Challenges and Solutions for Gear Metering Pumps' Oil Locking Phenomenon

In the meshing process of the main and passive gears in a gear pump, the number of gears meshing simultaneously should be more than a pair, i.e., the overlap factor ε should be greater than 1 (ε=1.4) for normal operation. The oil left between the teeth is trapped within a closed space formed by the two pairs of gears meshing at the same time. The volume of this space will also vary with the rotation of the gears. This is the phenomenon of trapped oil in gear pumps.

Vapor Lock Dangers: Increased bearing loads, power loss, oil heating, noise and vibration, and impact on the performance, stability, and lifespan of the oil pump.

Note: The volume of a confined space is dynamically changing, fluctuating between large and small, and then back to large. When it becomes smaller: The oil fluid is incompressible, and when it is compressed, the pressure increases and is forced out through the gaps in the mating surfaces of the parts (this pressure is much higher than that of the oil pump, sometimes reaching hundreds of atmospheres), exerting significant radial pressure and additional loads on the gears and bearings. When it becomes larger, a local vacuum is created, air is precipitated, vaporization occurs, leading to cavitation.

Solution (the basis for elimination or mitigation is pressure relief):

① Correcting the tooth shape minimizes the volume change in enclosed spaces; this method is less commonly used.

② Relief Hole Method: Drills radial through-holes from the tooth tip to the root of the driven gear, and milled two grooves on the driven gear shaft (complex processing).

③ The relief grooves (卸荷槽) are machined on the inner side of the pump's cover plates, along the tangent line to the wheel teeth' pitch circle. Four rectangular grooves are cut (one on each side cover for the intake and exhaust oil directions). The distance between the grooves must be greater than the thickness of one tooth space to prevent direct communication between the intake and exhaust cavities.

Pressure Relief Slot Method

Symmetrical Pressure Relief Groove Method: Pumps can operate in both clockwise and counterclockwise directions, significantly reducing oil locking, although it is not perfect.

Asymmetrical relief slot method: This method involves moving a suitable distance towards the suction side, allowing for additional recovery of high-pressure liquid, with a significant reduction in noise. However, the pump is not allowed to reverse.

The extent of the application of the pressure relief trough method in reducing oil lock is significant.

Jinan Lujujia's gear metering pumps, featuring gears that undergo precise displacement correction, minimize the impact of oil locking to ensure long service life, stable operation, and precise flow.