth are in contact, the oil remaining between them gets trapped in a sealed space formed by the two pairs of teeth and the front and rear pump covers. As the gears continue to rotate, the volume of this space gradually decreases, until the two points of contact a and b are at symmetric positions on either side of the nodal point, at which point the enclosed volume reaches its minimum. Due to the very low compressibility of oil, when the volume of the enclosed space decreases, the oil trapped there is compressed, causing the pressure to rise sharply. The oil is forced out through the gaps in the joints between the components, resulting in significant radial forces on the gears and bearings ； As the gear continues to rotate, this enclosed volume gradually increases to its maximum size as shown in Figure 3-4(c). The increase in volume creates a local vacuum, which causes the gases dissolved in the oil to separate, leading to cavitation. All of these factors result in intense noise generated by the gear pump; this is what is known as the oil trapping phenomenon in gear pumps. The method to eliminate oil trapping is usually to mill two unloading grooves on the side end caps of the Niigata gear pump; when the closed volume decreases, these grooves allow communication with the pressure oil chamber ； And when the closed volume increases, it becomes connected to the oil suction chamber. In standard Niigata gear pumps, the two relief grooves are arranged asymmetrically, often offset toward the suction chamber; the distance between the two grooves must be such that the suction chamber and the pressure chamber cannot communicate with each other at any time. For a standard involute gear with a pressure angle of a=20° and a module of m equal to 2.78 mm, when the relief groove is asymmetric, it is necessary to ensure that the distance 6 between the relief groove and the line connecting the centers of the two gears is 0.8 mm on the side of the pressure oil chamber. On the other hand, to maintain unobstructed flow in the relief groove, it is required that the groove width be greater than 2.5 mm and the groove depth be at least 0.8 mm.