Vertical blowdown pump shaft seal form for power seal can be divided into back blade seal and auxiliary impeller seal two categories. When the pump works, the centrifugal action of the backrest blade (or auxiliary impeller) makes the medium pressure at the shaft seal drop to the state of normal pressure or negative pressure, so that the pump does not leak in the process of use. When the centrifugal force disappears, the sealing effect of the back blade (or auxiliary impeller) fails, then the parking sealing device plays a sealing role. Packing seal is often used in the parking sealing device matching with the back blade (or auxiliary impeller).
Packing seal has two kinds: ordinary type and mechanical elastic type. The ordinary 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 with counterweight, so that the pump in operation when the packing loose, stop the packing pressure.
In order to ensure the life of the sealing device and reduce the leakage of the pump, the pump inlet pressure should be limited for the pump with power seal, that is, Ps<10%Pd type Ps -- pump inlet pressure, MPa; Pd -- pump outlet pressure, MPa. Power seal reliable performance, cheap price, easy maintenance, suitable for conveying medium containing more solid particles, such as industrial multi-suction blowdown pump. The disadvantage is that the power loss is larger than the mechanical seal, and the life of the parking seal device is shorter.
