The drawing shows a vertical cross-sectional view of the centrifugal pump for the pumping of gas containing media as, for example, medium consistency fiber suspensions in the pulp and paper industry. The centrifugal pump includes a housing 50 having an inlet channel 52 and a volute 54. The housing 50 is attached to the pump frame 56 having at one end thereof the bearing assembly (not shown) for supporting the pump shaft 58 at the end of which the centrifugal impeller 60 having a plurality of openings 62 extending through the back plate 64 thereof is mounted.FORGED STEEL VALVES The centrifugal impeller 60 is further provided with front vanes, i.e. working vanes 66, on the front side thereof and with back vanes 68 on the opposite side of the back plate 64. A rotor 87 having fluidizing blades 83 thereon may be mounted on the shaft 58 in front of impeller 60 for pumping fiber suspensions of medium or high consistency. The fluidizing blades may extend through the pump inlet 52 or be located only outside the inlet and within the pulp containing vessel. Located between the bearing unit and the centrifugal impeller 60 is the sealing assembly (not shown). Between the sealing assembly and the centrifugal impeller 60 there is mounted a vacuum pump 70 on the same shaft 58 as the centrifugal impeller 60. Water Power Control ValvesThe vacuum pump 70 is separated from the volute 54, i.e. from the space housing the centrifugal impeller 60, by means of an intermediate plate 72 which also forms the head or the front wall 112 of the vacuum pump 70. In this embodiment plate 72 has a non-annular volume or opening 146 in the vicinity of the shaft 58 for permitting the gas to flow from the space behind the centrifugal impeller 60 to the vacuum pump 70. The volume or opening 146 preferably extends proximate to the shaft 58 or, depending on the design, proximate to the impeller extension sleeve 92, and communicates with centrifugal pump volute 54 through preferably annular opening 74 and with the vacuum pump through gas inlet port 94. The location of non-annular volume 146 is preferably chosen in accordance with or depending upon the pressure distribution in the volute 54. As is known, for example, the point of lowest pressure in the pump volute is just behind the pump outlet when viewed in the direction of rotation of the pump impeller.Water Control valves Locating the non-annular volume 146 at this position substantially decreases the danger of the fibers being drawn into the volume together with the gas. The volume may also be located at the point of highest pressure thereby requiring less vacuum for the removal of gas; or the volume may be positioned at any other location between the highest and lowest pressure as described.

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2012-01-09

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