Patent Application
20190345955
The present invention relates to impeller-type pumps, such as centrifugal pumps, and more particularly to centrifugal pumps configured to pump fluids near the fluid's vaporization point, and still more particularly to centrifugal pumps including an inducer and impeller to pump a fluid while minimizing the potential for cavitation during pumping operations.
Centrifugal pumps utilize an impeller and volute to pump fluids. The impeller, along with other components of the pumping mechanism, may be contained within an adaptor that is connected to a motor. The adaptor is then positioned within a volute housing whereby the impeller is rotated by the motor to move fluid along the volute and out of the volute housing. Specifically, fluid is received through an inlet in the volute housing and is directed to the center of the impeller. The fluid received at the center of the impeller is, during rotation of the impeller, moved outward from the impeller's center. The fluid then leaves the edges of the impeller and is guided by the volute, which directs the flow of fluid through the volute housing.
Cavitation is a phenomenon that occurs when a fluid vaporizes then returns back to a liquid state. This phase change back to a non-compressible liquid state will emit shock waves through the fluid resulting in damage to the closest solid components in the pump or piping. The potential for cavitation to occur in a centrifugal pump system increases as the fluid being pump approaches its vaporization point. One performance characteristic of a centrifugal pump is its NPSHr (net positive suction head required) value. If the net positive suction head available (NPSHa) is lower than NPSHr, cavitation will occur. Thus, to minimize the potential for cavitation, pump designers seek to lower the NPSHr limit. One avenue to achieve the lowest NPSHr for a centrifugal pump application is to include an inducer placed in-line prior to the pump's impeller. Typically, the inducer is attached to the shaft in front of the impeller such that energy is imparted to the fluid by the inducer before the fluid encounters the impeller blades. In this manner, the inlet head may be raised by an amount sufficient to prevent significant cavitation in the impeller pumping stage.
The present invention has application to impeller-type pumps, such as centrifugal pumps. In general, an aspect of the present invention is directed to a centrifugal pump comprising a motor with a shaft rotatably extending therefrom. An adapter is configured to be mounted to the motor at a first side with the adapter defining an opening for permitting passage of the shaft therethrough. A volute housing is configured to be mounted to a second side of the adapter wherein the volute housing defines a volute chamber and the adapter and volute housing define a pumping chamber therebetween. The volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber wherein the impeller inlet wall defines an impeller inlet orifice whereby the inlet dogleg is in fluid communication with the pumping chamber. An impeller is configured to be disposed within the pumping chamber such that a hub of the impeller is rotatably mounted on the shaft and the impeller further includes a shroud portion having a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice. An inducer having an inducer body with a first end is configured to be coupled to a distal end of the shaft. A second end of the inducer body is configured to extend into the inlet dogleg. In this manner, a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet dogleg. The inducer further includes at least two helical blades extending a length of the inducer from proximate the first end to proximate the second end whereby, upon rotation of the shaft, a fluid within the inlet dogleg is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion.
In a further aspect of the present invention, each of the helical blades has a variable pitch wherein the pitch decreases linearly from the first end to the second end. In another aspect of the present invention, a leakage flow path is defined between volute housing and the shroud portion of the impeller proximate the impeller inlet orifice. A high pressure leakage flow may then exit the leakage flow path into the volute chamber along the second portion of the inducer.
In still another aspect of the present invention, a centrifugal pump comprises a motor with a shaft rotatably extending therefrom. An adapter is configured to be mounted to the motor at a first side with the adapter defining an opening for permitting passage of the shaft therethrough. A volute housing is configured to be mounted to a second side of the adapter wherein the volute housing defines a volute chamber and the adapter and volute housing define a pumping chamber therebetween. The volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber wherein the impeller inlet wall defines an impeller inlet orifice whereby the volute chamber is in fluid communication with the pumping chamber. An impeller is configured to be disposed within the pumping chamber such that a hub of the impeller is rotatably mounted on the shaft and the impeller further includes a shroud portion having a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice. An inducer having an inducer body with a first end is configured to be coupled to a distal end of the shaft. A second end of the inducer body is configured to extend into the volute chamber. In this manner, a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet dogleg. The inducer further includes at least two helical blades extending a length of the inducer from proximate the first end to proximate the second end. Each of the helical blades may have a variable pitch wherein the pitch decreases linearly from the first end to the second end. Thus, upon rotation of the shaft, a fluid within the volute chamber is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion. A leakage flow path is defined between volute housing and the shroud portion of the impeller proximate the impeller inlet orifice. A high pressure leakage flow may then exit the leakage flow path into the volute chamber along the second portion of the inducer.
Referring to
As shown in
To minimize, and preferably prevent, the potential for cavitation, pump 10 may further include an inducer 54 having an inducer body 56 with a first end 58 configured to be coupled to distal end 60 of shaft 18. To that end, first end 58 may include female threads 62 configured to threadably mate with male threads 44 on shaft 18. As shown most clearly in
Referring again to
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
