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Trapping Phenomenon
Views: 242 Update Date: Apr 11 , 2019

In the operation of gear pump, before the first pair of gear teeth will be separated from meshing, the latter pair of gear teeth will enter meshing, so there are two pairs of teeth meshing at the same time in a period of time. In this way, the oil between the two pairs of teeth is neither connected with the suction chamber nor with the discharge chamber to form a closed volume. Therefore, in the process of gear pump operation, there is a unique "gear seal phenomenon", or "oil trapping phenomenon". With the rotation of gears, the volume of the enclosed space is gradually reduced, and it is the smallest when the two meshing points are in the symmetrical position on both sides of the node. In this process, the oil is extruded and the pressure rises sharply. The oil will be forced out through the working clearance of the end face. At the same time, the gears and bearings will be subjected to extraordinary radial force. Thus, the accidents of bearing burning or pump shaft breaking will often occur.


The gear continues to rotate, and the enclosed volume gradually increases from the smallest to the largest. In this process, because it is difficult for oil to fill the rapidly increasing space through the clearance, local vacuum is generated and the oil in the closed volume is vaporized. The oil will rush rapidly into the closed volume to produce a hydraulic shock, which will erode the tooth surface and generate noise.


It can be seen that the consequences of the phenomenon of tooth seals are serious and must be eliminated. There are many ways to eliminate it. Whatever way to eliminate it, the following three requirements must be met at the same time:

In the process of shrinking the volume of the tooth seal, the squeezed oil should be discharged to the discharge chamber in time.

In the process of increasing the volume of the tooth seal, the oil in the suction chamber should be able to enter the volume of the tooth seal in time.

No matter where the meshing gear teeth are located, the suction and discharge cavities should not be communicated.


Gear pump has the advantages of simple structure, convenient management, low price and good quality. It is a kind of quantitative pump with wide application. The flow rate ranges from 0.75 to 550 L/min, the pressure ranges from 0.7 to 20 MPa, and the rotational speed is generally 1200 to 4000 r/min.

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