Idler gear for positive displacement gear pump

Abstract

One or more techniques and/or systems are disclosed for a gear pump for low speed transfers of viscous liquid slurries promotes growth of suspended particles, such as sugar crystals, by avoiding crushing of the particles. The pump includes a rotor gear in mesh with an eccentrically mounted idler gear supported on a boss of a pump head that includes a crescent seal extending into an opening resulting from the eccentricity of the idler gear relative to the rotor gear. The idler gear contains a radially extending land on each tooth profile, symmetrically oriented on adjacently spaced pairs of teeth. The lands, configured to minimize crushing of crystals passing through the pump, engage mating rotor teeth for sealing between inlet and outlet ports of the pump. To promote crystal growth, the lands cover only 10% to 30% of profile surface area of each tooth. To minimize gear tooth wear, the lands are axially staggered between successive adjacent pairs of teeth.

What is claimed is: 
     
         1 . A positive displacement gear pump comprising:
 a casing defining a casing interior, the casing comprising an inlet port and an outlet port for transferring a target fluid though the casing interior;   an external rotor gear supported within an inboard end of the casing by a rotor shaft, the external rotor gear comprising radially inwardly oriented teeth;   a head positioned at an outboard end of the casing; and   an internal idler gear rotationally supported on the head about an idler gear axis within the casing interior, the internal idler gear comprising radially outwardly oriented teeth, the internal idler gear being operably disposed on the head in a fixed, radially eccentric, relationship with the external rotor gear, and at least a portion of the internal idler gear teeth operably meshing with at least a portion of the external rotor gear teeth;   wherein the idler gear teeth comprise:
 two radially oriented surfaces respectively extending between a root and a tip of the idler gear tooth; 
 a land comprising a substantially planar surface rising from the radially oriented surface to a height, the height of the respective land from the surface being substantially constant along a length of the land, and the surface of the land configured to engage a meshing rotor tooth for sealing between the inlet port and the outlet ports of the pump; and 
 a relief area disposed adjacent to the land, the relief areas defined by the land, an edge of the idler gear tooth, and the root and the tip, wherein the relief area transiently forms a relief volume with the meshing rotor gear tooth, wherein the relief volume is sized to fit a target solid disposed in the target fluid. 
   
     
     
         2 . The positive displacement gear pump of  claim 1 , wherein a surface area of the land comprises from ten-percent to thirty-percent of a total surface area the corresponding radially oriented surface of the idler gear tooth. 
     
     
         3 . The positive displacement gear pump of  claim 1 , wherein, one of:
 a land is disposed on respective radially oriented surfaces of respective idler gear teeth; or   lands are axially staggered between successive adjacent pairs of the idler gear teeth.   
     
     
         4 . The positive displacement gear pump of  claim 1 , wherein respective relief areas are operably spaced apart from the meshing rotor gear tooth, and wherein the height of the land is equal to or greater than twenty-thousandths of an inch above the radially oriented surface of the idler gear tooth. 
     
     
         5 . The positive displacement gear pump of  claim 4 , wherein a total surface area of respective idler gear teeth with a land comprises a combination of a surface area of the land and a surface area of the relief area. 
     
     
         6 . The positive displacement gear pump of  claim 5 , wherein the surface area of the land comprises from ten-percent to thirty-percent of the total surface area the radially oriented surface of the idler gear tooth, and respective idler gear teeth comprises two relief areas respectively disposed on either side of the land. 
     
     
         7 . The positive displacement gear pump of  claim 1 , wherein the root of respective idler gear teeth is situated radially inwardly of the tip, with respective roots being shared with an adjacent tooth, and wherein one or:
 respective lands extend radially between the root and tip of the tooth; and   respective lands extend axially between respective edges of the tooth.   
     
     
         8 . The positive displacement gear pump of  claim 1 , wherein the head includes an inner surface containing a boss configured to retain the idler gear in meshed engagement with the rotor gear. 
     
     
         9 . The positive displacement gear pump of  claim 8 , wherein the inner surface further comprises a crescent seal configured to seal a crescent-shaped gap between unmeshed teeth of the idler and rotor gears. 
     
     
         10 . The positive displacement gear pump of  claim 8 , wherein the casing interior and the inner surface of the head define a pump chamber, the pump chamber comprising interior walls in proximity with the external rotor gear. 
     
     
         11 . The positive displacement gear pump of  claim 1 , wherein the casing interior and the inner surface of the head define a pump chamber, the pump chamber comprising interior walls in proximity with the edge of the idler gear, and the relief volume is defined by the interior walls of the pump chamber, the root, the tip, the land, and the meshing rotor gear tooth. 
     
     
         12 . An idler gear for use in a positive displacement gear pump having a casing that defines a casing interior, an inlet port and an outlet port in fluid communication with the casing interior, a head, an open outboard end enclosed by the head, a rotor shaft, a closed inboard end through which a rotor shaft passes, the head and casing defining a pump chamber, and a rotor gear driven by the rotor shaft, the rotor gear comprising radially inwardly oriented teeth, the idler gear comprising radially outwardly oriented teeth, the rotor gear teeth operably meshing with the idler gear teeth, the respective gears disposed within the pump chamber for rotation induced via the rotor shaft, wherein the idler gear comprises:
 axially-aligned lands disposed on respective sides of adjacently spaced pairs of the teeth that sealedly engage the operably meshing rotor gear teeth to provide a seal between the inlet port and the outlet ports of the pump, respective lands comprising a height from a surface of the idler gear tooth that remains substantially constant along length of the land; and   a clearance relief area disposed adjacent the land on respective idler gear teeth, a boundary of the relief area defined by the land, a root and tip of the idler gear tooth, and an edge of the idler gear tooth, and operably, transiently forming a clearance relief volume with the meshing rotor gear teeth, the relief volume sized to fit a target solid in a pumped fluid.   
     
     
         13 . The idler gear of  claim 12 , wherein a surface area of respective lands comprise from ten-percent to thirty-percent of a total surface area the surface of the idler gear tooth. 
     
     
         14 . The idler gear of  claim 12 , wherein the lands are axially staggered between the successive adjacent idler teeth. 
     
     
         15 . The idler gear of  claim 12 , wherein respective relief areas are operably spaced apart from the meshing rotor gear tooth, and wherein respective idler gear teeth comprises two relief areas respectively disposed on either side of the land, and the height of the land is equal to or greater than twenty-thousandths of an inch above the radially oriented surface of the idler gear tooth. 
     
     
         16 . The idler gear of  claim 12 , wherein the head comprises an inner surface containing a boss configured to retain the idler gear in mesh with the rotor gear. 
     
     
         17 . The idler gear of  claim 16 , wherein the inner surface further comprises a crescent seal configured to seal a crescent-shaped gap between unmeshed teeth of the idler and rotor gears. 
     
     
         18 . The idler gear of  claim 16 , wherein the casing interior and the inner surface of the head comprise a pump chamber, the pump chamber comprising interior walls in proximity with the external rotor gear. 
     
     
         19 . A pump, comprising:
 a casing defining a casing interior, the casing comprising an inlet port and an outlet port for transferring a target fluid though the casing interior;   a head comprising an inner surface   interior walls, which, in combination with the casing interior and head inner surface, define a pump chamber;   a rotor gear disposed in proximity with the interior walls inside the casing interior and operably supported by a rotor shaft, the external rotor gear comprising radially inwardly oriented teeth; and   an idler gear operably coupled with the head within the casing interior in a rotationally eccentric arrangement with the rotor gear, the idler gear comprising radially outwardly oriented teeth, at least a portion of which operably mesh with at least a portion of the rotor gear teeth, respective idler gear teeth comprising:   a tip disposed at a radially outward end of the tooth;   a root disposed at a radially inward end of the tooth, the root shared with an adjacent tooth;   two radial surfaces respectively disposed on either side of the tooth between the root and the tip;   a land portion of the respective radial surfaces, the land portion operably sealedly engaging with a meshing rotor tooth to seal the pumping chamber between the inlet port and the outlet ports of the pump; and   a relief portion comprising a relief cut from the land portion having a depth from the land that is substantially constant in a radial orientation between the root and the tip, the relief portion operably spaced apart from the meshing rotor tooth to operably fit a target solid in a pumped fluid between.   
     
     
         20 . The pump of  claim 19 , respective idler gear teeth comprising at least two relief portions on each radial surface, the relief portions respectively disposed on either side of the land portion.