The packing seal is the most commonly used seal type of slurry pumps, it is composed by packing ring, packing sleeve, packing, packing gland, stud bolts and nuts.
Through the packing and shaft surface contact pressure, it prevents the medium leakage to achieve the purpose of sealing. The existence of many of the small gap and the groove, making it possible to achieve necessary sealing pressure by sufficient pressing forcing the packing material into elastoplastic deformation to reduce the gap between the contact seal surface.
Since there is always a certain degree of roughness in the surface of the shaft, it is not possible with packing to achieve the desired contact, there must be a slight gap exists, thus forming numerous “labyrinth”. These fine tortuous gap damping play the role of the media repeatedly throttle and the “labyrinth effect” produced by the stagnation in gap boundary layer and other factors, lead to blocking and achieve sealing.
So, the sealing effect is formed at the obstruction within the gap between the contact surface of the medium into the packing and the pump shaft.
After we know the structure of packing seal, it is easily to get the seal leakage ways:
Leakage through the interface between Packing and Static parts;
Leakage through Packing itself;
leakage through the interface between the Packing and Moving parts.
It is the same way for leakage through static packing surface and leakage type. The leakage of Packing depends on the internal structure of the sealing and penetration itself, the plaiting packing prone to this leakage.
When the infiltration of the media or the media is gas, the penetration leakage through the packing is almost inevitable, but the specific mechanism of this kind leakage will be explored further. For the vast majority of the liquid medium, the leakage mainly through the interface between the packing and the moving parts. For slurry pumps, the large size particles make it difficult to close the small gaps in shaft seal, so,
when pumping the corrosive liquids or the liquids contains corrosive slurry, it will penetrate into the packing seal, these will cause wear and corrosion of the shaft.
Especially when two kinds of materials are constituting the friction pairs in the electrolyte solution, there may occur the galvanic corrosion that is much more accelerated corrosion damage to the shaft. So, when transporting toxic, corrosive and precious liquid, due to the small amount of leakage, and even allowed no leakage, it can not use packing seal.