Seal classification and description of shaft seal type

Seal classification and description of shaft seal type Shaft seal is a sealing device set to prevent leakage between the pump shaft and the casing. Commonly used shaft seal types include packing seals, mechanical seals and power seals. The shaft seal of a reciprocating pump is usually a packing seal. When transporting media that is not allowed to leak, a diaphragm reciprocating pump can be used. The shaft seals of rotary pumps (including vane pumps, rotor pumps, etc.) mainly include packing seals, mechanical seals and power seals. 1. Packing seal The packing seal has simple structure, low price and convenient maintenance. But the leakage is large and the power loss is large. Therefore, the packing seal is used to transport general media, such as water, etc.; it is generally not suitable for petroleum and chemical media, especially cannot be used in precious, explosive and toxic media. 2. Mechanical seal The mechanical seal (also known as the end face seal) has a good sealing effect, small leakage and long life. Mechanical shaft seals are expensive, and require higher processing, installation, and maintenance than general seals. Mechanical seals are suitable for transporting petroleum and chemical media, and can be used for a variety of media with different viscosities, strong corrosiveness, and particles. The American Petroleum Institute standard API610 (8th edition) stipulates that, unless specified by the user, a cartridge mechanical seal should be equipped. 3. Power seal Power seal can be divided into two types: back leaf seal and auxiliary impeller seal. When the pump is working, the centrifugal force of the backrest blade (or auxiliary impeller) causes the medium pressure at the shaft seal to drop to normal pressure or negative pressure, so that the pump does not leak during use. The centrifugal force disappears when parking, and the sealing effect of the back blade (or auxiliary impeller) fails. At this time, the parking sealing device plays a sealing role. Packing seals are often used in parking seals that are matched with the back blade (or auxiliary impeller). There are two types of packing seals: ordinary type and mechanical elastic type. Ordinary packing seal is similar to the general packing seal pump, requiring a slight positive pressure at the shaft seal to avoid dry friction of the packing. The mechanical elastic packing seal adopts counterweight to loosen the packing when the pump is running and compress the packing when the pump is stopped.