The application of gear pumps in operation

【1】 The impact of gear pump and host installation

(1) The installation of the oil pump and the main engine requires a coaxiality of less than 0.05.

Usually, the working pump is installed on the variable speed pump, which in turn is installed on the gearbox. If the runout of the end face of the gearbox or variable speed pump with respect to the rotation center of the spline shaft exceeds the tolerance, it forms a cumulative error, causing the gear pump to bear radial force under high-speed rotation, resulting in oil seal leakage.

(2) Is the installation gap between components reasonable.

Whether the clearance fit between the gear pump outer stop and the variable speed pump inner stop, as well as the gear pump outer spline and the gearbox spline shaft inner spline, is reasonable, all have an impact on the oil leakage of the gear pump. Because the inner and outer joints belong to the positioning part, the fitting gap should not be too large; The inner and outer splines belong to the transmission part, and the clearance should not be too small to interfere.

(3) The oil leakage of the gear pump is also related to its spline rolling key.

Due to the short contact length between the external spline of the gear pump shaft and the internal spline of the gearbox output shaft, and the large torque transmitted by the gear pump during operation, the spline bears high torque and undergoes compression wear and even rolling, generating huge heat, resulting in aging of the rubber lip of the skeleton oil seal and oil leakage. It is recommended that when selecting a gear pump, the host factory should check the strength of the external spline of the gear pump shaft and ensure sufficient contact length.

【2】 Methods for adjusting the flow rate of gear pumps

1. Adjusting the outlet valve of the gear pump can reduce the flow rate of the gear pump.

2. Change the pipeline curve. This is a simple and commonly used method to change the flow rate of gear pumps. As long as the opening of the pump outlet valve is well controlled, the flow rate of stainless steel pumps can be adjusted. Its essence is to change the position of the pipeline characteristic curve to change the working point of the pump.

3. When a single gear pump cannot meet the conveying task, parallel or series operation of gear pumps can be used. Using two gear pumps of the same model in parallel, although the pressure head does not change much, it increases the total conveying flow rate, and the overall efficiency of the parallel pump is the same as that of a single pump; When the gear pump is connected in series, the total pressure head increases and the flow rate does not change much. The total efficiency of the series pump is the same as that of a single pump.

4. According to the laws of proportion and cutting, changing the pump speed and changing the pump structure (such as cutting the outer diameter of the impeller method) can both change the characteristic curve of the gear pump, thereby achieving the goal of adjusting the flow rate (while changing the pressure head). However, for pumps that are already in operation, the method of changing the pump structure is not very convenient, and because the pump structure is changed, the versatility of the pump is reduced. Although it is economically convenient to adjust the flow rate at certain times, it is rarely used in production. The method of adjusting the flow rate by changing the speed of the gear pump can extend the service life of the pump, save electricity, and lower the speed of operation. It can also reduce the cavitation margin of the gear pump, keep the pump away from the cavitation zone, and reduce the possibility of cavitation in the gear pump. The disadvantage is that changing the pump speed requires variable frequency technology to change the speed of the prime mover, which is a complex principle, requires a large investment, and has a small range of flow regulation.

5. Adjust the axis position of the gear pump. The geometric center of each gear in traditional gear pumps coincides with its rotation center. Relevant literature introduces an external meshing gear pump with an eccentric support gear pair, where the geometric center of the gear does not coincide with its rotation center and there is an eccentricity between the two. In this way, a crescent shaped volume is formed between the top circle of the gear teeth and the inner wall of the pump body. When the left gear rotates 180 °, this crescent shaped volume appears at the right gear. Therefore, compared with traditional gear pumps, when the structural dimensions of the gears are the same, it outputs an additional two crescent shaped volumes of flow per revolution (usually 40% to 60% more). But the eccentricity of the eccentric pump mentioned in the article is fixed, and the position of the rotating shaft is also fixed, so its output flow rate is, which means it belongs to the category of quantitative pumps. Inspired by this article, this article envisions that if a specialized mechanism is designed to adjust the eccentricity between the axis of the rotating shaft and the geometric center of the gear within a range, the output displacement of the eccentric pump can be changed, becoming a variable gear pump. Of course, there is a lot of work to be done in the parameter design of variable eccentric gear pumps, sealing of suction and discharge oil chambers, noise, unloading, and other aspects.