Centrifugal pump with hydraulic thrust balance and tandem axial seals

Abstract

A centrifugal pump with hydraulic thrust balance and tandem axial seals. The centrifugal pump has an impeller with front and rear axial seals operating in unison to either reduce or increase the size of gaps therebetween. The gaps are of a minimal dimension to minimize leakage. The rear axial seal is located at the tip of the impeller with the front axial seat located either at the impeller eye or radially outwardly thereof. Hydraulic thrust balance is achieved and continuously maintained by axial movement of the impeller shaft and impeller to modulate the gap at the rear axial seal and, thus, control the value of an effective pressure acting on the back side of the impeller whereby an outward thrust force resulting therefrom counterbalances an inward thrust force resulting from pressure acting on the front shroud of the impeller. A clearance at the rear of the impeller communicates with suction pressure through a restricted passage. Impeller hydraulic thrust balance forces usually dwarf other thrust forces which are considered to be external thrusts without significant impact on overall thrust balance. Examples of external thrusts are those that arise from suction pressure acting over the process seal area and from helical gears in integral gear driven systems. A normally preferred thrust balance design is appropriate for the majority of pump applications, but design alternatives are offered for inordinate pump applications which provide maximum capacities to handle either outward or inward external thrust loads.