Selection of pump shaft seal

Selection of pump shaft seal

 

Shaft seal is a sealing device to prevent leakage of pump shaft and shell. Commonly used shaft seal types are packing seal, mechanical seal and power seal.

The shaft seal of the high temperature oil pump is usually a packing seal, and the diaphragm reciprocating pump can be used when the transmission does not allow the leakage medium. Rotary pump (including gear pump, gear pump, rotor pump, etc.) shaft seal mainly packing seal, mechanical seal and power seal.

1. Packing seal

Packing seal structure is simple, cheap, convenient maintenance, but large leakage, large power loss. Therefore, packing seal is used for conveying general media, such as water; Generally not suitable for petroleum and chemical media, especially can not be used in valuable, explosive and toxic media.

2. Mechanical seal

Mechanical seal (also known as end seal) sealing effect is good, the leakage is small, long life, but the price is expensive, processing, installation, maintenance and maintenance than the general seal requirements.

Mechanical seal is suitable for conveying petroleum and chemical media, can be used for a variety of different viscosity, strong corrosive and granular media. The National Petroleum Institute Standard API 610(8th edition) states that, unless otherwise specified by the customer, packaged mechanical seals shall be equipped.

3. Power seal

Dynamic seal can be divided into two types: back blade seal and auxiliary impeller seal. When the pump works, the centrifugal force of the backrest blade (or the auxiliary impeller) makes the medium pressure at the shaft seal drop to the normal pressure or negative pressure state, so that the pump does not leak in the process of use. When stopping, the centrifugal force disappears, and the sealing effect of the back blade (or auxiliary impeller) fails, then the sealing device plays a sealing role by stopping. Packing seal is often used in the stop sealing device supporting the back blade (or auxiliary impeller). There are two kinds of packing seal: normal type and mechanical elastic type. The common packing seal is similar to the general packing seal pump, requiring the shaft seal to maintain a small positive pressure to avoid dry friction of the packing. Mechanical elastic packing stop seal adopts counterweight to loosen the packing when the pump is running and compress the packing when the pump is stopping.