The shaft seal is a sealing device that prevents leakage at the pump shaft and the housing. Commonly used shaft seal forms are packing seals, mechanical seals and dynamic seals. The shaft seal of the reciprocating pump is usually a packing seal, and when conveying the leak-proof medium, a diaphragm type reciprocating pump can be used. The shaft seals of rotary pumps (including vane pumps, rotor pumps) mainly include packing seals, mechanical seals and dynamic seals.
1. Packing seal
The packing sealing structure is simple, the price is cheap, the maintenance is convenient, but the leakage amount is large, and the power consumption loss is large. Therefore, packing seals are used to transport general media, such as water: generally not suitable for petroleum and chemical media, especially in expensive, explosive and toxic media.
2. Mechanical seal
Mechanical seals (also known as end seals) have good sealing effect, small leakage and long life, but they are expensive, and processing, installation and maintenance are more demanding than general sealing. The mechanical seal is suitable for conveying and petroleum and chemical media. It can be used in a variety of different viscosity, highly corrosive media containing particles.
3. Dynamic seal
The dynamic seal can be divided into two types: the back blade seal box and the impeller seal. When the pump is working, the centrifugal force of the back blade (or the auxiliary impeller) is such that the medium pressure at the shaft seal drops to a normal pressure or a negative pressure state, so that the pump does not leak during use. When the vehicle stops, the centrifugal force disappears and the sealing action 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. The common packing seal is similar to a 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 parking seal uses a counterweight to make the packing loose during operation and the packing is tight when parked. In order to ensure the life of the parking seal and reduce the leakage, the inlet pressure of the pump should be limited to the use of the power-sealed pump, ie: Ps ≤ 10% Pd, Ps-pump inlet pressure, MPa: Pd-pump inlet pressure, MPa It has reliable dynamic sealing, low price and convenient maintenance. It is suitable for conveying medium containing more solid particles, such as slurry 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.
