Fault analysis and troubleshooting methods for gear oil pumps

Thread Content

A gear oil pump is an important component that raises the low-pressure oil in the tank to high-pressure oil suitable for performing work, through the mutual rolling engagement of a pair of involute gears with identical parameters and structure. It is a power unit that converts the mechanical energy of the engine into hydraulic energy. The Dongfanghong-75 tractor and the Dongfanghong-60, 70T bulldozers use CB46 gear pumps. The Dongfanghong-802/802K tractors and Dongfanghong-802KT bulldozers are equipped with CBN-E450 or CBTI-E550 gear pumps, which feature high flow rates and good reliability. The following faults are likely to occur during its use. 1. Wear of internal components in the oil pump: Wear of the internal components of the oil pump can cause internal leakage. Among them, the large leakage area between the floating bushing and the gear end face is the main location causing internal leakage. This portion of the leakage accounts for about 50% to 70% of the total internal leakage. In a gear pump with internal wear and leakage, its volumetric efficiency decreases, resulting in the pump’s output power being **lower than its input power**. All of its losses are converted into heat energy, which can cause the oil pump to overheat. If the bonding plane is compressed, wear will occur due to the slight movement of the floating bushing during operation, resulting in slow lifting or complete inability to lift the agricultural tool; such a floating bushing must be replaced or repaired. 2. Wear of the oil pump housing is mainly due to wear in the holes of the floating bushings (the normal clearance between the gear shaft and the bushing is 0.09–0.175 mm, with a maximum of 0.20 mm). The gears operate under the influence of pressurized oil; the tips of the gears are close to the oil pump housing, causing wear on the low-pressure chamber of the pump body. Another type of wear is the circumferential wear on the working surface inside the housing; this wear is mainly caused by impure oil, so it is necessary to use oil free from impurities. 3. Wear of the oil seal and aging of the rubber seal: The rubber oil seal in the unloading plate ages and deteriorates, losing its elasticity; as a result, it can no longer provide a seal between the high-pressure oil chamber and the low-pressure oil chamber. This allows the oil pressure from the high-pressure chamber to leak into the low-pressure chamber, a phenomenon known as \"internal leakage.\" It reduces the operating pressure and flow rate of the oil pump. The normal operating pressure of the CB46 gear pump is 100–110 kg/cm², its normal oil delivery rate is 46 L/min, and the standard rubber seal for the unloading plate is 57×43. The self-tightening oil seal is a skeleton-type oil seal of PG25×42×10; when it is damaged or becomes ineffective over time, air is drawn into the oil pump through the gaps between the oil seal and the spindle journal, or from the junction between the oil inlet flange and the oil pump housing. This air then enters the oil tank via the return pipe, where it causes numerous bubbles to form. This will result in a decrease in the amount of oil in the tank, along with an increase in the oil level in the engine’s sump, causing the agricultural equipment to lift slowly or not at all. The oil seal must be replaced to eliminate this fault. 4. Insufficient oil supply from the oil pump or no oil pressure: The working device lifts slowly, shakes during lifting, or fails to lift at all ； Bubbles in the fuel tank or fuel lines ； The hydraulic system makes a \"hiss, hiss\" sound during lifting ； When the tractor first starts, the working device can be raised; however, after operating for a while and the oil temperature rises, it raises slowly or cannot be raised at all ； It can be lifted under light load, but not under heavy load. Cause of failure: (1) Low oil level in the hydraulic oil tank ； (2) Hydraulic oil was not used according to the season ； (3) The oil inlet pipe is severely blocked by debris ； (4) The oil seal of the drive gear of the oil pump is damaged, allowing air to enter the hydraulic system ； (5) The \"O\"-ring seals at the inlet and outlet connections of the oil pump, or those on the elbow connectors, are damaged; the fastening bolts of the elbow connectors or the nuts on the inlet and outlet pipes are not tightened properly, allowing air to enter the hydraulic system ； (6) Internal leakage in the oil pump, aged seal ring ； (7) Wear or scarring 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 ； (8) Internal leakage caused by incorrect assembly of internal parts of the oil pump ； (9) Installing a “right-handed” oil pump in a “left-handed” setup, resulting in damage to the skeleton oil seal ； (10) The hydraulic oil is too dirty. 　　 Exclusion method: (1) Add or replace the oil with a grade that meets the requirements according to the season, up to the specified oil level. Remove the foreign objects from inside the oil pipe, and tighten the bolts or nuts at the joints ； (2) Replace the aged or damaged frame oil seal or “O”-ring seal ； (3) Replace the worn gear oil pump or oil pump shaft sleeve; if the wear is minor, grind the end face flat on a flat surface. Its flatness tolerance is 0.03 mm ； The end face of the upper shaft sleeve should be lower than the upper surface of the pump body (the normal value is below 2.5–2.6 mm); if this value is exceeded, a copper sheet of 0.1–0.2 mm thickness should be added to the lower shaft sleeve to compensate for it. During installation, it should be placed over the rear shaft sleeve before being inserted in place ； (4) The unloading plates and sealing rings must be installed in the oil inlet chamber so that the two shaft sleeves can remain balanced. The unloading plate seal ring should have a precompression of 0.5 mm ； (5) 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 closely together ； (6) The unloading groove on the shaft sleeve must be located on the low-pressure side in order to eliminate the harmful dead volume that is generated during gear meshing ； (7) Before pressing in the self-tightening 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 ； (8) A “right-handed” pump cannot be installed on a “left-handed” machine, otherwise it will damage the frame oil seal ； (9) Before installing the pump cover, a small amount of engine oil must be poured into the pump casing, and the meshing gears must be turned by hand ； (10) Before tightening the bolts after installing the oil pump cover, check the gap between the pump cover and the pump body to ensure it is within the range of 0.3–0.6 mm. If the gap is too small, replace the sealing ring and pressure relief components. After the hydraulic oil pump is installed, it should rotate smoothly without any sticking.