Abstract:
A method of calibrating a lost-motion metering pump is disclosed wherein the pump includes a relief port, a movable hollow plunger having a bypass hole which is aligned with the relief port when the plunger is moved to an aligned position and a control rod extending into the hollow plunger. According to one aspect, the method includes the steps of moving the plunger to the aligned position, inserting a gage pin through the relief port and the bypass hole into the plunger, moving the control rod into engagement with the gage pin and fixing the position of the control rod.

Description:
TECHNICAL FIELD 
     The present invention relates generally to metering pumps, and more particularly, to a method of calibrating a lost-motion metering pump. 
     BACKGROUND ART 
     In order to minimize the variation in output flow of hydraulic lost-motion metering pumps from one pump to another, it is necessary to perform a calibration procedure on each pump. The parameter that a user is most concerned with is the amount of fluid that is pumped over a given time. This parameter, in turn, is determined by the physical relationship between a bypass hole located in a hollow plunger and a control rod extending into the hollow plunger. Currently, this relationship is adjusted during a calibration procedure, which is conducted before filling of a pump reservoir, by an air gauging setup. Briefly, the air gauging setup measures the pressure drop across the bypass hole when the hollow plunger is disposed at a certain position. If a standardized pressure drop value is used for all pumps of a given configuration, then one can be assured that flow performance variations will be minimized. This pressure drop is related to the amount of air flowing through the bypass hole, which is, in turn, related to the equivalent size of the bypass hole when the plunger is at the certain position. The size of the bypass at the time that the plunger is disposed at the certain position can be adjusted by changing the position of the control rod relative to the bypass hole. Typically, a stamped metal linkage is bent to accomplish the actual adjustment of control rod position. 
     Bending the metal linkage to obtain the desired pressure drop value is a lengthy and tedious process. In addition, calibration must be performed very early in the assembly process. If it ever becomes necessary to re-calibrate the pump, substantial disassembly of the pump is required. Furthermore, if re-calibration of the pump is required once the pump is installed, either the pump will have to be returned to the manufacturer or an air gauge setup will have to be provided at the installation site. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a method of calibrating a lost-motion metering pump is provided wherein the pump includes a relief port, a movable hollow plunger having a bypass hole which is aligned with the relief port when the plunger is moved to an aligned position and a control rod extending into the hollow plunger. The method includes the steps of moving the plunger to the aligned position, inserting a gage pin through the relief port and the bypass hole into the plunger, moving the control rod into engagement with the gage pin and fixing the position of the control rod. 
     Preferably, the step of fixing comprises the step of threading a retention nut into a control rod bore in which the control rod is disposed. Also preferably, the control rod includes a bore that receives an anti-rotation pin and the method includes the further step of inserting a hollow seal cap having a slot into a pump housing and the step of moving the control rod comprises the step of inserting the control rod through the hollow seal cap such that the anti-rotation pin is disposed in the slot. Still further in accordance with the preferred embodiment, the step of fixing comprises the steps of inserting a hollow knob having a circumferential flange into the pump housing such that the hollow knob surrounds a portion of the control rod and a portion of the seal cap, securing the hollow knob to the control rod and threading a retention nut into the pump housing to capture the circumferential flange against the seal cap. 
     A threaded ring is preferably threaded onto the control rod and the step of securing the hollow knob to the control rod comprises the step of threading a set screw into engagement with the threaded ring. 
     In accordance with another aspect of the present invention, a method of calibrating a lost-motion metering pump is provided wherein the pump includes a pump housing having a control rod bore, a relief port formed in the pump housing and adapted to receive a relief valve assembly, a movable hollow plunger having a bypass hole which is aligned with the relief port when the plunger is moved to an aligned position and a control rod extending into the control rod bore and the hollow plunger. The method comprises the steps of moving the plunger to the aligned position, inserting a gage pin through the relief port and the bypass hole into the plunger while the relief valve assembly is removed from the relief port and inserting a hollow seal cap having a slot into the control rod bore. The control rod is placed into the control rod bore through the seal cap and into engagement with the gage pin. The position of the control rod is fixed by inserting a hollow knob having a circumferential flange into the second bore surrounding a portion of the control rod and a portion of the seal cap, securing the hollow knob to the control rod and threading a retention nut into the second bore to capture the circumferential flange and the seal cap against the pump housing. 
     In accordance with yet another aspect of the present invention, a method of calibrating a flow control assembly of a lost-motion pump is provided wherein the flow control assembly includes a control rod and a knob and the lost-motion pump includes a hollow plunger disposed in a pump housing. The method includes the steps of inserting the control rod into the hollow plunger, advancing the control rod into the hollow plunger until a particular portion of the control rod is aligned with respect to a certain portion of the pump housing and securing the knob to the control rod when the control rod is aligned with respect to the pump housing. 
     In accordance with a still further aspect of the present invention, a method of calibrating a flow assembly of a lost-motion pump wherein the flow control assembly includes a control rod and a knob and wherein the lost-motion pump includes a relief valve port and a hollow plunger disposed in a pump housing and having a bypass hole, includes the steps of advancing the hollow plunger to an extreme position such that the bypass hole is aligned with the relief port and installing a gauge pin through the relief valve port into the bypass hole. The control rod is inserted into the hollow plunger until the control rod contacts the gauge pin and an indicator is applied to at least one of the flow control assembly and the pump at an aligned position while the control rod is contacting the gauge pin to calibrate the flow control assembly. 
     In accordance with yet another aspect of the present invention, a method of calibrating a flow control assembly of a lost-motion pump, the flow control assembly including a control rod and a knob and the lost-motion pump including a hollow plunger disposed in a pump housing, includes the steps of inserting the control rod into the hollow plunger and advancing the control rod into the hollow plunger until a particular portion of the control rod is aligned with respect to a certain portion of the pump housing. An indicator is secured to at least one of the flow control assembly and the pump at an aligned position while the particular portion of the control rod is aligned with the certain portion of the pump housing to calibrate the flow control assembly. 
     Other aspects and advantages of the present invention will become apparent upon consideration of the following drawings and detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 comprises a trimetric view, with portions cut away, illustrating a hydraulic lost-motion metering pump that may be calibrated according to the method of the present invention; 
     FIG. 2 comprises a trimetric view, with portions cut away, of the pump of FIG. 1 taken from a different viewing angle and illustrating the control rod and associated apparatus; 
     FIG. 3 comprises a trimetric view, with portions cut away, of the pump of FIG. 1 taken from yet another viewing angle and illustrating the liquid end of the pump; 
     FIG. 4 comprises a full sectional view of the pump of FIG. 1 with the relief valve removed from the relief port and before assembly of the flow control components therein; 
     FIGS. 5-8 comprise full sectional views similar to FIG. 4 illustrating various stages of assembly and calibration according to the method of the present invention; and 
     FIG. 9 is a full sectional view similar to FIG. 8 illustrating a pump design which may be calibrated in accordance with a further embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a hydraulic lost-motion metering pump  20  includes a pump housing  22  containing a recess  24  which defines a reservoir  26 . A working fluid, such as oil, is disposed in the reservoir  26 , as is a bell crank assembly  28  which is eccentrically mounted on a shaft  30  and which is driven by a motor (not shown). The bell crank assembly  28  is secured to a hollow plunger  32  and reciprocates the plunger  32  between fully retracted and fully extended positions in a plunger bore  34 . At least one, and preferably two or more bypass holes  36  extend through the wall forming the plunger  32 . Referring also to FIG. 4, the plunger  32  includes a trailing portion  38  located on a trailing side of the bypass holes  36  which has an outer diameter sized to fit in a substantially fluid-tight fashion with the wall defining the plunger bore  34 . The plunger further includes a leading portion  40  disposed on a leading side of the bypass holes  36  opposite the trailing side. The leading portion  40  has a diameter smaller than the diameter of the wall defining the plunger bore  34  so that fluid can flow freely between the outer surface of the plunger and the wall defining the plunger bore  34 . The plunger  32  is open at a trailing end  42  to the oil in the reservoir  26 . 
     A relief port  44  is formed in the pump housing  22  and a relief valve  46  (similar to that shown in FIG. 9) is disposed in the relief port  44 . As seen specifically in FIG. 4, the pump housing  22  further includes a control rod bore  48  adjacent to and in communication with an end  50  of the plunger bore  34 . As seen in FIGS. 2 and 3, a working fluid passage  52  extends between an intermediate chamber  54  (seen in FIG.  4  and which comprises the portion of the plunger bore  34  forward of the relief port  44 ) and a working chamber  56  which is partially bounded by a sealed diaphragm  58 . A conventional liquid end  60  of the pump  20  is located on a side of the diaphragm  58  opposite the working chamber  56 . 
     As seen in FIGS. 1,  3  and  8 , a flow control assembly  62  is disposed in the control rod bore  48 . The assembly  62  includes a control rod  64  which extends through the control rod bore  48  into the plunger bore  34  and into the hollow plunger  32 . The outer diameter of the control rod  64  is sized to provide a fluid-tight fit with the inner surface of the plunger  32 . The position of an end surface  66  of the control rod  64  determines the amount of process fluid pumped per stroke of the pump  20 . Specifically, during operation of the pump  20 , the plunger  32  is reciprocated to produce alternating suction and discharge strokes. At the beginning of a discharge stroke, as the plunger is moved toward the end  50  of the plunger bore  34  but before the bypass holes  36  are covered and blocked by the control rod  64 , working fluid in the intermediate chamber  54  is circulated back to the reservoir  26  with no substantial pressurization of the fluid in the intermediate chamber  54 . Accordingly, no process fluid is pumped at this time. However, once the plunger  32  has been moved forward to a point where the bypass holes are covered by the control rod  64 , working fluid is trapped in the intermediate chamber  54 , the passage  52  and the working chamber  56 . Further displacement of the plunger  32  toward the end  50  of the plunger passage  34  pressurizes the working fluid in the working chamber  56 , causing the pump  20  to expel process fluid out of the liquid end through a first set of check valves (not shown) located in a discharge recess  68  (FIG. 2) of the liquid end  60 . The distance traversed by the plunger  32  from the point at which the bypass holes  36  are blocked to the fully extended position (during which the plunger  32  performs pressurization, as contrasted with the lost motion between the fully retracted position and the point at which the bypass holes are blocked by the control rod  64 ) determines the quantity of process fluid displaced during the pumping cycle. 
     During each suction stroke, as the plunger  32  moves from the fully extended position but before the bypass holes  36  are uncovered, the pressure of the working fluid in the intermediate chamber  54 , the passage  52  and the working chamber  56  is reduced, thereby causing process fluid to be drawn into the liquid end  60  through a second set of check valves (not shown) disposed in an intake recess  70 . The amount of process fluid drawn into the liquid end  60  during the suction stroke is dependent upon the distance between the fully extended position of the plunger  32  and the point at which the bypass holes are again uncovered by the control rod  64 . Once the bypass holes  36  are uncovered, no further process fluid is drawn into the liquid end  60 . 
     The method of the present invention will now be described in connection with FIGS. 4-8. The method may be performed at initial assembly of the pump  20 , or may be undertaken subsequent thereto. Referring first to FIG. 4, the method may begin prior to assembly of the flow control assembly  62  and with the relief valve  46  (similar to that shown in FIG. 9) not present in the relief bore  44 . The method begins with the step of manually or otherwise advancing the plunger  32  to the fully extended position, at which point the bypass holes  36  are aligned with the relief port  44 . Once this alignment has been accomplished, a gage pin  80 , which may be an elongate member of specified thickness, is placed into the relief port  44  such that it extends through one of the bypass holes  36  into the hollow interior of the plunger  32 . Once these steps have been accomplished, the flow control assembly  62  may be inserted into and fixed in the control rod bore  48 . 
     The flow control assembly  62  is assembled in the control rod bore  48  according to the sequence of steps illustrated in FIGS. 5-8. First, with reference to FIG. 5, a seal cap  90  together with associated shaft and seal rings  92 ,  94 , back-up ring  95  and a pair of spring pins  96  are placed in the control rod bore  48  such that an annular collar  98  is fitted snugly within the end  50  of the plunger bore  34 . A calibration retention nut  100  is threaded into a threaded portion  102  of the control rod bore  48  to temporarily retain the seal cap  90  against a wall  104  of the pump housing  22 . 
     Next, as seen in FIG. 6, a control rod assembly  106  is placed in the control rod bore  48 . The control rod assembly includes the control rod  64 , a threaded ring  108 , which is threaded on a threaded portion  110 , and a hollow anti-rotation spring pin  112 , which is placed into and retained in a rod bore  114 . The end surface  66  of the control rod  64  is inserted into the end  50  of the plunger bore  34  and into the hollow interior of the plunger  32  until the end surface  66  of the control rod  64  abuts the gage pin  80  and such that the anti-rotation pin is disposed in a slot  115  formed in the seal cap  90 . Preferably, the width of the gage pin  80  is selected so that the position of the end surface  66  when in abutment with the gage pin  80  and when the gage pin  80  is in abutment with the margins of the bypass hole(s)  36  results in a desired and repeatable calibration of the pump  20 . 
     Referring next to FIG. 7, a knob  120  is then inserted into the control rod bore  48  surrounding the control rod  64  until a surface  122  of the knob  120  abuts a surface  124  of the seal cap  90 . A set screw  126  is then tightened against the threaded ring  108  as the knob  120  is held in place so that the knob  120  is securely fixed to the threaded ring  108  and is rotatable therewith. As seen in FIG. 8, the assembly is completed by removing the calibration retention nut  100  (during this time the components are maintained in position by the control rod  64  and the seal cap  90 ) and threading a further retention nut  130  into the bore  48 . The further retention nut  130  includes a shouldered portion  132  which captures an annular flange  134  of the knob  120 . A nose portion  136  of the retention nut  130  has a length slightly greater than the axial dimension of the flange  134  so that the knob  120  is freely rotatable. 
     Once the foregoing is complete, the gage pin  80  is removed from the relief port  44  and the relief valve  46  is assembled therein. The flow rate of the pump  20  thereafter may be adjusted by turning the knob  120 , which, in turn, results in rotation of the threaded ring  108 . The control rod  64 , however, is held against rotation by capturing of the anti-rotation pin  112  in the slot  115 , and hence, rotation of the threaded ring  108  causes axial displacement of the control rod  64  (the control rod  64  includes threads to the right of the threaded ring  108  and which are engagegable by the threads of the ring  108 ). This displacement, in turn, advances or retracts the end surface  66 , as desired. 
     Re-calibration after installation in the field can be accomplished in a simple fashion by removing the relief valve  46  (similar to that shown in FIG. 9) from the relief port  44 , moving the plunger  32  to the fully extended position, removing the flow control assembly  62  and repeating the steps described above. This is a greatly simplified procedure as compared to the use of an air gauging setup. 
     It should be noted that the present invention comprehends calibration of a pump based upon positioning of the any portion of the control rod  64  relative to another point, such as a portion of the plunger  32  or a portion of the pump housing  22  (including the relief port  44  as described above). Thus, for example, the foregoing steps may be modified whereby a visually-observable mark is placed on a particular portion of the control rod  64  and the control rod  64  is inserted into the plunger  32  until the mark is visually observed to be coincident with a particular portion of the pump housing  22 . Thereafter the rest of the components of the flow control assembly  62  are assembled as noted above. Alternatively, no mark may be utilized, in which case a particular portion of the control rod  64  is visually observed (or otherwise determined to be) coincident with a particular portion of another structure before securing the knob  120  thereto. 
     Referring now to FIG. 9, an alternative pump design is illustrated and which may be calibrated according to an alternate embodiment of the present invention. Elements common to FIGS. 4-9 are assigned like reference numerals. Elements not shown in FIG. 9 are similar or identical to the pump of FIGS. 1-8. Also, FIG. 9 illustrates the various elements in assembled relationship, it should be understood that the parts are assembled and calibrated in a sequence of steps in a fashion similar to the sequence illustrated by FIGS. 4-8. 
     The assembly procedure begins by removing the relief valve  46  from the relief port  44  (if the valve  46  is present in the port  44 ) and then installing an O-ring  216  and a back-up ring  217  into a circumferential channel  226  in a seal cap  225 . A control rod  230  is then inserted into a bore  231  in the seal cap  225  such that the O-ring  216  makes sealing contact with the control rod  230 . Two alignment spring pins  281   a ,  281   b  are then inserted into corresponding bores  282   a ,  282   b , respectively in the seal cap  225  and a face seal O-ring  215  is installed into a face seal channel  283  in the seal cap  225 . 
     The seal cap  225  and installed components therein are then placed into a control rod bore  284 . A retention nut  175  is then threaded into the control rod bore  284 , thereby capturing the seal cap assembly in the pump housing  22 . A ring  170  having a smooth inner bore and a threaded outer surface is loosely placed on an end  285  of the seal cap  225 . A radial bore  286  in the ring  170  is aligned with a threaded bore  287  in the seal cap  225  and a stroke limit set screw  180  is threaded into the threaded bore  287  and extends into the bore  231  just short of contact with the control rod  230 . A calibration ring  200  is then loosely placed over a reduced diameter portion  288  of an internally-threaded stroke adjustment knob  210  and the knob  210  is threaded onto the ring  170 . An e-ring  220  is installed and captured onto an end of the control rod  230 , thus capturing the stroke adjustment knob  210  to the control rod  230 . 
     The structure of FIG. 9 is calibrated in a fashion similar to the embodiment of FIGS. 4-8. Specifically, the plunger  32  is manually or otherwise advanced to the fully extended position, at which point the bypass holes  36  are aligned with the relief port  44 . Once this alignment has been accomplished, the stroke adjustment knob  210  is rotated counterclockwise (when looking at the end of the knob  210  from the outside of the pump) to cause the knob  210  and the control rod  230  to be displaced to the right as seen in FIG. 9 until a shoulder  289  of the control rod  230  contacts the set screw  180 . At this point, an end  233  of the control rod  230  is located to the right of the bypass holes  36  in the plunger  32 . The gauge pin  80  may then be inserted through the relief valve port  44  and into the bypass holes  36 . 
     Once the gauge pin  80  has been inserted into the bypass holes  36 , the stroke adjustment knob  210  is rotated clockwise until the control rod  230  contacts the gauge pin  80 . At this point, the calibration ring  200  is affixed to the stroke adjustment knob  210  using any suitable adhesive or other securing means such that a legend “0” (zero) stamped in the calibration ring  200  is positioned facing straight up. The gauge pin  80  is then removed and the stroke adjustment knob  210  is rotated one full turn clockwise to achieve a zero percent capacity setting. A graduated percent stroke capacity sticker  190  is then affixed onto the seal cap  225  aligning a zero percent indicator line of the stroke capacity sticker  190  with the leading edge of the stroke control knob  210 . The stroke adjustment knob  210  is then rotated ten full turns clockwise to achieve a 100% stroke setting. At this point, the relief valve  46  and a seal ring  256  can be installed in the relief port  44 . 
     While this embodiment, like the first embodiment, utilizes the gauge pin  80  to position the control rod, it should be noted that any other manner of positioning the control rod could alternatively be used, as noted above. Also, any indicator other than the calibration ring  200  could alternatively be used, and/or the indicator could be placed on another part of the pump, if desired. 
     The gauge pin  80  may have a suitable diameter, such as 0.062″, or any other diameter which results in a desired calibration. 
     Numerous modifications to the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights of all modifications which come within the scope of the appended claims are reserved.