Sealing and Clearance Control
Axial Clearance: A small gap (approximately 0.025~0.04mm for small flow pumps, 0.04~0.06mm for large flow pumps) exists between the gear end face and the end cover, which is the main leakage path. To reduce leakage, medium and high pressure pumps often use floating bushings or floating side plates for automatic compensation, using pressurized oil to counteract axial forces and maintain minimal clearance.
Radial Clearance: A larger gap (approximately 0.13~0.16mm) exists between the gear tip and the inner wall of the pump body to prevent friction between the gear and the pump body under radial forces. However, this gap can also lead to some leakage.
Meshing Line Separator: The gear meshing line completely separates the suction chamber and the pressure chamber, acting as an oil distribution mechanism to ensure unidirectional liquid flow.
Trapped Oil Phenomenon and Unloading Measures: Due to the gear overlap coefficient being greater than 1, there is a moment when two pairs of teeth mesh simultaneously, forming a closed volume (trapped oil zone). When the volume decreases, the oil is compressed, causing a sudden increase in pressure; when the volume increases, a local vacuum is created, leading to cavitation, noise, and vibration.
Solution: Create unloading grooves on the front and rear end covers to connect the trapped oil area with the suction or pressure chamber, achieving pressure balance and effectively reducing noise and vibration.
Radial Unbalanced Force: The pressure in the pressure chamber is much higher than that in the suction chamber. The oil pressure acts on the gear tooth tips, creating a radial unbalanced force pointing towards the suction chamber. This force accelerates bearing wear and can cause shaft bending.
Mitigation Measures: Reduce the size of the pressure port to decrease the number of teeth affected by the high-pressure area.Create radial force balancing grooves to divert some high-pressure oil to the suction side, balancing the pressure (but this increases internal leakage and reduces volumetric efficiency). Increase the load-bearing capacity of the gear shaft and bearings.
Self-priming Capacity and Sealing Performance: Gear pumps rely on the local vacuum created when the gears disengage to draw in liquid, possessing strong self-priming capability and requiring no additional auxiliary devices. Its compact structure, lack of suction and discharge valves, and sealing performance relying on precision-machined clearances make it insensitive to oil contamination, suitable for lubricating or hydraulic oils with low impurity content.
Materials and Processes: Gears are typically made of high-strength alloy steel, heat-treated to improve hardness and wear resistance; pump bodies are mostly cast iron or aluminum alloy. Modern designs incorporate technologies such as DU self-lubricating bearings and ceramic end-face seals to further enhance lifespan and reliability.
