Back cooling or rapid cooling of the basic process of the mechanical seal system function-

Back cooling or rapid cooling of the basic process of the mechanical seal system function

　2019-06-13　　

Back cooling or rapid cooling of the basic function of the mechanical seal system:

The cooling method of cooling the static ring directly from the back of the static ring with a kind of coolant (water, oil, etc.) is back cooling. Because of the good cooling effect, it can directly cool the back of the static ring quickly, which is also called rapid cooling. In some books, quenching is defined as the injection of liquid or gas into the low pressure side of the sealing end surface. Sand mill mechanical seal

Back cooling is often used in combination with flushing. When the sealed medium is a high melting point liquid or a liquid with strong solidification and a liquid that is easy to crystallize, steam (for heat preservation), solvent or water can be used to prevent the back of the static ring The seal is solidified and washed around the sealing surface; when the sealed medium is a low-temperature liquid, a liquid that is not easy to freeze can be used to prevent freezing or methanol is used to thaw; when the low-pressure blower and other air seals use external mechanical seals, they can be rotated Partially injected liquid is cold back.

Common back cooling methods are shown in Figure 6-20. Figure (a) shows the back-cooling method of the externally mounted mechanical seal. It not only plays a role in cooling the sealing surface, but also acts as a water seal to prevent liquid leakage. It can be applied to such as acid pumps that contain harmful Liquids, dangerous liquids, and liquids that tend to crystallize when exposed to air. Figure (b) shows the back cooling method with baffle sleeve. Its structure is to add a set of tubes on the sealing gland to play the role of baffle. At the same time, the coolant can fully contact with the seal to achieve good The cooling effect.

Figure 6-20 Several common back cooling methods

Commonly used back cooling fluids include water, steam or nitrogen. When water is used as the back cooling liquid, auxiliary seals should be used to prevent its outflow. If the temperature of the sealed medium is above 100°C, scale will be generated in the small part of the moving ring to hinder the movement of the moving ring or the sealing surface wear. If the seal is broken or the seal is held, the seal will eventually fail; when steam is used as the back cooling liquid, such as a hot oil pump seal, it can not only cool the sealing surface, but also reduce the thermal deformation of the static ring. Therefore, when selecting the back cooling method and back cooling liquid, if the back cooling liquid is water, you must pay attention to the hardness of the water and ensure that it is not easy to scale at this temperature; if the sealing temperature is higher, steam can be used as the back cooling liquid ; When the gas phase is sealed, steam static ring back cooling can be used to make the seal in a full gas phase state.

The pressure of the back cooling liquid is usually 0.02~0.05MPa, and the temperature difference between inlet and outlet should be controlled at 3~5℃. The flow rate can generally be determined according to the shaft diameter: when the shaft diameter d<100mm, the flow rate is 0.2~2L/min; when the shaft diameter>100mm, the flow rate is 0.5~3L/min. Figure 6-21 shows a typical mechanical seal structure and pipeline interface, which includes auxiliary seals for back cooling and back cooling liquid.

Figure 6-21 Typical mechanical seal structure and pipeline interface

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Precautions when the mechanical seal adopts flushing fluid to control the temperature of the sealed cavity