fig1 a depicts a barrel 102 and a plunger 202 . the barrel 102 comprises a dispenser end 104 that provides a bottom opening 106 for withdrawing a liquid from a container . in use , the plunger 202 is inserted through a top opening 108 of the barrel 102 such that the plunger 202 is disposed inside a cavity 110 . the resulting dispenser assembly 100 is depicted in fig1 b . the plunger 202 is substantially rigid over its length and resists flexing in a radial direction . flexibility may be quantified by measuring the flexural modulus according to astm - d790 . the barrel 102 is thin - walled such that the barrel 102 will flex in the radial direction when a force is applied . exemplary wall thickness values for the barrel 102 are between about 0 . 014 inches and about 0 . 022 inches . in one embodiment , the thickness value for the barrel 102 is between 0 . 017 inches and 0 . 019 inches . in contrast , traditional barrels are about 0 . 035 inches thick and are relatively rigid . in one embodiment , a ring - shaped protrusion 200 is disposed at a distal end 214 of the plunger 202 . in one such embodiment , the ring - shaped protrusion 200 is disposed within 5 mm of a terminus of the distal end 214 . as shown in fig2 , the ring - shaped protrusion extends from an outer surface 212 of the plunger 202 in the radial direction to define a diameter that is slightly greater than a diameter of the plunger 202 . the ring - shaped protrusion 200 provides a raised bump that circumscribes the circumference of the distal end 214 of the plunger 202 . the diameter defined by the ring - shaped protrusion 200 is greater than a diameter of the barrel 102 when the barrel 102 is in an un - tensioned state . as a result of the difference in diameters the ring - shaped protrusion 200 applies a force against the barrel 102 as the ring - shaped protrusion 200 passes over the length of the barrel 102 . the force causes the barrel 102 to flex in the radial direction to maintain a liquid - tight seal . in one embodiment , the diameter of the plunger 202 is undercut ( relative to the diameter of the barrel 102 ) by a predetermined amount to provide a gap 216 . in one embodiment , the gap is between 0 . 0025 inches and about 0 . 010 inches . in another embodiment , the gap is between 0 . 004 inches and 0 . 008 inches . for example , the diameter of the plunger 202 may be undercut by 0 . 006 inches . this gap facilitates a sliding motion between the barrel 102 and the plunger 202 . in one embodiment , the plunger 202 is elongated and hollow . in some embodiments , the plunger 202 comprises a top opening 208 ( see fig1 a ) that is opposite a solid end 204 such that the plunger 202 forms an elongated tube that is open at only the top opening 208 . such a hollow configuration reduces the mass of material used in fabrication of the plunger 202 and thereby reduces costs . in one embodiment , the barrel 102 has a sufficiently high flexibility to be pulled onto the ring - shaped protrusion 200 when a vacuum is applied due to actuation of the plunger 202 . for example , the dispenser end 104 may be placed into a liquid and the plunger 202 withdrawn to produce a vacuum within the barrel 102 . the vacuum not only draws the liquid into the barrel 102 but also assists in the compression of the barrel 102 onto the ring - shaped protrusion 200 . when the liquid is dispensed by pushing the plunger 202 downward , a higher pressure is produced that is of a sufficiently low intensity to maintain a liquid - tight seal and prevent leaks while dispensing the liquid . advantageously , no additional sealing components ( e . g . rubber rings ) are needed . the flexibility of the plunger and barrel may be quantified using any suitable technique such as astm international standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulating materials d790 . fig3 a and fig3 b depict two views of the dispenser assembly 100 when connected to a container 300 . in the depicted embodiment , the container 300 is fitted with a press - in - bottle - adapter ( piba ) 302 that is disposed within a mouth of the container 300 . fig3 b is a perspective view of this configuration while fig3 a is a cross section view . fig4 a is a close - up view of a connection point of fig3 a wherein the dispenser assembly 100 is show in a compressed state . fig4 b is a close - up view of the connection point of fig4 a wherein the dispenser assembly 100 is shown in a partially withdrawn state . fig5 a is a cross section view of the dispenser assembly 100 engaging the piba 302 to form a liquid - tight seal between the dispenser assembly 100 and the piba 302 . fig5 b shows the container 300 and the dispenser assembly 100 in an inverted state . the inverted state facilitates the remove of liquid from the container 300 . fig6 a , fig6 b and fig6 c are cross section views of the dispenser assembly in a partially withdrawn state shown at different magnifications . in fig6 c , the ring - shaped protrusion 200 is labeled for the sake of illustration . fig7 a is a side view of the plunger 202 showing the ring - shaped protrusion 200 . in fig7 a , a conical tip 700 is depicted that mates with a corresponding shape on the barrel 102 . fig7 b is a top perspective view of the plunger 202 illustrating both the top opening 208 and the ring - shaped protrusion 200 . fig7 c is a bottom perspective view of the plunger 202 showing the ring - shaped protrusion 200 . fig7 d is another bottom perspective view of the plunger 202 showing the ring - shaped protrusion 200 . fig7 e is a side view of the distal end 214 of the plunger 202 showing the ring - shaped protrusion 200 . fig7 f is a cross section view of the distal end of fig7 e . in some embodiments , a proximal end 218 of the plunger 202 , which is opposite the distal end 214 , comprises a plunger flange 220 . the plunger flange 220 is proximate the top opening 208 of the plunger 202 . in such an embodiment , the plunger flange 220 provides a receptacle for a user &# 39 ; s finger and / or thumb during operation of the dispenser assembly 100 . likewise , in some embodiments , the barrel 102 comprises a barrel flange 112 proximate the top opening 108 of the barrel 102 that provides a receptacle for the user &# 39 ; s finger and / or thumb during operation of the dispenser assembly 100 . in one embodiment , the dispenser assembly 100 is formed by injection molding . in one embodiment , the plunger 202 and / or the barrel 102 consists of only the polymeric material and lacks additional components ( e . g . a rubber o - ring ). such a configuration is conducive to forming the plunger 202 and / or barrel 102 by injection molding which streamlines production of the dispenser assembly 100 and reduces costs . in one such embodiment , the plunger 202 and barrel 102 are respectively formed by injection molding from different polymeric materials . for example , the plunger may be formed from high density polyethylene ( hdpe ) while the barrel is formed of polypropylene ( pp ). a suitable polypropylene is a polypropylene random copolymer sold by exxonmobil ™ under the brand name pp9074med . pp9074med has a tensile strength at yield ( 510 mm / min ) of about 32 . 8 mpa , a tensile strength at break ( 510 mm / min ) of about 17 . 2 mpa , an elongation at yield ( 510 mm / min ) of about 13 %, an elongation at break ( 510 mm / min ) of about 51 % and a flexural modulus ( 1 % secant , 1 . 3 mm / min ) of about 1050 mpa ( measured according to astm d790 ). in one embodiment , the barrel 102 has a flexural modulus of less than 1200 mpa while the plunger has a flexural modulus of more than 1200 mpa . in another embodiment , the flexural modulus of the barrel is between 500 mpa and 1200 mpa . in one such embodiment , the difference in flexural modulus of the barrel and the plunger is at least 100 mpa . in another embodiment , the difference is at least 300 mpa . in yet another embodiment , the difference is at least 500 mpa . the use of different polymeric materials in the plunger and barrel , respectively , provides natural lubricity and thereby promotes the operation of the dispenser assembly 100 . in one embodiment , the plunger 202 , including the ring - shaped protrusion , is monolithic . in another embodiment , the barrel 102 is monolithic . this written description uses examples to disclose the invention , including the best mode , and also to enable any person skilled in the art to practice the invention , including making and using any devices or systems and performing any incorporated methods . the patentable scope of the invention is defined by the claims , and may include other examples that occur to those skilled in the art . such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims , or if they include equivalent structural elements with insubstantial differences from the literal language of the claims .
a dispenser assembly is provided that has a rigid plunger with a ring - shaped protrusion . the protrusion contacts the inner wall of a flexible barrel to form a liquid - tight seal . advantageously , the dispenser assembly does not require additional components , such as o - rings , and can be fabricated by injection molding techniques .