The method of adjusting the flow rate of gear pumps and the problem of sealing oil leakage

Firstly, the method of adjusting the flow rate of the gear pump

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

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 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

Secondly, the solution for gear oil pump seal oil leakage

"Gear oil pump seal oil leakage" refers to hydraulic oil or engine oil breaking through the skeleton oil seal and overflowing.

. This phenomenon is widespread, and the oil leakage of the gear oil pump seriously affects the normal operation of mechanical equipment, the usability of the gear oil pump, and environmental pollution. To facilitate the solution of the problem, the causes and control methods of oil leakage in the stainless steel gear oil pump oil seal are analyzed

1. Impact of component manufacturing

(1) Oil seal.

If the geometric shape of the oil seal lip is not qualified, the tightening spring is too loose, etc., causing air leakage in the airtightness test, and the gear pump is installed in the main engine and causes oil leakage. At this point, the oil seal should be replaced and the material and geometric shape should be inspected (there is a significant difference between domestic oil seals and oil seals)

(2) Processing and assembly of gear pumps

If there are problems with the machining and assembly of the gear pump, causing the rotation center of the gear shaft to be not concentric with the front cover seal, it will cause the oil seal to wear off. At this time, the symmetry and displacement of the front cover bearing hole to the pin hole should be checked, and the coaxiality of the skeleton oil seal to the bearing hole should be checked

(3) Sealing ring material and processing

If this problem exists, it can cause cracks and scratches on the sealing ring, resulting in loose or even ineffective secondary sealing. Pressure oil enters the skeleton oil seal (low-pressure channel), causing oil leakage in the oil seal. At this time, the sealing ring material and processing should be checked

(4) Processing of variable speed pumps

According to feedback from the host factory, the problem of oil leakage in the gear pump oil seal assembled with the variable speed pump is more serious, so the processing of the variable speed pump also has a significant impact on oil leakage. The variable speed pump is installed on the output shaft of the gearbox, and the gear pump is also installed on the output shaft of the gearbox through the positioning of the variable speed pump stop. If the end of the stop of the variable speed pump faces the runout of the gear rotation center beyond the tolerance (verticality), it will also cause the rotation center of the gear shaft to not coincide with the center of the oil seal, affecting the sealing. During the machining and trial production process of the variable speed pump, the coaxiality of the rotation center to the stop mouth and the runout of the stop mouth end face should be checked

(5) The front cover oil return channel between the CBG gear pump skeleton oil seal and the sealing ring is not unobstructed, causing an increase in pressure at this point and thus breaking through the skeleton oil seal. After improving this area, there has been a significant change in the phenomenon of oil leakage in the pump. 2. The impact of gear pump and host installation

(1) The installation of gear pump and host 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 outer stop of the gear pump and the inner stop of the variable speed pump, as well as the outer spline of the gear pump and the inner spline of the transmission shaft, 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

3. Impact of Hydraulic Oil

(1) Poor cleanliness of hydraulic oil, large pollution particles, and sand and welding slag in various hydraulic control valves and pipelines are also one of the reasons for pollution.

Because the clearance between the gear shaft diameter and the inner hole of the sealing ring is very small, larger solid particles in the oil enter between, causing wear, scratches, or rotation with the shaft in the inner hole of the sealing ring, causing the pressure oil of the secondary seal to enter the low-pressure area (at the skeleton oil seal), causing oil seal breakdown. At this time, the anti-wear hydraulic oil should be filtered or replaced

(2) After the viscosity of hydraulic oil decreases and deteriorates, the oil becomes thinner. Under the high-pressure state of the gear pump, the leakage through the secondary sealing gap increases. Due to the lack of time to return oil, the pressure in the low-pressure area increases, causing the oil seal to break through. It is recommended to regularly test the oil and select anti-wear hydraulic oil

(3) When the main engine operates under high load for a long time and the oil level in the tank is low, the oil temperature can rise to 100 ℃, causing the oil to become thinner and the lip of the skeleton oil seal to age, resulting in oil leakage; The oil tank liquid level should be checked regularly to avoid excessive oil temperature