Rotary seal assembly having a liquid filled bellows

Claim 1

A pump seal for a pump used to pump difficult liquids such as slurries and corrosive liquids, the seal in use sealing the shaft of the pump relative to the casing of the pump through which the shaft passes rotatably from the interior to the exterior of the casing which defines, during pumping, a fluid space containing the difficult liquid under pressure, the seal being located within a housing fixed to the casing and surrounding the shaft, and the seal comprising: first and third annular spaced sealing elements locatable fast with the shaft within the housing and each having a sealing surface; an axially extensible annular bellows fixed non-rotatably at a point between its ends to the housing, the bellows being spaced radially from and surrounding the shaft to define an annular space between the bellows and shaft; a second, annular sealing element carried at an end of the bellows away from the fluid space, the second sealing element having a sealing surface complemental in shape to that of the first sealing element and being located adjacent the first sealing element on the side thereof towards the fluid space; a fourth annular sealing element carried at the opposite end of the bellows towards the fluid space, the fourth sealing element having a sealing surface complemental in shape to that of the third sealing element and being located adjacent the third sealing element on the side thereof away from the fluid space, the first and second sealing elements in combination, and the third and fourth sealing elements in combination defining respective ends of a service liquid compartment existing in the annular space between the bellows and shaft, the bellows resiliently urging the second and fourth sealing elements axially in opposite directions towards the first and third sealing elements respectively; and a radial inlet communicating with the interior of the service liquid compartment for the introduction of a fixed volume of pressurized service liquid into the compartment, the pressurized liquid in the compartment forcing the second and fourth sealing elements axially in opposite directions to seal against the first and third sealing elements respectively and creating a service liquid barrier preventing the difficult liquid from entering the service liquid compartment, getting between sealing surfaces of the sealing elements and deteriorating those surfaces.