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.

Description

BACKGROUND

Positive displacement gear pumps are commonly used to pump moderate to high viscosity liquids. A typical positive displacement gear pump includes a rotor gear mounted on a shaft; the rotor gear contains a plurality of circumferentially disposed, spaced-apart, radially inwardly directed gear teeth that also extend axially toward an open end of the pump casing. A head covers the open end of the pump casing, and the head supports an idler pin to which an idler gear is mounted eccentrically with respect to the rotor gear. The idler gear also contains a plurality of gear teeth circumferentially disposed between successive idler gear roots. In contrast to the rotor gear teeth, which extend radially inwardly, the idler gear teeth extend radially outwardly.

A crescent-shaped seal is disposed radially between unmeshed teeth of the idler gear and rotor gears, the seal being positioned within a crescent-shaped gap, generally directly opposite a point of fully engaged meshing rotor and idler gear teeth. The crescent seal is necessary to assure sufficient pressure differentials between an inlet (suction) port and an outlet (discharge) port of the pump. The idler gear teeth engage an inboard, radially inwardly curved, portion of the seal, while the rotor gear teeth engage an outboard, radially outwardly curved, portion of the seal. In addition, the intermeshing idler and rotor teeth also act as a seal between the inlet and outlet ports. Thus, sealing effects of the intermeshing teeth, as well as of the crescent seal, cooperate to retain desirable pressure differentials between the inlet and outlet ports.

Although considerable progress has been made in sealing technologies related to positive displacement gear pumps, additional improvements are needed. For example, in pumping of slurries that include growing particles, such as crystals suspended in liquid slurries, idler and rotor gear teeth often undesirably crush the suspended particles.

Thus, there is a particular need to avoid crushing of suspended particles, as for example sugar crystals within a sugar slurry during their movements through a positive displacement gear pump

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key factors or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

This disclosure generally relates to positive displacement gear pumps involved in the pumping of viscous liquids. More particularly the disclosure relates to construction of an idler gear for pumping of slurries containing growing particles retained in suspension, such as sugar crystals, without crushing the particles.

In one form of this disclosure, a positive displacement gear pump includes a casing defining a casing interior. The casing includes inlet and outlet ports for transferring fluids though the casing interior. An external rotor gear is supported within an inboard end of the casing by a rotor shaft. A head is positioned at an outboard end of the casing, and an internal idler gear is rotationally supported on the head about an idler gear axis, the head supporting the idler gear for rotation within the casing interior. The idler gear is positioned on the head in a fixed, radially eccentric, relationship with respect to the rotor gear, having a portion of its teeth meshing with a portion of the rotor gear teeth. As disclosed, the idler gear has radially outwardly oriented teeth, while the rotor gear has radially inwardly oriented teeth.

The teeth of the idler gear also extend axially, and each meshing surface of each idler gear tooth contains a radially oriented land. Adjacently spaced pairs of the teeth define pairs of symmetrically aligned lands, each of the pair lands spaced by a root between the spaced teeth. The lands are configured to engage meshing rotor teeth for sealing between inlet and outlet ports of the pump. The lands define boundaries of clearance relief volumes transiently formed between meshing idler gear teeth and rotor gear teeth to minimize crushing of crystals passing through the pump.

In another form of this disclosure, an idler gear is configured 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. The idler gear is farther configured for a positive displacement gear pump that includes 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 having radially inwardly oriented teeth, the idler gear having radially outwardly oriented teeth, the rotor gear teeth meshed with the idler gear teeth, with the gears disposed within the pump chamber for rotation induced via the rotor shaft. The idler gear has teeth that contain symmetrically oriented, radially extending, lands on each side of adjacently spaced pairs of the teeth to engage and mesh with rotor gear teeth for sealing between inlet and outlet ports of the pump. The lands are configured to provide clearance relief volumes transiently formed between the meshing idler and rotor gear teeth to minimize crushing of crystals passing through the pump.

In yet another form of the disclosure, a method of making a positive displacement gear pump, having an extelior rotor gear and an internal idler gear that includes clearance relief volumes between meshing idler gear teeth and rotor gear teeth to minimize crushing of crystals passing through the pump, includes modifying an involute gear tooth profile on a standard idler gear by cutting a pair of radially oriented clearance surfaces on each tooth profile of the idler gear to form a radially oriented land on the profile, the land configured to make direct contact with teeth of the meshing rotor gear. The method further includes forming the clearance surfaces to have a depth of 20 to 40 thousandths of an inch lower than the height of each land. Under the method, each land is a raised surface, oriented radially along a radially extending profile of each tooth, and each land extends axially over a range of 10° 10 to 30% of the total surface area of each tooth.

The features, functions, and advantages disclosed herein can be achieved independently in various other forms or embodiments, or may be combined in yet other forms or embodiments, the details of which may be better appreciated with reference to the following description and drawings. To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth certain illustrative aspects and implementations. These are indicative of but a few of the various ways in which one or more aspects may be employed. Other aspects, advantages and novel features of the disclosure will become apparent from the following detailed description when considered in conjunction with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the disclosed positive displacement gear pump.

FIG. 2 is an elevation of the positive displacement gear pump embodiment of FIG. 1, as viewed along lines 2-2 of FIG. 1.

FIG. 3 is an enlarged view of a portion of FIG. 2, with the head of the pump removed to reveal rotor gear and idler gears hidden in the view of FIG. 2.

FIG. 4 is a perspective view of the head not included in FIG. 3.

FIG. 5 is a perspective view of several pump elements, including the rotor gear shaft, the rotor gear, the idler gear, and the head.

FIG. 6 is a perspective view that includes details of an embodiment of an internal idler gear constructed in accordance with this disclosure.

It should he understood that the drawings are not necessarily to scale, and that disclosed embodiments are illustrated only schematically. It should be further understood that the following detailed description is merely exemplary and not intended to be limiting in application or uses. As such, although the present disclosure is, for purposes of explanatory convenience, depicted and described in only the illustrative embodiments presented, the disclosure may be implemented in numerous other embodiments, and within various other systems and environments not shown or described herein.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are generally used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to facilitate describing the claimed subject matter.

Referring initially to FIGS. 1-3, a positive displacement gear pump 10 includes a case or casing 12, having interior walls that define a casing interior 14. The pump case 12 includes a pump inlet port 16 and an outlet port 18 to accommodate transfers of liquids through the casing interior 14 of the gear pump 10. As an enlarged view of a portion of FIG. 2, FIG. 3 provides an internal view of the disclosed positive displacement gear pump 10, revealing a so-called external rotor gear 20 supported within an inboard end 22 of the casing 12 through which a rotor shaft 24 passes. The rotor shaft 24 drives the rotor gear 20 via a motor, not shown. The rotor gear 20 includes a plurality of radially inwardly oriented teeth 26 (FIG. 3).

Referring now also to FIG. 4, a pump head 28, adapted to he bolted to the casing 12, is configured to close an outboard, otherwise open, end 29 of the casing 12. An internal idler gear 30 (FIG. 3) is configured to be mounted for rotation on an idler pin 58 supported on a boss 56 that extends from an interior surface 54 of the head 28. The idler gear 30 is driven by the rotor gear 20 about an idler gear axis 32 (FIGS. 2 and 3). The head 28 thus supports and retains the idler gear 30 in mesh with the rotor gear 20 for rotation of the idler gear about the idler gear axis 32. For this purpose, the idler gear 30 has a plurality of radially outwardly oriented teeth 34, a portion of which mesh with a portion of the inwardly oriented teeth 26 of the rotor gear 20. The rotor gear 20 rotates about a separate rotor gear axis 36 (FIGS. 2 and 3), and is thus offset from the idler gear axis 32 to provide for rotational eccentricity between the rotor gear 20 and the idler gear 30. In the described embodiment, the casing 12 may also include a relief valve assembly 35, as shown in FIGS. 1 and 2, and as will be appreciated by those skilled in the art.

FIG. 5 illustrates physical relationships of various elements of the pump 10 that are absent from the view of FIG. 2, including the head 28, rotor gear 20, and rotor shaft 24, the rotor shaft being directly connected to the rotor gear 20 for driving rotation thereof. The radially inwardly oriented teeth of the rotor 20 define a plurality of circumferentially spaced rotor teeth 26 that extend axially into a pump chamber 70 (FIG. 3). The pump chamber 70 is defined by the casing interior 14, essentially the interior walls of the casing 12, as, well as the head 28, which encloses an outboard end 29 of the casing 12. As such, the rotor gear 20 and the idler gear 30 are eccentrically positioned with respect to one another within the pump chamber 70.

In this disclosure, the term “tooth” refers to a single gear tooth of either the rotor gear or the idler gear. In this disclosure, the term “teeth” refers to a plurality of gear teeth of either the rotor gear or the idler gear, or both in the case of meshing teeth. Moreover, the disclosed gear pump 10 need not be portrayed exclusively in the orientation shown in the drawings. For example, the inlet port 16 may have a 90° orientation with respect to the outlet port 18, instead of the 180° orientation depicted. Additional variations of elements and components may apply within the context of this disclosure.

Referring now also to FIG. 6, the idler gear 30 includes the plurality of radially outwardly 0 liented idler teeth 34 disposed between alternating idler roots 38. In contrast to the depicted radially inward taper of the inwardly oriented rotor teeth 26, the idler teeth 34 taper outwardly, as they extend radially away from the roots 38. Further, the circumferentially disposed rotor teeth 26 are separated by spaces 27 (FIG. 5), which receive the idler teeth 34 within the casing interior 14 of the pump 10 as shown in FIG. 3. At the top of the pump 10, the idler gear teeth 34 fully intermesh with the rotor gear teeth 26, and each meshing surface 42 of each tooth 34 has a total surface area (FIG. 6), as further referenced below.

Referring now specifically to FIG. 6, eight teeth 34, identified herein as 34A through 34H, are symmetrically and circumferentially positioned about the axis 32 of the idler gear 30. This disclosure, however, is not limited to only eight teeth, as there may be more or less teeth than as described herein, depending on size of gear pump. Each meshing surface 42 of each tooth 34A through 34H contains a corresponding raised land 40, referenced herein as 40A through 40H, in correspondence with a specific tooth. Each land, farther described below, is a radially extending surface configured to intermesh with rotor gear teeth 26. Right and left axial edges 48 (A through H) and 50 (A through H) of the lands respectively define boundaries of left and right clearance surfaces 44 (A through H) and 46 (A through H), juxtaposed on each side of each land. Rather than contact with or engage intermeshing rotor gear teeth 26, the clearance surfaces 44, 46 are configured to provide clearance relief volumes 80 (FIG. 3) between the intermeshing teeth 26 of the rotor 20 and teeth 34 of the idler gear 30, to avoid crushing of particles suspended within liquids that flow through the gear pump 10, for example, sugar crystals suspended within a liquid sugar slurry.

As disclosed, each land 40 constitutes a proud or raised surface on each tooth 34 that extends 20 to 40 thousandths of an inch above the pair of clearance surfaces 44 and 46 that extend across each tooth 34. Each land 40 extends radially between a root 38 and a tip 52 (A through H) of each tooth. Adjacently spaced pairs of meshing surfaces 42 of each tooth 34, such as those of teeth 34G and 34H have axially aligned lands 40, such as the lands 40G and 40H′. Successive adjacent pairs of meshing surfaces 42, such as those of teeth 34F and 34G also have symmetrically aligned lands, such as 40F and 40G′, although the latter lands 40F, 40G′ may be axially staggered with respect to the lands 40G and 40H′, as depicted, to minimize gear tooth wear. Since each tooth has two sides, primes are used to distinguish between the counterclockwise side of any particular tooth from its clockwise side. Thus, the land 40H′ is situated on the counterclockwise side of tooth 34H, and is thereby distinguished from land 40G (a non-prime referenced element) situated on the clockwise side of tooth 34G. For reference purposes, it will be noted that the clockwise side of tooth 34H is hidden from view in FIG. 6.

With respect to minimizing gear tooth wear, it also should be pointed out that the idler gear 30 will normally have fewer teeth 34 than the rotor gear 20. As such, the two gears, turning at different speeds, will interact in a manner so that each rotor tooth 26 will contact an idler tooth land 40 in a different position upon each rotation. This operational aspect will tend to further minimize tooth wear.

To avoid crushing of particles, the lands 40, as disclosed, cover only 10% to 30% of meshing surfaces 42 of each tooth 34, with a total meshing surface defined by the area of a land 40 and the areas of its associated clearance surfaces 44, 46. In the disclosed embodiment, each meshing surface 42 comprises two clearance surfaces spaced by a single land, and each land extends over at least 90% of the radial distance between the root 38 and the tip 52 of the meshing surfaces of each tooth.

Finally, referring again to FIGS. 3 and 4, a crescent seal 60 extends from the interior surface 54 of the head 28. The crescent seal 60 is fixedly supported on the head 28 to close a crescent-shaped gap 62 that exists between transiently unmeshed idler and rotor gear teeth 34, 26 (at bottom of idler gear 30 in FIG. 3). The eccentric relationship between the idler gear and the rotor gear give rise to the gap 62, as well as the need for sealing the gap to maintain desired pressure differentials between inlet and outlet ports, as those skilled in the art will appreciate.

A method of making a positive displacement gear pump having an exterior rotor gear and an internal idler gear that includes clearance relief volumes between meshing idler gear teeth and rotor gear teeth to minimize crushing of crystals passing through the pump may include modifying an involute gear tooth profile of a standard idler gear by re-machining or cutting a pair of radially oriented clearance surfaces on each tooth profile of the idler gear to form a radially oriented land on the profile, the land configured to make direct contact with teeth of the meshing rotor gear. The method further includes forming the clearance surfaces as reliefs; having a depth of 20 to 40 thousandths of an inch lower than the height of each land. In accordance with this method, each land is formed of a raised surface along a radially extending profile of each tooth, and each land axially extends over a range of 10% to 30% of the total surface area of each tooth.

The method also provides that when the idler and rotor gears are meshed, the clearance surfaces cooperate with the rotor gear teeth to form transient clearance relief volumes between meshing idler and rotor gears.

While only certain embodiments have been described, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. For example, although the pump as described and shown herein is a unidirectionally rotating pump, the pump may be configured to rotate in both directions; i.e., such that the intake or suction port may become the outlet or discharge port, and vice versa. In addition, although the suspended particles within the liquids being pumped have been described as growing crystals of the type involved in sugar slurries, the described pump may also accommodate microspheres and polymers suspended in liquids. In such cases, the described idler gear structure will operate to minimize any crushing or damage to such particles as caused by shear forces associated with the pumping action. These and other alternatives may be considered equivalents, and as such may fall within the spirit and scope of the present disclosure.

The disclosed positive displacement gear pump 10 may enable a variety of operations with reduced risks of crushing particles, such as emerging or growing crystals within a sugar slurry being transferred by pumping action. Even more broadly, such disclosed idler gear structures may be employed in a variety of industrial and service pumps that include transfers of microspheres and polymers suspended in liquids.

The word “exemplary” is used herein to mean serving as an example, instance or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Further, At least one of A and B and/or the like generally means A or B or both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims may generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Also, although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements, resources, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

The implementations have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.

Claims

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; andan 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; anda 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; orlands 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; andrespective 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; anda 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 surfaceinterior 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; andan 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; anda 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.