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Pump Up Thrust Protection Enhancement

IP.com Disclosure Number: IPCOM000194572D
Publication Date: 2010-Mar-31
Document File: 1 page(s) / 44K

Publishing Venue

The IP.com Prior Art Database

Abstract

In operation a multi stage centrifugal pump is subject to thrust forces that attempt to push the impeller downward of upward. The hydraulic thrust acting in the downward direction is greatest when the developed head is the greatest. The inertial flow force acting in the upward direction is greatest at maximum flow. The force developed by the vane is radial in a radial flow pump and cancels itself out, but adds to the hydraulic down thrust in mixed and axial flow pumps. As the operating point of the pump is moved from wide open flow to shut in, the thrust moves from mostly dominate up thrust at wide open to dominate down thrust at shut in. If it is desired for the pump to operate over the total performance curve, it must be designed to handle both the up and down thrust. This can be problematic and therefore most pumps restrict their operating range to the down thrust region. In a "fixed" design, the impellers are fastened solidly to the shaft in order that the generated thrust can be transferred to an external thrust bearing below the pump. In a floater design the impellers are keyed to the shaft so that they are forced to rotate with the shaft but they are free to "float" axially. The floater impellers individually settle into their running position in their diffuser and transfer their thrust to their diffuser by means of a thrust washer. Pumps that are designed to operate in down thrust will upon starting with an empty fluid column above them with momentarily go into up thrust. Both the floater and fixed impellers are protected from this momentary up thrust by use of bumpers or up thrust washers between the impeller and the diffuser located above the impeller. Prolonged up thrust can wear through this protection and damage the pump. To increase the utility of pump designs, pumps have been designed to allow prolonged up thrust by improving the up thrust bearing using materials that can tolerate the trust load and poor lubricity of the pumped fluid. These schemes have had some problems with the fixed impeller design because the first impeller to contact the up thrust bearing takes the thrust load for the entire pump. When this bearing is destroyed, the next bearing to contact takes the entire load. Rather than spreading the load among all the up thrust bearings, a chain failure occurs, overloading and destroying each bearing as it contacts. This invention proposes a method to prevent the chain failure when running a pump in up thrust. The pump is built with each impeller keyed to the shaft as in a floater design, however they are prevented from moving down the shaft by a collet, snap ring of similar devices. They are in a fixed position as with the fixed impeller when the thrust is downward, but individually move axially when the thrust is upward. This allows each impeller to contact its own up thrust bearing without having to carry the up thrust form the other impellers.

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Pump Up Thrust Protection Enhancement

In operation a multi stage centrifugal pump is subject to thrust forces that attempt to push the impeller downward of upward. The hydraulic thrust acting in the downward direction is greatest when the developed head is the greatest. The inertial flow force acting in the upward direction is greatest at maximum flow. The force developed by the vane is radial in a radial flow pump and cancels itself out, but adds to the hydraulic down thrust in mixed and axial flow pumps. As the operating point of the pump is moved from wide open flow to shut in, the thrust moves from mostly dominate up thrust at wide open to dominate down thrust at shut in. If it is desired for the pump to operate over the total performance curve, it must be designed to handle both the up and down thrust. This can be problematic and therefore most pumps restrict their operating range to the down thrust region. In a “fixed” design, the impellers are fastened solidly to the shaft in order that the generated thrust can be transferred to an external thrust bearing below the pump. In a floater design the impellers are keyed to the shaft so that they are forced to rotate with the shaft but they are free to “float” axially. The floater impellers individually settle into their running position in their diffuser and transfer their thrust to their diffuser by means of a thrust washer. Pumps that are designed to operate in down thrust will upon starting with an empty fluid column above them with momentarily go into up thrust. Both the floater and fixed impellers are protected from this momentary up thrust by use of bumpers or up thrust washers between the impeller and the diffuser located above the impeller. Prolonged up thrust can wear t...