Abstract:
A portable backpack sprayer for spraying liquid chemicals such as pesticides, fungicides, and fertilizers having a large storage tank in which is mounted a pressure vessel. A manually actuated pumping assembly is connected with the bottom portion of the pressure vessel and also with the bottom portion of the tank. The pumping assembly comprises a reciprocating piston to draw liquid from the storage tank and pressurize it within the pressure vessel. The operator may discharge the pressurized liquid using a hose and a control valve affixed to the pressure vessel. The pumping assembly further comprises a double-walled piston and a leak barrier to collect any liquid that may leak from the piston. The reciprocating action of the piston is utilized to return the leaked liquid to the storage tank via a return siphon.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the invention is backpack-type sprayers for spraying liquid under pressure. 
     2. Prior Art 
     Various United States patents have been obtained for hand-operated backpack-type sprayer combinations adapted to spray liquid chemicals such as insecticides, fertilizers, fungicides, etc. These include U.S. Pat. Nos. 4,690,331; 4,702,416; 4,702,419; 4,768,714; 4,798,333; and 5,335,853, each of which is incorporated herein by reference. The constructions shown and described in the specified patents, with the exception of U.S. Pat. No. 5,335,853, include relatively large-diameter diaphragms that are used to pump liquid from a storage tank to a pressurized container. The diaphragms are often combined with a piston such that the diaphragm-piston combination not only pumps and pressurizes the liquid, but also agitates and mixes the liquid in the bottom of the storage tank. 
     An important consideration for portable sprayers is leak prevention. As indicated above, the sprayers are frequently used to spray insecticides, fungicides, and fertilizers, all three of which may be hazardous to either the operator or the surroundings if not properly protected. Diaphragms are very good at sealing against leakage. However, after prolonged use in association with certain types of chemicals, even the best diaphragms may eventually fail. Upon occurrence of diaphragm failure, the chemicals within the sprayer tend to leak out the bottom of the structure and may come into contact with the operator or the surroundings. 
     The invention claimed in U.S. Pat. No. 5,335,853 replaces the diaphragm with a piston assembly in order to help reduce leakage. However, leakage may still occur through the piston assembly if portions of that assembly fail to operate as intended due to extended use or wear and tear. Regular preventive maintenance becomes necessary to replace parts of the sprayer before a failure, and the associated leakage, can occur. A sprayer capable of protecting against leakage when such failure occurs is therefore desirable. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a compact, strong, long-lasting portable sprayer having a piston assembly which protects against leakage is disclosed. The piston has a double-walled construction, which in conjunction with the piston cylinder define a primary leak collection chamber. Liquid leaking from the piston assembly is collected in the primary chamber and expelled into a secondary leak collection chamber by the reciprocating action of the piston. The secondary collection chamber is defined by affixing a leak barrier, preferably an expandable bellows, to both the piston and the pressure vessel. Once in the secondary chamber, liquid may be pumped into the tank through a siphon by the reciprocating action of the piston. In returning the liquid to the storage tank, the siphon disperses liquid in an upper interior portion of the tank so that the reciprocating action does not pump liquid from the tank through the siphon. 
     In an alternative embodiment, a one-way valve may be placed on the siphon so that liquid may not be pumped from the tank through the siphon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear sectional view of a preferred embodiment of the invention; 
     FIG. 2 is a detailed sectional view of a portion of the apparatus of FIG. 1; and 
     FIG. 3 is a side sectional view of the apparatus of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, FIG. 1 illustrates a preferred embodiment of a portable sprayer  11 . The portable sprayer comprises a liquid storage tank  13  preferably constructed using a synthetic resin, or other similarly light weight and durable materials, and having a substantially flat backside (not shown) adapted to rest against the back of an operator carrying and operating the sprayer  11 . The storage tank  13  may be filled with liquid chemicals, such as insecticides, fungicides, fertilizers, etc., through a large fill opening  15  defined by a neck  17 . Once the storage tank  13  is full and ready for use, a screw-type cap  19  preferably seals the fill opening  15 . 
     The bottom-rear portion of the storage tank  13  has an integrally molded support structure  21 , the back of which is substantially co-planar with the back side of the storage tank  13  so that the entire structure may rest against the back of an operator. Strong apertures  23  are formed at the upper-rear portion of the storage tank  13  to support shoulder straps, not shown, that extend over the shoulders and then downwardly for securing to a support frame  25  that is disposed in a generally horizontal plane. The ends of the support frame  25  are bent upwardly to form legs  27  that are anchored fixedly in vertical bosses  29  of the support structure  21 . 
     Referring next to FIG. 2 as well as FIG. 1, the bottom wall  31  of the storage tank  13  is generally horizontal and has a relatively large vessel opening defined by a downwardly-bent cylindrical flange  33  extending from the bottom wall  31 . A vertically elongated pressure vessel is inserted through the vessel opening, extending into the interior of the storage tank  13 . The pressure vessel  35  is constructed of a strong material, preferably synthetic resin, which is capable of withstanding pressures created therein by operation of the pump as described below. 
     The bottom portion of the pressure vessel  35  comprises an exteriorly cylindrical end  37  which fits closely against the interior cylindrical surface of the flange  33 . The cylindrical end  37  comprises a first annular groove  39  integrated into the outer surface of the cylindrical end  37  and a radial end flange  41 . An O-ring is placed into the first annular groove  39  to provide a seal between the cylindrical end  37  and the flange  33 . When the pressure vessel  35  is inserted into the storage tank  13 , the radial end flange  41  rests against the flange  33  to prevent the pressure vessel  35  from sliding further into the storage tank  13 . The pressure vessel  35  is held firmly in place and the seal between the cylindrical end  37  and the flange  33  is strengthened by the application of appropriate mechanical pressure, such as through the use of a large diameter hose clamp  45  mounted and tightened around the flange  33  and the pressure vessel  35 . Circumferentially-spaced lugs  47  (shown in FIG. 2) may be attached to the clamp  45 , the lugs  47  extending around the radial end flange  41  and, in combination with the clamp  45 , immobilizing the pressure vessel  35  in relation to the storage tank  13 . 
     As is illustrated in FIG. 2, a pump assembly is disposed at the bottom wall  36  of the pressure vessel  35  within the cylindrical end  37 . The pump assembly chiefly comprises a pump cylinder  49 , a reciprocating piston  51 , a leak barrier  53 , a return siphon  55 , and a piston crank  57 . The pump cylinder  49 , preferably constructed using a synthetic resin material, comprises an enclosed top end  59  which extends through the bottom wall  36  and into the pressure vessel  35  and an open bottom end  61  with a cylinder wall  63  which defines a smooth-walled piston chamber  65 . The overall length of the cylinder wall  63  is preferably at least twice the total linear displacement of the piston  51  during operation as herein described. The top end  59  has exterior threads which are threadedly associated with interior threads of an internally extending boss portion  67  of the pressure vessel  35 . The pressure vessel  35  is sealed against leakage by O-rings placed in two annular grooves  69 ,  71  formed in the top end  59  of the pump cylinder  49 . The first annular groove  69  is positioned such that a seal is created between the boss portion  67  and the top end  59 , and the second annular groove  71  is positioned such that a seal is created between the top end  59  and a cylindrical flange extending from the pressure vessel  35 . 
     The piston  51 , preferably constructed using a synthetic resin material, comprises an inner wall  75  having an integral piston head  77  at one end and at the other end the inner wall  75  folds back upon itself to form an outer wall  79 . The piston head  77  and the inner wall  75  are disposed within the piston chamber  65  and the outer wall  79  is disposed outside the piston chamber  65 , such that the cylinder wall  63  is disposed between the inner and outer walls  75 ,  79 . The combination of the cylinder wall  63 , the inner wall  75 , and the outer wall  79  defines a primary leak collection chamber  81  which collects any liquid that may leak from the piston. During operation, the piston reciprocates between a first position, illustrated in FIG. 1, wherein the piston head  77  is disposed adjacent to the top end  59  of the piston chamber  65  and a second position, illustrated in FIG. 2, wherein the piston head  77  is linearly displaced away from the top end  59  of the piston chamber  65 . 
     A fustoconical piston cup  83  formed of a suitable flexible and preferably resilient sealing (not porous) material is disposed over the piston head  77 . The piston cup  83  has a sealing edge  85  that is held against the cylinder wall  63  by the resilience of the cup  83  and by the pressure within the piston chamber  65 . When the piston  51  moves towards the top end  59  of the pump cylinder  49 , hereinafter the “upstroke”, pressure in the piston chamber  65  is increased and the upper sealing edge  85  is held more tightly against the cylinder wall  63 . When the piston  51  moves away from the top end  59  of the pump cylinder  49 , hereinafter the “downstroke”, pressure in the piston chamber  65  is reduced. 
     The top end  59  of the piston  51  further comprises an outlet passage  87  which permits liquid to flow between the piston chamber  65  and the pressure vessel  35  and an inlet passage  89  which, in combination with an inlet notch  91  in the pressure vessel  35 , permits liquid to flow between the storage tank  13  and the piston chamber  65 . A first flexible valve disc  93  is mounted on a knob  95  that is integral to the exterior top end  59  of the pump cylinder  49  such that the first disc  93  is disposed over the end of the outlet passage  87 . A second flexible valve disc  97  is mounted on the top end  59  within the piston chamber  65 , such that the second disc  97  is disposed over the opening of the inlet passage  89 . The second disc  97  is held in place by a screw  99  that is threaded into the top end  59  of the pump cylinder  49 . 
     When the piston  51  is on the downstroke, the decreased pressure in the piston chamber  65  will draw liquid from the storage tank  13 , through the inlet passage  89 , and into the piston chamber  65 , but because of the decreased pressure in the piston chamber  65 , the first disc  93  will block the outlet passage  87  and no liquid will flow into the piston chamber  65  from the pressure vessel  35 . When the piston  51  is on the upstroke, the increased pressure in the piston chamber  65  will force liquid from the piston chamber  65 , through the outlet passage  87 , and into the pressure vessel  35 , but because of the increased pressure in the piston chamber  65 , the second disc  97  will block the inlet passage  89  and no liquid will flow into the storage tank  13  from the piston chamber  65 . Therefore, through repeated upstrokes and downstrokes of the reciprocating piston  51 , liquid will be pumped from the storage tank  13  and pressurized within the pressure vessel  35 . 
     The leak barrier  53  portion of the pump assembly preferably comprises a suitably flexible and resilient material and is illustrated in FIG. 2 as an extendible conical bellows. Preferably, the bellows is constructed using rubber that is weather and chemical resistant. Such an extendible bellows reduces and nearly eliminates stress on the leak barrier  53  due to repeated extensions and contractions during piston  51  reciprocation. As shown in FIG. 2, one end of the bellows is sealingly affixed to the outer wall  79  of the piston  51  and the opposite end is sealingly affixed to the cylindrical end  37  of the pressure vessel  35 . A secondary leak collection chamber  101  is thereby defined by the bellows, the piston  51 , and the pressure vessel  35 . Attached thusly, when the piston  51  is on the downstroke, the volume of the secondary chamber  101  is expanded, with the maximum volume occurring at the end of the downstroke. FIG. 2 illustrates the secondary chamber  101  at a point of maximum volume. Conversely, when the piston  51  is on the upstroke, the volume of the secondary chamber  101  is reduced, with the minimum volume occurring at the end of the upstroke. FIG. 3 illustrates secondary chamber  101  at a point of minimum volume. 
     The return siphon  55  is sealingly affixed to the secondary collection chamber  101  via a siphon duct  103 . The return siphon  55  passes through a sealing connector  105  in the bottom wall  31  of the storage tank  13  and extends to an upper interior portion  107  of the storage tank  13  where the siphon  55  opens up into the storage tank  13 . Between the sealing connector  105  and the secondary collection chamber  101 , the siphon  55  is preferably either a flexible hose or a rigid tube. Within the storage tank  13 , the siphon  55  is preferably a rigid tube to ensure that the open end remains in the upper interior portion  107  of the storage tank  13  because if the siphon is submersed in the liquid stored in the storage tank  13 , the reciprocating action of the piston  51  will cause liquid to be drawn from the storage tank  13 , through the siphon  55 , and into the secondary collection chamber  101 . In an alternative embodiment, a the siphon  55  may additionally comprise a one way flow valve  111 , such as those commonly known in the art, to prevent water from being drawn out of the storage tank  13  and into the secondary collection chamber  101 . 
     In the event of leakage from the piston  51 , liquid will first collect in the primary collection chamber  81 . The reciprocating action of the piston  51  will pump liquid from the primary collection chamber  81  and into the secondary collection chamber  101 . During the downstroke, the volume of the primary collection chamber  81  is expanded by the downward motion of the inner and outer walls  75 ,  79 , thus filling the primary collection chamber  81  with any liquid that leaks from the piston chamber  65 . During the upstroke, the upward motion of the inner and outer walls  75 ,  79  reduces the volume of the primary collection chamber  81 , expelling liquid out of the primary collection chamber  81  and into the secondary leak chamber  101 . Liquid accumulates within the secondary chamber  101  until the volume of liquid is at least equal to the minimum volume of the secondary chamber  101  at the end of the upstroke. As liquid continues to leak and the volume of liquid in the secondary chamber  101  exceeds the minimum volume of the secondary chamber  101 , the reciprocating action of the piston  51  causes the bellows to pump liquid through the siphon  55  and back into the storage tank  13 . In this manner, liquid from a leaking piston is prevented from falling on the operator or the surroundings. 
     As illustrated in FIGS. 1 and 3, the piston crank portion of the pump assembly effects the reciprocation action of the piston and comprises a horizontal rotatable cross-member  113  integrally mounted to the support structure  21  using bearings  115 . The cross-member  113  connects to a handle  117  which may be used by the operator with great mechanical advantage to rotate the cross-member  113  and reciprocate the piston  51 . A bellcrank  119  is fixedly mounted on the cross-member  113  such that the bellcrank  119  is centered upon the piston  51 . The bellcrank  119  attaches to the center of the piston  51  by passing through a slot  121  in the inner and outer walls  75 ,  79 , which are appropriately connected to maintain the integrity of the primary collection chamber  81 , and the cylinder wall  63 , as illustrated in FIG.  1 . The slot  121  is preferably no longer than the total linear displacement of the piston  51  during reciprocation. 
     Returning to FIG. 2, the bellcrank  119  is preferably pivotally connected to an extender  123  which is in turn pivotally connected to the piston  51 . The dual pivot connection between the bellcrank  119 , the extender  123 , and the piston  51  permits flexibility in precisely where the cross-member  113  is mounted to the support structure  21 . Such flexibility substantially prevents the piston  51  from binding with the piston chamber  65  during reciprocation. 
     Referring again to FIG. 1, once the liquid is pressurized within the pressure vessel  35 , it may be discharged through a pressure outlet  125  in the cylindrical end  37  of the pressure vessel  35 . The pressure outlet  125  is sealingly affixed to a hose  127  and a control valve  129  which may be used at the discretion of the operator to discharge pressurized liquid from the pressure vessel  35 . 
     Thus, a compact portable sprayer with a leak prevention pump system is disclosed. While embodiments of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.