Seal classification and description of shaft seal type1

Seal classification and description of shaft seal type

The shaft seal is a sealing device set up to prevent leakage between the pump shaft and the casing. Commonly used shaft seal types are packing seals, mechanical seals and dynamic seals. The shaft seal of a reciprocating pump is usually a packing seal. When the medium is not allowed to leak, the diaphragm type reciprocating pump can be used. The shaft seals of rotary pumps (including vane pumps, rotor pumps, etc.) mainly include packing seals, mechanical seals and dynamic seals. 1. Packing seal The packing seal has a simple structure, low price and convenient maintenance. However, the leakage is large and the power loss is large. Therefore, the packing seal is used for conveying general media, such as water, etc. It is generally not suitable for petroleum and chemical media, especially in precious, explosive and toxic media. 2. Mechanical seal Mechanical seal (also known as end face seal) has good sealing effect, small leakage and long service life. Mechanical shaft seal is expensive, and its processing, installation and maintenance requirements are higher than that of general seals. Mechanical seals are suitable for transporting petroleum and chemical media, and can be used for 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. Dynamic seals Dynamic seals can be divided into two types: back vane seals and auxiliary impeller seals. When the pump is working, the centrifugal force of the back vane (or auxiliary impeller) reduces the medium pressure at the shaft seal to the normal pressure or negative pressure state, so that the pump does not leak during use. When the centrifugal force disappears when parking, the sealing effect of the back blade (or auxiliary impeller) is invalid, and the sealing effect is achieved by the parking sealing device. Packing seals are often used in the parking seals matched with the back vane type (or auxiliary impeller). There are two types of packing seals: ordinary type and mechanical elastic type. The ordinary packing seal is similar to the general packing seal pump, and requires a slight positive pressure at the shaft seal to avoid dry friction of the packing. The mechanical elastic packing seal adopts counterweight, so that the packing is loosened when the pump is running, and the packing is compressed when the pump is stopped.