A Brief Discussion on Wear Issues and Repair Methods of Gear Pumps

The concept of a gear pump is very simple. Its basic form is that two gears of the same size mesh and rotate with each other in a tightly fitting housing. The interior of this housing is similar to; 8” Character shape, two gears are installed inside, and the outer diameter and sides of the gears are tightly matched with the housing. The material from the extruder enters the space between two gears at the suction port and fills it. It moves along the shell with the rotation of the teeth and is then discharged when the two teeth mesh. The characteristics of gear pumps are mainly reflected in the following aspects:

(1) Compact structure, easy to use and maintain.

(2) It has self-priming properties, so there is no need to inject liquid before each pump start.

(3) The lubrication of gear pumps is automatically achieved by the liquid being transported, so there is no need to add lubricating oil during daily operation.

In terms of terminology, a gear pump is also known as a positive displacement device, which is like a piston in a cylinder. When one tooth enters the fluid space of another tooth, because the liquid is incompressible, the liquid and the tooth cannot occupy the same space at the same time, so the liquid is mechanically squeezed out. Due to the continuous meshing of the teeth, this phenomenon occurs continuously, thus providing a continuous discharge at the pump outlet. The amount discharged is the same for each rotation of the pump. As the drive shaft rotates continuously, the pump also continuously discharges fluid. The flow rate of a pump is directly related to its rotational speed. So how should we deal with the wear problem of gear pumps, and how should we deal with gear pumps? The following is a specific content introduction:

1. The inner cavity of the gear pump casing and the worn gear teeth

The wear of the pump casing cavity and gear teeth has a significant impact on the pump oil volume. When the shaft and bushing or shaft hole are severely worn, the tooth tip and the inner surface of the pump housing will make unnecessary contact during operation. Due to the higher pressure in the oil outlet chamber compared to the oil inlet chamber, under the pressure difference, there is more contact between the tooth tip and the pump housing near the oil inlet chamber. Therefore, there is more wear on the inner cavity of the pump housing at this location, which increases the gap between the inner cavity and the tooth tip.

2. Wear on the gear end face and pump cover of the gear pump

The gap between the gear end face and the inner plane of the pump cover is called the end face gap. The wear generated by the contact surface between the gear end face and the inner plane of the pump cover during work will increase the clearance between this end face. When exceeded, it will have a significant impact on the pump oil volume.

When the gear end face wears out, the end face can be ground flat, and at the same time, the separation surface of the gear pump housing can be ground to ensure that the end face clearance of the pump is within the required range.

Secondly, due to the wear of the gear teeth in the direction of tooth thickness, the meshing clearance between the active and passive gears increases. Its wear characteristic is heavy wear on one side, so the gear can be flipped 180 degrees for use.

1. Check for any looseness in the gear pump pipeline and joints. Rotate the gear pump by hand to see if it is flexible.

2. Add bearing lubricating oil into the bearing body, and observe that the oil level is at the centerline of the oil gauge. Lubricating oil should be replaced or replenished in a timely manner.

3. Unscrew the water inlet plug of the gear pump body and inject water (or slurry).

4. Close the gate valve, outlet pressure gauge, and vacuum gauge of the water outlet pipeline.

5. The specific principle is as follows: a stainless steel gear pump is equipped with a pair of rotating gears in the pump body, one active and one passive. By relying on the mutual meshing of the two gears, the entire working chamber inside the pump is divided into two separate parts. A is the suction chamber, and B is the discharge chamber. When the gear pump is running, the active gear drives the passive gear to rotate. When the gear disengages from meshing, a local vacuum is formed on the suction side (A), and the liquid is sucked in. The liquid sucked in fills the various tooth valleys of the gear and is carried to the discharge side (B). When the gear enters meshing, the liquid is squeezed out, forming high-pressure liquid and discharged outside the pump through the pump outlet. As a result, the pressure difference between the inlet and outlet chambers of the gear pump is reduced, leading to a decrease in the scraping and pressure of the gear teeth, resulting in a decrease in the supply pressure and a decrease in the pump oil volume. The wear of the inner cavity of the pump casing is generally treated by the inner cavity embedding method.