Vane pump oil seal oil leakage analysis!

The oil seal (also called shaft seal) in vane pumps and oil pumps usually has a pressure limit of less than 2 kg. If the pressure exceeds this pressure, the oil seal will open outwards, resulting in oil leakage from the shaft head. The high and low pressure oil chambers in the product structure The seals are relatively strict, and the high-pressure oil generally does not flow to the oil seal in the low-pressure area, and part of the oil that leaks to the oil seal will also flow from the shaft end through the shaft hole to the low-pressure oil inlet chamber, and the shaft seal is always at zero. If there is a problem with the seal itself or the assembly of the oil seal, it will cause the oil seal to leak.

However, in practical applications, strange oil seal leakage has become a relatively common failure in oil pumps. However, after inspection, no seal failure or improper installation was found. Therefore, oil leakage of many types of oil seals has become a mystery.

First of all, we must confirm that the oil seal is open outward, the spring is leaking, and the oil seal skeleton is weak. The oil leakage in this situation is the focus of today's research, and other oil leakage methods are not included. This kind of oil seal damage is the worst, most serious, and most difficult to understand in oil seal leakage.

After analysis, there is only one reason for the oil seal to open outwards, that is, the inside encounters a strong pressure (more than 2 kg), and the high-pressure oil flows to the oil seal, and the first thing to check is how it can enter the low-pressure area. , Is the high-pressure seal invalid? If the seal is not invalid, how did the high-pressure oil come in?

After a long period of exploration, the author used the principle of oil pump sealing to invert, and treated the phenomenon that should not be established as a fact, and finally found the crux of the problem, and theoretically deduced the principle of oil leakage from the oil seal.

This kind of outward opening must meet three conditions at the same time, one of which is indispensable, and the absence of one cannot be established. This is:

1. The oil suction port of the vane oil pump must be equipped with a one-way valve, the oil can only be sucked in and cannot be discharged back into the oil tank.

2. There must be no one-way valve installed at the oil outlet of the vane oil pump.

3. The vane oil pump must be in the state of just stopping.

The reason is that when the oil pump just stops, the system load is very strong, and the pressure oil is forced into the inside of the vane pump in an instant. If the high-pressure return oil is blocked by the one-way valve of the oil inlet at the same time, it cannot be effectively unloaded, and the pressure oil is forced from the center hole of the low-pressure area of the pressure side plate to the oil seal, so that the oil seal is instantly bared outward. opened.

The reason for installing the one-way valve at the oil suction port is that if the oil suction line is long or installed vertically, the remaining oil in the pump will be discharged back to the oil tank after the oil pump stops, and the oil pump will be damaged due to difficulty in oil suction when the oil pump is restarted. Installing a check valve will keep the oil in the oil pump or pipeline in place, which is conducive to re-oiling.

The reason for installing a check valve at the oil outlet is that if the system stops under pressure, the system will continue to maintain high pressure, and the oil pump will be unable to withstand the pressure due to low speed. The strong oil return pressure will damage the oil pump. Install an oil pump The outlet one-way valve is to block the high-pressure oil at the one-way valve and prevent it from flowing back, so as to protect the safety of the oil pump.

When the vane pump is at a normal speed or under a certain pressure, the vane is always in close contact with the stator. At this time, the high and low pressure oil chambers in the pump are mutually closed. When the speed drops to a certain speed, the pressure is low. When it is not enough to push out the blades, the blades are retracted to the bottom of the rotor, and the high and low pressure oil chambers in the pump are channeled through.

When the above three conditions are met at the same time, it is necessary to open the oil seal. If the oil return pressure is not so high (how high cannot be calculated), if the parking speed does not drop so fast, if there is a check valve at the outlet, if the oil suction If there is no one-way valve at the port, it is impossible for the oil seal to be bared open.