Regarding the impeller seal
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Last week, I encountered a self-priming pump; it was a mobile pump used for temporary material transfer. A few months ago, when it was in use, users reported shaft seal leakage. During maintenance (the first time this type of pump was repaired), it was found that the shaft seal area contained only a secondary impeller, with no mechanical seal or packing seal. Moreover, the cavity of the secondary impeller was stuck shut and could not be opened; there were only a few small holes, through which it was possible to see that the impeller was fixed to the shaft and rotated circumferentially within the seal cavity, with slight axial movement. After thinking for a while, I believe this is a shaft seal with a pure impeller seal; it’s likely possible to achieve sealing only by adjusting the axial position of the impeller within the sealing chamber. Its motor is directly connected to the shaft, with a flange connection between the motor and the pump body. I added a 0.5mm gasket between these flange connections to keep the clearance at the impeller mouth ring at 0.5mm. Test run, uh, okay, there’s no more leakage at the shaft seal. Some experience, for reference only.
The sealing principle of the auxiliary impeller is to draw the fluid medium flowing toward the shaft seal in the opposite direction; the auxiliary impeller is generally an open impeller； In fact, this creates a slight negative pressure at the shaft seal, preventing leakage ； The secondary impeller seal generally requires a packing seal as a supplement ； The clearance between the auxiliary impeller and the pump body is very important; if it is too large, the performance will be poor
I have only seen vertical types with pure auxiliary impeller sealing
All the pumps with impellers in our area are fitted with packing seals. I’ve only heard of using a secondary impeller for sealing before; I’m not sure what the effect will be
Our pump is a type that uses a secondary impeller for sealing; seal gaskets can be installed at the hub of the secondary impeller. There is no compression, and the distance between the secondary impeller and the rear cover plate is maintained at 0.2 mm. With the sealing in place, there is generally no leakage, while during startup and shutdown, auxiliary sealing is provided by packing.