Packing Nut and Rod Guide for Piston Paint Pumps

This invention relates to piston paint pumps, more particularly, to those pump assemblies having a drag link subassembly between a rotating eccentric and a linearly reciprocating piston rod.

FIG. 1 is a section view of a prior art piston pump assembly having a conventional packing nut.

FIG. 2 is an end view partially in section of a piston pump having an eccentric drive and drag link subassembly.

FIG. 3 is a section view of a piston pump assembly utilizing the packing nut and rod guide of the present invention.

FIG. 4 is an end view of the packing nut and rod guide of the present invention.

FIG. 5 is a side view of the packing nut and rod guide of FIG. 4.

FIG. 6 is a section view taken along line 6--6 of FIG. 4.

FIG. 7 is a section view taken along line 7--7 of FIG. 4.

FIG. 8 is a detail view of a portion of FIG. 3 showing certain aspects of the invention.

Referring now to the Figures, and more particularly to FIG. 1, a prior art piston pump assembly 10 may be seen. Assembly 10 has a piston rod 12 connected to and formed integrally with a piston 14 carried in a pump housing 16. When piston rod 12 and piston 14 are drawn upward or out of housing 16, paint is drawn in the inlet 18 to an inlet chamber 20 and any paint in an outlet chamber 22 is discharged via housing outlet 24. An inlet check valve 26 is open and an outlet check valve 28 is closed during the preceding operation. Rod 12 and piston 14 are then reciprocated and pushed back into housing 16. During this time, the inlet check valve 26 is closed and the outlet check valve 28 is open causing paint within the pump to move from the inlet chamber 20 to the outlet chamber 22. A set of V-ring packings 30 seals piston rod 12 to housing 16. A second set of V-ring packings 32 is axially preloaded by a wave spring 33 to seal piston 14 to housing 16 thereby separating chambers 20 and 22. The V-ring packing set 30 is preferably compressed between end pieces 34, 36 via a packing nut 38. It is to be understood that packing nut 38 and housing 16 are each threaded and engaged together, retaining the packing nut 38 to housing 16 and allowing axial compression of end piece 36 against the V-ring packing set 30. An enlarged bore 42 provides clearance between the internal diameter of nut 38 and the piston rod 12. In this design any side loads on rod 12 must be taken up by end pieces 34, 36 and the packing set 30.

Referring now to FIG. 2, the piston pump assembly of the prior art and that of the present invention are each intended to be driven by an eccentric 44 driving a connecting rod 46 which is shown in solid lines in a bottom dead center position and in phantom in a top dead center position. Connecting rod 46 is coupled to piston rod 12 via the yoke 48. It is to be understood that connecting rod 46 and yoke 48 are secured together by a yoke pin 50. To maintain alignment of yoke 48 and piston rod 12, a drag link 52 is connected between yoke pin 50 and stationary pump frame 54. Link 52 is shown in a bottom dead center position in solid lines and in a top dead center position in phantom in FIG. 2. It is to be further understood that pump housing 16 is secured to the pump frame 54 via a set of threads 56 and a lock nut 58.

As drag link 52 reciprocates, it will be apparent that yoke pin 50 will travel in an arc and not exactly in line with the axis of the cylindrical piston rod 12 as it reciprocates in and out of the cylindrical housing 16. Such arcuate movement, transmitted via yoke 48, will impose a side load on piston rod 12.

Referring now to FIGS. 3-8, various details of the present invention may be seen. It is to be understood that the environment shown in FIG. 2 is suitable for the prior art assembly 10 and, alternatively, for the assembly 60 (shown in FIG. 3) which utilizes the packing nut and rod guide of the present invention, shown in more detail in FIGS. 4-8. Assembly 60 is similar or identical in most respects to assembly 10, but differs from it in that it has a novel packing nut and rod guide 62 supporting piston rod 12 against side loads. Certain other features of the body of nut 62 also differ from that of packing nut 38 of the prior art. Assembly 60 also differs in that the rod V-ring packing set 64 is compressed by nut 62 against a wave spring 66 providing a predetermined and constant axial load on V-ring packing set 64. A similar structure and operation is provided for piston V-ring packing set 67.

As may be seen by reference to FIGS. 4-7, nut body 62 preferably has a plurality of reliefs 68 passing entirely axially through nut body 62 from a first or top end 85 to a second or bottom end 86. A plurality of lands 69 are interposed between the reliefs 68 and lands 69 collectively form the surface of bore 78. It is to be understood that lands 69 describe a generally cylindrical surface interrupted by reliefs 68. Lands 69 provide a bearing surface for side loads on piston rod 12, while each relief 68 provides a lubricating passageway for piston rod 12. In addition, (and as may be seen in detail in FIG. 8) nut 62 preferably has a lower chamfer 70 which, together with end piece 72 and piston rod 12 form an annular chamber 74 for lubricating oil to circumferentially surround piston rod 12. Reliefs 68 and chamber 74 form a reservoir for lubricating oil for piston rod 12. An upper chamfer 76 avoids the risk of burrs or a "rolled" edge along the upper edge of central bore 78 in nut body 62. Nut body 62 also has a diametral piloting surface 80 on which nut body 62 and piston rod 12 are piloted for maintaining concentricity with housing 16. A mating piloting surface 82 is formed in housing 16. Nut body 62 further includes an axial stop surface 84 to positively locate the position of the bottom or second end 86 of nut body 62 with respect to pump housing 16 to enable applying the predetermined and repeatable amount of axial load to the rod packing set 64 because of the consequent predetermined deflection of wave spring 66.

Nut 62 also has at least two diametrically opposed wrench flats, and preferably a hexagonal shaped head 88 located at the first end of the nut body 62 for removably securing the nut body 62 to the pump housing 16.

It is to be understood that reliefs 68 also provide a path for paint leakage at such time as the rod packing set 64 fails to seal piston rod 12 against housing 16. It has been found that if a closely interfitting cylindrical bore is provided in nut 62 without one or more reliefs 68, that paint leaking along the rod 12 can build up between the rod and the packing nut and cause substantially increased friction and loading of the prime mover driving the pump with the consequent adverse consequences to operation. Reliefs 68 thus serve the dual purpose of providing a lubrication path and reservoir for piston rod 12 while also providing for a "designed in" leakage path if the rod V-ring packing set 64 is not serviced before it fails. Furthermore, in an emergency, pump apparatus 60 may be operated while leaking (possibly with reduced pressure) without the paint coating the entire circumference of rod 12 with the consequent increased friction that would be present if reliefs 68 were absent. It is to be further understood that lands 69 may, in certain instances serve as "chip breakers" or scrapers to clear a path axially along rod 12 in the event of continued leakage and buildup of paint on rod 12. The nut body 62 is preferably formed of a brass material, more particularly, type SAE CA360 free cutting brass.

The invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention.