Pump sealing system with throttle bushing

Abstract

A sealing arrangement is disclosed for a rotating shaft. A mechanical seal and a throttle bushing are mounted in a pump casing having a process fluid chamber and an end region. A shaft is rotatably mounted in the pump casing. The seal has a stationary portion mounted to the pump casing, and a rotatable portion mounted to the shaft. A throttle bushing surrounds the shaft and is connected to the casing. The throttle bushing has an inner surface that provides a fluid passageway between the inner surface of the throttle bushing and the shaft. The throttle bushing is spaced along the shaft at an axial distance from the mechanical seal, thus forming a barrier fluid space. The mechanical seal separates the barrier fluid space from the process fluid chamber. Barrier fluid migrates past the throttle busing inner surface, lubricates the pump bearings and gears, and is collected for reuse.

What is claimed is: 
     
         1 . A sealing arrangement for a rotating shaft, comprising:
 a pump casing having a process fluid chamber and an end region;   a shaft rotatably mounted with respect to the pump casing;   a mechanical seal having a stationary portion and a rotatable portion, the stationary portion associated with the pump casing and the rotatable portion associated with the shaft;   a throttle bushing having an outer surface coupled to the pump casing and an inner surface surrounding a portion of the shaft, the throttle bushing inner surface configured to provide a fluid passageway between the inner surface of the throttle bushing and an outer surface of the shaft;   wherein the throttle bushing is spaced along the shaft at an axial distance from the mechanical seal to form a barrier fluid space therebetween; and   wherein the mechanical seal separates the barrier fluid space from the process fluid chamber.   
     
     
         2 . The sealing arrangement of  claim 1 , wherein the barrier fluid space is coupled to a pressure regulator for maintaining a pressure of barrier fluid in the barrier fluid space within a predetermined pressure range. 
     
     
         3 . The sealing arrangement of  claim 2 , wherein the predetermined pressure range is greater than a pressure of process fluid in the process fluid chamber so that barrier fluid passes through the mechanical seal into the process fluid space. 
     
     
         4 . The sealing arrangement of  claim 1 , wherein the inner surface of the throttle bushing is configured to allow a predetermined amount of barrier fluid to pass from the barrier fluid space between the throttle bushing and the shaft during operation. 
     
     
         5 . The sealing arrangement of  claim 4 , wherein the inner surface of the throttle bushing has no inner diameter groove. 
     
     
         6 . The sealing arrangement of  claim 5 , wherein the at least one inner diameter groove is a labyrinth type seal. 
     
     
         7 . The sealing arrangement of  claim 1 , further comprising a bearing assembly coupled to the shaft, the bearing assembly positioned between the throttle bushing and the end region of the pump so that barrier fluid passing through the fluid passageway between the inner surface and an outer surface of the shaft contacts the bearing assembly. 
     
     
         8 . The sealing arrangement of  claim 1 , wherein the throttle bushing comprises an outer surface, the outer surface defining a groove for receiving a sealing element, the sealing element for sealing at least a portion of the outer surface of the throttle bushing to the pump casing. 
     
     
         9 . The sealing arrangement of  claim 8 , wherein the sealing element is an elastomeric o-ring. 
     
     
         10 . The sealing arrangement of  claim 1 , the barrier fluid space having a barrier fluid inlet for receiving barrier fluid from a barrier fluid source, the end region having a fluid outlet for discharging collected barrier fluid therefrom. 
     
     
         11 . The sealing arrangement of  claim 1 , wherein the source of barrier fluid comprises a fluid loop coupled between the barrier space and the end region of the pump casing, the fluid loop further including a cooling element and a filter element for cooling and filtering barrier fluid collected from the end region. 
     
     
         12 . The sealing arrangement of  claim 11 , wherein the fluid loop includes a pressure regulator. 
     
     
         13 . The sealing arrangement of  claim 12 , wherein the stationary portion and the rotatable of the mechanical seal comprise respective seal faces, and wherein the pressure regulator is configured to maintain barrier fluid in the barrier fluid space at a pressure higher than a pressure of process fluid in the process fluid chamber.