The shaft seal is a sealing device that prevents leakage of the pump shaft and the housing. Commonly used shaft seal types are packing seals, mechanical seals and dynamic seals.
1, packing seal
The packing seal structure is simple, the price is cheap, and the maintenance is convenient, but the leakage amount is large and the power consumption loss is large. The packing seal is therefore used to transport general media such as water. Generally not applicable to petroleum and chemical media, especially in expensive, explosive and toxic media.
2, mechanical seal
Mechanical seals (also known as end seals) have a good sealing effect, a small amount of leakage, and a long life, but they are expensive. Processing, installation and maintenance are more demanding than general sealing.
Mechanical seals are suitable for transporting petroleum and chemical media. Can be used in a variety of different viscosity, strong corrosive and particle-containing media.
3, 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 a normal pressure or a negative pressure state. Keep the pump from leaking during use. When the pump working 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 (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 parking seal uses a counterweight. The packing is released when the pump is running, and the packing is pressed when stopping.
In order to ensure the life of the parking seal and reduce the leakage of the pump, the pump inlet pressure should be limited for pumps with dynamic seals.
Namely: Ps<10% Pd
Ps - pump inlet pressure
Pd—pump inlet pressure
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. The disadvantage is that the power loss is greater than the mechanical seal and the life of the parking seal is shorter.
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