Common faults in the maintenance of Yuen Yan hydraulic pumps and their solutions

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Common faults and troubleshooting methods for repairing Japanese YUKEN hydraulic pumps: Japanese YUKEN hydraulic pumps are hydraulic components that supply pressurized fluid for hydraulic transmission; they are a type of pump. Its function is to convert the mechanical energy of a power source (such as electric motors and internal combustion engines) into the pressure energy of a liquid. The diagram shows the working principle of a single-plunger pump. The cam is rotated by an electric motor. When the cam pushes the plunger upward, the sealed volume formed by the plunger and the cylinder decreases, and the oil is forced out of this sealed volume and discharged to the desired location through a one-way valve. When the cam rotates to the descending part of the curve, the spring forces the plunger downward, creating a certain degree of vacuum; under atmospheric pressure, the oil in the tank enters the sealed volume. The cam causes the plunger to move up and down continuously, resulting in the sealing volume decreasing and increasing periodically, which enables the pump to continuously draw in oil and discharge it. Common faults and their causes: 1) Low oil level in the hydraulic oil tank ； Exclusion methods: Adding hydraulic oil 2) Not using hydraulic oil according to the season ； Exclusion methods: 46# hydraulic oil (or 68#) is generally suitable and no special replacement is needed; in extremely cold conditions in the north during winter, 32# oil can be considered. 3) The oil inlet pipe is severely clogged with dirt ； Exclusion methods: Remove foreign objects from the tube; 4) The oil seal of the oil pump’s driving gear is damaged, allowing air to enter the hydraulic system ； Exclusion methods: Replace aged or damaged oil seals and O-rings. 5) If the O-rings at the inlet and outlet connections of the oil pump are damaged, or if the bolts securing the elbow fittings or the nuts on the inlet and outlet pipes are not tightened properly, air may enter the hydraulic system ； Exclusion methods: Replace the O-ring, tighten the bolts or nuts at the joint. 6) Internal leakage in the oil pump, worn-out seal ring ； Exclusion methods: Replace the seal ring. 7) Wear or scratches on the end face of the oil pump or on the end faces of the shaft sleeves of the driving and driven gears; the unevenness of the end faces of these two shaft sleeves is out of tolerance ； Exclusion method: Replace the worn gear oil pump or oil pump shaft sleeve; in cases of mild wear, grind the end face on the flat plate until it is smooth. Its flatness tolerance is 0.03 mm ； The end face of the upper sleeve is lower than that of the pump body; the height of this upper surface should be below 2.5–2.6 mm under normal conditions. If this value is exceeded, a copper sheet with a thickness of 0.1–0.2 mm should be added to the lower sleeve to compensate for it. During installation, an 8) internal leakage may occur due to incorrect assembly of the oil pump’s internal components ； Exclusion method: The unloading plates and sealing rings must be installed in the oil chamber for the two shaft sleeves to remain balanced. The elasticity of the guide wire should be sufficient to twist both the upper and lower shaft sleeves by a slight angle in the direction of rotation of the driven gear, so that the machined surfaces of the shaft sleeves of the driving and driven gears fit tightly together ； The unloading groove on the shaft sleeve must be located on the low-pressure side in order to eliminate the harmful trapped volume that is generated during gear meshing ； Before pressing in the self-sealing oil seal, apply a layer of lubricant to its surface. Also, make sure that the oil-blocking edge faces the front cover; it must not be installed in the reverse direction ； Before installing the pump cover, a small amount of hydraulic oil must be poured into the pump casing, and the meshing gear 9) must be turned by hand – in a \"clockwise\" direction for left-hand rotation oil pumps and in a \"counterclockwise\" direction for right-hand rotation oil pumps – to prevent damage to the skeleton oil seal ； Exclusion method: A “right-handed” pump cannot be installed on a “left-handed” machine, otherwise it will damage the frame oil seal ； 10) The hydraulic oil is too dirty. Exclusion methods: Clean the system and replace the hydraulic oil. 11) The pump’s filter is clogged with dirt and cannot perform its oil-filtering function. Solution: Use clean cleaning oil to remove the dirt from the filter. 12) Insufficient oil level, the oil suction position is too high, and the oil suction pipe is above the oil surface: Solution: Fill the tank to the mark and lower the oil suction position. 13) No paper pads are placed on either side of the pump body and pump cover ； The pump body and pump cover are not sealed vertically: Solution: Air is drawn in during rotation; insert a paper pad between the pump body and the pump cover ； The pump body is ground on a flat surface using emery to ensure that the deviation in perpendicularity between the pump body and the pump cover is no more than 0.005 mm. The connection between the pump body and the pump cover must be tightened properly, with no leaks allowed. 14) The drive shaft of the pump is not aligned with the motor coupling, resulting in twisting friction: Solution: Adjust the alignment between the pump and the motor coupling so that the error does not exceed 0.2 mm. 15) The meshing accuracy of the pump gears is insufficient: Solution: Lube the gears to achieve the required meshing accuracy. 16) The oil seal frame of the pump shaft has come loose, resulting in a leaky pump body: Solution: Replace it with a qualified pump shaft oil seal.