"Gear pump oil" refers to hydraulic oil that leaks through the skeleton oil seal, a common issue that has been widely reported by the host factory. This problem seriously affects the normal operation of the loader, the reliability of the gear pump, and causes environmental pollution. To address this issue effectively, it is essential to analyze the root causes and implement control measures for oil seal failure in gear pumps.
1. Impact of Component Manufacturing Quality
(1) Oil Seal Quality
If the geometry of the oil seal lip is not up to standard or the tightening spring is too loose, it can result in leakage during the sealing test. Once the gear pump is installed in the main machine, the seal may be damaged. In such cases, the oil seal should be replaced, and the material and geometry should be inspected. Domestic oil seals often have greater quality variations compared to imported advanced ones.
(2) Gear Pump Processing and Assembly
Improper processing or assembly of the gear pump can lead to misalignment between the gear shaft's rotational center and the front cover stop, causing the oil seal to become eccentric. At this point, it's important to check the symmetry, displacement, and coaxiality of the front cover bearing hole relative to the pin hole, as well as the alignment of the skeleton oil seal with the bearing hole.
(3) Sealing Ring Material and Processing Quality
Poor-quality sealing rings may crack or get scratched, leading to an ineffective secondary seal. This allows pressurized oil to enter the low-pressure area of the skeleton oil seal, resulting in oil leakage. In such situations, the material and quality of the sealing ring should be carefully examined.
(4) Variable Speed Pump Processing Quality
Feedback from the main engine factory indicates that issues are more severe when the gear pump is assembled with a variable speed pump. The variable speed pump is mounted on the gearbox output shaft, and the gear pump is connected via the shifting pump stop. If the end face of the variable speed pump is out of tolerance in terms of verticality relative to the gear’s center of rotation, the gear shaft’s center will not align with the oil seal, affecting its performance. During the production process, the coaxiality of the rotating center and the runout of the end face should be checked.
(5) Poor Oil Return Passage in CBG Gear Pump
If the oil return passage between the gear pump oil seal and the sealing ring is not smooth, pressure can build up in that area, eventually breaking through the skeleton oil seal. Improving this design significantly reduces oil leakage, as shown in Figure 1.
2. Impact of Gear Pump and Host Installation Quality
(1) Installation Requirements
The installation accuracy between the gear pump and the main machine must be less than 0.05 mm. Usually, the working pump is mounted on the variable speed pump, which is then attached to the gearbox. If the end face of the gearbox or variable speed pump is out of tolerance relative to the spline shaft’s center, cumulative errors can occur, causing radial forces on the gear pump at high speeds and leading to oil seal damage.
(2) Reasonable Clearance Between Components
The clearance between the outer stop of the gear pump and the inner stop of the variable speed pump, as well as between the external spline of the gear pump and the internal spline of the gearbox, must be appropriate. Excessive clearance in the positioning parts or insufficient clearance in the transmission parts can both affect the gear pump’s oil sealing performance.
(3) Influence of Spline Roller
The gear pump’s shaft extension spline and the gearbox output shaft have a short effective contact length. However, the gear pump transmits a large torque, which can cause the spline to experience excessive wear or even rolling keys, generating heat. This can damage the rubber seal of the skeleton oil seal, leading to oil leakage. It is recommended that the main engine factory check the strength of the gear pump’s external spline to ensure sufficient contact length.
3. Effect of Hydraulic Oil
(1) Poor Cleanliness of Hydraulic Oil
If the hydraulic oil is contaminated with large particles, such as sand or welding slag from pipelines, it can cause wear and scratching inside the gear pump. These particles can enter the small clearance between the gear shaft and the seal ring, damaging the secondary seal and allowing pressurized oil to leak into the low-pressure area of the skeleton oil seal. In such cases, the hydraulic oil should be filtered or replaced with new anti-wear oil.
(2) Reduced Viscosity of Hydraulic Oil
When the viscosity of the hydraulic oil decreases due to aging, the oil becomes thinner. Under high pressure, this increases leakage through the secondary seal gap, raising the pressure in the low-pressure zone and causing the oil seal to fail. Regular oil testing and the use of anti-wear hydraulic oil are recommended.
(3) High Oil Temperature Due to Long Operating Time
If the main load operates for extended periods and the oil level in the tank is low, the oil temperature can rise to 100°C, causing the oil to thin and the skeleton oil seal to age. This leads to oil leakage. Therefore, the oil level in the tank should be regularly checked to avoid overheating.
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