PISTON OF PUMP OF TRIGGER TYPE LIQUID DISCHARGER

Abstract: A structure of a piston of the pump of the trigger type liquid discharger in which pistons (101, 105) have annular skirts (102, 104, 106, and 108) extending to the approach end side and the stroke end side of the piston, and being structurally integral with each other to be in close contact with the inner wall of the cylinder (H) of said pump part (E); the entire width of each of said annular skirts (102, 104) in the axial direction is adapted to be as small as approximating to the axial length of the suction port (100) opened in the peripheral wall of said cylinder (H), or at least one underfill part (109 or 110) is formed in a position corresponding to said suction port (23) of the annular skirts (106, 108) on the stroke end side; so that the air can surely be sucked into the liquid container even when pistons (101, 105) move over only a short stroke as required by discharge of only a small quantity of liquid.

Description: FIELD OF THE INVENTION This invention relates to an improvement in a piston of a pump section of a trigger-type liquid dispenser or sprayer to be fitted to an opening of a liquid container for exhausting or ejecting the liquid content of the container. BACKGROUND OF THE INVENTION In US-A-4,480,768 there is disclosed a hand-operated pump for dispensing a fluid from a container which includes a body containing a pumping chamber having an inlet and an outlet conduit. A piston is reciprocably mounted in the pumping chamber, the piston having a convexly contoured outer end surface. A trigger pivotally mounted and locked to the body has a plurality of triangular supports cojoined to form a tapered socket receiving the outer end surface of the piston. A channel-defining insert is received in the outlet conduit, the insert having a centrally situated, forwardly facing, fixed protuberance. An elastic, cup-shaped member secured at its periphery to the body has a central aperture situated in contact with and closed by the fixed protuberance. The central aperture of the cup-shaped member is a cavity in the center of the interior surface of the member extending only partway through the member, at least two depressions on the exterior surface of the member spaced from each other and yet each intersecting the cavity, and a swirl chamber situated between and connected to the depressions. The top of the pump is mechanically secured to the outside of the outlet conduit by tabs straddling and locking to the conduit. Fig. 10 of the accompanying drawings illustrates a conventional trigger-type liquid dispenser or ejector to be fitted to an opening of a liquid container for exhausting or ejecting the liquid content in the container, where a tilted pump section A is arranged between a vertically disposed dispenser main body B and a horizontally disposed exhausting section C to allow a piston section D to have a sufficient stroke so that the liquid content in the container may be exhausted by a large amount in a single stroke. When, however, the dispenser is made of synthetic resin, it requires a cumbersome operation of being three-dimensionally released from a mold in X-, Y- and Z- directions, entailing necessarily the problem of the low productivity. U.S. Patent No. 4,819,835 discloses an improved dispenser for solving the problem of the low productivity. Fig. 8 of the accompanying drawings schematically illustrates a trigger-type liquid dispenser disclosed in the U.S. Patent No. 4,819,835. It includes a pump section E and an exhausting section F arranged horizontally and in parallel with each other so that the operation of releasing the molded product from the mold may be carried out only two-dimensionally in X- and Y-directions to raise the manufacturing efficiency. However, since the pump section E is arranged horizontally, a stroke of a piston section G of the dispenser is reduced so as to reduce an amount of liquid that can be exhausted by a single stroke of the piston section G when compared with the dispenser of Fig. 10. In order to avoid the exhausted amount is reduced, the U.S. Patent discloses to use a cylinder H having a large diameter and a piston I having a large diameter so that the dispenser may exhaust a desired amount of liquid in as single stroke of the piston. The trigger-type liquid dispenser illustrated in Fig. 8 also includes a container fitting section 1 and is rigidly fitted to the opening of a liquid container at the container fitting section 1. When a trigger 2 is pushed along the direction of arrow J, a press member 3 presses a horizontal groove 5 cut along a lateral side of a head 4 of a piston section G to displace piston I until its end surface 6 abuts a bottom wall 7 of a cylinder H. Thus, liquid contained in a cylinder chamber 8 is flowed out through a liquid inlet/outlet port 9 into a liquid path 10 so as to press a discharge valve body 11. Then, the discharge valve body 11 is moved upwardly by the resilience of an elastic section 12 of the discharging valve body 11 to open a discharging valve seat 13. Thus, the fluid flows out from a discharging valve chamber 14 into a flow path 15 and then into other flow paths 16 and 17 so that it is finally exhausted or discharged through a nozzle 18. Meanwhile, the piston I compresses a spring 19 contained therein, while the liquid in the liquid path 10 presses a ball valve 20 against a suction valve seat 21. When the liquid is completely exhausted through the nozzle 18 and the trigger 2 is released, the piston I is returned to the position as shown in Fig. 8 by a resilient force of the spring 19. Thus, the cylinder chamber 8 is enlarged so as to decrease a pressure in the chamber 8. Since such negative pressure in the cylinder chamber 8 acts on the discharge valve body 11 and the ball valve 20, the discharge valve body 11 comes into contact with the discharge valve seat 13 to close the valve seat 13 and the ball valve 20 moves away from the suction valve seat 21 so that the liquid contained in the liquid container is drawn into the cylinder chamber 8 via a suction pipe 22, the liquid path 10 and the port 9 and stored there for the next exhausting operation. An air intake port 23 is provided on a peripheral wall of said cylinder H and communicates with an inside of the liquid container, to which the container fitting section 1 is fitted, by way of air passages 24 and 25. Said piston I is provided with an annular skirt 26 extending at an approach side (or the bottom wall 7 side of the cylinder H) and an annular skirt 27 extending at a stroke end (or an open end side of the cylinder H). The annular skirts 26, 27 are held in close contact with the inner wall surface of the cylinder H. When the surface 6 of the approach end of said piston I abuts the bottom wall 7 of the cylinder H, a front edge 28 of the annular skirt 27 of the stroke end of said piston I is located closer to the bottom wall 7 of the cylinder H than the air intake port 23 of the cylinder. In such a case, the air intake port 23 communicates with an opening 29 of the cylinder H, and an air is introduced into the liquid container. On the other hand, when the piston I is located at the stroke end position as shown in Fig. 8, the air intake port 23 is located between the two annular skirts 26 and 27 and thus closed, so that the content of the liquid container may not flow out through the air intake port 23 if the liquid container is inadvertently turned upside down. The above described trigger-type liquid dispenser disclosed in U.S. Patent No. 4,819,835 can satisfactorily exhaust liquid so long as a user operates the trigger properly and the piston I is fully moved from the stroke end to the approach end of the piston I. However, if the user repeatedly moves the trigger 2 by only a short stroke in an attempt to exhaust liquid at a reduced rate, the piston I is found in a position as illustrated in cross section in Fig. 9. Since the air intake port 23 of the cylinder H is located between the two annular skirts 26 and 27, the port 23 remains closed so that no air is allowed to flow into the liquid container, while the content of the liquid container is forced out repeatedly. Thus, the pressure in the container is significantly reduced and the container would eventually be collapsed by atmospheric pressure. SUMMARY OF THE INVENTION It is, therefore, an aim of the present invention to provide a piston of a pump section of a trigger-type liquid dispenser of the type as shown in Fig. 8 that can ensure air intake if the trigger is moved by only a short stroke and hence avoid any deformation or collapse of the liquid container by atmospheric pressure while maintaining its proper operation of liquid ejection. According to the invention, the above aim is addressed by providing a piston and cylinder arrangement of a pump section of a trigger-type dispenser to be moved back and forth within a cylinder of the pump section by a trigger, the piston having a first annular skirt directed towards a rearward end of travel of the piston and a second annular skirt directed towards a forward end of travel of the piston and formed integrally with the first annular skirt, the annular skirts being held in close contact with an inner wall surface of the cylinder and an air intake port being provided in a peripheral wall of the cylinder, characterised in that a forward edge of the second annular skirt is adjacent to that side of the air intake port which is closer to the forward end of travel of the piston, whereby liquid is unable to pass through the air intake port should the dispenser be accidentally inverted, whilst even a short stroke of the piston in the rearward direction of travel thereof will open the air intake port, in that a rear edge of the first annular skirt is adjacent to that side of the air intake port which is closer to the rearward end of the travel of the piston, whereby liquid is unable to pass through the air intake port should the dispenser be accidentally inverted, whilst at the same time substantially the whole distance from that side of the air intake port to a bottoming-out end wall of the cylinder is available for travel of the piston, and in that the distance between the respective edges of the said first and second annular skirts does not extend substantially beyond the axial length of the air intake port when the piston is at its forward end of travel. Preferably, the forward edge of the second annular skirt is provided by a notch therein. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic perspective view of a first embodiment of the invention. Fig. 2 is an enlarged partial sectional side view of the embodiment of the piston of Fig. 1, showing the piston under an operating condition. Figs. 3, 4, 5 and 6 are schematic perspective views of a second embodiment of the invention and its variations. Fig. 7 is an enlarged partial sectional side view of the embodiment of the piston of Fig. 3, showing the piston under an operating condition. Fig. 8 is a sectional side view of an improved trigger-type liquid dispenser. Fig. 9 is an enlarged partial sectional side view of the liquid dispenser of Fig. 8, showing the piston under an operating condition. Fig. 10 is a schematic side view of a conventional trigger-type liquid dispenser, showing it partly in cross section. BEST MODES OF CARRYING OUT THE INVENTION A trigger-type liquid dispenser for a piston in accordance with the present invention has a construction identical with the one illustrated in Fig. 8 except the piston. Thus, an example of the present invention will be described referring to Fig. 8. Therefore, in Fig. 2, same reference symbols or numerals are used to indicate components that are same as those of Fig. 8. Referring to Fig. 2, an air intake port 100 is provided on a peripheral wall of the cylinder H of the pump section E and communicates with the liquid container, to which the trigger-type liquid dispenser is fitted, via air passages 24 and 25. A piston 101 is moved back and forth by means of a trigger 2. As illustrated in Figs. 1 and 2, the piston 101 is provided and integrally formed with a first annular skirt 102 and a second annular skirt 104. The first annular skirt 102 extends at the approach end (or the bottom wall 7 side of the cylinder H) and held in close contact with the inner wall surface of the cylinder H. The second annular skirt 104 extends at the stroke end (or the opening 103 side of the cylinder H) and also held in close contact with the inner wall surface of the cylinder H. A distance between a rear end of said annular skirt 102 and a front end of said annular skirt 104, or an overall axial length L 1 of the annular skirts 102 and 104 is as small as approximating to, or slightly longer than an axial length L 2 of the air intake port 100. With this arrangement, if the user moves the trigger 2 by only a short stroke to exhaust little amount of liquid and consequently the piston 101 halts at a position as indicated by a solid line or a broken line 101A, air is securely introduced into the liquid container through the air intake port 100 to prevent any remarkably reduced pressure from occurring in the liquid container even if the user tries to repeatedly exhaust liquid at a reduced rate. In order to ensure satisfactory air intake, it is preferable that the overall axial length L 1 between the end the annular skirt 102 and the end of the annular skirt 104 is arranged as short as possible, but in the extent that the skirts can completely close the air intake port 100 having the axial length L 2 when the piston 101 is positioned at the end of stroke of the piston 101. Fig. 3 is a schematic perspective view of a second embodiment of the piston in accordance with the present invention, which is generally indicated by reference numeral 105. Fig. 7 is an enlarged partial sectional side view of the embodiment of the piston of Fig. 3 under an operating condition. In this embodiment, a trigger-type liquid dispenser for a piston in accordance with the present invention also has a construction identical with the one illustrated in Fig. 8 except the piston. Thus, the same component is indicated by the same reference numeral in Fig. 8. As illustrated in Figs. 3 and 7, the piston 105 is provided and integrally formed with a first annular skirt 106 and a second annular skirt 108. The first annular skirt 106 extends at the approach end (or the bottom wall 7 side of the cylinder H) and held in close contact with the inner wall surface of the cylinder H. The second annular skirt 108 extends at the stroke end (or the opening 107 side of the cylinder H) and also held in close contact with the inner wall surface of the cylinder H. Said second annular skirt 108 extending at the stroke end is provided with a notched section, (two notched sections 109, 110 in the illustrated embodiment) at positions corresponding to the air intake port 23. A head 111 of the piston 105 is also provided with a horizontal groove 112 which receives the press member 3 of the trigger 2. Since the horizontal groove 112 is fixedly provided in a relative position relating to the fixed cylinder H, the above described positions corresponding to the air intake port 23 is fixedly defined by defining the positions of the notched sections 109 and 110 relative to the groove 112. A length L 3 of the notched sections 109 and 110 is, as shown by a broken line 105A in Fig. 7, so determined that the piston 105 can completely close the air intake port 23 when it is located at the stroke end position. Because of the provision of the notched sections 109 and 110, the air intake port 23 is located vis-a-vis the notched sections 109 and 110 to ensure air to be introduced into the liquid container even when the trigger 2 is moved by only a short stroke and the piston 105 is made to halt at a position as indicated by a solid line in Fig. 7. As indicated by a broken line in Fig. 7, an end surface 113 of the piston 105 abuts the bottom wall 7 of the cylinder H at the approach end position, as in the case of a conventional piston illustrated in Fig. 8. The notched sections 109 and 110 of a first variation of the embodiment of Figs. 3 and 7 which are cut from an edge 114 of the annular skirt 108 may be replaced by a pair of through holes 115 and 116 as shown in Fig. 4, illustrating a second variation of the second embodiment. Alternatively, they may be replaced by a pair of recesses 117 and 118 as shown in Fig. 5, illustrating a third variation of the second embodiment. Still alternatively, the notched sections may be replaced by a series of axially extended and peripherally arranged slots 119 of a cogwheel as shown in Fig. 6, illustrating a fourth variation of the second embodiment. Such an arrangement is advantageous in that the air intake port 23 of the cylinder H may be peripherally displaced anywhere without adversely affecting its operational effect. According to the embodiments of the invention described above, air is securely and surely introduced into the liquid container even if the trigger is moved repeatedly by only a short stroke in order to exhaust liquid at a reduced rate so that the container is prevented from deformation or collapse due to reduced internal pressure and operates properly for liquid discharge without entailing any structural complication and increase in the number of components and assembling steps.

Claims: A piston (101, 105) and cylinder (H) arrangement of a pump section of a trigger-type dispenser to be moved back and forth within a cylinder (H) of the pump section by a trigger (2), the piston (101, 105) having a first annular skirt (102, 106) directed towards a rearward end of travel of the piston (101, 105) and a second annular skirt (104, 108) directed towards a forward end of travel of the piston (101, 105) and formed integrally with the first annular skirt (102, 106), the annular skirts (102 and 104, 106 and 108) being held in close contact with an inner wall surface of the cylinder (H) and an air intake port (100) being provided in a peripheral wall of the cylinder (H), characterised in that a forward edge of the second annular skirt (104, 108) is adjacent to that side of the air intake port (100) which is closer to the forward end of travel of the piston (101, 105), whereby liquid is unable to pass through the air intake port (100) should the dispenser be accidentally inverted, whilst even a short stroke of the piston (101, 105) in the rearward direction of travel thereof will open the air intake port (100), in that a rear edge of the first annular skirt (102, 106) is adjacent to that side of the air intake port (100) which is closer to the rearward end of travel of the piston (101, 105), whereby liquid is unable to pass through the air intake port (100) should the dispenser be accidentally inverted, whilst at the same time substantially the whole distance from that side of the air intake port (100) to a bottoming-out end wall of the cylinder (H) is available for travel of the piston (101, 105), and in that the distance between the respective edges of the said first and second annular skirts does not extend substantially beyond the axial length of the air intake port when the piston is at its forward end of travel. A piston and cylinder arrangement according to claim 1, characterised in that the forward edge of the second annular skirt (108) is provided by a notch (109, 110, 115, 116, 117, 118 or 119) therein.

Inventors: TASAKI TAKAHARU, TASAKI, TAKAHARU
Applicants: YOSHINO KOGYOSHO CO LTD, YOSHINO KOGYOSHO CO., LTD.
Application year: 1992
Main classification: F04B9
IPC codes: B05B11