Patent Publication Number: US-7905717-B2

Title: PD pumps with a common gearbox module and varying capacities and easy access to mechanical seals

Description:
BACKGROUND 
     1. Technical Field 
     Improved positive displacement pumps are disclosed. More specifically, circumferential piston pumps and rotary lobe pumps are disclosed wherein a single gearbox module can be used with numerous heads of varying capacities and configurations. As a result, manufacturing costs are reduced because a single gearbox module with a drive shaft/driven shaft set can be used with numerous heads of varying capacities. Thus, the capacity can be varied without changing the gearbox or shaft length. Further, the mechanical shaft seals can be accessed for servicing or replacement without removal of the pump or rotor casing. Specifically, the mechanical shaft seals can be accessed merely by removal of the head cover plate and rotors, which are easily detachable from the drive and driven shafts. 
     2. Description of the Related Art 
     A positive displacement pump emits a given volume of fluid for each revolution of the motor or drive shaft. Bellows, double-diaphragm, flexible impeller, gear, oscillating, piston, progressing cavity, rotary vane, peristaltic, rotary lobe and circumferential piston pumps are all examples of positive displacement pumps. This disclosure is directed primarily towards new rotary lobe pump (RLP) and circumferential piston pump (CPP) designs. Both RLPs and CPPs employ a drive shaft and a driven shaft with rotors mounted on both shafts. The rotors are disposed in the pump casing sandwiched between a head cover and a gearbox. The head cover and rotor or pump casing are often collectively referred to as the “head” and the terms rotor casing and pump casing are used interchangeably. 
     Rotary lobe pumps use timing gears to eliminate contact between the rotors, which enables their use on non-lubricating fluids. Various rotor forms are available, including bi-wing (or bi-lobe) and multi-lobe options. These pumps offer both sanitary and hygienic designs which meet various standards imposed for food, dairy, beverage, bio-tech, and pharmaceutical applications. RLPs are also used in chemical and specialty chemical industries. Industrial RLP designs may include bearings on both sides of the rotors for higher pressure capabilities. 
     While circumferential piston pumps are timed like rotary lobe pumps, the rotor wings (i.e., the “pistons” in circumferential piston) rotate in chambers machined into the pump casing. This provides a large sealing surface which minimizes slip and provides increased efficiencies for low viscosity fluids. However, with the chambers machined into the pump casing, CPPs are significantly more difficult to clean and therefore can be less preferred for sanitary or hygienic applications. 
     In general, CPPs are preferred for lower viscosity liquids (less than 500 centipoise) and applications where cleaning and sanitization is not frequently needed; RLPs are preferred for higher viscosity liquids (greater than 500 centipoise) and sanitary or hygienic applications because of the ease in which an RLP can be cleaned. 
     One problem associated with both RLP and CPP designs is the inability to vary capacity without changing the overall pump design. Specifically, current RLP and the CPP designs require different gearboxes and shaft lengths for different capacities. 
     Another problem associated with RLP and CPP designs is the servicing of the mechanical shaft seals. Specifically, the mechanical shaft seals are traditionally mounted between the casing and a gearbox thereby requiring the head cover, rotors and casing to be removed in order to service the seals. This procedure is time-consuming and therefore costly. Accordingly, there is a need for improved CPP and RLP designs wherein access to the mechanical shaft seals is facilitated. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with the aforenoted needs, an improved positive displacement pump is disclosed which comprises a drive shaft that passes through a gearbox and that is detachably connected to a first rotor. The rotor may be of a circumferential piston type (i.e. wing-type or wing-style) or of the rotary lobe type. The drive shaft is rotatively coupled to a driven shaft and the driven shaft is detachably connected to a second rotor. The first and second rotors are disposed in a pump casing, which is sandwiched between a head cover and the gearbox. The drive and driven shafts pass through first and second mechanical seals respectively, which are sandwiched between the first and second rotors and the gear box respectively. 
     An advantage of the disclosed designs lies in the ease in which the seals can be serviced or replaced. Specifically, removal of the head cover and the first and second rotors from the drive and driven shafts respectively provides access to the first and second mechanical seals, without removing the casing. 
     Further, in a refinement, the first and second rotors each comprise a central hub for accommodating the drive and driven shafts respectively. The central hubs of the first and second rotors are connected to annular sections. The annular sections connect their respective central hub to at least one radially outwardly directed wing or lobe. 
     In another refinement, the casing comprises a rear wall with first and second openings for accommodating the drive and driven shafts respectively. In this refinement, the annular sections of the first and second rotors are each connected to a rearwardly extending outer hub. The rearwardly extending outer hubs are, in turn, accommodated in first and second recesses disposed in the rear wall of the casing. 
     In another refinement, the first and second recesses in the rear wall of the casing that accommodate the rearwardly extending outer hubs are disposed along outer peripheries of the first and second openings in the rear wall of the casing through which the drive and driven shafts pass. 
     In another refinement, the first and second mechanical seal assemblies are at least partially disposed within the rearwardly extending outer hubs of the first and second rotors respectively. 
     In another refinement, the rearwardly extending outer hubs of the first and second rotors are journalled into the rear wall of the casing. 
     In yet another refinement, the first and second rotors each comprise a central hub for accommodating the drive and driven shafts respectively. Each central hub includes a distal end directed towards the head cover and a proximal end directed towards the gear box. The proximal ends of the central hubs of the first and second rotors are each connected to an annular section that connects its respective proximal end to at least one radially outwardly directed wing as well as the rear annular hub. 
     In yet another refinement, the first and second rotors each include an annular slot between their respective central hubs and their respective wing or lobe. The head cover, in such an embodiment, includes first and second cup-shaped structures with first and second cylindrical walls. In this CPP design, the annular slots of the first and second rotors receive the first and second cylindrical walls of the head cover respectively. 
     In a refinement, the pump is a rotary lobe pump (RLP) or a circumferential piston pump (CPP). 
     A method for changing a capacity of a positive displacement pump is also disclosed. The method comprises: removing the head cover; removing the first and second rotors; removing the pump casing; replacing the pump casing with a second casing sized to accommodate third and fourth rotors with the third and fourth rotors having different sizes than the first and second rotors; mounting the third and fourth rotors on the drive and driven shafts; and mounting a second head cover on the second casing. 
     In a refinement, a second head cover is not necessary as the original head cover will fit onto the second pump casing and new rotors. 
     In another refinement the method further comprises removing the first and second seals after removing the first and second rotors and before removing the pump casing. 
     A method for removing mechanical seal assemblies from CPPs and RLPs is also disclosed. The method comprises: removing the head cover; removing the first and second rotors from the drive and driven shafts; 
     for one of the mechanical seal assemblies, 
     inserting a tool into an opening between a rear wall of the pump casing and a gearbox to obtain access to a disk or ring member disposed between the mechanical seal assembly and the gearbox; applying a biasing force on the disk or ring member to move the mechanical seal assembly in a proximal direction or towards the pump cavity from which its respective rotor has been removed; removing the mechanical seal assembly by hand; replacing the mechanical seal assembly; and 
     repeating the process for the other mechanical seal assembly. 
     In another refinement, the above method is carried out without removing the pump casing. 
     Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a circumferential piston pump made in accordance with this disclosure; 
         FIG. 2  is a side sectional view of the CPP shown in  FIG. 1 ; 
         FIGS. 3-5  are partial and enlarged sectional views of three different size head covers/rotors/casings on the same drive or driven shaft thereby illustrating the ease in which the capacity of the CPPs illustrated in  FIGS. 1-5  can be changed without changing the drive and driven shafts and without changing the gearboxes; 
         FIG. 6  is a sectional view of a rotary lobe pump made in accordance with this disclosure; 
         FIGS. 7-9  are partial and enlarged sectional views of three different size rotors/casings on the same drive or driven shaft thereby illustrating the ease in which the capacity of the RLPs illustrated in  FIGS. 6-9  can be changed without changing the drive and driven shafts and therefore without changing the gearboxes; 
         FIG. 10  is a partial sectional view of an alternative seal assembly for use in the disclosed pump designs; 
         FIG. 11  is a front perspective view of a CPP-style rotor for use in the pumps illustrated in  FIGS. 1-5 ; 
         FIG. 12  is a rear perspective view of the rotor illustrated in  FIG. 11 ; and 
         FIG. 13  is a front sectional perspective view of the rotor illustrated in  FIGS. 11-12 . 
     
    
    
     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. 
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
       FIG. 1  illustrates, generally, a CPP  15  which includes a gearbox  16  connected to a rotor or pump casing  17  which is sandwiched between the flange  18  of the gearbox  16  and a head cover or cover plate  19 . Supporting legs or brackets are shown at  21 , while the drive shaft is partially visible at  22 , and an inlet or outlet is shown at  23  and  FIG. 1 . 
     The CPP  15  is illustrated in greater detail in  FIG. 2 . The gearbox  16  includes a housing or shell  24  with an opening  25  that accommodates the driveshaft  22 . An enclosing seal  26  is disposed between the mid-section  27  of the driveshaft  22  and the opening  25  in the gearbox housing  24 . The proximal section  28  of the driveshaft  22  is connected to a motor (not shown). Another mid-section  29  of the driveshaft  22  passes through a drive gear  31 . The drive gear  31  is enmeshed with a driven gear  32 . The driven gear  32  is mounted onto the driven shaft  33 . The drive and driven shafts  22 ,  33  pass through the gearbox casing  34  which includes first and second elongated openings  35 ,  36  for accommodating the drive and driven shafts  22 ,  33  and the supporting bearings  37 ,  38 ,  37   a ,  38   a  and bushings  39 ,  40  respectively. The drive and driven shafts  22 ,  33  pass through the flange  18  of the gearbox casing  34  which is connected to the rotor or pump casing  17  by a plurality of bolts or fasteners shown at  41  in  FIG. 1  that pass through the head cover  19  and rotor casing body  17  before reaching the flange  18  of the gearbox casing  34 . The bearings  37 ,  38  are connected to the flange  18  of the gearbox casing  34  by the bolts or fasteners shown at  42  in  FIG. 2 . 
     Distal sections  43 ,  44  of the drive and driven shafts  22 ,  33  respectively pass through first and second openings  45 ,  46  of the pump casing  17  respectively. The distal sections  43 ,  44  of the drive and driven shafts  22 ,  33  are connected to a first and second rotors  47 ,  48  respectively by the bolts or threaded fasteners  51 ,  52 , which, as explained below, make it fast and easy to remove the rotors  47 ,  48  to provide quick access to the seal assemblies  53 ,  54 . 
     In the embodiment illustrated in  FIG. 2 , the head cover  19  further comprises a head plate  55  and a pair of cup-shaped members  56 ,  57  which include inwardly directed cylindrical walls  61 ,  62  that are received in the annular recesses  63 ,  64  of the rotors  47 ,  48 , which can be more clearly seen in the exemplary CPP rotor  47  illustrated in  FIGS. 11-13 . 
     One frequent maintenance task associated with the pump  15  illustrated in  FIGS. 1-2  is repair or replacement of the seal assemblies  53 ,  54 . In the embodiment  15  illustrated in  FIG. 2 , to access the seal assemblies  53 ,  54 , a technician only needs to remove the head cover assembly  19  (the plate  55  and cup-members  56 ,  57  are connected and therefore removed together) and the rotors  47 ,  48 . The pump casing  17  does not need to be disconnected from the gearbox  16 . Accordingly, the time-consuming task of removing the pump or rotor casing  17  is avoided when servicing the seal assemblies  53 ,  54  which, in turn, makes repair or replacement of the seal assemblies  53 ,  54  much faster and less costly in terms of downtime than currently available CPPs (or RLPs as illustrated in connection with  FIGS. 6-9 ). 
     In the embodiment illustrated in  FIG. 2 , the seal assemblies  53 ,  54  each include a front polymeric seal member  65 , one or more inner seal members  66  and a rigid seal housing  67  that substantially contains the inner seal members  66 . With the head cover  19  and rotors  47 ,  48  removed, a thin tool (not shown), such as a flat head screwdriver, can be inserted downward through the upper opening  71  to access the annular ring or member  72 . A biasing force on the annular disc  72  towards the front of the pump  15  or towards the left in  FIG. 2  will push the rigid seal housing  67  disposed around the driveshaft  22  towards the left in  FIG. 2 , thereby enabling hand access to the front seal  65  and eventually the rigid steel housing  67  so that the driveshaft seal assembly  53  can be repaired or replaced. Similarly, the same tool (not shown) can be inserted upward through the bottom opening  73  to access the annular disc or ring  72  that surrounds the driven shaft  33 . A biasing force to the left in  FIG. 2  will enable access to the front seal  65  through the rotor casing  17  (as the rotor  48  has been removed) and the rigid seal housing  66  so that the driven shaft seal assembly  54  can be replaced or serviced. 
     A technician may also access the seal assemblies  53 ,  54  from the front side of the pump  15 , as space is provided when the rotors  47 ,  47  and their annular hubs  83  are removed as shown in  FIG. 2 . 
     Turning to  FIGS. 3-5 , the versatility of the CPP  15  is illustrated. Specifically, three different rotors  47   a ,  47   b ,  47   c  of different sizes are illustrated. However, the size and length of the driveshaft  22  remains unchanged (and the driven shaft  33  and gearbox remain unchanged in  FIGS. 2-5 ). To accommodate the different sized rotors  47   a ,  47   b ,  47   c , only the head covers  19   a ,  19   b ,  19   c  and rotor casings  17   a ,  17   b ,  17   c  need to be modified. The driveshaft  22  (and driven shaft  33 ) and therefore the gearbox  16  (not shown in  FIGS. 3-5 ; see  FIG. 2 ) do not require modification or changing. Therefore, one set of drive and driven shafts  22 ,  33  and one gearbox  16  can accommodate multiple pump configurations  15   a ,  15   b ,  15   c  of varying capacities. Current CPP pump designs do not permit the capacity of the pump to be substantially modified without changing the gearbox and shaft lengths and are therefore less versatile than the disclosed CPP  15 . While only three different rotor sizes are shown in  FIGS. 2-6 , using the disclosed CPP pump design  15 , many different pump capacities can be obtained using a single gearbox  16 /driveshaft  22 /driven shaft  33  combination. The only components that need modification or changing to modify the pump  15  capacity are: the rotors  47 ,  48 ; the pump casing  17 ; and the head cover  19 . As shown below in connection with  FIGS. 6-9 , a universal head cover  19  is also possible, which would mean only the rotors  47 ,  48  and pump casing  17  would need to be changed to alter the capacity of the pump  15 . 
     Turning to  FIG. 6 , a RLP  115  is disclosed. The same or similar components in the RLP  115  described above in connection with the CPP  15  will be referred to using like reference numerals with the prefix “1”, or beginning with the reference numeral  115  instead of  15 , etc. Hence, the functional descriptions of each part or component of the RLP  115  that finds a like part or component in CPP  15  will not be repeated here. However, it will be noted that RLP  115  includes upper and lower openings  171 ,  173  which enables a thin tool to access the annular discs  172  to push the seal assemblies  153 ,  154  forward or to the left in  FIG. 6 , after the head cover  119  and rotors  147 ,  148  have been removed. Hence, to service the seal assemblies  153 ,  154 , the rotor casing  117  does not need to be removed. Also, the seal assemblies  153 ,  154  may be accessed directly from the front of the pump  115 , using the space vacated by the annular hubs  183  when the rotors  147 ,  148  are removed. 
     The capacity versatility of the RLP  115  is illustrated in  FIGS. 7-9 . Similar to the CPP  15 , to change the capacity of the RLP  115 , only the rotors  147   a ,  147   b ,  147   c  and rotor or pump casings  117   a ,  117   b ,  117   c  need to be changed. Because the head cover  119  comprises a flat plate  155 , it is possible that the RLP  115  capacity can be modified without changing the head cover  119  and the head cover  119  is “universal” for a given gearbox  116 . Therefore, changing the capacity of the RLP  115  may be even simpler than changing the capacity of the CPP  15  because only the rotors  147 ,  148  and casing  117  need to be changed. 
       FIG. 10  illustrates an alternative seal assembly to  53 . The rotor  247  includes a rear annular recess  263  that accommodates front seal elements  265 . The seal assembly  253  also includes rear seal elements  266  that are held in place by a seal housing  267 . Upper and lower slots openings are shown at  271 ,  273  that enable a tool to gain access to the disk  272  or fastener  274  to bias the seal assembly  253  to the left in  FIG. 10  once the rotor to  47  has been removed from the distal end to  43  of the driveshaft to  22 . Thus, access to the seal assembly  253  is essentially the same as that for the assemblies  53 ,  153  of  FIGS. 2 and 6 . 
       FIGS. 11-13  illustrate a typical CPP rotor  47 . The rotor  47  includes a central hub  81  that accommodates the drive or driven shaft  22 ,  33 . The central hub is connected to a rear annular member  82  that connects a central hub  81  to a rear hub  83  and one or more rotor wings for lobes  88 . As seen in  FIGS. 2 and 6 , the rear hubs  83 ,  183  are received in recesses disposed in the pump casings  17 ,  117 . In the embodiments illustrated in  FIGS. 2 and 6 , the rear annular hubs  83 ,  183  are received in recesses  84  ( FIG. 2 ),  184  ( FIG. 6 ) that are coaxial with or form a radial extension of the first and second openings  45 ,  46  ( FIG. 2) and 145 ,  146  ( FIG. 6 ) through which the drive and driven shafts  22 ,  33  and  122 ,  133  respectively pass. In other embodiments, the rear annular hubs  83 ,  183  may be accommodated within a groove or slot disposed in the rear wall  85  ( FIG. 2 ),  185  ( FIG. 6 ) of the pump casing  17 ,  117 . The design of a RLP rotor  147  is similar to the CPP rotor  47  illustrated in  FIGS. 10-12 , without an annular slot  63  as the head cover  119  of the RLP  115  does not include the cup-shaped members  56 ,  57 . 
     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.