Follower packing unit for grease guns and the like

An improved follower packing unit for a grease gun is disclosed. The unit includes a hollow annular body of elastomeric material having a front wall, an annular side wall and a rear wall defining a cavity in the body. Rigid front and back structural supports rigidly support the front and rear walls of the elastomeric seal. The elastomeric seal and the front and back structural supports are fastened together to prevent separation and to form a unitary follower structure movable as a unit on a follower rod. The annular side wall of the elastomeric seal is resiliently deformable under pressure in a radial direction for sealing tightly against an interior surface of the barrel of the grease gun or against the interior surface of a tubular cartridge loaded in the barrel of the gun.

FIELD OF INVENTION

This invention relates to a sealing mechanism for lubrication equipment and, more particularly, to a follower packing unit for a grease gun.

BACKGROUND OF INVENTION

In grease gun applications, lubricant is loaded into the barrel of the gun using a variety of different methods. In a first method, the barrel of the gun is loaded with lubricant using one of several bulk loading techniques. In one such technique, referred to as pressure loading, lubricant is pumped into the barrel through the dispensing head of the gun from a source of lubricant under high pressure. In another bulk loading technique, referred to as suction loading, the follower assembly of the gun is retracted manually to create a suction pressure in the barrel which draws lubricant from a suitable source into the barrel. In a third technique, bulk loading is accomplished simply by hand-packing the barrel with heavy lubricant.

In addition to bulk loading, the barrel of the gun can be loaded with a lubricant cartridge that consists of a sleeve open at both ends and pre-packed with lubricant. With the pump head end of the lubrication gun removed, the cartridge is slid into the gun barrel and the end replaced.

With this background, it has proven difficult to construct a follower assembly that will adequately seal with respect to both the inner diameter of the gun barrel, in the case of bulk loading, and the inner diameter of the cartridge, in the case of cartridge loading, since the barrel and cartridge have different inner diameters. In the past, this problem has been approached in a variety of ways, none of which have been totally satisfactory.

U.S. Pat. No. 4,247,023 describes a follower assembly that seals against the barrel of the lubrication gun or against the smaller diameter of a lubrication cartridge positioned in the barrel. During manual priming, a follower rod moves the follower body forward by engagement between a projection on the rod and a back-up plate behind the follower body, and rearward by engagement of a washer carried by the rod with the front of the follower body.

U.S. Pat. No. 3,038,768 describes a follower packing adapted for use in a grease gun loaded either with bulk grease or grease in a cartridge. The follower is adapted for easy entry into a cartridge and to make a tight seal against the cartridge to prevent by-passing of grease around the follower rod.

The devices described in the above patents have drawbacks. For example, in U.S. Pat. No. 4,247,023, the use of an engagement washer on the follower rod disrupts the sealing surface between the follower rod and seal assembly when the user is pulling the grease follower in a rearward direction away from the pump head to prepare the grease gun for refill. Eventually, after repeated applications, this disruption causes by-pass of grease from the front portion of the follower assembly to the back portion of the follower assembly. This is an undesirable because any grease in the back portion of the follower assembly is wasted.

In the case of U.S. Pat. No. 3,038,768, the sealing ability of the follower seal denoted 53 against the grease tube denoted 1 or cartridge denoted T is limited when moving the grease follower rod forward for priming purposes. Users complain there is by-pass of grease between the follower seal and the grease tube or cartridge causing undesirable situations as grease is wasted.

Another grease gun of conventional design is shown inFIG. 1. The gun has a follower rod1, an elastomeric seal3forming a cavity, a rear support5and a two-piece front support7. The rear support5is not fastened to the elastomeric seal3and is only retained by a spring15against the elastomeric seal. When there is a need to prime the grease gun after loading of grease, an engagement pin17on the follower rod1is positioned in contact with a back surface21of the front support. A pushing force on the follower rod6acts against the back surface23of the elastomeric seal3, causing distortion of the seal. This distortion allows grease from the lubricant chamber to by-pass the seal.

There is a need, therefore, for a lubrication gun having a follower assembly providing a more effective seal against the inside surface of the barrel, in the case of bulk loading of lubricant in the barrel, and against the inside surface of a cartridge of grease in the barrel, in the case of cartridge loading.

SUMMARY OF INVENTION

In general, this invention is directed to a lubricating gun comprising a barrel for holding either lubricant in bulk or a tubular cartridge containing lubricant. The lubricating gun also includes a follower packing unit in the barrel, and a follower rod for moving the follower packing unit in the barrel along a longitudinal axis of the barrel. The follower packing unit comprises an elastomeric seal comprising a hollow annular body of elastomeric material having a front wall, an annular side wall and a rear wall defining a cavity in the body. A first opening in the front wall allows entry of lubricant into the cavity under pressure. A second opening in the rear wall is aligned with the first opening such that the follower rod extends through both openings. The rear wall is configured at the second opening for sealing engagement with the follower rod. A rigid back structural support is provided for rigidly supporting the rear wall of the elastomeric seal, and a rigid front structural support is provided for rigidly supporting the front wall of the elastomeric seal. The front and back structural supports have openings therein aligned with the first and second openings in the elastomeric seal for receiving the follower rod. One or more fasteners are provided for fastening the elastomeric seal, the front structural support and the back structural support to one another in a manner preventing separation such that the elastomeric seal and front and back structural supports form a unitary follower structure movable as a unit in the barrel. The annular side wall of the elastomeric seal is resiliently deformable under said pressure in a radial direction for sealing against an interior surface of the barrel or the tubular cartridge.

In another aspect, this invention is directed to a follower packing assembly incorporating a follower packing unit and follower rod of the type described above.

DETAILED DESCRIPTION

Referring to the drawings,FIGS. 2-4show an embodiment of a lever action grease gun, generally designated20, comprising a container in the form of a barrel22defining a lubricant chamber24for containing a supply of grease. As shown, the grease is in bulk form but it can be contained in a cartridge, as will be described later. The barrel22may be in the form of a metal tube or cylinder, for example. A pump, generally designated30, is positioned at one end of the barrel constituting its forward end. The pump30comprises a head32screwed on the forward end of the barrel22and having a bore34extending transversely with respect to the barrel. This bore34forms a pump cylinder, also designated34. A pump plunger36reciprocates in the cylinder34and projects out one end of the cylinder (i.e., its rearward end). A hand lever40is pin-connected at42adjacent one end of the lever to the end of the plunger36extending out of the cylinder34. A link44is pin-connected at46to this end of the lever40and pin-connected at48to the pump head32. The arrangement is such that by swinging the lever40away from the barrel22, the plunger36is pulled out of the cylinder34through a priming stroke to a retracted position (not shown), and by swinging the lever toward the barrel, the plunger is pushed into cylinder34through a pressure stroke to a pressure position (FIG. 3). The pump head32is formed with an inlet port52through which grease may flow from the barrel22into the cylinder34when the plunger is in its retracted position. A follower packing unit, generally designated60, is slidable in the barrel22and is biased toward the pump head30by a spring62for forcing grease from the barrel into the cylinder34. The forward end of the cylinder34is closed by a plug70. The pump head30is formed with a lateral outlet port74adjacent the forward end of the cylinder34. An outlet fitting (not shown) may be screwed in the outlet port74for connection of a hose or tube (not shown) through which lubricant can be delivered from the grease gun to a bearing or other device to be lubricated. The forward end portion of the cylinder34is enlarged to provide a forwardly facing valve seat80inward of the outlet port74. A ball valve82is biased against this seat by a spring86reacting against the plug70fitted in the forward end of the cylinder34.

Referring toFIGS. 5-8, the follower packing unit60has a central longitudinal axis88and comprises an elastomeric seal90of a resilient material sandwiched between a substantially rigid rear structural support92and a substantially rigid front structural support94. The follower packing unit60is moved back and forth in the barrel by a follower rod100having an engaging element102adjacent its front end and a handle104at its rearward end. The rod100extends rearward through an opening106(FIG. 3) in an end cap108on the barrel22. As will be described, the follower rod100is rotatable about its own longitudinal axis, coincident with axis88, to turn the engaging element102to different positions allowing selective movement of the follower packing unit60in either a forward direction toward the pump head30or in a rearward direction away from the pump head. The engaging element is illustrated as a cross pin (also designated102) extending transversely with respect to the follower rod100, but it can have other configurations within this invention.

Referring toFIGS. 6-8, the elastomeric seal90comprises a hollow body110having a front wall112, an annular side wall114, a rear wall118, and a rounded transition120connecting the annular side wall and the rear wall. The front wall, side wall, rear wall and transition define a cavity126inside the body. The front wall112has a first relatively large-diameter opening130for communication of the lubricant chamber24with the cavity126. The rear wall118includes a second smaller-diameter cylindrical opening134generally aligned with the first opening130for receiving the follower rod100. Two longitudinally spaced annular protrusions138are provided in the second opening134for sealing against the follower rod. The protrusions138form a smaller inside diameter to provide high-pressure contact surfaces for better sealing against the rod. The number of protrusions138may vary. The elastomeric seal90is desirably integrally formed as a one-piece member of suitable material, such as Buna-N (Nitrile) rubber. The material has a suitable hardness and stiffness sufficient to maintain the general shape of the body (as indicated inFIG. 7) in all modes of operation of the grease gun. By way of example, the material may have a durometer in the range of 60-70, and desirably about 65, as measured on the Shore A scale. Desirably, the front and rear walls112,118have thicknesses T1and T2, respectively, substantially greater than (e.g., about twice) the thickness T3of the annular side wall114and are thus more rigid than the side wall. The rounded transition120has a thickness approximately the same as the side wall114. The rear wall118of the elastomeric seal90has a central portion surrounding the opening134of increased thickness defining an outside conical sealing surface140. Rivets144extend through two holes148in the rear wall and through corresponding holes152in the front and rear structural supports92,94(FIG. 8) to hold the components fixed together in a manner preventing separation of the components, the arrangement being such that the elastomeric seal90, the front structural support94and the back structural support92form a unitary follower structure movable as a unit in the barrel22. The number of rivets used to hold the parts in assembly can vary. Other types of mechanical fasteners may be used.

As shown inFIG. 6, the rear structural support92comprises an elongate member160having a front annular wall162and stiffening ribs164extending lengthwise of the member. A hole168extends longitudinally through the member160. The hole168has a lower generally cylindrical portion168A which is sized to seal against the follower rod100and an enlarged upper portion168defined by an inside conical surface (also designated168B) for sealing against the outside conical surface140of the elastomeric seal90. The length172(FIG. 6) of the elongate member160is desirably substantially greater than (e.g., about 5 times greater than) the diameter of the lower portion168A of the hole168for providing proper support to the follower rod100. The rear structural support92is of a suitably rigid material such as plastic or metal (e.g., steel). Desirably, the support92is of integral, one-piece construction. The rear support92can have other configurations.

The front structural support94comprises a back support member in the form of an annular base plate180having a bushing182defining an access hole184. The hole184has diameter larger than the diameter of follower rod100but smaller than the length of the cross pin102. The plate180has two rivet holes152for the rivets144. The front structural support94also includes a channel-shaped front support member190having a front wall196spaced from the base plate180. The front support member190also includes flanges198which are secured to the base plate180by the rivets144passing through holes152in the flanges198. A slot200is provided in the front wall196of the front support member190. For reasons which will appear, the slot200has a length202(FIG. 8) greater than the length of the cross pin102on the follower rod100and a width204less than the length of the cross pin. The front structural support94is of a suitably rigid material such as plastic or metal (e.g., steel). The front support94can have other configurations.

Referring toFIGS. 9 and 10, the follower rod100is rotated to a “loading” position in which the cross pin102is out of alignment with the slot200and in contact with the front surface of the front wall196of the front member190of the front structural support94. With the follower rod100in this position, the rod is pulled in a rearward direction (to the right inFIG. 4), which causes the entire follower packing unit60to move away from the pump head30to allow loading of lubricant into the barrel22, either in bulk or by using a cartridge tube. After loading is complete, the follower rod100is rotated on its axis to align the cross pin102with the slot200(FIG. 11) and then pulled in a rearward direction to move the cross pin through the slot and into the space or gap between the front wall196of the front support member190and the bushing182on the base plate180, as shown inFIG. 12. The cross pin102is sized so that it cannot pass through the access hole184in the base plate180. The follower rod100is then rotated to a “dispensing” position (FIG. 13) in which the cross pin102is out of alignment with the slot200and in contact with the back surface of the front wall196of the front support member190. In this position, a forward force applied to the follower rod100will push the entire follower packing unit60forward in the barrel22or cartridge tube through a priming stroke to expel any air from the lubricant chamber24. As the follower packing unit60moves back and forth in the barrel22, no direct force is applied to the elastomeric seal90. Rather, the force is distributed over the front and back support structures92,94.

When the follower packing unit60is moved in a rearward direction, the relatively rigid rear wall118of the body110of the elastomeric seal90supports the less rigid annular side wall114. Additional support is provided by the rigid front wall162of rear structural support92. This support maintains the shape of the annular side wall114for sealing effective against the leakage of air when the follower packing unit60is moved rearward to create a vacuum in the lubrication chamber24.

When the follower packing unit60is in the position shown inFIG. 3, with the lubricant chamber24full of grease, and the unit is pushed forward toward the pump head30through a priming stroke for expelling any air, the pressure developed in the lubricant chamber24and the cavity126in the elastomeric seal90produces a generally radial outward force on the annular side wall114of the elastomeric seal. The annular side wall114deforms outward in a generally radial direction under this pressure to form a tighter seal between the side wall and the barrel22or the cartridge tube. In addition, a rearward axial force is applied to the rear wall118. This force causes the conical outside surface140of the rear wall118to wedge against the mating inside conical surface168B of the back structural support92to increase the sealing force exerted by the annular protrusions138against the follower rod100, thereby providing an exceptionally tight seal between the follower rod and the elastomeric seal90.

FIGS. 14 and 15show the gun20in use as a cartridge gun, i.e., loaded with a cartridge tube250which is filled with grease and which, as supplied, has closure caps (not shown) at its ends. The cartridge250has a large opening at one end and a small opening at its other end. To load the cartridge in the gun, the pump head30is removed from the barrel22. The follower rod100is moved to its “loading” position and pulled rearward against the bias of the spring62to a position in which a grooved portion260of the rod is aligned with a lateral extension or notch262of the opening106in the barrel cap108. The follower rod100is locked in this position by angling the follower rod to move the grooved portion260of the rod into the notch. With the follower100thus locked, the follower packing unit60is held against the bias of the spring62in a position adjacent the back end of the barrel22. After removing the end caps from the cartridge250, the cartridge is inserted into the pump end of the barrel22with the end of the cartridge having the large opening being inserted first.

After the cartridge250is loaded, the pump30is replaced on the barrel22, and the follower rod100is unlocked from the barrel cap108and moved to its “dispensing” position in which the cross pin102is out of alignment with the slot200and disposed between the front wall196of the front support member190and the bushing182on the base plate180. The follower rod100is then pushed in a forward direction to move the follower packing unit60toward the pump30. As the follower packing unit is pushed forward, the smaller-diameter front wall112of the elastomeric seal90acts as a lead-in so that the packing unit readily and easily enters the cartridge250and comes into sliding sealing engagement with the interior surface of the cartridge to force grease in the cartridge toward the pump30without leakage of grease past the elastomeric seal. As the packing unit60enters the cartridge, the annular side wall114of the elastomeric seal90is axially compressed. This compression, in combination with the pressure in the lubricant chamber24and cavity126of the seal, produces a radial outward force on the side wall114to create a tighter seal between the cartridge250and the elastomeric seal, and also a rearward axial force to create a tighter seal between the follower rod100and the annular protrusions138due to the wedging action between the mating surfaces140and168B.

As the follower packing unit90moves forward, grease and any air in the cartridge250and barrel22is forced into the cylinder34of the pump30, causing the ball valve82to open, and then through the outlet opening74in the pump head32. The follower rod100is then rotated to align the cross pin102with the slot200, pushed forward to move the cross pin through the slot in which the pin is forward of the front wall196of the front support member190(e.g., to the position shown inFIG. 14), and then rotated to a position in which the cross pin in out of alignment with the slot. The gun is then ready for use, with the spring62urging the follower packing unit60in a forward direction to move lubricant through the inlet52of the cylinder34where it is in position for being dispensed through the outlet74by using the lever40.

Alternatively, the gun1can be loaded with bulk grease instead of a cartridge, as illustrated inFIG. 2. The gun may be loaded with bulk grease either by utilizing a filling pump to pump grease into the barrel22via a filler nipple (not shown) or by removing the pump head32. Alternatively, the open end of the barrel22may be inserted in a container of grease and the follower rod100pulled to move the follower packing unit60away from pump head to create a suction force drawing grease into the lubrication chamber24. In this case, the rearward force exerted by the follower rod100on the packing unit60causes the conical outside surface140of the elastomeric seal90to wedge against the mating inside conical surface168B of the rear structural support92to create a tighter seal around the follower rod100. As a result, leakage of air around the follower rod100is prevented to maintain the suction in the lubrication chamber24.

It will be observed from the foregoing that the follower packing unit60described above provides a more robust method of sealing in both bulk filling and cartridge applications. The cavity126in the elastomeric seal90of the follower packing unit receives lubricant under pressure. This pressure creates a generally radial outward force tending to push the side wall114more tightly against the grease tube or cartridge150. The pressure also creates a generally axial rearward force which pushes the outside conical sealing surface140of elastomeric seal90against the inside conical surface168B of rear structural support92to wedge the annular protrusions138of the seal90more tightly against the follower rod100. Also, the surface of the follower rod100which engages the sealing protrusions138is smooth and uninterrupted over the entire range of movement of the follower packing unit60in the barrel22, which creates a good sliding sealing fit between the rod and the elastomeric seal over the entire range of movement. This construction is in contrast to conventional designs such as shown in U.S. Pat. No. 4,247,023, where the sealing surface between follower rod and the central bore in the packing unit is interrupted by swaged wings44on the follower rod which can result in leakage of grease past the follower body.

Experimental results have shown that the present invention can effectively seal grease even after the follower packing unit has been moved through more than 1000 “load and dispense” cycles by applying axial compression and tension forces of at least 40 lbs to the follower rod. The application of tension force during the loading stroke of each cycle was measured to produce a negative pressure in the lubrication chamber of 8-11 psi. Conversely, the application of compression force during the dispensing stroke of each cycle was measured to produce a positive pressure in the lubrication chamber of 9-12 psi. This was validated through repeated experiments and is an improvement over the prior art. Results of tests on conventional grease guns show that an axial compression or tension force of 20 to 35 pounds transmitted to the seal assembly by the follower rod produces only about a 5-10 psi of positive pressure during a dispensing stroke and about 5-8 psi of vacuum during a loading stroke. Further, the sealing capability of the sealing assembly is reduced substantially after 100-200 cycles.