Croos Pump (Shanghai) Co., Ltd.

Seven Kinds of Sealing Knowledge of Chemical Pump

With the development of industrial technology and sealing technology, the pump is widely used in power, chemical, petroleum and other industries. The sealing and reliability of pump seal are higher and more stringent. The seal of chemical pump plays an important role in the operation of the whole equipment. The leakage of the sealing system of chemical pump will seriously affect the normal operation of the equipment. In particular, the development of high temperature and high pressure pumps makes the pump more tightly sealed. At present, the main shaft seals used in China are as follows: packing seal, labyrinth seal, floating ring seal, mechanical seal, oil seal, gasket seal, thread seal, power seal, here is a brief introduction to these seals.

1. Oil seal of chemical pump

Chemical pump oil seal is a kind of self-tightening lip seal with simple structure, small size, low cost, convenient maintenance and low torque. It prevents leakage of the medium and prevents the invasion of external dust and other harmful substances. Moreover, it has certain compensation ability for wear, but not high pressure resistance, so it is commonly used in low-pressure chemical pump.

Chemical pumps rely on centrifugal principle to extract liquid materials. Chemical pumps made from special materials are suitable for extracting corrosive liquids in bottles, barrels, tanks, pools or other containers. Due to the existence of corrosion, volatilization, explosion and other hazardous materials extracted by the chemical pump, the sealing performance of the pump body is much higher than that of other kinds of pumps.

In choosing this kind of sealing method, it is necessary to take full account of the performance and requirements of the chemical pump in order to avoid unnecessary leakage and prevent accidents.

2. Gasket seal of chemical pump

The usual sealing method of chemical pump has gasket sealing method. The gasket is the basic element of centrifugal pump static seal and is widely used. The selection of gasket is mainly determined by factors such as chemical pump conveying media, temperature, pressure and corrosion.

Sealing mechanism of gasket: leakage is the phenomenon that the medium flows from within the limited space to the outside, or from the outside to the limited space. The flow of the medium through the interface of internal and external space is the leakage of the sealing surface. The root cause of the leakage is due to the gap in the contact surface. The pressure difference and concentration difference between the contact surfaces are the driving force of the leakage. Due to the influence of the cover form and the processing precision, there is a gap in the sealing surface, which can cause the sealing surface to be incomplete and leak out. To reduce the leakage, the contact surface must be made to the maximum extent to reduce the area of the leakage passage, increase the leakage resistance, and make it more than the leakage force.

Press the compaction load on the sealing surface to produce pressure force to improve the contact degree of the sealing surface.When the stress increases enough to cause apparent plastic deformation on the surface, it can fill the gap of the sealing cover and block the leakage passage. The purpose of using the gasket is to make use of the gasket material to produce the characteristics of plastic deformation under the compression load, and fill the flange sealing surface of the small uneven relief, thus sealing.

3. Packing seal of chemical pump

The packing seal of the chemical pump is filled with the compressibility and elastic packing into the stuffing box, and the axial compression force of the gland is converted into the radial sealing force, thus providing sealing effect. This sealing method is known as packing seal, which is called sealing filler. Due to the simple structure convenient replacement, low price, adaptive speed, pressure and medium of packing seal, so they are widely used in the design of chemical pump.

4.  Power seal of chemical pump

When the chemical pump is in operation, the pressure head produced by the vice impeller balances the main impeller outlet high-pressure liquid to achieve the seal. When parking, the secondary impeller does not work, so it must be equipped with a stop-sealing device to solve the chemical pump leakage that may occur when parking. The auxiliary impeller seal structure is simple, reliable and it has long service life, and the chemical pump can be used in the operation of chemical pump. Therefore, it is often used in the pump of chemical pump containing impurity medium.

The power seal has centrifugal seal, screw seal, magnetic fluid seal, etc. The spiral seal is very promising. The closed seal has diaphragm type and shielding type etc.

5. Mechanical seal

It is widely used to prevent the leakage of liquid. Any type of seal must be used to prevent the idling of the chemical centrifugal pump, which can be destroyed once the airtight seal is sealed

The problem of mechanical seal in the use of chemical pump

In the operation of the fault rotating equipment of mechanical seal parts, the sealing face often shows wear, thermal crack, deformation, breakage and so on. The spring will also relax, break and corrode with long time. The auxiliary sealing ring will also have cracks, distortion and deformation, fracture and so on.

6. Thread seal of chemical pump

There are two types of thread seal on the chemical pump, one is the threaded joint gasket seal, one is the screw and the filler seal, both are used in the sealing situation of small diameter thread connection. The seal of the threaded connection electric diaphragm pump sealing is gasket, and the thread only provides the action of the compaction force.

7. Labyrinth seal of chemical pump

When the design is reasonable, the processing is fine, the assembly is in good condition, the speed is high, the labyrinth seal is very good. However, in practical application, there are many leakage of chemical pump, so it is not commonly used in chemical pump seal. The main reasons are:

1) The sealing side (such as shaft and bearing gland) is too large for the clearance, and the clearance is inversely proportional to the sealing effect. In some cases, the leakage trend of chemical pump is also increased.
2) There is too much oil injection in the chemical pump bearing room, and its overflow pressure exceeds the sealing resistance.
3) The installation position of oil window or oil level meter is wrong, which misleads the correct judgment of the amount of lubricating oil in the oil chamber.
4) The increase of oil temperature in operation makes its viscosity decrease, increasing the possibility of chemical pump leakage.
5) Small size of oil return tank or oil return hole, or other obstacles, causing the blocked liquid to fail to return smoothly and cause leakage.

The medium that is extracted by chemical pump has the existence of corrosion, volatilization, explosion and so on. The sealing performance requirement of pump body is much higher than that of other kinds of pumps. If the labyrinth seal is used, it increases the risk of leakage of the chemical pump. Therefore, chemical pump generally does not use this kind of sealing method.
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