Analysis of Damage Causes and Maintenance Points of Dynamic Seals for Pumps


Release time:

2022-07-14

K-type dynamic seal is a commonly used shaft seal for anti-corrosion slurry pumps. Its main advantages are: first, simple structure, low maintenance technical requirements, and convenient use; second, good versatility, suitable for both clear liquid and slurry transportation; The third is good anti-corrosion performance, almost all kinds of corrosive media can be used. But there is also a big disadvantage: easy to leak. Judging from the leakage situation, the first leakage time is 15~50 days, mainly distributed in the positions that pressurize and convey the slurry, such as the feed pump of the filter press; the first leakage time is 5~6 months. The result of statistical analysis is that the positions are distributed in the circulation of conveying materials at atmospheric pressure, and most of them belong to this situation (generally, the actual working pressure is below 80% of the design pressure of the pump, for example, the rated design pressure of the pump is 0.5MPa, and the actual working pressure is 0.4 MPa. Posts below MPa); there are also posts where the first seal leakage occurs in about a year. Most of the conclusions drawn through research and analysis are distributed in posts where clear liquid is transported and the operating pressure is lower than the design pressure, such as sulfuric acid engineering purification. Dilute acid circulation pump in the system. According to the comprehensive analysis of the above situation, we found that the life of K-type dynamic seal is mostly related to the operating pressure.

1. Analysis of the actual situation

K-type dynamic seal is a commonly used shaft seal for anti-corrosion slurry pumps. Its main advantages are: first, simple structure, low maintenance technical requirements, and convenient use; second, good versatility, suitable for both clear liquid and slurry transportation; The third is good anti-corrosion performance, almost all kinds of corrosive media can be used. But there is also a big disadvantage: easy to leak. Judging from the leakage situation, the first leakage time is 15~50 days, mainly distributed in the positions that pressurize and convey the slurry, such as the feed pump of the filter press; the first leakage time is 5~6 months. The result of statistical analysis is that the positions are distributed in the circulation of conveying materials at atmospheric pressure, and most of them belong to this situation (generally, the actual working pressure is below 80% of the design pressure of the pump, for example, the rated design pressure of the pump is 0.5MPa, and the actual working pressure is 0.4 MPa. Posts below MPa); there are also posts where the first seal leakage occurs in about a year. Most of the conclusions drawn through research and analysis are distributed in posts where clear liquid is transported and the operating pressure is lower than the design pressure, such as sulfuric acid engineering purification. Dilute acid circulation pump in the system. According to the comprehensive analysis of the above situation, we found that the life of K-type dynamic seal is mostly related to the operating pressure.

2. Evidence from further tests

After we mastered the relationship between the operating pressure of the pump and the life of the dynamic seal, we conducted further tests. The test results are (the test method is clear liquid, normal temperature, and circulating transportation, and the method is to install a positive and negative pressure gauge on the sealed cavity):

When the pressure of the sealing part is 0.1MPa, the sealing will be damaged within two hours;
When the pressure of the sealing part is 0.06MPa, the sealing will be damaged within two days;
When the pressure of the sealing part is 0.02MPa, the sealing life is 6~12 days;
When the pressure of the sealing part is 0.001MPa, the sealing life is 30 days;
When the pressure of the sealing part is -0.001MPa, the sealing life is 3-4 months;
When the pressure of the sealing part is -0.02~-0.04MPa, the sealing life is 6~8 months;
When the pressure of the sealing part is below -0.06MPa, the sealing life may be longer (the test has not been completed), but a large amount of air has entered the pump.

The above tests show that the life of the seal is obviously inversely related to the pressure of the seal. The lower the pressure, the longer the life of the seal, and vice versa. Then, to control the life of the seal, it is necessary to reduce the pressure of the seal cavity.

3. The specific causes that affect the life of the seal when the pump is used

Experiments have shown that reducing the pressure of the seal chamber can prolong the life of the seal. To solve this problem, we must first find out where the pressure of the seal chamber comes from? The reason is clear: the backflow pressure of the pressurized fluid from the pump outlet through the gap between the impeller and the pump casing! Once the cause is found, as long as you find the reason for reducing reflux, you can find a way to decompress. After analysis, the main reasons for reflux are as follows:

First, the gap between the pump casing and the impeller is too large (generally more than three millimeters, and the backflow is more serious). There are two reasons for this:
1. The size of the pump is not well controlled during assembly.
2. The scouring and wear of the conveyed material causes wear of the impeller, pump casing and other components, resulting in an increase in the gap, which in turn increases the pressure of the sealing chamber and damages the seal. At this point, there are many users who don't know it yet. They only know that a headache is a pain in the head, a sore foot is a pain in the foot, and the seal is leaked and the sealing ring is replaced. However, they do not know that the bad seal is caused by the wear of the impeller and the pump casing: the seal is damaged, and the root is in the impeller. , if the impeller is not replaced, the seal has to be replaced at both ends every three days, and the root of the disease has not been eliminated;

Second, the actual operating pressure of the pump is higher than the design rated pressure, and the pump is often in a pressurized state. such situations.

4. How to find a solution for long sealing life

One of the methods: increasing the auxiliary impeller and increasing the height and diameter of the back impeller blade, it can also be relatively sealed and decompressed, but the disadvantage is to increase the power consumption of the pump and reduce the efficiency.
Method 2: Replace the new impeller and pump casing frequently to ensure that the gap between the pump casing and the impeller is less than 3mm, which can also prolong the life of the pump seal. The disadvantage is the high maintenance cost.
Method 3: Reduce the time for the pump to run under pressure (disadvantage).
Method 4: Design a slurry pump with the pump suction port and seal in the same direction (see the picture on the right). This type of pump seal is always in a negative pressure or low pressure state, so the seal is not easy to be damaged. The modified pump has been used for more than 100 years. It has been fully proved the reliability of sealing by domestic users.
Method 5: Design the back blade of the labyrinth impeller (see the picture on the left), artificially bend the flow path of the backflow fluid, and reduce the flow rate of the fluid from the pump outlet to the seal cavity. Under the premise of manufacturing cost, it can prolong the life of the shaft seal. After thousands of users use it, this kind of pump seal we call the B-type structure proves that the life of the shaft seal can be extended by 50~100% under the same working conditions. .

5. Summary

In order to increase the service life of the widely used anti-corrosion pump dynamic seal, we believe that the following matters should be paid attention to in the selection, use and maintenance of the three links:
When selecting the model, you should choose the one with better pressure resistance, especially for the position of conveying materials under pressure, it is best to choose a back suction pump, such as the HFM type slurry pump produced by our company.
When using, try to pay attention that the actual operating pressure is lower than the rated pressure of the purchased pump. At the same time, try to turn on the boring pump as little as possible, or run it under pressure, or turn on the empty pump, and use cooling water as much as possible to use cooling water, which can also relatively improve the service life of the seal.
During maintenance, pay attention to observe whether the back blade of the impeller is worn, change the impeller frequently, and adjust the gap between the impeller and the pump casing.

The above is only for communication, and customers and friends are welcome to give us valuable opinions.