US 3901416 A
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0 United States Patent 1 [111 3,901,416 Schultz 1*Aug. 26, 1975  TOP-LOADED PRESSURE OPERATED 3,066,836 12/1962 Trumbull 222/389 X CONTAINER FOR DISPENSING VISCOUS 3,132,570 5/1964 Hoffman, Jr. et a1 222/389 X PRODUCTS 3,207,385 9/1965 Fetherstone et a1. 222/389 3,381,863 5/1968 Towns 222/3865  Inventor: Robert S. Schultz, Old Greenwich,
 Assignee: Robert S. Schultz, Old Greenwich,
[ Notice: The portion of the term of this patent subsequent to Aug. 6, 1991,
has been disclaimed.
 Filed: Mar. 18, 1974  Appl. No.: 452,447
Related U.S. Application Data  Continuation-in-part of Ser. No. 290,977, Sept. 21, 1972, Pat. No. 3,827,607, which is a continuation-in-part of Ser. No. 175,253, Aug. 26, 1971, abandoned.
 U.S. Cl 222/389; 92/243  Int. Cl B67d 1/04  Field of Search 92/245, 237, 243, 253, 92/249; 222/3865, 389
 References Cited UNITED STATES PATENTS 2,992,052 7/1961 De John 222/389 UX Primary Examiner-Robert B. Reeves Assistant Examiner-Hadd Lane Attorney, Agent, or Firml-lopgood, Calimafde, Kalil, Blaustein & Lieberman  ABSTRACT The invention contemplates a piston-operated pressurized container adapted for top-loading with viscous foods or other viscous products, the body of the piston having a substantially smaller diameter than the diameter of the container. The outer periphery of the piston is provided with a resilient flange member that maintains a light sealing pressure on the interior surfaces of the container, allowing the piston to move smoothly upwardly within the container. The inventive method provides enhanced assurance against product leakage and against propellant-contamination of product, prior to selective product discharge as desired.
21 Claims, 13 Drawing Figures PATENTEB AUG 2 61975 SHEET 1 OF 3 F1650. Her-5b FIG.1
PATENTED 2 1975 Plait sum 3 o 3 PATENTED AUG 2 6 I975 Hafi- I 1 $47 45 ill d 4 5 %9 AU a a m m a M M z; w 1/? iv TOP-LOADED PRFSSURE OPERATED CONTAINER FOR DISPENSING VISCOUS PRODUCTS This application is a continuation-in-part of my copending application Ser. No. 290,977, filed Sept. 21, 1972, (now US. Pat. No. 3,827,607) which copending application is a continuation-in-part of my nowabandoned parent application Ser. No. 175,253, filed Aug. 26, 1971.
The present invention relates to a top-loaded pressure packaging system for viscous products, whereby the system is characterized by improved operation.
It is an object of the invention to provide smoother discharge flow, more precisely controlled valve action, and inherently greater capacity in a given size container of the character indicated.
A specific object is to achieve the foregoing objects in a top-loaded valved pressure container having a piston operable therein in which the viscous product is in the valved end of the container and ahead of the piston while a gas, such as nitrogen, is introduced under pressure behind the piston to urge the latter against the product and expel the product through the valved opening.
Another specific object is to provide in such a container a piston and seal construction which permits the piston to operate smoothly within the container in spite of any piston expansion, as may be caused by piston absorption of oils present in the viscous product to be dispensed.
A general object is to achieve the foregoing objects with a method which inherently simplifies container assembly, which enables smooth and reliable operation, and which also ensures (a) against product-seepage past the piston and (b) against propellantcontamination of product.
Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification, in conjunction with the accompanying drawings. In said drawings:
FIG. 1 is a longitudinal sectional view of a pressurized container of the invention;
FIG. 2 is an enlarged fragmentary sectional view of the piston and adjacent container wall of FIG. 1, and further illustrating a modification;
FIGS. 3a and 3b are fragmentary sectional views to illustrate another modification and showing a doubleacting piston in the container in both the unloaded.
(FIG. 3a) and loaded (FIG. 3b) condition thereof;
FIG. 4 is an enlarged fragmentary sectional view of a portion of FIG. 3;
FIG. 5 is a view similar to FIG. 1 to illustrate a further embodiment of the invention;
FIG. 6 is an enlarged fragmentary sectional view of a parts relationship for the structure of FIG. 5;
FIG. 7 is a similar view of a modified structure;
FIGS. 8 and 9 are similar enlarged fragmentary sectional views of the FIG. 5 combination, to show detail of the relation of parts for the uppermost position of the piston, in application to larger (FIG. 8) and smaller (FIG. 9) container bore sizes;
FIGS. 10 and 11 are respectively perspective and longitudinal sectional views of the piston in FIG. 8; and
FIG. 12 is a view similar to FIG. I], but for the piston of FIG. 9.
Referring to FIG. 1, a pressurized container or can 10 is formed with an integral conical top-end wall and provided with a valve, referred to generally by the reference numeral 12. The valve 12 is of the variety in which a valve stem 14 is pressed laterally in a well-known manner in order to release the valve seal and permit the viscous product 16, which is at super-atmospheric pressure, to be expelled to the atmosphere. A generally tubular elastomeric hollow piston 18, which may be constituted of a low-density polyethylene or a polypropylene material, is used to drive product 16 through the dispensing valve 12. Secured to or integral with the piston 18 is a relatively thin annular-shaped flange 20 provided with a depending skirt portion. In fact, the thickness of the flange 20 is less than half the. thickness of the wall of tubular piston 18. In this regard, the thickness of the flange 20 is in the order of 0.005 to 0.015 inches. Moreover, the flange 20 is provided with a large surface area for dependable but light sealing contact with the inner wall 10a of the container 10.
The container 10 is closed by a bottom wall 22 having a central opening having a sealing grommet 24 through which a gas 26, such as nitrogen, is introduced after the viscous product 16 and the piston 18 are inserted into the container. The gas 26 presses against the interior surfaces of the top of piston 18 as well as in the space A, beneath flange 20 and between the outer vertical walls of the piston and the inner wall 10a of the container 10. It will be apparent that the pressure of the gas 26 present in the space A will force the thin resilient flange 20 into light sealing contact with the inner wall 10a of the container 10.
The flange 20 may be separately secured or may be integral with the vertical wall of the piston 18 at various selected locations on the vertical wall of the piston; such a modified location of flange 20 is suggested by dashed outline in FIG. 2.
It will be noted that the space A, which permits the easy loading and operation of piston 18 in container 10, functions to provide room for the lateral expansion of the piston 18 especially when oily-type or flavored products are loaded in the container, and the piston expands due to the absorption of oils from the product. In that event, the resilient flange 20 is even further flattened against the inner wall 10a of the container 10; however, the light sealing pressure created by the resilient flange continues to seal the propellant from the product, but permits the piston 18 and associated structure to move smoothly in the container 10.
FIGS. 3 and 4 show an alternate type of piston 28 which is double-acting. This piston is provided with a thin resilient, annular flange 30 provided with a depending skirt portion, as already described in connection with FIGS. 1 and 2, as well as an additional annular flange 32 provided with a. depending skirt portion, which is seen, in the left-hand fragmentary view of FIG. 3a in the unloaded state of the container 10, to be vertically self-supporting. The loaded condition of the piston 18 in the container 10 is depicted in the right-hand fragmentary view of FIG. 3b. Thus, when the loaded condition occurs, pressure of the product on the flange 32 of the upwardly moving piston 28 causes the flange to bend backwardly against the inner wall 10a of the container 10. Consequently, the piston structure shown in FIGS. 3 and 4 results in an arrangement which double-seals the piston flanges against the container wall. Moreover, the vertical body wall of the piston 28 is provided with a reduced portion 19 at the top thereof which permits substantially all of the product present to be dispensed through the valve 12.
The nature of the thin resilient flanges 20-30-32 is to flex in and out of any indentations and over any projections or other imperfections that might be present on the interior wall surfaces of the pressurized container.
FIGS. 5 and 6 show another modification of the present invention in which like parts bear the same reference numerals applied to the structure shown'in FIGS. 1 and 2. In this embodiment, the container 10 is the type which is loaded with the product from the top of the container since the bottom and sides of the container are integral, the top panel 11 of the container being chime-connected to the cylindrical body 10, as shown. As seen in FIG. 5, the entire top unit with a valve assembly is inserted on the cylindrical can after the product is loaded through the top of the can. It will be noted that the upwardly projecting thin annular flange a provided with a depending skirt portion is normally in a position adjacent to the inner wall surface 10a which may include an actual light engagement of this wall surface by the flange; flange 20a extends no further upwardly than substantially to the geometrical projection of the upper surface of the piston 18, as is apparent in FIG. 6. Top-loading of the product 16 to be dispensed forces the upwardly projecting thin annular flange 20 a against the inner wall surface 10a of the container 10; this sealing force and action are enhanced upon closure of the top end 11 and subsequent pressurizing of the container in the manner already described, so that a tight seal is achieved between the piston l8 and the product 16 to be dispensed. The propellant gas 26 present within the hollow piston 18 moves the latter upwardly when the valve 12 is opened. Thus, as seen in FIG. 6, when the piston 18 reaches the end of its travel upwardly against the conical top part 11 of the container 10, the flange 20a is fully accommodated and remains sealingly engaged to the cylindrical body 10; and substantially all of the product in the container 10 is expelled therefrom. It will be understood that the same result is achieved for the bottom-loaded configuration of FIG. 3 by eliminating the lower annular flange 30 from the FIG. 3 construction, and thereby relying on only the additional annular flange 32 formed integral with the piston 18.
In the modification of FIG. 7, the cylindrical body of piston 18 is slightly reduced, at 18', i.e., at overlap with flange 20a, to provide a greater local radial clearance A with flange 20a for products of relatively high viscosity. The larger clearanceof A will be understood to be readily fillable, without voids, for such products.
FIG. 8 provides illustrative detail for the FIG. 5 organization applied to a container of medium or relatively large diameter. The conical end wall 11 is tapered, as in the range of to 55 and, preferably, at approximately 1r/4 radian to the container axis, terminating at a neck bead or shoulder 33 at the central opening. Shoulder 33 serves to frictionally retain the skirt of a removal nozzle-protecting closure cap 34, as will be understood. An elastomeric grommet-like fitting or bushing 35 is locked to the reduced central end of wall 11, and the dispensing stem 14 of the valve is, in turn, locked to the fitting 35. More specifically, the fitting 35 is held at a reduced circumferentially continuous groove or waist 36, between an upper shoulder portion 37 and a lower conical flange portion 38, the latter ineluding a substantial downwardly and outwardly projecting region that is relatively free of back-up connection to the central or main generally cylindrical body portion 39. To facilitate longitudinal assembly of fitting 35 via the interior of the container, the shoulder 37 is upwardly tapered to a reduced nose-end diameter at 40, well within the diameter of the opening of wall 11, the taper angle being less with respect to the central axis of the container than the slope angle of the conical end wall 11.
To complete the description of valve structure, the stem 14 has a central product-dispensing passage 41 which terminates at, but does not extend through, an enlarged integral head 42. Head 42 and a shoulder 43 define longitudinal limits of a reduced cylindrical body 44 which is retained by the bore of fitting 35, and one or more radial passages 45 open the lower end of passage 41 within the bore of fitting 35 and adjacent head 42. Preferably, the lower exposed surface of head 42 is spherical, as shown, about a center which approximates the instantaneous center 53 of tilt displacement of stem 14.
The closed end of the body of piston 18 (FIG. 8) is characterized by a conical portion 46 conforming in slope to the taper of wall 11. A spherically dished central portion 47 conforms to the exposed contour of head 42, and a flat radial annulus 48 integrally unites the portions 46-47, in close proximity to the lower limit of flange 38. FIGS. 10 and 11 provide further detail, revealing the cylindrical body of the piston as a relatively thin peripheral shell or skirt 49, integrally reinforced at regular angular spacings by thin elongate and radially inward stiffening ribs 50. The juncture of the still thinner suspension and seal flange 20a may be continuous with the shell 49, the upper edge of flange 20a being substantially within the geometric projection of the outer surface of the conical portion 46, as shown.
The arrangement of FIGS. 9 and 12 illustrates how precisely the same dispensing valve and its supporting structure may be made to serve containers of smaller diameter. For this reason, the same reference numbers are used, where applicable. However, in view of the smaller container diameter, the conical upper end wall 11 is similarly limited, to the extent that flange 38 extends so near the lower (outer) end of wall 11 that it is impractical to form a conical portion in the closed end of piston 18". The end-wall portions 47-48 are thus directly connected at a rounded corner 51 to the relatively thin cylindrical skirt 49', backed by ribs 50, and the upper edge of the flange 20a lies substantially within the geometrical projection of a cone sloped to match the slope of the container end 11' and tangent to the piston corner 51.
In the carrying out of my invention, the axial extent of the waist 37 of fitting 35 preferably exceeds, as by 0.020 to 0.030 inch, the corresponding axial extent of the bore of the can opening in which it is retained, and the unstressed conical angle of flange 38 preferably slightly exceeds, as by 5, the conical slope of end wall 11; thus, for a wall 11 of 45 slope from the container axis, the unstressed slope of flange 38 is preferably substantially 50. This relationship will be understood to facilitate assembly of a stem 14 and its fitting 35 to the wall 11, while assuring resiliently loaded, peripherally continuous contour-adapting fit of flange 35 to adjacent lapped areas of wall 11. a
Several important advantages will be seen to flow from the described cone-to-cone fit at 38-11, quite aside from the assembly feature just noted. For example, valve operation is more easily controlled, and the precision of valve actuation is enhanced. In operation, the fitting 35 serves as a resilient pivotal suspension, stem 14 being tilted about an instantaneous center (suggested by point 53 in FIGS. 8 and 9) within the waist region 36. Initial tilting movement is not stiffly opposed, since the root end of flange 38 is in slight clearance relation with the wall 11 near the central opening thereof; furthermore, flange 38 can be said to have a somewhat tangential connection to body 39 (in the sense about the instantaneous pivot center 53) so that flange 38 is either locally pulled down or pushed outward along wall 11, in the course of its sliding adaptation to the magnitude of tilt actuation. Stated in other words, for normal desired extents of valve-stem tilt, there is no substantial shear-force development between body 39 and flange 38. Additionally, the employment of a small-diameter container (e.g., a 1-inch diameter container, as in FIG. 9), or of a larger-diameter container (e.g., a 1.5-inch or larger diameter container, as in FIG. 8), both with conically tapered end walls 11 (11'), means greater facility for index-finger actuation of stem 14 while grasping the container body with the remaining fingers of the same hand. Still further, the use ofa conical end wall (11) inherently provides more extensive area, within a given limiting container diameter, to accomplish extensive resilient overlap of a seal flange, such as the flange 38 of fitting 35.
As to the piston 18 (l8'l8), the employment of a conical tapering portion (for the larger sizes), and the use of the particular spherical-surface relationship described in connection with 42-47-53, means less axial draft in the formation of the piston end wall, while achieving a contour which can assuredly expel virtually all the viscous product. The seal skirt or flange 20a is initially of preferably slightly less diameter (e.g., 0.002 to 0.005 inch) than the container bore and has a length B in the order of one third the piston length L (FIGS. 11 and 12), the axial extent B of the portion in contact with the container wall being in the order of onequarter of the length L. The clearance C between flange 20a and the piston body shell 49 is in the order of 0.040 inch, for the l-inch and 1.5-inch sizes thus far mentioned, wherein the ratio of overall piston length L to overall piston diameter D is less than unity, being preferably approximately 3:4; stated in other words, the radial offset of the tubular flange 20 from the body structure or shell 49 is in the order of 5 to percent of the outer radius of flange 20, being preferably no greater than substantially ten percent of this outer radius. In these circumstances, the piston advances with uniform ease and smoothness, even though it may have cause to tilt or slightly misalign, in the course of its travel. The lower end of the piston body shell (49) always provides a limit to the possible tilt, and throughout the range of tilt angles, the seal flange a maintains a smoothly continuous circumferential seal between the gas-pressure region 26 and the viscouscontents region 16. Also, the spherical conformity of the convex and concave surfaces 42-47 and their relation to the instantaneous center 53 for stem (14) tilt will be seen as assuring no interference with smooth control of tilt of stem 14 (with related smooth control of discharged product flow) upon approach to final discharge of the container, and regardless of whether or not piston 18 (18") may have been slightly tilted in the course of such approach.
Quite aside from the foregoing considerations, the top-fillable embodiments of the invention (FIGS. 3 to 12) present the obvious advantage of square supportability for the container bottom, and by introducing product over the central region of the top of piston 18,
v the product must then flow radially outward, to fill the clearance A and to deflect flange 20a into assuredly sealed relation with body wall 10a before the level of loaded product rises above the top of flange 20a. Pressure loading of the underside of the closed container immediately upwardly displaces product and piston, to produce a much reduced pocket of compressed air local to nozzle 12, and sealing contact with the container wall is never jeopardized, thus assuring against product leakage into the pressurized-gas region 26. Also, in the event that freon or other gas-producing liquid is relied upon for propellant purposes in region 26, the mere development of gas pressure is found to be adequate to assure leakage of such propellant liquid into contaminating contact with the product. Product quality, dischargeable product volume, and gas pressure are thus found to be maintainable for substantially increased shelf life of the filled package, as compared with prior constructions and methods.
Quite aside from and in addition to the foregoing, it will be noted that by reason of equilibrium between hydrostatic pressure in the product region and gas pressure in the pressure region 26, in conjunction with the convergent resilient conical annulus (e.g., at 38-39, in bushing 35) between the conical end wall 11 and the valve stem 44, a residual pressure loading is automatically established in the upward direction and over the inwardly exposed effective area at- 38-39-42, resulting in a strong axially upward wedging force on bushing 35,
such that substantially continuous and highly effective seal action exists as between bushing 35 and container end 11, and between bushing 35 and stem 44. This strong and effective seal action is achieved as long as valve 12 is closed and as long as product remains to be dispensed, and regardless of the fractional extent to which product may have been dispensed; such seal action is a direct result of the indicated geometry of structural relation and of the indicated method steps which result in pressure-loading of the product.
While the invention has been described in detail for preferred and illustrative contexts, it will be understood that modifications may be made without departure from the scope of the invention.
What is claimed is:
l. A piston for a pressurized container having a viscous product and provided with a dispensing valve, said piston comprising a piston body portion of a generally tubular configuration and a resilient annular elastomeric flange provided with an upstanding skirt portion on the outer wall of said piston body portion, said piston body portion being radially spaced from the inner wall of said skirt portion, said upstanding skirt portion being for contact with a container wall and being the only means of piston support, said skirt portion being relatively thin with respect to the space between said skirt portion and the piston body portion, said skirt portion having a large surface area of substantial axial length; whereby, when said piston is inserted in a suitable container and when the space within said skirt portion and above said piston is loaded with viscous product and the space beneath said skirt portion and piston is subjected to a predetermined charge of gas under pressure, said skirt portion will be pressure-loaded into peripheral and axially continuous light sealing and stabilizing contact with the container wall.
2. A piston as claimed in claim 1, wherein said piston body portion includes reinforcement means whereby said piston body portion is relatively stiff in relation to the resilience of said skirt portion.
3. A piston as claimed in claim 1, wherein the thickness of said skirt portion is in the range of 0.005 to 0.015 inch.
4. A piston as claimed in claim 1, wherein said skirt portion is integrally formed with said piston body portion.
5. A piston as claimed in claim 1, wherein said piston body is constituted of a plastic.
6. A piston as claimed in claim 1, wherein said resilient flange projects radially outwardly and axially toward the head end of said piston body portion.
7. A piston for a pressurized container having a viscous product and provided with a dispensing valve, said piston comprising a piston body portion of a generally tubular configuration, a first resilient annular elastomeric flange provided with an upstanding skirt portion on the outer wall of said piston body portion, a second resilient annular elastomeric flange provided with a skirt portion on the outer wall of said piston body portion and axially beneath said first flange, said piston body portion being radially spaced from the inner walls of said skirt portions, said skirt portions being for contact with a container wall and being the only means of piston support, said skirt portions being relatively thin with respect to the space between said skirt por tions and the piston body portion, said skirt portions each having a large surface area of substantial axial length; whereby, when said piston is inserted in a suitable container and when the space within said first skirt portion and above said piston is loaded with viscous product and the space beneath said second skirt portion and piston is subjected to a predetermined charge of gas under pressure, said skirt portions will be pressure-loaded into peripheral and axially continuous light sealing and stabilizing contact with the container wall.
8. A piston as claimed in claim 7, wherein said second flange projects axially downwardly and radially outwardly from said outer wall to a location axially spaced from the location of said first annular flange.
9. In combination, a pressure container comprising an elongate cylindrical body with a closed upper end, dispensing-valve means in said upper end, a piston having a closed upper end and integral body structure extending downwardly within a cylinder spaced from the container wall and united to the closed end of said piston, a peripherally continuous axially upwardly directed flexible tubular elastomeric flange carried by said piston within the annular space between the piston body structure and the container wall and of axial ex tent substantially less than that of said piston, said flange being relatively thin with respect to the space between said tubular flange and the piston body having a periphery of substantially the inner wall-surface peripheral extent of the container body, with a substantial axially extensive area of circumferential flange-seal contact with the container wall by reason of the tubular structure of said flange, said tubular flange being the only means of piston suspension with respect to the container wall, whereby a product chamber is defined in the container space between the flanged piston and the valved end of the container, a viscous product in said product chamber, pressure-sealing means closing the lower end of said container to define a pressure chamber beneath said piston, and a predetermined charge of gas under pressure in the pressure chamber, whereby viscous product pressure loads said tubular flange into peripheral and axially continuous light sealing and stabilizing contact with the container wall.
10. The combination of claim 9, in which said container body has a top opening, said dispensing-valve means being assembled to said body at the top opening after dispensable product is loaded through the opening.
11. The combination of claim 9, in which the radial offset of said tubular flange from said body structure is substantially ten percent of the outer radius of said tubular flange.
12. The combination of claim 9, in which said closed upper end of said container is a conical reduction from said cylindrical body to a central valve-locating opening.
13. The combination of claim 12, in which said valve means comprises a resilient bushing having a central body and an integral conical flange generally conforming to the inner surface of the conical reduction of the container and peripherally continuously sealing said bushing to the container, and a headed dispensingvalve member having a stem portion extending through said bushing and located thereby.
14. The combination of claim 9, wherein said piston body and tubular flange are parts of the same single injection-molded plastic article, the wall thickness of the closed end of said piston being substantially greater than that of said tubular flange.
15. The combination of claim 14, wherein said piston body comprises a cylindrical sheath with internal elongate stiffening ribs at angularly spaced locations.
16. The combination of claim 9, wherein the upper wall-surface contour of the closed end of said piston includes an outer frusto-conical annulus of slope conforming to that of said conical reduction.
17. The combination of claim 16, in which said tubular flange is connected to said piston body. near the upper end thereof, said tubular flange being of effective axial length less than one half the overall axial length of said piston, and the upper edge of said flange being at substantially the elevation at which the geometrical projection of the slope of the frusto-conical annulus in tersects the cylinder defined by the outer surface of said tubular flange.
18. The combination of claim 9, wherein the portion of said valve means exposed internally of said container is characterized by a central convex spherical contour, and wherein the upper surface of the closed end of said piston is characterized by a central spherical concavity substantially matching the said convex contour.
19. The combination of claim 9, in which the peripheral extent of said tubular flange is slightly less than that of the adjacent cylindrical container-body wall surface, the material of said flange being sufficiently flexible to inflate into peripherally continuous containerwall contact in response to piston-loading of product by reason of super-atmospheric pressure in said pressure chamber.
20. In combination, a pressure container comprising an elongate cylindrical body with a closed upper end, dispensing-valve means in said upper end, a piston having a closed upper end and integral body structure extending downwardly within a cylinder spaced from the container wall and united to the closed end of said piston, a peripherally continuous axially upwardly directed flexible tubular elastomeric flange carried by said piston within the annular space between the piston body structure and the container wall, said flange being relatively thin with respect to the space between said piston body and the container wall and being the only means of piston suspension with respect to the container wall, said flange having a periphery of substantially the inner wall-surface peripheral extent of the container body and being of substantial axial extent which is substantially less than that of said piston body structure, whereby a product chamber is defined in the container space between the flanged piston and the valved end of the container, a viscous product in said product chamber, pressure-sealing means closing the lower end of said container to define a pressure chamber beneath said piston, and a predetermined charge of gas under pressure in the pressure chamber, whereby viscous product pressure-loads said tubular flange into peripheral and axially continuous light sealing and stabilizing contact with the container wall,
21. A piston for a top-loaded pressurized container having above said piston a viscous product and a dispensing valve, and a gaseous propellant at superatmospheric pressure beneath said piston, said piston comprising a piston-body portion of generally tubular configuration and a resilient annular elastomeric flange provided with an upwardly directed skirt portion which projects upwardly and outwardly relative to the outer vertical wall of the piston body, said piston body being spaced from the inner wall of said container and nonsealing therewith and said flange skirt portion being the only means of piston-body suspension with respect to the inner wall of said container, the included effective transverse sectional area of said piston body substantially exceeding the included effective transverse sectional area of said space between said piston body and the inner wall of the container, said skirt portion having a substantial axially extensive surface area and being of such a length that substantially the total portion of said surface area when the piston body is inserted in said container engages the inner wall of said container with a light sealing pressure by the force exerted by said gaseous propellant acting on the piston body and thereby transmitting the predominant fraction of said force to compressionally load the viscous product and, hence, said skirt into radially outward sealing contact with the inner wall of said container.