CN213110538U

CN213110538U - Liquid pump with elastic piston

Info

Publication number: CN213110538U
Application number: CN202021561662.3U
Authority: CN
Inventors: 丁要武
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2021-05-04
Anticipated expiration: 2030-07-31

Abstract

The liquid pump comprises a pressure head, a tooth socket and an air cylinder, wherein a piston rod is connected below the pressure head, an elastic piston is arranged on the piston rod, and the tooth socket and the air cylinder are connected together. Wherein, this piston includes: a lower ring located at a lower portion of the piston, having a first outer diameter; and the combining part is provided with a second outer diameter smaller than the first outer diameter, so that the combining part is inwards sunken relative to the lower ring to form a thin-wall part, and the combining part is matched with the at least one through hole of the piston rod to form the upper one-way valve of the liquid pump. A method of manufacturing the liquid pump is also disclosed. The liquid pump having the above-described structure allows easy opening of the check valve thereon, and the piston can also be easily provided on the piston rod.

Description

Liquid pump with elastic piston

Technical Field

The present invention relates to a liquid pump for pumping a product from a container, in particular to a liquid pump with an elastic piston.

Background

On packaging containers for household products such as shampoos, shower milks or similar products, liquid pumps are often fitted for pumping the product out of the container for use by the consumer. As used herein, the term "liquid pump" includes any pump mechanism capable of pumping any flowable or semi-flowable product, including liquids, emulsions, suspensions, and the like.

Fig. 14a and 14b show an exemplary prior art liquid pump 1, wherein the liquid pump 1 shown in fig. 14a is in an up-position state, and the liquid pump 1 shown in fig. 14a is in a down-pressure state. As shown, the liquid pump 1 generally includes a ram 10, a mouthpiece 20, a cylinder 30, and a piston rod 40. The tooth socket 20 is connected with the air cylinder 30, and the piston rod 40 is connected below the pressure head 10 and extends into the air cylinder 30. A piston 50 is provided at the lower end of the piston rod 40. More specifically, the piston 50 is fitted over a recess in the lower end of the piston rod 40. A through hole is formed at a portion of the piston rod 40 where the piston 50 is provided, communicating with a cavity inside the piston rod 40, and the through hole, in cooperation with the piston 50, constitutes an upper check valve 51 of the liquid pump 1. In the up state shown in fig. 14a, the piston 50 covers the through hole on the piston rod 40 so that the upper check valve 51 is in the closed position, and as shown in fig. 14b, when the ram 10 is pressed down, the piston rod 40 moves down therewith, during which the piston 50 is deformed due to the frictional force between the piston 50 and the inner wall of the cylinder 30, opening the through hole on the piston rod 40 so that the upper check valve 51 is opened.

In practice, it has been found that there are problems with the liquid pump of the above-described construction. For example, in this liquid pump, the middle part of piston clamps in the depressed part of piston rod, when pushing down the pressure head, the middle part non-deformable of piston leads to last check valve to be difficult to open, or needs the consumer to apply great pressing force just to make and goes up check valve and open to consumer's use experience has been influenced. Also, difficulty or delay in opening the upper check valve can potentially lead to the risk of stuffiness in the fluid pump, backflow of the lower check valve, etc.

In addition, it can be seen from the figures that in order to ensure that the position of the piston on the piston rod can be limited to a certain extent, the piston fits into a recess of the piston rod, which also presents challenges for the mounting of the piston. In the process of mounting the existing liquid pump of this type, it is necessary to forcibly expand the piston so that the piston can be fitted over the larger diameter portion above or below the recess of the piston rod and then slid toward the recess to enter the recess. Such assembly is time consuming and labor intensive for the assembly personnel, and during the installation process, since the piston is forcibly expanded, there is a risk that the piston is damaged during the installation process, which in turn may affect the normal implementation of the function of the liquid pump.

Accordingly, there remains a need in the art for an improved construction of a liquid pump that overcomes at least one of the problems set forth above.

SUMMERY OF THE UTILITY MODEL

The present invention has been made to solve at least one of the problems occurring in the prior art. The utility model aims at providing a liquid pump with improve structure, this liquid pump can open its check valve easily when being pressed the process. Still further, the liquid pump of the present invention can also be easily installed.

The utility model discloses a liquid pump includes pressure head, facing and cylinder, and the below of pressure head is connected with the piston rod, and facing and cylinder link together, and inside the lower extreme of piston rod extended to the cylinder, be formed with the depressed part on the piston rod, be formed with in the depressed part from the surface of piston rod extend to at least one through-hole of the inside cavity of piston rod, wherein, the depressed part department cover at the piston rod is equipped with elastic piston, and the piston includes: a lower ring located at a lower portion of the piston, the lower ring having a first outer diameter; and the combining part is provided with a second outer diameter smaller than the first outer diameter, so that the combining part is inwards sunken relative to the lower ring to form a thin-wall part, and the combining part is matched with at least one through hole of the piston rod to form an upper one-way valve of the liquid pump.

With the liquid pump of the above-described structure, the joint portion of the piston and the piston rod is in the form of a thin-walled portion, so as to be more easily deformed than the existing piston, thereby facilitating easy opening of the check valve thereon. Moreover, the piston having a thin-walled portion is easier to mount on the piston rod and is less likely to be damaged during mounting.

Further, the piston also has an upper ring located at an upper portion of the piston, and the coupling portion is located at the upper ring and the lower ring, wherein the upper ring has a third outer diameter that is smaller than the first outer diameter and larger than the second outer diameter. The connection of the piston and the piston rod can be more stable through the upper ring.

Preferably, a convex ring is formed on an inner surface of the upper ring, and a groove is formed on the piston rod, in which the convex ring is embedded when the piston is mounted on the piston rod. The male ring-groove configuration may facilitate a sealing engagement between the upper portion of the piston and the piston rod.

Preferably, a step part is formed on the piston rod, the step part is positioned above the piston, and when the pressure head is at the top dead center of the stroke of the pressure head, the step part is contacted with the tooth socket. Thereby preventing the ram from continuing to move upward past its top dead center of travel.

Preferably, the lower ring of the piston comprises a sealing surface which is contacted with the part of the tooth socket extending into the cylinder when the pressure head moves to the top dead center of the stroke of the pressure head. The sealing surface helps to prevent leakage of product.

In another arrangement, the liquid pump further includes a cylinder head mounted on the boss, and the lower ring of the piston includes a sealing surface that contacts a portion of the cylinder head that extends into the cylinder when the head moves to its top dead center of travel.

Preferably, a mold release assisting portion is further formed on the piston, the mold release assisting portion assisting in peeling the piston from the piston rod after the piston is molded. For example, the demolding assistance portion may be a groove or a projection formed on the upper surface of the lower ring of the piston.

In an alternative arrangement, the liquid pump further comprises a piston head, the piston rod, the piston and the piston head being assembled together to form a piston assembly.

Preferably, the cylinder has formed on an inner wall thereof: the upper bulge part is contacted with the piston when the pressure head is at the top dead center of the stroke of the pressure head; and/or a lower protrusion that comes into contact with the piston when the ram is at its stroke bottom dead center. The upper and lower protrusions increase the frictional force between the piston and the inner wall of the cylinder, thereby further contributing to the deformation of the piston and improving the sensitivity of the upper check valve.

It also relates to a method of manufacturing the above liquid pump, wherein the piston rod and the piston are formed by the steps of:

molding a piston rod in a piston rod mold, wherein the piston rod mold comprises a mold core and an outer mold;

after the piston rod is manufactured, removing the outer die and keeping the die core in the manufactured piston rod;

sleeving a piston mold at the position of the concave part of the piston rod for molding the piston, wherein the piston mold comprises an insert sheet extending inwards in the radial direction, and the shape of the insert sheet corresponds to that of the joint part of the piston;

after the piston is made, the piston mold and the mold core of the piston rod mold are removed from the piston rod and the piston.

It can be seen that the method employs a two-shot forming process, enables the piston to be easily formed on the piston rod, avoids forcible diameter expansion of the piston when the piston is fitted over the piston rod, and also enables the thin-walled portion to be easily formed on the piston.

The piston rod is made of a first molding material and the piston is made of a second molding material. Wherein preferably the first molding material has a molding temperature higher than the molding temperature of the second molding material; and/or the first and second molding materials are difficult to adhere together. In this way, it is possible to facilitate the peeling of the piston from the piston rod after the molding is completed, avoiding them from sticking together.

Further preferably, in order to avoid sticking together of the piston rod and the piston, the mold for molding the piston rod may be polished, particularly, a polishing process may be performed on a position of the mold corresponding to a portion of the piston rod to be in contact with the piston. In this way, the surface of the piston rod, particularly the surface of the portion in contact with the piston, can be made smoother, thereby facilitating the separation of the piston and the piston rod from each other.

Drawings

The features and advantages of the present invention will become more apparent from the following non-limiting description of the preferred embodiments of the invention, as illustrated in the accompanying drawings. Wherein:

fig. 1a shows a cross-sectional view of a liquid pump of a first embodiment of the invention, wherein the liquid pump is at its top dead center of travel.

Fig. 1b shows another cross-sectional view of the liquid pump of the first embodiment of the present invention, in which the liquid pump is in a depressed state.

Fig. 2a shows a cross-sectional view of a piston rod and piston assembly of the liquid pump of fig. 1a and 1b, wherein the piston is in an undeformed state.

Figure 2b is another cross-sectional view of the piston rod and piston assembly shown in figure 2a wherein the piston is deformed such that the upper check valve is opened.

Fig. 2c is a partial enlarged view of a portion I in fig. 2 b.

Fig. 3a is a front view of the piston rod of the first embodiment.

Fig. 3b is a cross-sectional view of the piston rod shown in fig. 3 a.

Fig. 3c is a perspective view of the piston rod shown in fig. 3 a.

Fig. 4a is a cross-sectional view of the piston of the first embodiment.

Fig. 4b is a perspective view of the piston shown in fig. 4 a.

Fig. 5 is a cut-away perspective view of a piston of a modified construction.

Fig. 6a shows a cross-sectional view of a liquid pump of a second embodiment of the present invention, showing a state in which the pressure head is initially depressed.

Fig. 6b shows another cross-sectional view of the liquid pump of the second embodiment, showing a state in which the head is initially reset.

Fig. 7 shows a cross-sectional view of the piston assembly of the liquid pump of the second embodiment.

Fig. 8 shows a cross-sectional view of the piston rod of the piston assembly shown in fig. 7.

Fig. 9 shows a cross-sectional view of the piston assembly shown in fig. 7.

FIG. 10 illustrates a cross-sectional view of the piston head of the piston assembly shown in FIG. 7.

Fig. 11 shows a sectional view of a cylinder of the liquid pump of the second embodiment.

Figure 12 shows a cross-sectional view of a piston assembly of a modified construction.

Fig. 13 shows a cross-sectional view of a piston assembly of another modified construction.

Fig. 14a shows a sectional view of a prior art liquid pump in an upper standby state.

FIG. 14b illustrates another cross-sectional view of the liquid pump of FIG. 14a, wherein the liquid pump is in a depressed state.

Detailed Description

In order to facilitate understanding of the present invention, the following detailed description of the embodiments of the present invention will be made with reference to the accompanying drawings. It is understood that only the preferred embodiment of the present invention has been shown in the drawings and should not be considered as limiting the scope of the invention. Various obvious modifications, variations and equivalents of the present invention can be made by those skilled in the art on the basis of the embodiments shown in the drawings, and the technical features in the different embodiments described below can be arbitrarily combined with each other without contradiction, and these are within the scope of the present invention.

In the following detailed description of the present invention, terms indicating directions and orientations such as "upper" and "lower" are used with reference to the orientation of the liquid pump shown in the drawings. It will be appreciated that the orientation of the liquid pump may vary depending on the particular application.

< first embodiment >

Fig. 1 a-5 show a liquid pump 100 of a first embodiment of the invention. As shown in fig. 1a and 1b, the liquid pump 100 generally includes a ram 110, a mouthpiece 120, a cylinder 130, and a piston rod 140. The mouthpiece 120 and the cylinder 130 are connected together, and one end of the piston rod 140 is connected to the lower portion of the ram 110, and the other end thereof extends into the cylinder 130. A piston 150 is provided at one end of the piston rod 140 that protrudes into the cylinder 130. The piston 150 is a deformable elastic piston, and during the process of pressing the ram 110 downward as shown in fig. 1b, the piston 150 can be deformed by the frictional force between the piston 150 and the inner wall of the cylinder 130, thereby exposing the through-hole provided on the piston rod 140. It can be seen that the through holes in the piston 150 and the piston rod 140 cooperate to form an upper check valve 160 of the fluid pump 100.

Fig. 2a and 2b show sectional views of the piston rod 140 and the piston 150 assembled together, and fig. 2c shows a partial enlarged view of a portion I in fig. 2 b. It can be seen that the intermediate portion of the piston 150 in the liquid pump 100 in the longitudinal direction is in the form of a thin wall portion 153 hollowed out in the radial direction. During the downward movement of the plunger rod 140 with the ram 110, the thin wall 153 is easily deformed to expose a through hole (fig. 2 b) provided on the plunger rod 140, thereby allowing the product to enter the inner cavity of the plunger rod 140 through the through hole as indicated by arrow a in the figure, and then to be dispensed out of the container by the ram 110.

Fig. 3a-3c show a specific structure of the piston rod 140. The piston rod 140 includes a recess 141 disposed near the lower end, at which recess 141 at least one through hole 142 is formed, the through hole 142 extending from the outer surface of the piston rod 140 up to the cavity inside the piston rod 140, thereby forming a passage for the product to enter. In a preferred embodiment, two or more through holes 142 may be included, and the through holes 142 are spaced apart from each other around the circumference of the piston rod 140, and preferably, the through holes 142 are equally spaced.

Preferably, the piston rod 140 is further formed with a step 143, and the step 143 is located above the piston 150, for example, and when the ram 110 is located at the top dead center of the stroke of the piston rod 140, the step 143 may contact the mouthpiece 120 to prevent the ram 110 and the piston rod 140 from moving upwards.

Fig. 4a and 4b show a sectional view and a perspective view, respectively, of the piston 150 arranged on the piston rod 140. The piston 150 has a lower ring 151 at a lower portion, an upper ring 152 at an upper portion, and a coupling portion therebetween, which is fitted to the recess 141 on the piston rod 140. The lower ring 151 of the piston 150 has a larger first outer diameter, the coupling portion has a second outer diameter smaller than the first outer diameter of the lower ring 151, and the upper ring 152 has a third outer diameter smaller than the first outer diameter and larger than the second outer diameter. In the present invention, the joint portion is a thin wall portion 153 formed by hollowing radially inward, or the thin wall portion 153 is a radially inward concave structure. The thin wall portion 153 is more easily deformed than the elastic piston in the related art.

The lower ring 151 of the piston 150 further includes a sealing surface 155 thereon, and the sealing surface 155 is formed on an upper portion of the lower ring 151. When ram 110 and piston rod 140 move upward to the top dead center of their travel, sealing surface 155 may contact the portion of mouthpiece 120 that extends into cylinder 130, as shown in figure 1 a. In this manner, a seal is formed between piston 150 and mouthpiece 120 at top dead center to help prevent product located below piston 150 in cylinder 130 from leaking out of the point of contact between piston 150 and cylinder 130.

A preferred method of forming the piston rod 140 and the piston 150 in the liquid pump 100 of the present invention will be described below.

First, the piston rod 140 is injection molded in a mold. A mold for injection molding of the piston rod 140 includes a mold core and an outer mold, and a molding material is injected into a mold cavity between the mold core and the outer mold and cured to form a blank of the piston rod 140. After the injection molding of the piston rod 140 is completed, the outer mold is removed while the mold core remains in the resulting piston rod 140.

Next, a mold for forming the piston 150 is fitted at the position of the recess 141 of the molded piston rod 140. The mold for forming the piston 150 has a radially inwardly extending insert having a shape corresponding to the concave shape of the thin wall portion 153 of the piston 150. The molding material for forming the piston 150 is injected into the mold. Here, it is preferable that the molding material for forming the piston 150 is different from the molding material for forming the piston rod 140, especially their forming temperatures are largely different. Specifically, the molding material used to form the piston rod 140 has a higher forming temperature, while the molding material used to form the piston 150 has a lower forming temperature. More preferably, the material used to form the piston 150 and the material used to form the piston rod 140 have poor adhesion characteristics to each other. In this manner, it may be convenient to peel the piston 150 and the piston rod 140 away from each other after the piston 150 is molded.

Fig. 5 also shows a perspective cut-away view of a further preferred piston 150. It is shown that a groove 154 is formed on a portion of the thin-walled portion 153 of the piston 150, such as the groove 154 formed in the upper surface of the lower ring 151 shown in the drawing. The groove 154 may include a plurality of discrete grooves distributed around the circumference or an annular groove formed to extend continuously along the circumference. Alternatively, in other embodiments, the recess 154 shown in the figures may be replaced by a projection.

With this structure such as the groove 154, when the mold release is performed after the molding of the piston 150, the frictional force between the piston 150 and the mold can be increased, thereby facilitating the peeling of the piston 150 from the piston rod 140 at the time of mold release.

Further preferably, in order to facilitate peeling of the piston 150 from the piston rod 140 at the time of mold release, a mold for molding the piston rod 140 may be polished, for example, a portion of the mold corresponding to a portion of the piston rod 140 to be in contact with the piston 150, for example, a portion of the mold corresponding to an outer surface of the recess 141 of the piston rod 140, whereby a finish of the molded piston rod 140 at the portion may be improved, thereby facilitating peeling of the piston 150 from the piston rod 140.

It can be seen that in the present invention, the piston 150 is formed on the piston rod 140 through the secondary injection molding process. In this way, the piston 150 can be mounted on the piston rod 140 without forcibly expanding the diameter as in the conventional art, and the thin portion 153 can be easily formed in the piston 150.

Additionally, in the illustrated embodiment, the mouthpiece 120 is a one-piece mouthpiece. In addition, a cylinder head may be included, which is mounted with the mouthpiece and which extends into the interior of the cylinder 130 is part of the cylinder head. Further, the above-mentioned sealing surface 155 may be in contact with a portion of the cylinder head that protrudes into the interior of the cylinder 130.

< second embodiment >

Fig. 6a to 11 show a liquid pump 200 according to a second embodiment of the present invention. In the following description of the second embodiment, the technical features of the second embodiment different from those of the first embodiment will be mainly described, and unless there is a contrary description in the following or conflicting with other technical features, the features described in the first embodiment are also applicable to the second embodiment, and will not be described in detail herein.

In a second embodiment, as shown in fig. 6a and 6b, a liquid pump 200 generally includes a ram 210, a mouthpiece 220, a cylinder 230, and a piston assembly 240. The mouthpiece 220 is connected to a cylinder 230. The piston assembly 240 has one end (upper end) connected to a lower portion of the ram 210 and the other end (lower end) extending into the cylinder 230.

A cross-sectional view of the piston assembly 240 is shown in fig. 7. Wherein the piston assembly 240 includes a piston rod 241, a piston 242, and a piston head 244. The piston rod 241 and the piston head 244 are connected together, and after the connection, a recess is formed, which is similar to the recess 141 in the first embodiment.

A through-hole 245 is formed in the piston rod 241 or the piston head 244, and the through-hole 245 is positioned such that the through-hole 245 is exposed when the piston rod 241 and the piston 242 are coupled together. For example, as shown in fig. 7, a through hole 245 is formed on the piston head 244 on a portion of the piston head 244 that does not overlap with the piston rod 241 in an installed state.

Of course, in a further variant, the through-hole 245 can also be formed on the piston rod 241 on a portion of the piston rod 241 which does not overlap the piston head 244 in the mounted state.

Alternatively, through holes may be formed in the piston rod 241 and the piston head 244, respectively, and the through holes of the piston rod 241 and the piston head 244 may be aligned with each other in a state where the piston rod 241 and the piston head 244 are coupled to each other to form the through hole 245 of the assembled piston assembly 240. The through hole 245 cooperates with the combined portion of the piston 242 to form an upper check valve of the liquid pump 200.

The piston assembly 240 further includes a piston 242, the piston 242 is substantially the same in structure as the piston 150 in the first embodiment, for example, it also includes a thin-walled portion 243 formed at a substantially longitudinally intermediate portion of the piston 242, the thin-walled portion 243 is also formed by hollowing radially inwardly, and in an assembled state, the thin-walled portion 243 is engaged with a recessed portion formed after the piston rod 241 and the piston head 244 are connected, thereby functioning as a joint portion of the piston 242.

In the construction of the second embodiment, the piston rod 241, the piston 242 and the piston head 244 may be separately molded and then assembled together to form the piston assembly 240. Also, in assembling the piston assembly 240 of the second embodiment, the piston 242 may be fitted over one of the piston rod 241 and the piston head 244 and then coupled to the other of the piston rod 241 and the piston 242 without forcibly expanding the diameter of the piston 242.

Of course, the piston assembly 240 may also be manufactured using the two-shot molding process disclosed above in the first embodiment. For example, the piston rod 241 may be molded first, the piston 242 may be molded over the piston rod 241, and the preformed piston head 244 may be attached to the piston rod 241. Alternatively, the piston 242 may be molded over the molded piston head 244 and then the piston head 244 may be coupled to the preformed piston rod 241 along with the piston 242.

In addition, as shown in fig. 11, in a preferred modification of the second embodiment, an upper boss 231 and a lower boss 232 are further formed on the inner wall of the cylinder 130. The upper and

lower bosses

231 and 232 may each be in the form of a continuous raised ring, or may be in the form of discrete protrusions distributed along the circumference of the cylinder 230.

Preferably, the upper and

lower protrusions

231 and 232 are arranged such that when the ram 210 is at its top dead center of stroke, the upper protrusion 231 contacts the piston 242, particularly the lower ring of the piston 242, having a larger diameter, and when the ram 210 is at its bottom dead center of stroke, the lower protrusion 232 contacts the piston 242, particularly the lower ring of the piston 242, having a larger diameter.

Thus, when the ram 210 starts to be pressed, the upper protrusion 231 comes into contact with the piston 242, increasing the frictional force between the piston 242 and the inner wall of the cylinder 230, so that the piston 242 can be deformed more quickly to open the upper check valve. When the ram 210 is reset by removing the pressure applied to the ram 210, the lower protrusion 232 contacts the piston 242, increasing the friction between the piston 242 and the inner wall of the cylinder 230, so that the piston 242 can be deformed more quickly to close the upper check valve. In other words, the upper check valve can be opened or closed in response more quickly by the provision of the upper and

lower protrusions

231 and 232.

It will be appreciated by those skilled in the art that the structure of the upper and

lower bosses

231, 232 shown in fig. 11 is equally applicable to the liquid pump 100 of the first embodiment.

< other modified Structure >

Fig. 12 and 13 show other possible modified constructions of the piston assembly in the liquid pump of the present invention.

In a first variant, as shown in figure 12, the piston 350 mounted on the piston rod 340 comprises a lower ring 351 having a larger diameter and a coupling portion 352 having a smaller diameter. The coupling portion 352 is fitted to the recessed portion of the piston rod 340 and has a thin wall portion recessed radially inward with respect to the lower ring 351. In addition, the lower ring 351 of the piston 350 is generally in the form of a cone. The lower ring 351 of the piston 350 will be more easily deformed upwards when the head of the liquid pump is pressed, so that the upper non-return valve can be opened more quickly.

As shown in fig. 13, in the second modification, the piston 450 mounted on the piston rod 440 includes a lower ring 451, an upper ring 452, and a joint 453 between the lower ring 451 and the upper ring 452, the joint 453 forming a thin-walled portion by being inwardly depressed in the radial direction, similarly to the first and second embodiments. A collar 454 is formed inside the upper ring 452, and a groove 441 is formed in the piston rod 440 in correspondence thereto. After the molding is completed, the male ring 454 of the piston 450 is inserted into the groove 441 of the piston rod 440. The sealing engagement between the upper portion of the piston 450 and the piston rod 440 may be facilitated by the engagement between the raised ring 454 and the groove 441.

Claims

1. A liquid pump, the liquid pump includes pressure head, facing and cylinder, connect with the piston rod below the pressure head, the facing links together with the cylinder, and the lower extreme of the piston rod extends to the cylinder inside, be formed with the depressed part on the piston rod, be formed with in the depressed part from the surface of piston rod to the at least one through-hole of the internal cavity of piston rod, characterized by,

at the piston rod the depressed part department cover is equipped with elastic piston, the piston includes: a lower ring located at a lower portion of the piston, the lower ring having a first outer diameter; and a combining portion having a second outer diameter smaller than the first outer diameter such that the combining portion is recessed inwardly with respect to the lower ring to form a thin-walled portion, and the combining portion cooperates with the at least one through-hole of the piston rod to form an upper check valve of the liquid pump.

2. The fluid pump of claim 1, wherein the piston has an upper ring located on an upper portion of the piston, the junction being located on the upper ring and the lower ring, wherein the upper ring has a third outer diameter that is smaller than the first outer diameter and larger than the second outer diameter.

3. The liquid pump as claimed in claim 2, wherein a convex ring is formed on an inner surface of said upper ring, and a groove is formed on said piston rod, said convex ring being embedded in said groove when said piston is mounted on said piston rod.

4. The fluid pump of claim 1 wherein said lower ring of said piston includes a sealing surface that contacts a portion of said mouthpiece that extends into said cylinder when said head moves to top dead center of its travel.

5. The fluid pump of claim 1, further comprising a cylinder head mounted on said boss, and wherein said lower ring of said piston includes a sealing surface that contacts a portion of said cylinder head that extends into said cylinder when said head moves to its top dead center of travel.

6. The liquid pump as claimed in claim 1, wherein a mold-release assisting portion that assists in peeling the piston from the piston rod after the piston is molded is further formed on the piston.

7. The liquid pump as claimed in claim 6, wherein the demolding-assistance portion is a groove or a projection formed on an upper surface of the lower ring of the piston.

8. The liquid pump as defined in claim 1, wherein said liquid pump further comprises a piston head, said piston rod, said piston and said piston head being assembled together to form a piston assembly.

9. The liquid pump as claimed in claim 1, wherein the cylinder has formed on an inner wall thereof:

the upper protruding part is in contact with the piston when the pressure head is at the top dead center of the stroke of the pressure head; and/or

And the lower protruding part is in contact with the piston when the pressure head is at the stroke bottom dead center.