Patent Application
20070248480
1. Technical Field
An external gear pump is disclosed with multiple, discrete pumping sections. The separate pumping sections or separate pumps are fed by a single inlet and communicate with a single outlet. Manifold functions between the inlet and pump sections and between the pump sections and outlet are disposed within the pump casing thereby requiring only a single inlet pipe connection and a single outlet pipe connection without any manifolds external to the pump casing.
2. Description of the Related Art
External gear pumps are a popular pumping principle and are often found in lubrication pumps in machine tools, in fluid power transfer units, and as oil pumps in engines.
External gear pumps are similar in pumping action to internal gear pumps in that two gears come into and out of mesh to produce flow. However, an external gear pump uses two identical gears rotating against each other—one gear is driven by a motor and it in turn drives the other gear. In contrast, the gears of an internal pump rotate in the same direction as a smaller inner idler gear is disposed within a larger outer rotor gear.
Each gear of an external pump is supported by a shaft with bearings on both sides of the gear. As the external pump gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate. Liquid travels around the interior of the external pump casing in the pockets between the teeth and the casing. In contrast to an internal gear pump, liquid does not pass between the external pump gears; it travels circumferentially around the gears. The meshing of the external pump gears forces liquid through the outlet port under pressure.
External gear pumps may employ spur, helical, and herringbone gears. Helical and herringbone gears offer a smoother flow than spur gears, although all gear types provide relatively smooth operation. Large-capacity external gear pumps typically use helical or herringbone gears. Small external gear pumps usually operate at 1750 or 3450 rpm and larger models operate at speeds up to 640 rpm. External gear pumps handle viscous and watery-type liquids, but speed must be properly set for thick liquids. Reduced speeds with high-viscosity liquids results in greater efficiency.
The design of external gear pumps allows them to be made to close tolerances. Tighter internal clearances provide for a more reliable measure of liquid passing through a pump and for greater flow control. Because of this, external gear pumps are popular for precise transfer applications involving polymers, fuels, and expensive liquids. Because the gears are supported on both sides, external gear pumps are quiet-running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft typically cannot deflect and wear prematurely.
To increase capacity or functions while employing a single power source, external gear pumps may be provided with multiple sections. Each section of the pump includes a pair of gears disposed within a pump chamber. The pump chambers are separated by a plate through which the pump shafts pass. Seals are disposed between the shafts and the separation plate to prevent cross communication between the pump chambers.
While providing multiple pump sections (or multiple pumps within a single pump casing) is a convenient and inexpensive way to increase capacity and provide versatility, the employment of discrete pump sections requires the use of multiple inlets or a manifold on the intake side as well as multiple outlets or a manifold on the output side. Thus, with the multiple inlets and outlets, the size or footprint of the pump increases. In certain cases, the use of exterior manifolds is not permissible due to space limitations. Further, the requirement of an additional manifold or manifolds as additional expense and can result in sealing problems as leakage from port misalignment is a common problem.
Thus, improvements in the design of multiple section external gear pumps are needed that simplify porting and provide high but variable capacities in small spaces.
In satisfaction of the aforenoted needs, an improved expandable external gear pump is disclosed without input or output manifolds. A single inlet is provided that is in fluid communication with each pump chamber and a single outlet is provided that is also in communication with each pump chamber. Therefore, the pump sections or pumps may be expanded or contracted in number and because the pump includes no inlet or outlet manifolds, such a change in pump capacity is simple and straightforward.
In an embodiment, an external gear pump is disclosed which comprises a drive shaft that passes through a plurality of drive gears. Each drive gear is enmeshed with a driven gear or idler gear, thereby providing a plurality of gear pairs or gear sets. Each gear pair or gear set includes one drive gear and one driven or idler gear. Each of the gear pairs is disposed within a casing. The casing comprises a single inlet and defines a single inlet chamber that links the single inlet to each gear pair without an inlet manifold external to the casing.
In a refinement, the casing comprises a single outlet and the casing also defines a single outlet chamber that links each gear pair with the single outlet without an outlet manifold external to the casing.
In another refinement, the casing comprises a plurality of stacked casing sections connected to a head that defines the inlet and the outlet. Each casing section accommodates one of the gear pairs. The stacked casing sections, together with the head, defined a single inlet chamber and the single outlet chamber. Although the disclosed pump does not include external inlet and outlet manifolds, the manifold functions are essentially internal to the pump casing and therefore the pump casing provides inlet and outlet manifold functions.
In another refinement, one of the casing sections is an end casing that receives the drive shaft and includes a means for connecting the casing to the pump motor assembly.
In another refinement, the drive and idler gears are mounted to a common driven or idler shaft.
In another refinement, the drive and idler shafts are supported by at least the head and end casing. In a further refinement, each casing section provides a support structure for both of the gear shafts.
In an embodiment, an expandable multiple section external gear pump is disclosed that does not include an inlet manifold that is external to the pump casing.
In an embodiment, an expandable multiple section external gear pump is disclosed that does not include an outlet manifold that is an external to the pump casing.
In a refinement, common input and output chambers are provided by a multiple section casing assembly without the need for external input or output manifolds and the piping associated therewith.
Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.
For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein:
It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.
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The head 13 connects the inlet conduit 11 to a plurality of casings shown generally at 18 and
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Further, instead of an outlet manifold being connected to the outlet chamber or chambers 34, the design of the head 13 enables only a single outlet 14 that is in communication with the continuous outlet chamber 34 and thereby permitting only a single outlet pipe or pipe connection to be made at the outlet 14 (see
With the stacked casing 18 structure sandwiched between the head 13 and end casing/bracket 21 of the disclosed design, the pump 10 is both expandable and contractible in terms of output capacity. Further, because the pump 10 does not require inlet or outlet manifolds, modifying the pump 10 to increase or decrease capacity merely involves changing drive shafts 24 and idler shafts 42 (i e., changing shaft length) and the number of casings 18. No modifications or substitutions need be made to the inlet 11 or outlet 14 because of the internal manifold structure of the pump 10.
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Each gear set 39, 41 is isolated from its adjacent to gear set 39, 41 by the bushings/seals 53 so that each gear set 39, 41 essentially acts as an independent pump, only minimally affecting adjacent pumps or gear sets 39, 41.
The construction of the pump 10 is illustrated in
Thus, an improved expandable external gear pump 10 is shown and described with internal input and output manifolds that render the pump 10 more compact and easier to expand or contract in terms of pump capacity. The pump 10 is more suitable for confined spaces and because of the ease in which it can be expanded or contracted in terms of pump capacity, the pump 10 is ideal for easy modification by the end user.
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.
