Abstract:
An improved positive displacement rotary pump apparatus and method is provided including a front cover, a rotor body forming a chamber with the front cover, a gear case supporting a pair of hollow drive shafts, and a pair of rotors disposed in the chambers and each detachably mounted to one end of a respective hollow drive shaft via a stud that extends from the rotor through the hollow shaft to a fastener. The pump can also have at least one respective face seal between each rotor and the body with at least one first rotating seal ring disposed at the backward facing face of each rotor, and at least one respective second stationary rotating seal ring disposed on a forward facing face of the pump body. The pump further has a pair of bearings that rotatably support the shaft in the gear case, with each bearing being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that each bearing is axially adjustable relative to the gear case. The pump also has a contoured inner relief region located adjacent one of the inlet port and the outlet port, and located next to the front of the rotor swept area to facilitate movement of material through the pumped rotor area

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to Provisional Patent Application Ser. No. 60/836,122 filed Aug. 8, 2006, the entire disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Pumps are in wide use in industry. One popular type of pump for certain applications is known as a rotary positive displacement pump. Such pumps have two counter-rotating rotors that form a moving entrapped volume between the rotor and the inside of a stationary body forming a chamber inside which the rotors move, thus forcing the material from an inlet on the body to an outlet on the body. This type of pump has many applications including for example in the processing of food, chemicals, paint, cosmetics and other materials. In some cases the rotors have intermeshing lobes. In other designs the rotors have wing shaped projections that form moving circumferential pistons together with the inside of a swept body cavity.  
         [0003]     Usually, such pumps are subject to cleaning procedures, and also servicing for repair or replacement of wearable parts, from time to time. While all rotary displacement positive displacement pumps are able to be disassembled to some extent, depending on the application, it may be more desirable to either disassemble the pump for each cleaning, or to instead perform clean-in-place procedures where the pump is cleaned by flushing with cleaning and/or rinsing materials.  
       SUMMARY OF THE INVENTION  
       [0004]     Some embodiments of the present invention provide an improved positive displacement rotary pump apparatus and method.  
         [0005]     In one aspect, a pump is provided having a front cover, a pump body forming a chamber with the front cover, a pair of hollow drive shafts, a gear case supporting the pair of hollow drive shafts, with each drive shaft having a first end and a second end, a pair of mounting studs, a pair of fasteners, and a pair of rotors disposed in the chamber and each detachably mounted to a first end of a respective hollow drive shaft via a respective mounting stud that extends from the rotor through the hollow drive shaft to a respective fastener.  
         [0006]     In another aspect, a pump is provided having a front cover, means for forming a chamber with the front cover, a pair of hollow drive shafts, means for supporting the pair of hollow drive shafts, a pair of mounting studs, a pair of fastening means, and a pair of rotors disposed in the chamber and each detachably mounted to a first end of a respective hollow drive shaft via a respective mounting stud that extends from the rotor through the hollow drive shaft to a respective fastening means.  
         [0007]     In another aspect, a pumping method is provided that includes providing a front cover, a rotor body forming a chamber with the front cover, a gear case supporting a pair of hollow drive shafts, and a driving pair of rotors disposed in the chamber using the drive shafts, with each drive shaft being detachably mounted to one end of a respective hollow drive shaft via a stud that extends from the rotor through the hollow shaft to a fastener.  
         [0008]     In another aspect, a pump is provided having a front cover, a pump body forming a chamber with the front cover, a pair of hollow drive shafts, a gear case supporting the pair of hollow drive shafts, a pair of rotors disposed in the chambers, and at least one respective face seal between each rotor and the body having at least one first rotating seal ring disposed at the backward facing face of each rotor, and at least one respective second stationary rotating seal ring disposed on a forward facing face of the pump body.  
         [0009]     In another aspect, a pump is provided having a front cover, means for forming a chamber with the front cover, a gear case supporting a pair of hollow drive shafts, a pair of rotors disposed in the chambers, and at least one respective sealing means between each rotor and the body having at least one first rotating seal ring disposed at the backward facing face of each rotor, and at least one respective second stationary rotating seal ring disposed on a forward facing face of the chamber forming means.  
         [0010]     In another aspect, a pumping method is provided that includes providing a front cover, a pump body forming a chamber with the front cover, and a gear case supporting a pair of hollow drive shafts, a pair of rotors disposed in the chambers, and providing a seal of the chamber by providing at least one respective face seal between each rotor and the body by at least one first rotating seal ring disposed at the backward facing face of each rotor, and at least one respective second stationary rotating seal ring disposed on a forward facing face of the pump body. In one aspect, a pump is provided having a front cover, a pair of hollow drive shafts, a pump body forming a chamber with the front cover; a gear case supporting the drive shafts; and a pair of rotors disposed in the chambers, wherein each rotor is driven by a respective drive shaft and each drive shaft is mounted by a pair of bearings that rotatably support the shaft in the gear case, with each bearing being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that each bearing is axially adjustable relative to the gear case.  
         [0011]     In another aspect, a pump is provided having a front cover, a pair of hollow drive shafts, a pump body forming a chamber with the front cover, means for supporting the pair of hollow drive shafts; and a pair of rotors disposed in the chambers, wherein each rotor is driven by a respective drive shaft and each drive shaft is mounted by a pair of bearing means that rotatably support the shaft in the gear case, with each bearing means being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that each bearing means is axially adjustable relative to the gear case.  
         [0012]     In another aspect, a pumping method is provided that includes providing a front cover, a pair of hollow drive shafts, a rotor body forming a chamber with the front cover, a gear case supporting a pair of hollow drive shafts, and a pair of rotors disposed in the chambers; and mounting each shaft by a pair of bearings to rotatably support the shaft in the gear case, with each bearing being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that each bearing is axially adjustable relative to the gear case.  
         [0013]     In another aspect, a pump is provided having a front cover, a pair of hollow drive shafts, a pump body forming a chamber with the front cover, a gear case supporting the drive shafts; and a pair of rotors disposed in the chambers, wherein each rotor is driven by a respective drive shaft and each drive shaft is mounted by a pair of tapered bearings to rotatably support the shaft in the gear case, with each bearing being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that the internal clearance of each bearing is adjustable by adjusting the distance between the locating rings.  
         [0014]     In another aspect, a pump is provided having a front cover, a pair of drive shafts, a pump body forming a chamber with the front cover, means for supporting the drive shafts, and a pair of rotors disposed in the chambers, wherein each shaft is driven by a respective drive shaft and each drive shaft is mounted by a pair of tapered bearing means to rotatably support the shaft in the supporting means, with each bearing means being located relative to the supporting means by a respective locating ring that is axially movable relative to the supporting means, so that the internal clearance of each bearing is adjustable by adjusting the distance between the locating rings.  
         [0015]     In another aspect, a pumping method is provided that includes providing a front cover, a pair of drive shafts, a rotor body forming a chamber with the front cover, a gear case supporting the pair of drive shafts, and a pair of rotors disposed in the chambers and mounting each shaft by a pair of tapered bearings to rotatably support the shaft in the gear case, with each bearing being located relative to the gear case by a respective locating ring that is axially movable relative to the gear case, so that the internal clearance of each bearing is adjustable by adjusting the distance between the locating rings.  
         [0016]     In one aspect, a pump is provided having a front cover, a rotor body forming a chamber with the front cover and having an inlet port and an outlet port, a pair of drive shafts, a gear case supporting the pair of drive shafts, and a pair of rotors disposed in the chamber, wherein the front cover forming the front of the rotor chamber has a contoured inner relief region located adjacent one of the inlet port and the outlet port, and located next to the front of the rotor swept area to facilitate movement of material through the pumped rotor area.  
         [0017]     In another aspect, a pump is provided having a front cover, enclosure means for forming a chamber with the front cover and having an inlet port and an outlet port, a pair of drive shafts, means for supporting the pair of drive shafts, and a pair of rotors disposed in the chamber, wherein the front cover forming the front of the rotor chamber has a contoured inner relief region located adjacent one of the inlet port and the outlet port, and located next to the front of the rotor swept area to facilitate movement of material through the pumped rotor area.  
         [0018]     In yet another aspect, a pumping method is provided which includes providing a front cover, a rotor body forming a chamber with the front cover and having an inlet port and an outlet port, a gear case supporting a pair of drive shafts, and a pair of winged rotors disposed in the chamber, and pumping the material from the inlet to the outlet, with the front cover forming the front of the rotor chamber which has a contoured inner relief region located adjacent one of the inlet port and the outlet port, and located next to the front of the rotor swept area to facilitate movement of material through the pumped rotor area.  
         [0019]     There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.  
         [0020]     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.  
         [0021]     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a perspective view of a pump according to an example of a preferred embodiment of the present invention.  
         [0023]      FIG. 2  is a front view of the pump.  
         [0024]      FIG. 3  is a cross-sectional view taken through line A-A in  FIG. 2 .  
         [0025]      FIG. 4  is a detail view of a portion of  FIG. 3 .  
         [0026]      FIG. 5  is a more detailed view of a portion of  FIG. 4 .  
         [0027]      FIG. 6  is a rear view of the pump.  
         [0028]      FIG. 7  is a cross-sectional view taken through line B-B in  FIG. 6 .  
         [0029]      FIG. 8  is a cross-sectional view taken through line C-C in  FIG. 2 .  
         [0030]      FIG. 9  is a right side view of the pump.  
         [0031]      FIG. 10  is a left side view of the pump.  
         [0032]      FIG. 11  is a top view of the pump.  
         [0033]      FIG. 12  is a bottom view of the pump.  
         [0034]      FIG. 13  is a cutaway front view of the pump.  
         [0035]      FIG. 14  is a cutaway perspective view of the pump.  
         [0036]      FIG. 15  is a cutaway perspective view of the pump.  
         [0037]      FIG. 16  is a cutaway perspective view of the pump.  
         [0038]      FIG. 17  is an exploded perspective view of a portion of the pump including the gear case and drive shafts.  
         [0039]      FIG. 18  is a side view of a pump and filter assembly.  
         [0040]      FIG. 19  is an opposite side view of the pump and filter assembly.  
         [0041]      FIG. 20  is a cross-sectional view taken through line A-A in  FIG. 19 .  
         [0042]      FIG. 21  is a cross-sectional view taken through line B-B in  FIG. 19 .  
         [0043]      FIG. 22  is a cross-sectional view taken through line C-C in  FIG. 19 .  
         [0044]      FIG. 23  is an exploded perspective view of the pump and filter assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]     Some embodiments of the present invention provide an improved positive displacement rotary pump apparatus and method. Examples will be discussed below with reference to the drawing figures in which like reference numerals refer to like parts throughout.  
         [0046]      FIGS. 1 and 2  illustrate a pump  10  having an inlet port  12  and an outlet port  14 . The illustrated embodiment is bi-directional, in that it can pump in either direction, so the selection of inlet and outlet is given for example only in this description. Changing direction of the pump is accomplished simply by changing the direction of rotation of the motor or gear reducer that is driving the pump. The pump has a front cover  16  mounted by a series of bolts  18 , and alignment features such as dowel pin holes  20 , to a body  24 . The dowel pins and holes  20  serve to align the front cover  16  with the body  24 .  
         [0047]     The front cover  16  and body  24  substantially define an internal chamber for the internal rotors which are not visible in this view. The cover  16  on its outside shows a pair of domed regions  22 , which generally correspond to internal relief areas which are discussed in more detail below. The relief areas can be implemented with our without showing an external dome depending on the thickness of the front cover  16 , the depth of the internal relief, and the manufacturing method for the front cover  16 .  
         [0048]     The body  24  is attached to a gear case  26 , which supports drive shafts for the rotors, which are not visible in this view. Bolts  18  also extend through the body  24  and mount the body  24  to the gear case  26 , with this also being aligned by the dowel pins and holes  20 . Mounted to the gear case  26  is a filter  28  which is part of a pump assembly  30  that circulates and filters lubricating fluid or oil inside the gear case  26 . An oil drain plug  32  is shown, as well as on oil fill and breather cap  34 .  
         [0049]     A rear cover  36  encloses the back of the gear case  26 , and is mounted thereto by a series of bolts  38 . Although the rear cover is a separate part from the gear case  26 , it is included below as a part of the overall gear case structure. A sight glass  39  is provided for externally viewing the oil level in the gear case  26 . The gear case  26  also has a base  40  on which the pump rests and which can provide a stable mounting arrangement. This description will refer to the pump as being in a vertical orientation with the base  40  on a horizontal surface and will use the directions up and down to refer to when the pump is in this orientation. However, the pump can function also when turned sideways (with the base mounted to a vertical surface), or even in any orientation. Such different orientation might change the functionality of the oil pump assembly  30 . However, the oil pump pickup and distribution locations can be altered as desired so that oil is drawn from wherever the lower internal region of the gear case  26  is located, and released to wherever an upper part of the gear case  26  is located.  
         [0050]      FIG. 3  includes the front cover  16 , bolts  18 , domes  22 , body  24 , gear case  26 , drain plug  32 , old fill and breather cap  34 , rear cover  36 , and base  40  which were described above. The view does not show bolts  18  or locator features  20 , nor bolts  38  because those parts are not visible in this view. However,  FIG. 3  does depict the locator dowel pins  41  that align the rear cover  36  with the gear case  26 .  
         [0051]      FIG. 3  does not show the filter  28  and pump  30 , which are obscured in this view. However,  FIG. 3  shows an oil pump draw tube  42  and an oil pump distribution outlet  44 . As is discussed further below, oil is drawn via the draw tube  42 , which is located to have its end in a sump in a lower region of the interior of the gear case  26 , and is circulated to be distributed out the outlet  44 , which may be near the top of the interior of the gear case  26 , in order to supply lubrication, cooling, and or noise abatement to the moving parts in the gear case interior. In the example shown, a simple tube outlet  44  is shown, positioned to drip or spray directly onto a drive shaft gear. However, a more complex manifold or drip tray can be used, or internal porting can be used to supply the oil to any internal gears, bearings, or other parts, and also to cool any parts by internal circulation through conduits in parts or by direct application. Also the references to oil in this description include any other lubricating and/or cooling fluid and references to lubrication include not only oil but other lubricants and/or cooling fluids.  
         [0052]     The upper rotor  46  and lower rotor  48  each have wing-shaped ears that rotate about an upper hub  50  and lower hub  52  respectively. The upper hub  50  and lower hub  52  are shown in this example as integral with the front cover  16 , and project inward to fill the unswept area located radially inward of the rotor wings. As discussed in more detail below, each rotor  46  and  48  has a relatively flat center rear disc portion from which extend forward and outward a pair of wings. The wings essentially act as pistons to move material through a swept internal volume chamber area formed by the inside of the front cover  16  and the body  24 . A benefit in some examples of having the hubs  50  and  52  be located in front of the rotors  46  and  48 , and as integral with or extending from the front cover  16 , is that a close tolerance can be obtained if desired between the hubs  50  and  52  and the unswept area of the rotors  46  and  48 . In some cases reducing unswept volume can improve efficiency and/or reduce possible stagnant material in the unswept region.  
         [0053]     A generally face seal arrangement for enclosing the material area inside the pump body includes an upper face seal assembly  54  that seals between the rotating rotor  46  and the inside of the stationary body  24 , and a lower face seal assembly  56  that seals between the rotating rotor  48  and the inside of the stationary body  24 . These seals are depicted and described in more details in  FIGS. 4 and 5  and below.  
         [0054]     The rotors are supported, driven, and are positioned axially, by being mounted to respective hollow shafts. In the preferred example shown, an upper stud  58  and lower stud  60 , respectively, are each permanently or semi-permanently affixed to a respective rotor  46  or  48 , and have respective nuts  62  and  64  that attach the shafts  58  and  60  so they extend through the center of hollow drive shafts  66  and  68  respectively. In other embodiments the rotors  46  and  48  may be attached to the drive shafts such as  66  and  68  via other attachment arrangements. A projection at the rear of each rotor  46  and  48  has outer splines that mate with inner splines at the end of each hollow drive shaft  66  and  68 . The intermeshed spline areas are labeled  67  and  69 , respectively, in  FIG. 3 .  
         [0055]      FIG. 3  also shows an upper front bearing  70 , lower front bearing  72 , upper front bearing upper front adjustable bearing retainer  74 , lip seal  75 , lower front adjustable bearing retainer  76 , lip seal  77 , upper rear bearing  78 , lower rear bearing  80 , upper rear bearing retainer  82 , lip seal  83 , lower rear adjustable bearing retainer  84 , and lip seal  85 .  
         [0056]     Each bearing retainer  74 ,  76 ,  82 , and  84  is axially adjustable and lockable relative to the gear case  26  and rear cover  36 , for example by being in the form of an externally threaded ring and residing in an internally threaded bore of the gear case  26  or of the rear cover  36 , and having a locking set screw.  
         [0057]     An upper spacer ring  86  and lower spacer ring  88  maybe be used as spacers adjacent to upper drive gear  92  and lower drive gear  94  as shown. The drive gears  92  and  94  in this embodiment are for example mounted to the drive shafts  66  or  68  by a splined arrangement used with the shoulder that is shown on each shaft  66  and  68  adjacent to and abutting the drive gears  92  and  94 .  
         [0058]     Using the upper drive shaft  66  as an example, a load path exists from the upper front adjustable bearing retainer  74 , to the outer race of bearing  70 , to the tapered roller of bearing  70 , to the inner race of bearing  70 , to a shoulder on the hollow drive shaft  66 , the drive gear  92  via welding and/or the shoulder, to the spacer ring  86 , to the inner race of bearing  78 , to the tapered roller of bearing  78 , to the outer race of bearing  78 , and to the upper rear adjustable bearing retainer  82 .  
         [0059]     Since the retainers  74  and  82  can be set at any desired axial location relative to the gear case  26  and rear cover  36 , the distance between them can be adjusted, and also they can be shifted axially while resulting in the same spacing therebetween. In the case of bearings  70  and  78  being tapered, reducing the spacing between the retainers  74  and  82  will tighten up the axial and radial internal clearance or tightness of the bearings. This permits adjustment to a tightness inside the bearing parts that avoids slop and wear, but also does not cause binding. The axial shifting feature permits the axial position of the shaft relative to the gear case  26  to be adjusted, which in turn allows for axial position adjustment of the rotor  46  relative to the stationary parts of the pump, including the gear case  26 , but also the body  24  and the cover  16 . By virtue of this axial shifting adjustment, the rotor  46  can be located to have a close clearance with the inside of the cover  16 , and also the force of axial contact at the seal location  54  can be made to have a desired degree. The lower drive shaft  68  and associated bearings  72  are adjustable in a manner similar to that described above for the upper drive shaft  66 .  
         [0060]      FIG. 3  also shows an oil pump cam  96 , which is asymmetrical, in that its diameter is not constant from the axis, although the asymmetrical shape is not seen in this view. Since the oil pump cam  96  is at the largest diameter part of the shaft  68 , and since it can be smaller than its shaft&#39;s respective bearing retainer opening in the gear case  26 , it can be directly welded to the shaft  68  if desired. The oil pump cam  96  can alternatively be disposed on the other shaft  66 , or any other rotating shaft in the pump. The operation of the oil pump is described in further detail with reference to FIGS.  18  to  23  and also below.  
         [0061]     One feature of this embodiment is that by using substantially only four lip seals, including the four lip seals  75 ,  77 ,  83 , and  85 , an enclosed chamber is provided by the gear case  26  and rear cover  36  that encloses the shaft bearings, drive gears, and oil pump cam, in a compact fashion if desired. There is also a fifth seal: a drive shaft lip seal  126 , which is discussed below. This creates an arrangement that facilitates lubrication, cooling and/or noise reduction, while reducing the need for additional seals, and also keeps the lubricant away from the material seals  54  and  56  at the rotors. In the illustrated arrangement, even if lubricant breaches one of the four lip seals, it exits the pump to the environment, so it can be detected visually and also does not immediately contact the material seals  54  and  54 .  
         [0062]      FIGS. 4 and 5  are close up views showing in particular the material seal arrangement  54 . The seal material  56  is similar to seal material  54  and thus is not separately described. Referring now to  FIGS. 4 and 5 , a seal  54  is shown providing a material seal between the rotor  46  and the body  24 . The seal  54  includes an outer front seal ring that serves as a rotating primary seal  102 , an inner front seal ring that serves as a rotating secondary seal  104 , an outer rear sealing ring that serves as a stationary primary seal  106 , and an inner rear seal ring that serves as a stationary secondary seal  108 . If any of the material being pumped breaches this seal  56 , it will exit through a clearance  110  and become visible from outside the pump. Also any breached pumped material will not enter the gear case, since it will be blocked by the lip seal  75 .  
         [0063]     Turning to  FIG. 5 , o-ring channels  114  are provided on each seal  102 ,  104 ,  106 , and  108  to hold o-rings. The o-rings provide a frictional holding resistance to hold each seal in place during assembly and disassembly of the rotors and seals as will be explained in more detail below. A pin bore  116  is provided to hold a pin that is not shown. The pin extends into a feature in the seals  102  and  104  and thus ensures the seals  102  and  104  rotate together with the rotor  46 . Any number of such pins may be used, spaced around the circumference of the seal rings.  FIG. 5  also shows a corner relief  118  that can be provided for manufacturing reasons.  
         [0064]      FIG. 6  shows a third shaft, which is a main drive shaft  120  that is driven by a motor or a gear reducer from a motor, which is not shown. The drive shaft  120  extends outward from the pump to be coupled to such a drive source.  
         [0065]      FIG. 7  illustrates the main drive shaft  120  having a drive gear  122  that meshes with drive gear  94  on the shaft  68 . A spring biased follower pin  124  rides on the cam  96  and is reciprocated during operation. The reciprocation of the follower pin  124  operates the oil pump  30 , which uses a pair of check valves that are described in more detail below with respect to FIGS.  18  to  23 . A drive shaft lip seal  126  is provided where the main drive shaft  120  exits the rear cover  36 . Drive bearings  128  and  130  support the main drive shaft  120  in the gear case  26  and rear cover  36 .  
         [0066]      FIG. 8  shows the material inlet and outlet port regions. The front cover  16  has internal relief areas  132 . When the wings are in their rotational position where they are not blocking the inlet, material flows into the space between the ears that will become the closed pump volume on further rotation. Material can also at this time flow into the space formed by the relief. This material can also enter the space between the ears from the front as well as the side of the rotor. This extra inlet flow path can enhance overall throughput and efficiency by reducing the degree of tortuous path, corners, and restriction in the inlet flow path. Similar benefits occur by having relief area  132  at the outlet side. Another relief area  134  is provided on the back side of the rotors, allowing material to enter the rotor spaces from the rear in a similar fashion. An o-ring  135  seals the front cover  16  against the body  24 .  
         [0067]      FIG. 9  shows the pump  30  and filter  28  being attached to the gear case  26  by bolts  136 .  FIGS. 10, 11  and  12  show other views of the pump  10 .  
         [0068]     FIGS.  13  to  17  are cutaway views to show the pump  10  in that manner. In  FIGS. 13 and 14 , the ears  140  of the rotor  46  have been labeled. Other reference numerals are omitted from FIGS.  13  to  17  for clarity.  
         [0069]     FIGS.  18  to  23  illustrate the pump assembly  30  in more detail. The pump assembly  30  includes a mounting flange  201 , oil pump body  202 , check valves  203 , dowel pin  204 , spring  205 , and retaining ring  206 . The dowel pin  204  corresponds to the reciprocating can follower pin  124  in  FIG. 7 . Fittings  207  and nuts  208  attach tubes  209  and  210 . O-rings  211  and  212  are provided.  
         [0070]     Referring now to all the figures, and especially  FIG. 3 , an example of steps for disassembly of the pump for cleaning or servicing will be described. The nuts  18  are removed. This permits the front cover  16  to be removed. The nuts  62  and  64  are removed. If desired, the studs  58  and  60  may be tapped forward, for example with a rubber hammer. This will cause the rotors  46  and  48  to protrude out beyond the front edge of the body  24 . The rotors  46  and  48  can be grasped and pulled forward, thus removing the rotors  46  and  48  and their respective studs  58  and  60  each in one piece. The rotating seals  102  and  104  (see  FIG. 5 ) are retained with the rotors  46  and  48  by their o-rings and thus are removed from the pump together with the rotors  46  and  48 . The seals  102  and  104  then can be removed manually from the rotors as desired. The stationary seals  106  and  108  will remain retained in the body  24  due to their o-rings. The stationary seals  106  and  108  can also now be accessed and removed manually as desired. Upon completion of the steps described above, the hollow shafts  66  and  68  remain in the gearbox  26 , and the gearbox interior remains sealed from the outer environment.  
         [0071]     Some aspects of various features and embodiments described above can provide useful benefits. For example, in the disassembly steps described above, the rotors and seals all can be removed and serviced by removing the front cover  16 , without the need to remove the body  24  from the gear case  26 . Other than removal of the bolts  62 , this process can be referred to as being front-loaded. Also, the area contacted by the pumped material is sealed by only three seal locations: (1) the front cover o-ring  135  (see  FIG. 8 ), and (2 and 3) seals  54  and  56  for each rotor. Seals  54  and  56  each include the primary and secondary seal rings. There is no need for any seal to contact the rotating drive shaft, and no need to remove the drive shaft for rotor or seal replacement. Also any material that breaches any of the three seals is visible from outside the pump. Another feature of some embodiments is that there are no threaded connections located inside the pumped material flow path, and the connection of each rotor to its drive shaft occurs outside of the sealed material path. Also if desired a highly complimentary fit between the hubs  50  and  52  and the inside diameter of the wings of the respective rotors  46  and  48  can be accomplished which can reduce unswept/non-pumping area. Another feature of some embodiments is that an enclosed gear case chamber is provided that is sealed by five lip seals (lip seals  75 ,  77 ,  83  and  84 , as well as the drive shaft lip seal  126 ) and any oil that breaches the lip seals is also visible from outside the pump.  
         [0072]     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.