Dispensing pump with priming feature

Abstract: A precompression pump has a feature (40,41) to evacuate air trapped in a pump chamber thereby to assist in priming the pump. Gaps of very small size are created to bridge two seals (30,31) on a pump piston (2), in a way such that the small size of the gaps allows the passage of trapped air, but because of the viscosity of any liquid in the pump chamber does not allow the passage of liquid past the seals (30,31) on the pump piston (2). Flats which define a chord of the inner circumference of the cylinder wall (33) can be used to create the appropriate gaps and/or a core used to create the inner wall (33) can be photochemically etched to provide a roughened surface (70,71) with asperities which create the appropriate gaps. The priming mechanisms preferably create air gaps around both seals (30,31) of the pump piston (2).

Description: The invention relates to a dispensing pump and has particular though not exclusive application to a precompression pump with a feature to evacuate air trapped in a pump chamber, thereby to assist in priming the pump. A number of different patents describe precompression pumps with mechanisms for evacuating air from the pump chamber to assist in priming of the pump. For example, Patent Nos. US-A-3,746,260; US-A-3,774,849; US-A-4,051,983; US-A-4,144,987; US-A-4,317,531; US-A-4,365,729; US-A-4,437,588; US-A-4,530,449; EP-A-0,453,387 (US-A-5,064,105); and EP-A-0,346,167 all show mechanical mechanisms in the form of projections or grooves, which create a passage around a single seal of a pump piston or valve seal, thereby to create a passage for fluid to exit the pump chamber. Difficulties have been encountered in precompression pumps using priming features of the prior art. For example, priming features which exhaust the air and/or liquid in the pump chamber past the inlet valve, as in, e.g., Patent Nos. US-A-4,051,983; US-A-4,144,987; and US-A-4,437,588, can result in air remaining in the dip tube below the inlet valve. A result of this arrangement is that undesirable variations in dosage size can result because the pump chamber does not fill with liquid but instead with a liquid-air mixture. Furthermore, priming features which exhaust the air and/or liquid in the pump chamber past the pump piston as in, e.g., Patent Nos. US-A-3,774,849; US-A-4,317,531; US-A-4,365,729; US-A-4,530,449; EP-A-0,453,387 (US-A-5,064,105); and EP-A-0,346,167, often will leave residue in the area above the pump piston lower seal, which residue can clog or impede pump performance. In addition, these priming arrangements around the pump piston often require that an exhaust port be provided through the pump chamber sidewall between the top and bottom pump piston seals. This exhaust port can be difficult to mould and can impede the range of motion or designs available for the pump piston. Prior art priming arrangements are generally of a relatively large size in comparison to the size of the piston and cylinder diameters, such that a single groove or projection provides a passage of a sufficiently large area for exhausting compressed air from the pump chamber. Such large priming arrangements can cause undesirably large deflections of the seal being bridged, resulting in scoring or fatigue in the portion of the seal immediately adjacent the projection or groove. As a result, the pump can have a reduced lifetime or reduced effectiveness over a long lifetime. According to one aspect of the invention there is provided a dispensing pump, comprising: a cylinder having an inner wall; a piston reciprocally mounted in the cylinder and comprising at least one seal sealing against the inner wall, the piston being reciprocable in the cylinder from a first, axially outward, position to a second, axially inward, position; and at least one priming mechanism on the inner wall, the at least one priming mechanism being located at the location of the at least one seal on the inner wall at the second position of the piston and creating at least one gap between the at least one seal and the inner wall; characterised in that the at least one gap has a depth of no greater than .025 mm (.001 inches). According to a further aspect of the invention there is provided a method of venting air from a pump chamber, comprising the steps of: providing a cylinder having an inner wall; providing a piston reciprocally mounted in the cylinder and comprising at least one seal sealing against the inner wall, the piston being reciprocable in the cylinder from a first, axially outward, position to a second, axially inward, position; providing at least one priming mechanism on the inner wall; engaging the at last one seal with the at least one priming mechanism at the second position of the piston; creating at least one gap between the at least one seal and the inner wall; and exhausting air through the at least one gap; characterised in that the at least one gap is sufficiently small that air passes through the at least one gap but liquid is prevented from passing through the at least one gap. Thus, priming can be accomplished by providing a pair of priming features, one for bridging each of the top and bottom seals of the pump piston. The priming features are structured so as to create a plurality of very small sized gaps or passages around the pump piston seals. As a result, air will pass through the passages, while liquid will be prevented from passing through the passages because of the viscosity and surface tension characteristics of the liquid. The priming features of the present invention can be formed in several different ways. In one embodiment, the priming feature is formed by a series of flats around the inner circumference of the pump chamber wall, which form flats having a surface forming a chord of the inner circumference of the pump chamber wall. Directly adjacent the axially-inwardmost flats can be located slots for assisting the passage of air past the pump piston lower seal. The priming feature can also be formed by a roughened surface on the inner circumference of the pump chamber made by photochemically etching the core used to mould the pump cylinder. This embodiment can also include slots for assisting the passage of air past the pump piston lower seal. These priming features can be used in combination with one another, or in combination with other priming features. In both embodiments, a plurality of gaps are created for passage of air around each pump piston seal. The small size of these gaps allows air to pass through the individual gaps, but prevents or reduces the ability of liquid to pass through the individual gaps because of the viscosity and surface tension of the liquid. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 shows a cross-sectional, side assembly view of a pump according to the invention including a priming mechanism; Figure 2 shows a cross-sectional, side detail view of pump piston seals of a pump according to the invention interacting with a first embodiment of a priming mechanism; Figure 3 shows a cross-sectional, top detail view, taken on line III-III of Figure 2, of a pump piston seal interacting with a first embodiment of a priming mechanism; Figure 4 shows a perspective view, taken at location IV of Figure 1, of a bottom priming feature of a first embodiment of a pump according to the invention; Figure 5 shows a perspective view, taken at location V of Figure 1, of the priming feature of a second embodiment of a pump according to the invention. Figure 1 shows a first embodiment of the pump according to the invention. The pump is generally of the kind shown and described in Patent No. US-A-5,277,559. The pump includes a cylinder 1, in which a pump piston 2 slides. The pump piston 2 includes an outlet passage 3 which leads to an atomizing nozzle 4. The atomizing nozzle 4 is housed on an actuator assembly 5. The cylinder 1 can be mounted on a container or bottle (not shown) by means of a mounting cap 6, which can include a suitable sealing device 7. A passage 11 for air to exit the pump and to enter the container is created between the pump piston 2 and a wall 12 of the mounting cap 6. Contained within the cylinder 1 is a valve stem 8. The valve stem 8 includes an upper end which seats against a valve seat surface 10 on the pump piston 2, and a lower portion. A spring 22 biases the stem 8 axially-outwardly into engagement with the valve seat 10. The valve stem 8 is constructed such that there is an axially-outward facing net surface area within a pump chamber 32 after the inlet valve is closed, thereby allowing the outlet valve 8, 10 to open only when sufficient pressure is generated within the pump chamber 32. A sliding inlet seal 25 opens and closes the inlet to the pump chamber 32 within the pump cylinder 1, thereby allowing liquid to fill the pump chamber 32 during an upstroke of the pump piston 2, and thereby closing off the inlet to the pump chamber 32 during a downstroke of the pump piston 2. At an axially-inwardmost position of the pump piston 2, as shown in Figure 1, priming features 40,41 (shown in Figures 2 to 5) create gaps or passages around top 30 and bottom 31 seals of the pump piston 2, thereby to allow compressed air to exit the pump chamber 32 through the passage 11 in the path indicated by the arrows A. As is described hereinbelow, the priming features 40,41 create small gaps or passages G through which air, but not liquid, can escape between the top 30 and bottom 31 seals of the pump piston 2 and an inner wall 33 of the cylinder 1. Figure 2 shows a cross-sectional side view of the interaction of a first embodiment of the priming features 40,41 and the to 30 and bottom 31 seals of the pump piston 2. The size of the priming features 40,41 shown in Figure 2 is exaggerated for ease of explanation. Top 40 and bottom 41 priming features are located at axial positions along the inner wall 33 of cylinder 1 such that they interact with the top 30 and bottom 31 seals of the pump piston 2 at the axially-inwardmost position of the downstroke of the pump piston 2. Figure 3 shows a detail cross-sectional top view of a flat 50 used as part of the priming features 40,41 of the first embodiment. The flat 50 is a flattened section along the circumference of the inner wall 33 of the cylinder 1 which projects into the pump chamber 32 slightly beyond the location of the inner wall 33 of the cylinder 1. For example, in a pump having a inner wall 33 diameter of 7.62mm (.3 inches), the flat 50 could be approximately .610mm (.024 inches) in width W and .013mm to .025mm (.0005 to .001 inches) in depth d , as measured between a line tangent to the inner wall 33 of cylinder 1, and parallel to a flat surface 52, and the flat surface 52. As a result, a ratio R of flat depth d to inner wall 33 diameter can be approximately 1:600 to 1:300. The gaps G accordingly have a depth Δ of no greater than approximately .025mm (.001 inches). As shown in Figure 4, the flat 50 has a height H, which can be between .51mm and 1.5mm (.020 and .060 inches). The smaller the depth d, the smaller the size of the gaps G, and as a result the height H must be greater to ensure sufficient time to exhaust all trapped air from the pump chamber 32. For a flat 50 depth d of .013mm (.0005 inches), a height H of approximately 1.5mm (.060 inches) is desirable; for a flat 50 depth d of .025mm (.001 inches), a height H of approximately 1.02mm (.040 inches) is desirable. The flat 50 includes the flat surface 52 which defines a chord of the inner wall 33 of the cylinder 1. The flat 50 creates gaps G on either side of the flat 50 adjacent edges 51 of the flat 50. The axially inward or bottom end of the lower priming features 41, in the form of the flats 50, can contact a piston stop 60 of the cylinder 1. A venting recess 61 is located in the piston stop 60 and is situated directly below at least one edge 51 of the flat 50. This location of the venting recess 61 ensures a direct venting path to the gap created between the lower pump piston seal 31 and the cylinder wall 33 from the interior of the pump chamber 32. In a preferred first embodiment, two of the upper flats 50 are used to exhaust air around the upper seal 30 of the pump piston 3, and four to eight of the lower flats 50 are used to exhaust air around the lower seal 31 of the pump piston 3. Eight of the venting recesses 61 are used to ensure passage of compressed air to the gaps G created by the lower flats 50. The venting 61 recesses preferably have a width w of between .254mm and .51mm (.010 and .020 inches), and a height h of between .051mm and .127mm (.002 and .005 inches). The flats 50 create approximately triangular venting gaps G which have one obtuse angle α of approximately 162°. This angle ensures that the pump piston seals 30,31 are not deformed through any sharp angles, thereby eliminating any problems of premature excessive wear, scoring, or fatigue of the piston seals 30,31 caused by deformation of the piston seals 30,31 by the priming mechanisms 40,41. Furthermore, this gap G configuration ensures that the air passage gaps G are of a sufficiently small size that liquid viscosity and surface tension will prevent any liquid from passing through the gaps G, but air may freely pass through the gaps G. It is desirable to provide several of the flats 50 to ensure that the cumulative size of the gaps G created by the flats 50 is sufficient to vent a large enough volume of air from the pump chamber 32 once the gaps G are opened to clear the pump chamber 32 of compressed air. For example, two flats 50 are preferably used as the priming mechanism 40 for bypassing the pump piston 3 upper seal 30, thereby creating four gaps G (one on either side of each of the two flats 50). As a result, air can be successfully evacuated from the pump chamber 32, while liquids arc not passed through the gaps G potentially to hinder performance or cause dosage size variations. The upper 40 and lower 41 priming mechanisms create a path shown by the arrows A for the passage of air from the interior of the pressure chamber 32 around both of the piston seals 30,31 and out of the cylinder 1, when the piston 3 is at the bottom of its stroke. Compressed air is therefore expelled from the pump chamber 32 at the bottom of the pump stroke. Figure 5 shows a second embodiment of the priming mechanisms 40,41 of the present invention. In the embodiment of Figure 5, the flats 50 of the embodiment of Figures 2 to 4 are replaced with areas 70,71 which are roughened surfaces. The surface of the mould core which creates the inner wall 33 of the cylinder 1 is photochemically etched to produce the roughened surfaces. The photochemical etching creates roughened surfaces with asperities in the form of protrusions and/or indentations which range in height and/or depth from .025mm to .005mm (.001 to .0002 inches). These protrusions and/or indentations create very small gaps between the piston seals 30,31 and the inner wall 33 of the cylinder 1, which inner wall 33 can have a diameter of approximately 7.62mm (.300 inches), for the passage of air between the inner wall 33 of the cylinder 1 and the piston seals 30,31. As a result, the ratio R of asperity height/depth to inner wall 33 diameter can be approximately 1:1500 to 1:300. Compressed air in the pump chamber 32 passes through these gaps G, thereby bypassing the seals 30,31 and exhausting any trapped air from the pump chamber 32. The size of the gaps G is such that the surface tension and viscosity of any fluid within the pump chamber prevents the liquid from exiting the pump chamber 32 via the gaps G, and the gaps G do not exceed a depth of approximately .025mm (.001 inches). As with the embodiment of Figures 2 to 4, a venting recess 61 is used to allow air to pass through the piston stop 60 at the axially-inner end of the pump chamber 32.

Claims: A dispensing pump, comprising: a cylinder (1) having an inner wall (33); a piston (2) reciprocally mounted in the cylinder (1) and comprising at least one seal (30,31) sealing against the inner wall (33), the piston (2) being reciprocable in the cylinder (1) from a first, axially outward, position to a second, axially inward, position; and at least one priming mechanism (40,41) on the inner wall (33), the at least one priming mechanism (40,41) being located at the location of the at least one seal (30,31) on the inner wall (33) at the second position of the piston (2) and creating at least one gap (G) between the at least one seal (30,31) and the inner wall (33); characterised in that the at least one gap (G) has a depth ( d ) of no greater than .025 mm (.001 inches). A dispensing pump according to claim 1, wherein: the at least one priming mechanism (40,41) comprises a roughened surface (70,71) on the inner wall (33). A dispensing pump according to claim 2, wherein: the at least one roughened surface (70,71) is created by photochemically etching a core used to mould the inner wall (33). A dispensing pump according to claim 1, wherein: the at least one priming mechanism (40,41) comprises at least one flat (50), the at least one flat (50) having a surface (52) defining a chord of the inner wall (33). A dispensing pump according to claim 4, wherein: the ratio of the diameter of the inner wall (33) to the depth ( d ) of the at least one flat (50), measured from the surface (52) defining a chord to a line tangent to the inner wall (33) and parallel to the surface (52) defining a chord, is from 600:1 to 300:1. A dispensing pump according to claim 4, wherein: the at least one priming mechanism (40,41) comprises a plurality of flats (50). A dispensing pump according to claim 1, wherein: the piston (2) comprises a plurality of seals (30,31) and forms a pump chamber (32); the pump comprises a plurality of priming mechanisms (40,41) on the inner wall (33), the priming mechanisms (40,41) each being located at respective ones of the locations of the seals (30,31) on the inner wall (33) at the second position of the piston (2), and each creating at least one gap (G) between the respective ones of the seals (30,31) and the inner wall (33); and the cylinder (1) contains no openings between the priming mechanisms (40,41) such that air exiting the chamber (32) passes through the at least one gap (G). A dispensing pump according to claim 7, wherein: the priming mechanisms (40,41) each comprise a roughened surface (70,71) on the inner wall (33). A dispensing pump according to claim 8, wherein: the roughened surfaces (70,71) comprise asperities having a height between .025 mm and .005 mm (.001 and .0002 inches). A dispensing pump according to claim 8, wherein: the roughened surfaces (70,71) comprise asperities having a depth between .025 mm and .005 mm (.001 and .0002 inches). A dispensing pump according to claim 7, wherein: the priming mechanisms (40,41) each comprise at least one flat (50), the at least one flat (50) having a surface (52) defining a chord of the inner wall (33). A dispensing pump according to claim 11, wherein: the priming mechanisms (40,41) each comprise a plurality of flats (50). A dispensing pump according to claim 12, wherein: the inner wall (33) comprises a piston stop (60) comprising at least one venting recess (61), the at least one venting recess (61) being located axially inwardly of, and adjacent to, an edge of the axially-inwardmost priming mechanism (41). A dispensing pump according to claim 11, wherein: the at least one flat (50) has a depth ( d ) of approximately from .013 mm to .025 mm (.0005 to .001 inches) measured from the surface (52) defining a chord to a line tangent to the inner wall (33) and parallel to the surface (52) defining a chord. A dispensing pump according to claim 11, wherein: the ratio of the diameter of the inner wall (33) to the depth of the at least one flat (50), measured from the surface (52) defining a chord to a line tangent to the inner wall (33) and parallel to the surface (52) defining a chord, is approximately from 600:1 to 300:1. A dispensing pump according to claim 7, wherein: the at least one gap (G) comprises an obtuse angle (α). A dispensing pump according to claim 16, wherein: the obtuse angle (α) is approximately 162°. A method of venting air from a pump chamber, comprising the steps of: providing a cylinder (1) having an inner wall (33); providing a piston (2) reciprocally mounted in the cylinder (1) and comprising at least one seal (30,31) sealing against the inner wall (33), the piston (2) being reciprocable in the cylinder (1) from a first, axially outward, position to a second, axially inward, position; providing at least one priming mechanism (40,41) on the inner wall (33); engaging the at last one seal (30,31) with the at least one priming mechanism (40,41) at the second position of the piston (2); creating at least one gap (G) between the at least one seal (30,31) and the inner wall (33); and exhausting air through the at least one gap (G); characterised in that the at least one gap (G) is sufficiently small that air passes through the at least one gap (G) but liquid is prevented from passing through the at least one gap (G). A method according to claim 18, wherein: the step of providing at least one priming mechanism (40,41) comprises the step of producing at least one roughened surface (70,71) on the inner wall (33). A method according to claim 19, wherein: the step of producing at least one roughened surface (70,71) comprises the step of photochemically etching a core used to mould the inner wall (33). A method according to claim 18, wherein: the step of providing at least one priming mechanism (40,41) comprises the step of forming at least one flat (50) on the inner wall (33), the at least one flat (50) having a surface (52) defining a chord of the inner wall (33). A method according to claim 21, wherein: the step of forming at least one flat (50) on the inner wall (33) comprises the step of forming a plurality of flats (50) on the inner wall (33). A method according to claim 18, wherein: the step of creating at least one gap (G) comprises the step of creating at least one gap (G) comprising an obtuse angle (α).

Inventors: MESHBERG EMIL, MILLER PHILIP, SCHULTZ ROBERT, MESHBERG, EMIL, MILLER, PHILIP, SCHULTZ, ROBERT
Applicants: EMSAR INC, EMSAR, INC.
Application year: 1996
Main classification: B05B11
IPC codes: B05B11