Abstract:
A manually operated liquid foaming dispenser is attached to a bottle of liquid and pumps and mixes both the liquid and air to create a foam from the liquid and to dispense the foam. The dispenser includes a pump housing containing an air pump chamber and a liquid pump chamber, and a pump plunger that is manually reciprocated in both the air pump chamber and the liquid pump chamber. An air piston and a liquid piston are mounted on the plunger and are reciprocated by the plunger in the respective air pump chamber and liquid pump chamber. The air piston is mounted on the pump plunger for relative movement of the air piston on the plunger that enables an interior volume of the air pump chamber to be vented to an exterior environment of the dispenser on manual reciprocation of the pump plunger.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to a manually operated liquid foaming dispenser. Specifically, the invention pertains to a manually operated pump that is attached to the top of a bottle of liquid and that pumps and mixes both the liquid and air to create a foam from the liquid and dispense the foam. The dispenser includes a pump housing containing an air pump chamber and a liquid pump chamber, and a pump plunger that is manually reciprocated in both the air pump chamber and the liquid pump chamber. An air piston and a liquid piston are mounted on the plunger and are reciprocated by the plunger in the respective air pump chamber and liquid pump chamber. 
     (2) Description of the Related Art 
     There are various different types of manually operated liquid dispensers that pump liquid from containers attached to the dispensers and generate a foam from the liquid that is discharged from the dispensers. A familiar example of these types of foam generating liquid dispensers is the manually operated trigger sprayer. Trigger sprayers are designed to be comfortably held in one hand of a user with the trigger of the trigger sprayer being easily manipulated by the fingers of the user&#39;s hand. Pivoting movement of the trigger sprayer&#39;s trigger operates a liquid pump in the trigger sprayer. Operation of the pump draws liquid from a bottle container connected to the trigger sprayer and discharges the liquid in a spray pattern from a discharge nozzle of the trigger sprayer. The discharge nozzle of this type of trigger sprayer typically has an obstruction positioned in the path of the liquid sprayed from the trigger sprayer. The liquid spray hitting the obstruction mixes the liquid spray with the air of the exterior environment of the sprayer and thereby produces a foam that is discharged from the trigger sprayer. 
     The foaming liquid trigger sprayer of the type described above is well suited for dispensing a foam produced from a liquid where the desired foaming of the liquid is marginal, for example in dispensing foaming liquid kitchen or bathroom cleansers. However, the typical foaming liquid trigger sprayer cannot produce a more dense foam, such as that of shaving cream. 
     To produce a more dense foam dispensed from a manually operated foaming liquid dispenser requires that both the liquid and the air be pumped through the obstruction that produces the foam. Foaming liquid dispensers of this type comprise a pump housing containing an air pump chamber and a liquid pump chamber, and a pump plunger that is manually reciprocated in the pump housing. An air piston is mounted on the pump plunger and is received in the air pump chamber for reciprocating movement, and a liquid piston is mounted on the pump plunger and is received in the liquid pump chamber for reciprocating movement. Movement of the pump plunger toward a retracted position into the pump housing causes the air piston to move into the air pump chamber and exert a force on the air in the chamber and causes the liquid piston to move into the liquid pump chamber and exert a force on the liquid in the chamber. A pair of valves control the flow of air and liquid from the respective air pump chamber and liquid pump chamber through a center discharge passage of the pump plunger where the air and liquid is mixed to generate the foam. The foam is then discharged from the dispenser. 
     A spring of the foaming liquid dispenser causes the pump plunger to move from its retracted position in the pump housing to an extended position where the top portion of the pump plunger projects outwardly from the top of the pump housing. This movement of the pump plunger causes the air piston and the liquid piston to move out of their respective air pump chamber and liquid pump chamber, expanding the interior volumes of the two chambers. This creates vacuums in the two pump chambers that draw air into the air pump chamber interior volume and draw liquid into the liquid pump chamber interior volume. Valve assemblies are typically employed in controlling the flow of air and liquid into the respective air pump chamber and liquid pump chamber as their interior volumes are increased by the movement of the pump plunger. The valves allow air and liquid to enter the respective air pump chamber and liquid pump chamber as the pump plunger moves to its extended position, and the valves close preventing air and liquid from passing through the valves when the pump plunger is moved to its retracted position in the pump housing. 
     A substantial number of manually operated foaming liquid dispensers are manufactured to meet the needs of consumers. Reducing the manufacturing costs of a manually operated foaming liquid dispenser to only a small degree, for example by one penny or a fraction of a penny, significantly reduces the manufacturing costs of manually operated foaming liquid dispensers due to the significant number of the dispensers manufactured. Thus, a change in the design of a manually operated foaming liquid dispenser that results in even a small reduction in its manufacturing costs could result in a significant benefit to the manufacturing of manually operated foaming liquid dispensers. 
     SUMMARY OF THE INVENTION 
     The manually operated foaming liquid dispenser of the present invention has a novel and simplified construction with a reduced number of component parts from that of prior art dispensers that pump both air and liquid in generating a foam discharged from the dispenser. The novel construction of the foaming liquid dispenser eliminates a valve that controls the flow of air into the air pump chamber of the dispenser, thereby eliminating the cost of the valve and reducing the manufacturing costs of the dispenser. In addition, the manually operated foaming liquid dispenser of the invention has a more simplified construction than that of other prior art foaming liquid dispensers. The more simplified construction of the dispenser also results in a reduction in manufacturing costs. In addition, the novel construction of the foaming liquid dispenser vents the interior of the air pump chamber to the exterior environment of the dispenser immediately upon upward movement of the pump plunger. This ensures that the air pump chamber is vented with air even when the user of the dispenser quickly reciprocates the pump plunger in the pump housing without allowing the pump plunger to return to its fully extended position relative to the pump housing. 
     The pump housing of the foaming liquid dispenser of the invention combines a connector cap, an air pump chamber and a liquid pump chamber as one, monolithic piece. The liquid pump chamber, the air pump chamber, and the connector cap have a common center axis and are aligned axially in the pump housing. The cylindrical liquid pump chamber is positioned at the bottom of the pump housing. An opening in the top of the liquid pump chamber communicates the interior volume of the liquid pump chamber with the cylindrical air pump chamber just above. The air pump chamber also has an opening at its top that communicates the interior volume of the air pump chamber with the exterior environment of the dispenser through a top opening of the pump housing. The connector cap surrounds the pump housing top opening. 
     A dip tube is attached to the bottom of the pump housing and extends downwardly from the liquid pump chamber. A liquid inlet control valve is positioned at the bottom of the liquid pump chamber. The liquid inlet control valve controls a flow of liquid through the dip tube and into the liquid pump chamber, and prevents the reverse flow. 
     The pump housing is connected to a bottle containing a liquid by first inserting the liquid pump chamber and the air pump chamber through a bottle neck opening of the bottle. The connector cap is attached to the exterior of the bottle neck with the air pump chamber and liquid pump chamber positioned in the bottle. The dip tube extends downwardly from the pump housing into the liquid contained in the bottle to a position adjacent the bottom of the bottle. 
     A pump plunger is assembled into the pump housing through the top opening of the pump housing. The pump plunger has a tubular length with an interior discharge passage extending through the length of the pump plunger. A liquid piston is assembled to the exterior of the pump plunger and is received in the liquid pump chamber for reciprocating movement therein. An air piston is also assembled to the exterior of the pump plunger and is received in the air pump chamber for reciprocating movement therein. 
     A liquid outlet valve is assembled in the interior discharge passage of the pump plunger adjacent the bottom of the plunger. The liquid outlet valve controls the flow of liquid out of the liquid pump chamber and into the plunger discharge passage, and prevents the reverse flow of liquid. An air outlet valve is also assembled in the interior discharge passage of the pump plunger at an intermediate position along the passage. The air outlet valve controls the flow of air out of the air pump chamber and into the plunger discharge passage, and prevents the reverse flow of air. 
     A spring is assembled between the pump housing and the pump plunger. The spring biases the pump plunger to an extended position of the plunger relative to the pump housing where a top portion of the pump plunger projects outwardly from the top of the pump housing. 
     The pump plunger includes a dispenser head at the top of the pump plunger. The dispenser head has a tubular center column and a spout that both function as a portion of the pump plunger interior discharge passage. The dispenser head center column and spout conduct a foam produced by the dispenser, and the spout discharges the foam from the dispenser. 
     Manually depressing the pump plunger into the pump housing compresses the spring and causes the air piston to move downwardly into the air pump chamber decreasing the interior volume of the air pump chamber. The downward movement of the pump plunger also causes the liquid piston to move downwardly into the liquid pump chamber decreasing the interior volume of the liquid pump chamber. The downward movement of the pump plunger causes the air piston to pressurize the air in the air pump chamber. The pressurized air causes the air outlet valve to unseat, which allows air from the air pump chamber to pass the air outlet valve and enter the interior discharge passage of the pump plunger. The downward movement of the pump plunger also causes the liquid piston to exert a force on the liquid in the liquid pump chamber, which causes the liquid outlet valve to unseat. This results in the liquid in the liquid pump chamber being forced past the liquid outlet valve and into the interior discharge passage of the pump plunger. The air and liquid entering the interior passage of the pump plunger pass through a mixing element, which produces a foam from the air and liquid. The foam is forced upwardly through the pump plunger interior discharge passage and is dispensed from the pump plunger. 
     On completion of the downward movement of the pump plunger into the pump housing toward the retracted position of the pump plunger in the pump housing, the compressed spring causes the pump plunger to move out of the pump housing toward its extended position relative to the pump housing. This in turn causes the air piston and liquid piston to move upwardly in the respective air pump chamber and liquid pump chamber, creating a vacuum pressure in each of these chambers. The vacuum pressure in the liquid pump chamber causes the liquid inlet valve to unseat, thereby drawing liquid upwardly from the dip tube into the liquid pump chamber. 
     The novel construction of the manually operated foaming liquid dispenser of the invention does not include a separate valve that opens in response to the vacuum created in the air pump chamber to allow air to vent into the air pump chamber. Instead, the air piston of the dispenser is constructed with a center hole that functions as a vent hole for the air pump chamber. The pump plunger extends through the vent hole of the air piston. This mounts the air piston on the pump plunger for limited axial movement of the air piston relative to the pump plunger. 
     The pump plunger is constructed with a first, upper projection on its exterior and a plurality of second, lower projections on its exterior. The first projection and the plurality of second projections are on axially opposite sides of the piston. The axial spacing between the first projection and the plurality of second projections permits the air piston to move axially relative to the pump plunger between the projections. The exterior diameter dimension of the plunger between the first, upper projection and the second, lower projections is slightly smaller than the interior diameter dimension of the air piston vent hole. This provides a radial spacing between the exterior surface of the pump plunger and the interior surface of the air piston vent hole. This radial spacing defines a vent air flow path between the pump plunger and the air piston. 
     The first, upper projection is designed as an annular stopper. When the pump plunger moves downward relative to the air piston, the annular stopper engages in the air piston vent hole and seals the hole. The plurality of second, lower projections are spatially arranged around the exterior of the plunger. Each of the plurality of second, lower projections are dimensioned to engage in the vent hole of the air piston to stop the upward movement of the pump plunger relative to the air piston. However, because the plurality of second, lower projections are spatially arranged around the pump plunger, when the second, lower projections engage in the vent hole of the air pump piston they do not block the vent air flow path between the pump plunger and the air piston. 
     Thus, when the pump plunger is pushed manually downwardly into the pump housing, the pump plunger first, upper projection engages in and seals closed the vent hole of the air piston. This allows the air piston to compress the air in the air pump chamber as the pump plunger pushes the air piston downwardly into the air pump chamber. When the pump plunger is moved upwardly by the spring toward its extended position relative to the pump housing, the limited axial movement of the air piston relative to the pump plunger provided by the axially spaced first and second projections causes the first, upper projection to move out of the vent hole of the air piston. This opens the vent air flow path between the pump plunger and the interior surface of the air piston surrounding the vent hole. Thus, venting air from the exterior environment of the dispenser is allowed to pass through the vent air flow path between the pump plunger and the air piston as the air piston is moved upwardly through the air pump chamber by the pump plunger. This vents the interior volume of the air pump chamber without requiring an additional valve to control the venting of the air pump chamber. 
     Because the first and second projections on the pump plunger allow the air piston to move axially to a limited extent relative to the pump plunger, the air piston does not begin pressurizing air in the air pump chamber on the initial downward movement of the pump plunger into the pump housing. To ensure that both air and liquid are pumped into the pump plunger interior discharge passage at the same time, the liquid piston is also mounted on the pump plunger for limited axial movement of the liquid piston relative to the pump plunger. This allows the pump plunger to move downwardly into the pump housing the short distance required for the first, upper projection to seat in the vent hole of the air piston before the pump plunger begins pushing the liquid piston downwardly through the liquid pump chamber. The limited axial movement of the liquid piston relative to the pump plunger enables both the air piston and the liquid piston to begin their pumping operations from the respective air and liquid pump chambers at approximately the same time. 
     Thus, the foaming liquid dispenser of the invention enables mixing of air and liquid pumped into the dispenser discharge passage to generate a thick foam discharged by the dispenser while eliminating a valve required by prior art dispensers to vent air to the air pump chamber. The elimination of the valve results in a reduction of manufacturing costs. The simplified construction of the foaming dispenser with its reduced number of component parts also reduces the manufacturing cost of the dispenser. In addition, the assembly of the air piston on the pump plunger that enables limited axial movement between the air piston and the pump plunger vents the interior of the air pump chamber promptly on upward movement of the pump plunger. This ensures that the air pump chamber is vented with air even when a user of the dispenser quickly reciprocates the pump plunger in the pump housing without allowing the pump plunger to return to its fully extended position relative to the pump housing. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Further features of the invention are set forth in the following detailed description of the preferred embodiment of the invention and in the drawing figures wherein: 
         FIG. 1  is a front perspective view of the manually operated, foaming liquid dispenser of the invention attached to the top of a bottle container; 
         FIG. 2  is a side, sectioned view of the dispenser along the line  2 — 2  of  FIG. 1 , with the pump plunger in its fully extended position relative to the pump housing and the bottle container; 
         FIG. 3  is a partial, enlarged view of the relative positions of the air piston and pump plunger shown in  FIG. 2 ; 
         FIG. 4  is a side, sectioned view of the dispenser with the pump plunger in its fully retracted position relative to the pump housing and the bottle container; and, 
         FIG. 5  is a partial, enlarged view of the relative positions of the air piston and the pump plunger shown in FIG.  4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The foaming liquid dispenser  10  of the present invention is similar to the types of dispensers known in the prior art as lotion dispensers. These types of dispensers are typically operated by connecting the dispenser to the neck of a bottle container containing a liquid to be dispensed and by orienting the dispenser and the container vertically upright. In the description of the foaming liquid dispenser of the invention to follow, the terms “top” and “bottom”, “upper” and “lower”, or similar related terms will be used to describe the component parts of the dispenser and their relative positions. These terms are only used because the dispenser is typically oriented vertically upright when using the dispenser. The terms should not be interpreted as limiting. 
     The liquid foaming dispenser  10  shown in  FIGS. 1 ,  2 , and  4  is basically comprised of a pump housing  12 , a pump plunger  14  and a snap ring  16  that connects the pump housing and pump plunger together. The materials employed in constructing the component parts of the dispenser are the same as those typically used in the industry, usually plastics except for a metal coil spring employed on the pump plunger. 
     The pump housing  12  basically combines four cylindrical sections of the pump housing and a connector cap as one, monolithic piece. The cylindrical sections of the housing and the connector cap have a common center axis  18  and are axially aligned in the pump housing. 
     The cylindrical sections include a cylindrical dip tube connector  22  provided at the bottom of the pump housing. A cylindrical liquid pump chamber  24  is provided as the second cylindrical section of the pump housing just above the dip tube connector  22 . A valve seat surface  26  is positioned at the bottom of the liquid pump chamber  24 . The interior volume  28  of the liquid pump chamber  24  communicates with the interior of the dip tube connector  22  through the valve seat  26 . The liquid pump chamber  24  is open at its top end. 
     The third cylindrical section of the pump housing  12  is a cylindrical air pump chamber  32  positioned just above the liquid pump chamber  24 . The air pump chamber  32  has an interior volume  34  that communicates with the liquid pump chamber interior volume  28  through the top opening of the liquid pump chamber  24 . The air pump chamber  32  is open at its top end. 
     A cylindrical sleeve  36  forms the fourth cylindrical section of the pump housing  12 . The sleeve  36  extends upwardly from the top of the air pump chamber  32 . Several bottle container vent holes  42  pass through the sleeve  36 . The cylindrical sleeve  36  is also open at its top. 
     The cylindrical connector cap  44  is attached to the bottom of the sleeve  36 . As seen in  FIGS. 2 and 4 , the connector cap  44  extends downwardly over and is spaced radially outwardly from the air pump chamber  32 . An interior surface of the connector cap  44  is provided with a mechanical connector, for example a bayonet type connector or a screw-threaded connector. The particular connector employed on the connector cap  44  will be complementary to a connector on a bottle container with which the liquid foaming dispenser  10  is used. 
     As stated earlier, the dip tube connector  22 , the liquid pump chamber  24 , the air pump chamber  32 , the cylindrical sleeve  36  and the connector cap  44  of the pump housing  12  are all formed as one, monolithic piece. Forming all of these component parts as one piece reduces the total number of the separate component parts of the liquid foaming dispenser  10 . This reduction imparts also results in a cost savings in manufacturing the dispenser. 
     The pump housing  12  is shown mounted on a bottle container  46  in  FIGS. 1 ,  2 , and  4 . The bottle container  46  shown in the drawing figures is only one example of a bottle container with which the liquid foaming dispenser  10  may be used. In removably attaching the pump housing  12  to the bottle container  46 , the bottle container is provided with a neck  48  having a mechanical connector that is complementary to the mechanical connector of the pump housing connector cap  44 . With the pump housing  12  removably attached to the bottle container  46  by the connector cap  44 , the liquid pump chamber  24  and the air pump chamber  32  of the pump housing  12  are entirely contained inside the bottle container  46 . This reduces the overall size of the liquid foaming dispenser  10  and bottle container  46 . 
     A dip tube  52  is attached to the dip tube connector  22  at the bottom of the pump housing. The dip tube  52  extends downwardly from the pump housing  12  into the liquid of the container to a position adjacent the bottom of the bottle container  46 . 
     A liquid inlet control valve  54  is positioned at the bottom of the liquid pump chamber  24 . The liquid inlet control valve  54  is a flexible, resilient disk check valve that seats against the valve seat surface  26  at the bottom of the liquid pump chamber  24 . The liquid inlet control valve  54  is responsive to a vacuum pressure created in the interior volume  28  of the liquid pump chamber  24 . The valve  54  controls a flow of liquid from the bottle container  46  through the dip tube  52  and into the liquid pump chamber interior volume  28 , and prevents the reverse flow of liquid. 
     The snap ring  16  is assembled to the top of the pump housing  12 . The snap ring  16  has a top cover  58  and a cylindrical outer wall  62  that fits snug around the cylindrical sleeve  36  of the pump housing  12 . A cylindrical tube  64  extends upwardly from the snap ring cover  58 . A lock tab  65  projects inwardly from an interior surface of the tube  64 . The upper portion of the tube  64  above the snap ring cover  58  provides an aesthetic cover for an upper portion of the pump plunger  14  and a spring mounted on the pump plunger that is yet to be described. A portion of the tube  64  extends below the snap ring cover  58  to a circular bottom wall  66  of the snap ring. The snap ring bottom wall  66  has an opening  68  at its center to accommodate the pump plunger  14 , as will be described. A bottle vent hole  72  also extends through the snap ring bottom wall  66 . A cylindrical plunger tube  74  extends downwardly from the underside of the snap ring bottom wall  66 . The plunger tube  74  limits the upward movement of the pump plunger  14  relative to the pump housing  12  to the extended position of the pump plunger shown in  FIGS. 1 and 2 . 
     A cylindrical vent separator  76  is assembled onto the exterior of the snap ring plunger tube  74  and into the interior of the pump housing cylindrical sleeve  36 . The vent separator  76  is formed as a flat ring with a downwardly extending inner cylindrical wall  78 , a downwardly extending intermediate cylindrical wall  80 , and a downwardly extending outer cylindrical wall  82 . The inner cylindrical wall  78  of the vent separator  76  extends downwardly from the inner edge of the separator and engages tightly against the outer surface of the snap ring plunger tube  74 . The intermediate wall  80  extends over the interior surface of the air pump chamber  32 . The outer cylindrical wall  82  extends downwardly from an outer peripheral edge of the vent separator  76  over the interior surface of the pump housing cylindrical sleeve  36 . A gap is provided between the vent separator outer wall  82  and the pump housing sleeve  36 . This gap functions as a portion of an air venting flow path from the exterior environment of the dispenser, between the vent separator outer wall  82  and the sleeve  36 , and through the pump housing bottle vent holes  42 . 
     The pump plunger  14  is basically comprised of an upper dispenser head  84 , a lower piston rod  86 , an air piston  88  mounted on the piston rod  86 , and a liquid piston  92  mounted on the piston rod  86 . 
     The upper dispenser head  84  has a tubular center column  96  that extends downwardly through the dispenser head. The column  96  is open at its bottom. An interior bore of the column communicates with a discharge spout  98  of the dispenser head at the top of the column. 
     A metal coil spring  102  is mounted over the center column  96 . The spring engages against the snap ring bottom wall  66  at the bottom of the spring and engages against the dispenser head  84  at the top of the spring. The spring  102  urges the dispenser head and the pump plunger  14  upwardly to its extended position shown in  FIGS. 1 and 2 . 
     An inner cylindrical wall  104  of the dispenser head  84  extends downwardly over the spring. The inner cylindrical wall  104  has a lock tab  106  that projects outwardly from the wall. The dispenser head  84  can be pressed downwardly against the bias of the spring  102  and rotated so that the dispenser head lock tab  106  engages underneath the snap ring lock tab  65  to hold the dispenser head  84  in its downward, retracted position relative to the dispenser  10 . 
     The dispenser head also has an outer cylindrical wall  108 . The outer wall  108  telescopes over the snap ring tube  64 . The overlapping of the outer wall  108  and the snap ring tube  64  prevents liquid from entering into the pump plunger  14  and also gives the dispenser an aesthetically pleasing appearance. 
     The interior bore of the dispenser head center column  96  and an interior bore of the dispenser head spout  98  define a portion of an interior discharge passage  112  of the pump plunger that extends through the length of the dispenser head  84 . A foam producing obstruction is positioned in the interior discharge passage  112  adjacent the bottom of the passage. The obstruction is comprised of a cylindrical hub  114  having mesh screens  116  covering over the opposite open ends of the hub. Air and liquid passing through the two mesh screens  116  of the hub  114  produce a foam. 
     The pump plunger piston rod  86  is tubular and an upper end of the piston rod is attached to a lower end of the dispenser head center column  96 . The tubular piston rod  86  has an interior bore that extends through the length of the rod and communicates with the interior bore of he dispenser head center column  96 . The interior bores of the piston rod  86 ; the dispenser head center column  96  and the spout  98  define the length of the interior discharge passage  112  extending through the pump plunger  14 . The portion of the discharge passage  112  extending through the piston rod  86  and the dispenser head center column  96  has a center axis that is coaxial with the center axis  18  of the pump housing  12 . 
     The piston rod  86  has a cylindrical, upper air piston portion  122  and a cylindrical, lower liquid piston portion  124 . The air piston portion  122  has a cylindrical interior surface that extends downwardly through the piston rod to an annular bottom wall  126  that joins the air piston portion  122  to the liquid piston portion  124  of the piston rod. A pair of diametrically opposed valve openings  128  (only one of which is visible in  FIG. 5 ) extend through the annular bottom wall  126 . The liquid piston portion  124  of the piston rod also has a cylindrical interior surface that extends downwardly from the annular bottom wall  126  to the bottom end of the piston rod  86 . 
     The exterior surface of the air piston portion  122  of the piston rod is provided with a first, upper projection  132  and a plurality of second, lower projections  134 . The first projection  132  is an annular projection that extends completely around the air piston portion  122  of the piston rod. As best seen in  FIGS. 3 and 5 , the first projection  132  tapers radially outwardly as it extends axially upwardly over the exterior surface of the piston rod. Each of the plurality of second projections  134  is formed as a narrow ridge that projects radially outwardly from the piston rod air piston portion  122  as it extends axially over the exterior surface of the rod. The second projections  134  are spatially arranged around the exterior surface of the piston rod air piston portion  122 . 
     An axial rib  136  is provided on the exterior surface of the piston rod liquid piston portion  124 . The rib  136  extends downwardly over the exterior surface of the liquid piston portion  124  but stops short of the bottom end of the piston rod, forming a radial shoulder  138  that projects outwardly from the liquid piston portion  124  of the rod. 
     A one-piece valve assembly including a tubular sleeve valve  142 , a center stem  144 , a resilient spring  146  and a plug check valve  148  is assembled into the interior of the dispenser piston rod  86 . The tubular sleeve valve  142  projects upwardly from an annular bottom wall  152  of the valve assembly. The bottom wall  152  has an opening at its center that communicates with the interior of the liquid piston portion  124  of the piston rod and forms a portion of the interior discharge passage  112  extending through the pump plunger. The outer periphery of the bottom wall  152  engages against the interior surface of the air piston portion  122  of the piston rod and secures the valve assembly in place. A pair of diametrically opposed notches  154  pass through the bottom wall  152  in positions that coincide with the valve openings  128  of the piston rod annular wall  126 . The resilient sleeve  142  of the valve assembly extends upwardly from the bottom wall  152  inside the pair of notches  154  and engages against the interior surface of the dispenser head center column  96  in a sealing engagement. 
     The center stem  144  of the valve assembly has a +-shaped cross section. The stem  144  engages against the interior surface of the liquid piston portion  124  of the piston rod to securely hold the valve assembly in place while allowing liquid to flow axially along the center stem  144 . The resilient spring  146  extends downwardly from the bottom end of the stem  144  and biases the plug check valve  148  downwardly. 
     A valve seat plug  156  is inserted into the opening at the bottom of the liquid piston portion  124  of the piston rod. The valve seat plug  156  has a seating surface  158  against which the plug check valve  148  engages. An annular ring  162  on the valve seat plug  156  engages against the bottom of the liquid piston portion  124  of the piston rod to insure that the valve seat plug is properly positioned. The plug check valve  148  engaging against the seating surface  158  of the valve seat plug  156  functions as a liquid outlet valve of the liquid pump chamber  124 . 
     The liquid piston  92  is mounted on the bottom end of the liquid piston portion  124  of the piston rod between the annular ring  162  of the valve seat plug  156  and the radial shoulder  138  of the piston rod axial rib  136 . As best seen in  FIG. 4 , an axial spacing between the valve seat plug annular ring  162  and shoulder  138  of the axial rib  136  allows the liquid piston  92  to move axially over the pump plunger  14  for a short distance. The liquid piston  92  is positioned in the liquid pump chamber  24  in a sliding sealing engagement of the liquid piston against the interior surface of the liquid pump chamber. The engagement of the liquid piston  92  against the interior surface of the liquid pump chamber  24  causes the liquid piston to move upwardly relative to the pump plunger  14  when the plunger is moved downwardly until the liquid piston  92  engages against the shoulder  138  of the axial rib  136 . The liquid piston  92  also moves downwardly relative to the pump plunger  14  when the pump plunger is moved upwardly until the liquid piston  92  engages with the annular ring  162  of the valve seat plug  156 . 
     The air piston  88  is formed as a flat ring  164  with a downwardly extending inner cylindrical wall  166  at an inner peripheral edge of the ring and a downwardly extending outer cylindrical wall  168  at an outer peripheral edge of the ring. The air piston inner cylindrical wall  166  has an interior surface  172  that is spaced a small distance radially outwardly from the exterior surface of the piston rod air piston portion  122 . This creates a small annular gap between the exterior surface of the piston rod air piston portion  122  and the interior surface  172  of the air piston inner cylindrical wall  166  that functions as an air vent flow path. The radial spacing between the exterior surface of the piston rod air piston portion  122  and interior surface  172  of the air piston inner cylindrical wall  166  defines a vent opening or a vent hole through the air piston  88  through which the pump plunger  14  extends. The radial spacing between the exterior surface of the piston rod air piston portion  122  and the air piston inner cylindrical wall interior surface  172  enables the air piston  88  to move axially to a limited extent relative to the pump plunger  14 . The extent of axial movement of the air piston  88  on the pump plunger  14  is limited by the first, upper projection  132  of the pump plunger above the air piston, and the second, lower projections  134  below the air piston. 
     The air piston flat ring  164  extends radially outwardly from the air piston inner cylindrical wall  66  to the air piston outer cylindrical wall  168  to position the outer cylindrical wall where it will engage in a sliding, sealing engagement with the interior surface of the air pump chamber  32 . The sliding, sealing engagement of the air piston outer cylindrical wall  168  with the air pump chamber  32  exerts a sufficient frictional resistance to movement of the air piston  88  relative to the air pump chamber  32  to cause the air piston  88  to move relative to the pump plunger  14  when the pump plunger is moved upwardly and downwardly in the pump housing  12 . 
     The first, upper projection  132  of the pump plunger piston rod  86  is designed as an annular stopper. The upper projection  132  has an outer diameter dimension that is slightly larger than the inner diameter dimension of the air piston inner cylindrical wall interior surface  172 . When the pump plunger  14  moves downward relative to the air piston  88 , the annular stopper formed by the upper projection  132  engages in the air piston vent hole formed by the inner cylindrical wall interior surface  172  and seals the hole. Each of the plurality of second, lower projections  132  on the piston rod  86  are dimensioned to engage in the vent hole of the air piston defined by the inner cylindrical wall interior surface  172 . The plurality of second, lower projections  134  stop the upward movement of the pump plunger  14  relative to the air piston  88 . However, because the plurality of second, lower projections  134  are spatially arranged around the pump plunger  14 , when the second, lower projections  134  engage in the vent hole of the air piston defined by the inner cylindrical wall interior surface  172 , they do not block the vent air flow path between the exterior surface of the piston rod air piston portion  122  and the interior surface  172  of the air piston inner cylindrical wall  166 . 
     Thus, when the pump plunger  14  is pushed manually downwardly into the pump housing  12 , the pump plunger first, upper projection  132  engages in and seals closed the vent hole of the air piston defined by the interior surface  172  of the air piston inner cylindrical wall  166 . This allows the air piston  88  to compress the air in the air pump chamber  32  as the pump plunger  14  pushes the air piston  88  downwardly into the air pump chamber  32 . When the pump plunger  14  is moved upwardly by the spring  102  toward its extended position relative to the pump housing  112 , the limited axial movement of the air piston  88  relative to the pump plunger  14  provided by the axially spaced first projection  132  and second projections  134  causes the first, upper projection  132  to move out of the vent hole of the air piston defined by the inner surface  172  of the air piston inner cylindrical wall  66 . This opens the vent air flow path between the exterior surface of the piston rod air piston portion  122  and the air piston inner cylindrical wall interior surface  172 . Thus, venting air from the exterior environment of the dispenser  10  is allowed to pass through the telescoping coupling of the dispenser head outer cylindrical wall  108  and the snap ring tube  64 , and between the exterior surfaces of the pump plunger upper dispenser head  84  and lower piston rod  86  and the interior surface of the snap ring plunger tube  74 , to the vent air flow path between the exterior surface of the piston rod air piston portion  122  and the air piston inner cylindrical wall interior surface  172  as the air piston  88  is moved upwardly through the air pump chamber  32  by the pump plunger  14 . This vents the interior volume  34  of the air pump chamber  32  without requiring an additional valve to control the venting of the air pump chamber. 
     Because the first  132  and second projections  134  on the pump plunger  14  allow the air piston  88  to move axially to a limited extent relative to the pump plunger, the air piston  88  does not begin pressurizing air in the air pump chamber  32  on the initial downward movement of the pump plunger  14  into the pump housing  12 . To ensure that both air and liquid are pumped into the pump plunger interior discharge passage  112  at the same time, the liquid piston  92  has been mounted on the piston rod liquid piston portion  124  for a limited axial movement of the liquid piston relative to the pump plunger. This allows the pump plunger  14  to move downwardly into the pump housing  12  a short distance required for the first, upper projection  132  to seat in sealing engagement in the vent hole of the air piston defined by the air piston inner cylindrical wall interior surface  172  before the pump plunger begins pushing the liquid piston  92  downwardly through the liquid pump chamber  24 . The limited axial movement of the liquid piston  92  relative to the pump plunger  14  enables both the air piston  88  and the liquid piston  92  to begin their pumping operations from the respective air pump chamber  32  and liquid pump chamber  24  at approximately the same time. 
     Thus, the foaming liquid dispenser of the invention enables mixing of air and liquid pumped into the dispenser discharge passage to generate a thick foam discharged by the dispenser while eliminating a valve required by prior art dispensers to vent air to the air pump chamber. The elimination of the air vent valve results in a reduction of manufacturing costs. The simplified construction of the foaming dispenser also combines several different component parts of prior art foaming dispensers into one piece. This simplified construction also reduces the manufacturing cost of the dispenser. In addition, the assembly of the air piston on the pump plunger that enables limited axial movement between the air piston and the pump plunger vents the interior of the air pump chamber promptly on upward movement of the pump plunger. This ensures that the air pump chamber is vented with air even when a user of the dispenser quickly reciprocates the pump plunger in the pump housing without allowing the pump plunger to return to its fully extended position relative to the pump housing. Although the manually operated foaming liquid dispenser of the invention has been described above by reference to a single embodiment, it should be understood that modifications and variations could be made to the dispenser without departing from the intended scope of the invention defined by the following claims.