Shaft seal is a friction seal or stuffing box that prevents liquid leakage between the shaft of the compressor or other fluid transfer equipment and the bearing. It is also a seal that prevents leakage at the pump shaft and housing. Commonly used shaft seal types are packing seals, mechanical seals and power seals.
The shaft seal of a reciprocating pump is typically a packing seal. A diaphragm type reciprocating pump can be used when conveying a medium that is not allowed to leak. The shaft seals of rotary pumps (including vane pumps, rotor pumps, etc.) mainly include packing seals, mechanical seals and dynamic seals.
Types
Packing seal
The packing sealing structure is simple, the price is cheap, and the maintenance is convenient. However, the amount of leakage is large and the power consumption is large. Therefore, the packing seal is used to transport general media such as water; it is generally not suitable for petroleum and chemical media, especially for valuable, explosive and toxic media.
Mechanical Seal
Mechanical seals (also called end seals) have good sealing effect, small leakage and long service life, but they are expensive, and the processing, installation and maintenance are more demanding than general sealing.
The mechanical seal is suitable for transporting petroleum and chemical media and can be used in a variety of different viscosity, highly corrosive and particle-containing media. The American Petroleum Institute Standard API 610 (8th Edition) stipulates that: in addition to the user's provisions, it should be equipped with a cartridge type mechanical seal.
Dynamic seal
The dynamic seal can be divided into two types: the back-blade seal and the auxiliary impeller seal. When the pump is working, the centrifugal force of the backrest blade (or the auxiliary impeller) causes the medium pressure at the shaft seal to drop to the normal pressure or negative pressure state, so that the pump does not leak during use. When the vehicle stops, the centrifugal force disappears, and the sealing effect of the back blade (or the auxiliary impeller) fails. At this time, the parking seal device acts as a sealing. A packing seal is often used in the parking seal device matched with the back blade type (or the auxiliary impeller). Filler seals are available in both conventional and mechanically elastic versions. Ordinary packing seals are similar to general packing seal pumps, requiring a slight positive pressure at the shaft seal to avoid dry friction of the packing. The mechanical elastic packing seal adopts the counterweight, so that the packing is loosened during operation and the packing is pressed when stopping.
The dynamic sealing performance is reliable, the price is cheap, and the maintenance is convenient. It is suitable for conveying medium containing more solid particles, such as slurry pump and slurry pump in the phosphoric acid industry. The disadvantage is that the power loss is larger than the mechanical seal and the life of the parking seal is shorter.
The seal between the rotating pump shaft and the fixed pump casing is called a shaft seal. Its function is to prevent high pressure liquid from leaking out of the shaft along the shaft, or outside air infiltrating along the shaft. For the shaft seal of a centrifugal pump, it is a dynamic seal.
According to whether the sealing joint surface is in contact, it can be divided into a contact dynamic seal and a non-contact dynamic seal.
The sealing device of the contact dynamic seal is in contact with the shaft, and there is relative friction between the two. The contact type dynamic seal has a packing seal and a mechanical seal.
