Abstract:
A backpack sprayer having a tank, an interior pressure chamber, and a piston assembly that is used to draw fluid into the pressure chamber and also to pressurize the chamber so as to expel the fluid under pressure, which piston assembly is connected by a linkage assembly to a handle bar that is manually operated by the operator of the sprayer to cause movement of the piston within a piston cylinder, the improvement including a piston cylinder cap that attached to the end of the piston cylinder and restrains downward movement of the piston arm.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to a mechanical pumping device that utilizes a piston mechanism to create pressure within a confined space. In particular, this invention pertains to such a device that is particularly well adapted for use in a manually-operated backpack sprayer.  
         [0002]     Just about every home, garden, landscape, farm, ranch and business requires, at one time or another, the application of a liquid-based substance in a localized way. For example, in and around every home isolated plants may need to be watered that cannot be easily watered with a garden hose, or an herbicide, pesticide, fungicide, fertilizer or other chemical agent may need to be applied. Such applications are an almost daily requirement on most farms and ranches, and around many homes and business.  
         [0003]     For large applications, motorized spraying units on wheeled vehicles are commonly used. But there are innumerable instances in which the size or location of the job does not permit the use of such large equipment. For these type applications, a device that is typically known as a “backpack sprayer” has become ubiquitous.  
         [0004]     As the name suggests, the backpack sprayer is one that is designed and constructed so as to be attachable to the back of the operator, much like the backpacks used by hikers and school children. It generally has a three- to five-gallon leak-proof tank that is contoured to rest comfortably against the operator&#39;s back, straps that usually slip over the operator&#39;s shoulders and a waist strap for correctly positioning and securing the device snuggly to the operator. The tanks also normally have a large, selectively openable and resealable opening on its upper surface (relative to when the tank is in place on the operator&#39;s back), through which the liquid-based material can be added to the tank.  
         [0005]     At the other end of the tank (that is, the bottom of the tank when it is in place on the operator&#39;s back) are normally situated the “working” parts of the sprayer—the pumping and spraying mechanisms. These normally include some form of a piston-based mechanism for generating increased air pressure within a pressure chamber within a tank, and a handle bar, typically 18 inches to 2 feet in length, attached to the piston-based mechanism and extending forwardly from the tank (relative to the operator wearing the tank) that the operator manually operates with one hand in an up-and-down motion to cause some linkage assembly to rotate so that movement of the handle bar is thereby communicated to the piston.  
         [0006]     A length of flexible hose through which the now-pressurized fluid contents are sprayed is also typically attached to the tank in that bottom area, and the distal end of that hose is usually equipped with a hand-operated valve and nozzle by which the operator directs the spray as desired. So, once the backpack sprayer is filled with the desired fluid, and it is properly secured to the operator, the operator uses one hand to move the handle bar in an up and down motion to pressurize the fluid, and the other hand to hold, activate and direct the valve-and-nozzle end of the hose to control and direct the spray.  
         [0007]     Although there are various different mechanisms employed for pressurizing the contents of the tank, one often used, and the one which is used in the preferred embodiment displayed here, involves the use of a separate pressure chamber within the tank, into which liquid from the tank is drawn, and then pushed out under pressure through the hose that is attached to the pressure chamber. In this type device, the piston assembly is attached to the separate pressure chamber. Down-stoke on the piston (that is, pulling up on the handle bar) pulls fluid from the large tank into the piston cylinder chamber through a one-way valve. Up-stroke of the piston (that is, pushing down on the handle bar) pushes and pressurizes the fluid into the pressure chamber. Additional up and down strokes can be utilized to both push more fluid into and increase the pressure within the pressure chamber. Accordingly, the operator has the option of more or less continuous pumping of the handle bar while keeping the hose valve open to create a more or less steady stream of fluid at constant pressure, or, repetitively pumping of the handle bar while keeping the hose valve closed, which will create more fluid and greater pressure, thereby allowing for a subsequent spray of fluid that is initially released at higher pressure, and is sustained longer in between handle-bar pumping sessions, but at a steadily decreasing flow rate.  
         [0008]     Such backpack sprayers are not new. In fact, the earliest patent known to have issued for what is now called a backpack sprayer issued well over 100 years ago in 1888 (U.S. Pat. No. 383,261). Since then, and certainly in recent years, quite a number of patents have issued relating to improvements in the design of backpack sprayers. For example, representative of such patents are U.S. Pat. Nos. 4,768,714, 4,798,333, 5,478,015, 5,636,791, 5,671,884, 5,775,543, 5,785,245, 5,984,199, and 6,412,707.  
         [0009]     As is the case with most personal, portable mechanical devices intended for home and commercial use, the primary design goals, in no particular order, are: performance; reliability; durability; ease of use; light weight; low cost; and ease of manufacture. In the case of backpack sprayers, these are particularly important. First, because the sprayer is worn by the operator in all types of weather, any leakage will be uncomfortable at least (no one likes to have liquid spilled down the back of their pants, particularly so in cold weather), and could be dangerous at most if the liquid being sprayed is a chemical that may present health risks to the operator if he or she is unduly exposed to the chemical. Therefore, the sprayer must not only be capable of leak-free operation when it leaves the factory, it must remain leak-free during its lifetime of use, and these devices are expected to have a lengthy lifetime. Also, the “use” to which these sprayers are most often put can create challenges for the designer to meet the design of goal of long-term durability and reliability while maintaining acceptable cost, ease of manufacture and resultant weight. These sprayers are most often used in commercial settings, by workmen who may not be always concerned with the proper care and use of the machine. The sprayers may therefore be mishandled from time t0 time, not only during use but also after use when being stored or transported.  
         [0010]     In use, the power that some operators can generate manually on the end of the handle bar is enormous, putting tremendous stress on the linkage and piston assemblies. For example, some operators desire to create extremely high pressure within the pressure chamber. Accordingly, they will push and pull on the handle bar numerous times before ejecting any liquid. Of course, as the pressure within the chamber builds, the force required to move the piston increases as well. Before long, the operator has to apply tremendous force to the end of the handle bar. Because of the leverage that is obtainable given the length of the handle and fact that the handle bar is attached to the linkage at one end, and the operator applies force at the other end, the resultant force that can be generated on the piston assembly can be huge. Therefore, those assemblies must not only be durable and reliable, but must also be able to maintain those characteristics in the face of rigorous usage over a long period of time.  
         [0011]     It would of course be possible to design the linkage and piston assemblies to be entirely constructed of large, heavy gauge material that could be expected to withstand such rigorous use and treatment. However, as mentioned above, the preferred design goals include low cost, ease of manufacture, and light weight. Therefore, the use of large amounts of steel or other heavy gauge material is ultimately counterproductive.  
         [0012]     For example, the use of plastic (usually polyethylene) components in backpack sprayers is common, as plastic provides for reasonable strength and durability on the one hand, and for light weight, ease of manufacture and low cost on the other. Some of the components that are often made of plastic include the tank, the pressure chamber, the tank opening and closing apparatus, the piston cylinder, and large portions of the piston itself.  
         [0013]     But, while plastic does provide for reasonable strength and performance at low cost with light weight, it simply cannot generally withstand the forces generated by many operators. Therefore, a combination of plastic and steel or aluminum must be used.  
         [0014]     One area in which steel or aluminum must be used in is the handle bar, and the piston and linkage assemblies. Because the piston cylinders in the sprayers can be quite large, it is undesirable to use steel or other heavy gauge material for the cylinder as that would add materially to cost and weight. But, the piston and cylinder, and the adjacent linkage, are where the greatest forces must be accommodated, and is also the area where damage and leakage can most readily occur.  
         [0015]     Therefore, so as to be able to use plastic for portions of the piston and the entirety of the piston cylinder, means must be provided that restrict the movement of the piston within the cylinder. This is made doubly important because of the way in which the piston is caused to move within the cylinder. In other words, the piston is made to move by manual pressure placed upon the end of the handle bar. That up-and-down movement of the handle bar in turn causes the main linkage member that is attached to the proximal end of the handle bar and also to the piston to rotate about its axis. That axial rotational movement is communicated to the piston via a piston arm that is attached at one end to the linkage member and at its other end to the piston. The linkage member and the piston arm rotate, but linear movement of the piston within the piston cylinder is desired for proper operation of the device. Therefore, the amount of distance that the piston is allowed to move within the piston cylinder must be carefully controlled. Otherwise, the piston is pulled out of alignment with the cylinder resulting in one or more undesirable things: 1) the liquid in the tank may leak out of the device onto the operator; 2) the rubber seal on the head of the piston may become unattached; and 3) in extreme cases, the piston and/or the piston cylinder cracks, rendering the device useless until repaired.  
         [0016]     For this reason, various means and methods have been designed for limiting the piston&#39;s travel within the piston cylinder. Two such ways that the inventor has tried before include a large R-shaped metal pin that was inserted strategically within the handle bar and linkage assemblies such that the ends of the pin would impact the tank upon the maximum desired up and down movement of the handle so as to restrict movement of the linkage. (See  FIG. 7A ). That, however, proved unworkable because even a large metal pin could be bent if sufficient force were applied to the handle bar by the operator. Also, even if not bent in one event, the wear and tear on the pin over time would be sufficient to deform it sufficiently so that it permitted more than the desired movement of the piston. Instead of a metal pin, the inventor also tried a hard plastic wedge that was strategically attached to the handle to similarly restrict its movement within allowable tolerances. (See  FIG. 7B ). This too proved unworkable as the force that could be generated by some operators over time would cause sufficient deformation of the wedge that it ceased to function properly.  
         [0017]     While these prior art devices are useful to a degree, they still suffer from certain drawbacks in that they did not provide sufficient durability and reliability. Therefore, there existed a need in the art for an improved way to properly limit the piston&#39;s movement within the cylinder, and to do so in a way that does not add materially to the cost or weight of the device.  
       SUMMARY OF THE INVENTION  
       [0018]     This invention provides such an improved device with an elegant solution to the problem that not only effectively and appropriately limits the movement of the piston within the cylinder, but also provides other benefits as well, such a protecting the piston and piston cylinder from physical damage, limiting their exposure to dust and other unwanted elements, and providing some protection to the operator and others in close proximity to the piston linkage from injury.  
         [0019]     To accomplish these multiple goals, a piston cylinder cap is attached to the exposed end of the piston cylinder, leaving only enough space for the piston arm to operate. The cap is designed and constructed so as to act as a stop for the piston during its down stroke.  
         [0020]     In the preferred embodiment, for ease of construction and assembly, the piston cylinder cap is held into the correct axial and lateral position on the cylinder by being designed so that it has an interior area that fits snuggly up against the end of the cylinder when properly positioned, a pair of exterior tabs that reside above and abut the upper edge an exterior projection (or projections) on the cylinder, and an appropriately sized and shaped open area in the wall of the cap, such that the sidewalls of the cap on either side of the open area laterally abut against the lateral edges of the exterior projection (or projections). That interior end of the cylinder cap also has a number of upwardly-extending interior flanges with intermediate pegs around its lower interior periphery. The flanges are sized, shaped and placed away from the cap interior so as to act as a guide for the exterior wall portion of the piston body on its down stroke, and the intermediate pegs act as a stop for the piston when the exterior bottom edge of the of the piston comes into contact with them at the desired maximum down stroke of the piston. The cap is also designed and constructed so as to have an integral channel within which the piston arm generally resides.  
         [0021]     Therefore, in the preferred embodiment of this invention, the combination of the pegs on the bottom of the cap on the one hand, and the tabs and open area of the cap in conjunction with the exterior projection (or projections) on the cylinder on the other hand, act together to provide the restraining function that can withstand the forces generated by even the biggest, strongest and most aggressive operators on the down stroke of the piston, whether in a single event or repetitively over a long period of time.  
         [0022]     There are, of course, other means by which the same inventive concept can be implemented. In the way of example and not limitation, the cap can be held in proper position on the piston cylinder through a myriad of other well-known ways, such as any other arrangement of projections, tabs, openings, mortise and tenon arrangements, threads, etc., or combination thereof, or by being glued or welded, or having an exterior flange that resides between two exterior projections on the cylinder, or being attached directly to the tank or the piston linkage. In addition, ways in which the cap can limit the movement of the piston and piston arm would include other tab and stop designs, and other arrangements what would be functionally equivalent to the interior flanges and pegs disclosed in the preferred embodiment of the cap. For example and not by way of limitation, instead of single flanges with intermediate pegs, the flanges could be extended such that they become a one-piece skirt and the pegs become a circular element instead of individual pegs; or they could be removed and the bottom of the cap itself could be used as the mechanism to restrain downward movement of the piston. 
     
    
     DESCRIPTION OF THE FIGURES  
       [0023]      FIG. 1  is a perspective view of the preferred embodiment of this invention, shown in right-side-up position as it would be when attached to the back of the operator. This drawing is in partial “exploded” format, showing the piston cap removed from the piston cylinder.  
         [0024]      FIG. 2  is an isolation, perspective, partially exploded view showing the piston assembly, linkage assembly, and cap in greater detail. As in  FIG. 1 , the cap is still shown as removed from its intended position on the piston cylinder.  
         [0025]      FIG. 3  is a side, cross-sectional view taken along Line  3 - 3  in  FIG. 2 , showing the proper alignment of the piston assembly (piston, piston arm and piston cylinder) upon the up-stroke of the piston. As will be noted, the piston cap is not shown.  
         [0026]      FIG. 4  is similar to  FIG. 3 , but shows what happens to the alignment of the piston and piston cylinder if the piston arm is allowed to rotate too far during the down stroke of the piston. As can be appreciated, further rotation of the piston arm would cause even greater misalignment and localized pressure by the piston on one side of the piston chamber that could cause either it or the piston to break.  
         [0027]      FIGS. 5A and 5B  are similar views to  FIGS. 3 and 4 , but show the piston, piston arm and piston cylinder with the cap installed.  FIG. 5A  shows the piston in fully up-stroke position; whereas  5 B shows the piston in fully down-stroke position, with its down-stroke travel within the piston cylinder being restrained by the cap.  
         [0028]      FIGS. 6A, 6B  and  6 C show various views, respectively the side, front and top views, of the cap and the flange/peg arrangement in isolation.  
         [0029]      FIGS. 7A and 7B  show in isolation two of the prior art ways in which restriction of the rotational movement of the piston linkage was attempted. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     Throughout this Specification and the attached Claims, reference to direction such as “top,” “above” or “upwardly” etc. shall refer to the upward direction for the components as oriented and shown in the Figures; whereas references to “bottom,” “down” and “below” etc. shall refer to the downward direction for the components as oriented and shown in the Figures, which is how the sprayer would be oriented when attached to the back of the operator ready for use. References to “front” or “side” or “back” are used relative to the operator upon whom the sprayer is attached. For example, the “front” refers to the side or direction facing in the same direction as the operator would be facing.  
         [0031]     Looking at  FIG. 1 , it is seen that the preferred embodiment of this invention has the usual primary components for a high-end backpack sprayer—the tank  10 , the piston assembly  12 , the linkage assembly  14 , and the handle bar  16 . (The straps that are used to secure the sprayer to the operator are not shown, but could be of any design that provided for comfortable and secure attachment. Also not shown is the upper side of the tank  10  where the fill opening and cap are located. Those too can be of any conventional design, and is most often a fairly wide opening of 5 or 6 inches in diameter, with a filter and screw-on cap. The caps usually also include a venting mechanism to prevent dangerous build-up of pressure or fumes within the tank itself.).  
         [0032]     In this embodiment, the tank is of one-piece molded construction of a polyethylene or other suitable material. The tank also has an integrally formed downwardly extending flat portion  18  which is used for additional stabilizing area against the operator&#39;s back, and as the surface to which the linkage assembly  14  is attached. Also in this embodiment, a metal tube frame  20  is attached at either side of the bottom of the tank  10 , and extends outwardly and rearwardly therefrom, providing the dual function of protecting the linkage and piston assemblies  14  and  12  from damaging blows, and acting as a stand upon with the sprayer can be placed upright when not in use. In this embodiment, the tube frame  20  is very easily but securely attached to the tank  10  by inserting each end of the tube frame  20  through two bosses  22  formed integrally with the flat portion  18  and into a terminal  24  that is formed integrally with both the flat portion  18  and the underside of the tank  10 . The terminals  24  each also have a flange  25  that is attached to it and to the underside of the tank  10  for even greater stability and strength. The size of the apertures in the bosses  22  and the terminals  24  are such that once the ends of metal tube frame  20  is inserted through and into them, the metal tube  20  is held very snuggly in place. The ends of the metal tube frame  20  can also be heated before insertion to ease insertion and to secure them more tightly after insertion. The ends of the metal tube frame  20  can also be formed integrally with the formation of the tank  10  itself by inserting the tube ends an appropriate distance into the mold (not shown) for the tank  10  and then molding the tank  10  around the ends of the tube fame  20 .  
         [0033]     Looking now at  FIG. 2 , the components of the linkage and piston assemblies  14  and  12  are shown in isolation and enlarged for easier viewing. Looking first to the linkage assembly  14 , it comprises a hollow metal spindle  26  that is rotatably attached to the flat portion  18  of the tank  10  via two large spindle bosses  28  that are also constructed of a polyethylene material and formed integrally with the tank  10 . The spindle  26  should fit snuggly, but still be freely rotatable within the spindle bosses  28 . Because the spindle  26  will be held in proper alignment by the piston assembly  12  as hereinafter described, it is not absolutely necessary to provide for other alignment or restraining means so as to keep spindle  26  properly positioned within the spindle bosses  28 , but such means can be easily provided, for example by use of a cotter key or dimples on the outside of the spindle  26  adjacent the spindle boss  28 .  
         [0034]     One end of the spindle  26  terminates at the outer edge of one boss  28 . The other end of the spindle  26  extends a distance beyond the other boss  28  where it is welded to a short hollow segment  30  at a right angle thereto. Hollow segment  30  acts as the housing into which fits one end of the handle bar  16 . Preferably, the outside diameter of this end of the handle bar  16  is very close to the inside diameter of the segment  30 , so that the end of the handle bar  16  can slide easily but snuggly into it. Any conventional means can be used to secure the handle bar  16  within the segment  30 , such as a simple pin that is inserted through aligned holes in each (not shown).  
         [0035]     The handle bar  16  is elongate and is sized and shaped so that it extends forwardly (relative to the user when the sprayer is in position on his or her back), and is positioned there in an ergonomically appropriate way so that the operator can easily grasp the distal end of the handle bar (equipped with a handle grip  32 ) so that the operator can easily grip the end of the handle bar  16  and move it up and down. The sprayer as shown is a left-handed unit in which the handle bar  16  would be moved by the left hand of the operator. As can be appreciated, a right-handed unit can be constructed simply by having the handle bar  16  and segment  30  attached on the other side of the unit.  
         [0036]     Turning now to the piston assembly  12 , which is best seen in  FIG. 2 , it comprises a piston cylinder  34 , a piston  36 , an H-link  40  that is rotatably attached at one end to the bottom of piston  36 , and rotatably attached at its second end to a first end of curved piston arm  42 . The other end of piston arm  42  has an elongate attachment portion  44  that mates with spindle  26 , to which it is securely attached by any suitable means, as shown here via nuts and bolts  46  that extend through appropriately sized and aligned holes in spindle  26  and attachment portion  44 .  
         [0037]     As best seen in  FIG. 3 , the piston cylinder  34  and the piston  36  both are cylindrical in shape and of course have corresponding interior and exterior diameters, respectively. The body of piston  36  preferably is fairly long so as to provide significant surface contact with the piston cylinder  34 . In addition, the top portion  37  of the piston  36  is fitted with a gasket  38  of a rubber or neoprene type material that will form a fluid-tight seal against the sides of the piston cylinder  34 , but still be slideable within the cylinder. A circumferential metal spring (not shown) resides within the gasket  38  so as to create and maintain uniform outward pressure on the gasket  38  and thereby to maintain its seal with the piston cylinder  34 .  
         [0038]     The piston cylinder  34  is air-tightly and securely inserted into the bottom of, and is in fluid communication with, pressure chamber  48 . Pressure chamber  48  is in turn air-tightly and securely inserted into an appropriately-sized collared aperture  49  in the bottom of, and is in fluid communication with the interior space of, the tank  10 . Appropriately placed O-rings (not shown) are used around the outside of the piston cylinder  34  and pressure chamber  48  so as to create a leak-proof seal. A small, short hollow tube  50  is in fluid communication with the interior of the pressure chamber  48  and extends a short distance beneath it for attachment to the hose (not shown). The bottom of the pressure chamber  48  has an outwardly extending circumferential flange  51  that mates with a circumferential flange (not shown) on the collared aperture  49  in the bottom of tank  10 . A removable circular bracket  53  encases the mated flanges on the pressure chamber and on the collared aperture (not visible) and is tightened via nut and bolt means (not shown) to securely hold the pressure chamber  48  immovably in place within the tank  10 , and concomitantly, to hold the piston cylinder  34  immovably in place within the pressure chamber  48 . A simple mortise and tenon arrangement (not shown) consisting of a small slot in flange  51  that fits snugly over a slight downwardly extending projection on collared aperture  49  prevents the pressure chamber  48  from rotating once fully inserted and the bracket  53  secured in place.  
         [0039]     As best seen in  FIGS. 1 and 2 , the piston cylinder  34  has a narrow slot  52  formed in the bottom end thereof and extending a short distance up the piston cylinder  34 . The piston arm  42  moves within slot  52  during movement of the piston  36 , so slot  52  has to be sufficiently large and of sufficient length to accommodate that movement, but is preferably no larger than need be so as to guard against the introduction of unwanted material into the piston cylinder  34 .  
         [0040]     It will now be appreciated that in the sprayer herein described, movement of the handle bar  16  up and down by the operator causes rotational movement of spindle  26 . Rotational movement of spindle  26  within bosses  28  is in turn communicated to and causes rotational movement of curved piston arm  42 . As piston arm  42  rotates, its end that is attached to the H-link  40  moves up and down, as well as side to side. The H-link  40 , however, absorbs the side to side movement such that only the up and down movement of the piston arm  42  is communicated to piston  36 , causing it to move up and down within cylinder  34 . This action is best seen in  FIGS. 3, 4  and  5 A and B.  
         [0041]     As described above, movement of the piston  36  during up-stroke is controlled by the top of the cylinder  34 , although in operation the piston typically does not extend that far on the up-stroke. Movement of the piston  36  during down stroke is controlled by means of the piston cylinder cap  60 .  
         [0042]     The piston cylinder cap  60  is best seen in  FIGS. 1, 2 ,  5 A and B, and  6 A to C. In this preferred embodiment, the cap  60  is of unitary construction, made of any suitable material, such as polypropylene. It is has a cylindrical, elongate side portion  62 , and largely hollow interior body portion  64  that is sized to fit snugly over the end of piston cylinder  34  for a significant and material distance (here about 2½ inches) for secure and stable attachment. The top portion of the cap has a slit collar  66  and a pair of opposing end portions  67  that each have a hole through which bolt  69  can be inserted, and against which the head of the bolt  69  and the nut  69   a  can be tightened so as to tightly secure the cap  60  to the cylinder  34 .  
         [0043]     The bottom portion  68  of the cap  60  is completely enclosed, but has formed integrally in it a piston arm channel  70  that extends downwardly and outwardly therefrom. In order to provide both lateral and other support for that portion of the channel  70  that extends outwardly from the remainder of the cap  60 , a flange  72  extends from both sides of the exterior surface of the channel  70  to the exterior of the side portion  62 .  
         [0044]     On one side of the cap  60  there is an open area  74  that extends from above the flange  72  to the collar  66 . The width of the open area  74  is such that it will fit over and abut against either end of outwardly extending projection  76  on the exterior of the cylinder  34 . By having this open area  74  abut the projection  76  on either side thereof, the cap  60  is held in place laterally, and by having the collar  66  reside and abut against the upper surface of the projection  76 , the cap  60  is held in place on the cylinder  34  axially. Through appropriate sizing and placement of the projection  76  and the open area  74 , the piston arm channel  70  is held in proper alignment with the piston arm  42 , and with the slot  52  in the piston cylinder  34 . The size, shape and arrangement of the opening, tabs and projections shown here are a preferred embodiment only. Other such arrangements could be easily substituted, as the important thing here is that the cap be held in place laterally (so that it does not twist on the cylinder) and even more importantly, that it does not move axially downward on the cylinder, but is held in position so that it effectively operates as a stop for the down stroke of the piston at its maximum desired travel, and that it is able repeatedly to withstand the force exerted by even the strongest and most aggressive operators.  
         [0045]     Looking at  FIG. 6C , the interior section of the bottom portion  68  of the cap  60  has several useful features. First, it has a number of upwardly extending flanges  80  around its interior circumference, which flanges are separated from the side wall of the cap a distance that is equal to the side wall width of the cylinder body, so that when the cap is in place on the cylinder, the flanges abut the interior of the cylinder body and thus act as a holding member. Also, within the area between each flange  80  and the side wall of the cap  60  is a peg  82  that acts as a stop for the bottom of cylinder  34  upon full insertion of the cap  60  on the bottom of the cylinder  34 . The tops of each of the flanges  80  also act as the “stop” against which the bottom edge of the piston abuts upon the maximum down stroke of the piston  36 . In other words, the relative sizes and placements of the various components in the piston assembly and the cap are designed so that the down stroke of the piston  36  is stopped when the bottom of the piston  36  comes into contact with the multiple flanges  80 . Therefore, the forces generated are spread amongst these various contact points such that no one of them is over-stressed. Also, in this arrangement, the force on the flanges  80  is a direct force, rather than an indirect force as was the case in the prior art attempts to limit movement of the piston.  
         [0046]     Cap  60  thus provides a number of important functions. First, the cap protects the piston arm, piston cylinder and H-link from damaging blows; second, the cap substantially encases the movement of the piston arm to prevent fingers or garments from becoming entangles and perhaps injured; third, the cap substantially prevents dust and foreign objects from entering the piston cylinder where it might adversely affect the operation of the piston assembly or the piston itself; fourth, the channel helps guide the movement of the piston arm to keep it properly aligned so as to maintain efficiency and not place unwanted torque on the piston or piston cylinder; and fifth, the cap restrains downward movement of the piston so as to maintain the piston&#39;s travel within the cylinder to allowable tolerances so as not to cause leakage or damage.  
         [0047]     Although preferred embodiments have been shown and described, the disclosed invention and the protection afforded by this patent are not limited thereto, but are of the full scope of the following claims, and equivalents thereto.