WO2008051008A1

WO2008051008A1 - Disposable syringe

Info

Publication number: WO2008051008A1
Application number: PCT/KR2007/005226
Authority: WO
Inventors: Woo In Baik
Original assignee: Baik Woo Inn
Priority date: 2006-10-24
Filing date: 2007-10-23
Publication date: 2008-05-02

Abstract

The present invention relates to a disposable syringe. More specifically, the present invention relates to a disposable syringe in which no suction force is applied to an inside of a cylinder (11 ) even if a pushing rod (13) is pulled backward again once an initial injection is done, leading to no feeding of injectable solution into a space in the cylinder (11 ), thereby preventing the syringe from being used again. The disposable syringe includes a cylinder (11 ) having a space therein with front and rear ends in communication with each other and a connection portion (12) formed at a front as one unit therewith, a pushing rod (13) movably placed in the space of the cylinder (11 ), the pushing rod (13) having a piston (14) mounted to a front side for providing compression force or suction force in a state the piston (14) is in air tight contact with the cylinder (11), a needle holding tube (15) placed in the connection portion (12) and secured thereto in a hooked state, the needle holding tube (15) having a needle (16) secured to a front end, an inserting hole (18) in a front of the pushing rod (13) an inserting piece (20) detachably placed in the inserting hole (18) in a state a portion of a front portion thereof is exposed to an outside of the inserting hole (18) so that the portion of the front portion exposed to the outside of the inserting hole (18) is placed in the needle holding tube (15) to close a passage of the needle holding tube (15) in a state the pushing rod (13) is moved forward fully, inserting piece holding means for limiting movement of the inserting piece having closed the tube passage of the needle holding tube (15) and inserting piece separation means for separating the inserting piece having closed the tube passage of the needle holding tube (15) from the inserting hole (18).

Description

Description DISPOSABLE SYRINGE

Technical Field

[1] The present invention relates to a disposable syringe. More specifically, the present invention relates to a disposable syringe in which no suction force is applied to an inside of a cylinder even if a pushing rod is pulled backward again once an initial injection is done, leading to no feeding of injectable solution into a space in the cylinder, thereby preventing the syringe from being used, again.

[2]

Background Art

[3] Referring to FIGS. 1 to 3, a related art disposable syringe is provided with a cylinder

1 having a space therein and a connection tube 2 on a front with a step thereto, a pushing rod 3 inserted in the space of the cylinder 1 such that the pushing rod 3 is movable in front/rear directions following a length direction of the cylinder 1, a piston 4 secured to a front of the pushing rod 3 such that the piston 4 is movable together with the pushing rod 3 when the pushing rod 3 moves forward/backward in a state the piston 4 is in air tight contact with the cylinder 1 for providing compression force or suction force, a needle holding tube 5 detachably secured to an outside of the connection tube 2 on the cylinder 1, a needle 6 secured to the needle holding tube 5, and a needle protection cap 7 detachably secured to the needle holding tube 5 to protect the needle 6 in a state the needle 6 is enclosed, completely.

[4] The steps of a process for using the related art disposable syringe will be described.

[5] FIG. 2 attached hereto illustrates a longitudinal section of a related art disposable syringe, in a state the pushing rod 3 with the piston 4 is moving backward before injection. In this state, the injectable solution is drawn from a left portion of the space in the cylinder 1 with reference to the piston 4 secured to the pushing rod 3 on the drawing and filled in the space.

[6] In order to draw the injectable solution and fill the space in the cylinder 1 with the injectable solution, it is required for a user (a doctor or a nurse) to separate the protection cap 7, which is protecting the needle 6 secured to the needle holding tube 5, from the needle holding tube 5 to expose the needle 6 to an outside of the syringe. Then, the user is required to push the pushing rod 3 in the space of the cylinder 1 forward to place the pushing rod 3 to a front side, dip an end of the needle 6 in the injectable solution in a vial (not shown), and pull the pushing rod 3 backward again, to move the piston 4 backward together with the pushing rod 3. Therefore, in a case the piston 4 secured to the pushing rod 3 moves backward as the pushing rod 3 is pulled backward, the suction force is applied to the space in the cylinder 1, to draw the injectable solution from the vial into the space in the cylinder 1 through the needle 6 secured to the needle holding tube 5.

[7] In a state shown in FIG. 2, if the user moves the cylinder 1 forward, which is a patient side, sticks the needle 6 into skin of the patient, and pushes the pushing rod 3 forward to move the piston 4 at the pushing rod 3 forward, compression force is applied to the left portion of the space in the cylinder 1 with reference to the piston 4 on the drawing. As a result of this, the injectable solution escapes through the connection tube 2 on the cylinder 1 as the injectable solution in the space of the cylinder 1 has the compression force applied thereto, and the injectable solution escaped through the connection tube is injected into the skin of the patient through the needle 6 secured to the needle holding tube 5. FIG. 3 illustrates a state the injection of the injectable solution is finished according to above steps.

[8] Once the injection is finished, the user caps the needle protection cap 7 on the needle holding tube 5 again for protecting the needle 5 from an outside of the syringe, and disposes of the syringe.

[9]

[10]

Disclosure of Invention

Technical Problem

[11] However, since the related art disposable syringe has a structure that can be used again even if used once, medical accidents caused by reuse of the syringe happen, frequently. Particularly, because an extremely serious accident caused by negligence of safety can be foreseen if the syringe used for a patient having infectious pathogen, such as an AIDS patient, is used to other patient, it is required that reuse of the syringe is forbidden, without fail.

[12]

Technical Solution

[13] To solve the problems, an object of the present invention is to provide a disposable syringe in which no suction force is applied to an inside of a cylinder even if a pushing rod is pulled backward again once an initial injection is done, leading to no feeding of injectable solution into a space in the cylinder, thereby preventing the syringe from being used, again.

[14] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a disposable syringe includes a cylinder having a space therein with front and rear ends in communication with each other and a connection portion formed at a front as one unit therewith, a pushing rod movably placed in the space of the cylinder, the pushing rod having a piston mounted to a front side for providing compression force or suction force in a state the piston is in air tight contact with the cylinder, a needle holding tube placed in the connection portion and secured thereto in a hooked state, the needle holding tube having a needle secured to a front end, an inserting hole in a front of the pushing rod, an inserting piece detachably placed in the inserting hole in a state a portion of a front portion thereof is exposed to an outside of the inserting hole so that the portion of the front portion exposed to the outside of the inserting hole is placed in the needle holding tube to close a passage of the needle holding tube in a state the pushing rod is moved forward fully, i nserting piece holding means for limiting movement of the inserting piece having closed the tube passage of the needle holding tube, and inserting piece separation means for separating the inserting piece having closed the tube passage of the needle holding tube from the inserting hole. [15]

Advantageous Effects

[16] If the user pulls the pushing rod backward for reuse of the syringe after initial use of the syringe, because opposite sides of the space of the cylinder are made to be in communication with reference the piston on the pushing rod, or only the pushing rod is moved backward in a state the pushing rod is separated from the piston owing to the inserting piece separation means, failing to form suction force in the space of the cylinder, the reuse of the syringe of the present invention can not be used again.

[17]

Brief Description of the Drawings

[18] The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure.

[19] In the drawings :

[20] FIG. 1 illustrates an exploded perspective view of a related art disposable syringe;

[21] FIG. 2 illustrates a longitudinal section for explaining a state of use of a related art disposable syringe;

[22] FIG. 3 illustrates a longitudinal section for explaining a state of use of a related art disposable syringe;

[23] FIG. 4 illustrates an exploded perspective view of a disposable syringe in accordance with a preferred embodiment of the present invention;

[24] FIG. 5 illustrates a longitudinal section for explaining a state of use of a disposable syringe in accordance with a preferred embodiment of the present invention; [25] FIG. 6 illustrates a longitudinal section for explaining a state of use of a disposable syringe in accordance with a preferred embodiment of the present invention;

[26] FIG. 7 illustrates a longitudinal section for explaining a state of use of a disposable syringe in accordance with a preferred embodiment of the present invention;

[27] FIG. 8 illustrates an enlarged view of a section across a line I-I in FIG. 5;

[28] FIG. 9 illustrates an exploded, and enlarged perspective view of key parts of a disposable syringe in accordance with a preferred embodiment of the present invention;

[29] FIG. 10 illustrates an exploded perspective view of inserting piece separation means of a disposable syringe in accordance with another preferred embodiment of the present invention;

[30] FIG. 11 illustrates a section showing a state of use of inserting piece separation means of a disposable syringe in accordance with another preferred embodiment of the present invention;

[31] FIG. 12 illustrates a section showing a state of use of inserting piece separation means of a disposable syringe in accordance with another preferred embodiment of the present invention; and

[32] FIG. 13 illustrates an exploded, and enlarged perspective view of key parts of inserting piece separation means of a disposable syringe in accordance with another preferred embodiment of the present invention.

[33]

[34]

Best Mode for Carrying Out the Invention

[35] Reference will now be made in detail to the specific embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[36] FIG. 4 illustrates an exploded perspective view of a disposable syringe in accordance with a preferred embodiment of the present invention, FIGS. 5 to 7 illustrate longitudinal sections for explaining states of use of a disposable syringe in accordance with a preferred embodiment of the present invention, respectively, FIG. 8 illustrates an enlarged view of a section across a line I-I in FIG. 5, and FIG. 9 illustrates an exploded, and enlarged perspective view of key parts of a disposable syringe in accordance with a preferred embodiment of the present invention.

[37] Referring to FIGS. 4 to 9, the disposable syringe includes a cylinder 11 having a space therein with front and rear ends in communication with each other and a stepped connection portion 12 at a front formed as one unit therewith, a pushing rod 13 placed in the space in the cylinder so as to be movable in front and rear directions following a length direction of the cylinder 11, a piston 14 mounted to a front side of the pushing rod 13 such that the piston 14 is movable together with the pushing rod 13 when the pushing rod 13 moves forward/backward in a state the piston 14 is in air tight contact with the cylinder 11 for providing compression force or suction force, a needle holding tube 15 placed in and secured to the connection portion 12 in a hooked state with a front exposed to an outside of the syringe, a needle 16 secured to a front of the needle holding tube 15, and a needle protection cap 17 detachably secured to the needle holding tube 15 to protect the needle 16 in a state the needle 16 is enclosed.

[38] The cylinder 11 has a first holding step 1 Ia formed on the front side which is one end of the space along an inside circumference, and the needle holding tube 15 has a first holding projection 15a formed on an outside circumference along a circumference. Therefore, when the needle holding tube 15 is being placed into the cylinder 11, the needle holding tube 15 is secured to the cylinder 11 in a hooked state as the first holding projection 15a is engaged with the first holding step 11a.

[39] The connection portion 12 of the cylinder has a guide surface 12a at a front edge formed along an inside circumference in conformity with the first holding projection inwardly sloped toward the pushing rod 13 which is in rear of the connection portion

12. Accordingly, when the needle holding tube 15 is being pushed into the cylinder 11, the placing of the needle holding tube 15 into the cylinder 11 is smooth since the first holding projection 15a is guided by the guide surface 12a.

[40] The pushing rod 13 has an inserting hole 18 in a front opened toward the needle holding tube 15, for inserting to an inserting piece 20. The inserting piece 20 is placed in the inserting hole 18 with a front portion exposed to an outside of the pushing rod

13. Therefore, when the pushing rod 13 is pushed toward the needle holding tube 15 which is a front direction for injection, a portion of a front end of the inserting piece 20 is placed in the needle holding tube 15, to close the tube passage of the needle holding tube 15.

[41] The inserting piece holding means limits movement of the inserting piece 20 having closed the tube passage of the needle holding tube 15. The inserting piece holding means includes an inward flange 21 formed along a circumference of the cylinder 11 for limiting backward movement of the inserting piece 20 secured to the needle holding tube 15 and setting a size of a passage of the cylinder 11, a second holding step 21a of a cone shape formed at an edge of the inward flange 21 having a diameter which becomes the smaller as it goes toward the needle holding tube 15 the more so that the second holding step 21a is in contact with the inserting piece 20 in a state the second holding step 21a surrounds an outside circumference of the inserting piece 20 when a portion of the inserting piece 20 is placed in the needle holding tube 15, a plurality of cut away portions formed in the second holding step at regular intervals for improving elastic force of the second holding step 21a, and a second holding projection 20a formed on a front portion of the inserting piece 20 along a circumference thereof. In the step the inserting piece 20 is being placed into the needle holding tube 15, the second holding projection 20a is forcibly passed through the second holding step 21a, and secured to the second holding step 21a.

[42] In the meantime, it is preferable that the needle holding tube 15 has a contact projection 15b having a sharp edge formed along, and extended inwardly from, an inside circumference, so that the contact projection 15b is in air tight contact with the second holding projection 20a of the inserting piece 20 in a state one portion of the front portion of the inserting piece 20 is placed in the needle holding tube 15.

[43] In order to separate the inserting piece 20 having closed the tube passage of the needle holding tube 15 by using the inserting piece holding means from the pushing rod 13, the present invention includes an inserting piece separation means.

[44] The inserting piece separation means can be a communication hole 19 in the pushing rod 13 for making a rear side space of the piston 14 and the inside of the inserting hole 18 in communication.

[45] Alternatively, referring to FIGS. 9 to 13, the inserting piece separation means can be a gap 30 formed in a contact portion between the pushing rod 13 and the piston 14, and a close contact hole 31 formed in a center of the piston 14 such that the piston 14 is press fit to a front side of the inserting piece 20. In this case, the piston 14 is secured to the front of the pushing rod 13 as a rear portion of the inserting piece 20 is press fit into the close contact hole 31 and a rear side of the piston 14 is placed onto the front side of the pushing rod 13.

[46] An assembling process of the disposable syringe of the present invention will be described before describing a process for using the same.

[47] The needle holding tube 15 having the needle 16 secured thereto is secured to an inside of the cylinder 11 through the connection portion 12 of the cylinder 11. In this instance, since an outside diameter of the first holding projection 15a is slightly greater than an inside diameter of the connection portion 12 of the cylinder 11, the needle holding tube 15 interferes with the cylinder 11 in a process the needle holding tube 15 is being placed into the cylinder 11. However, since the cylinder 11 and the needle holding tube 15 are formed of synthetic resin, the first holding projection is placed in the cylinder 11 without application of great force as the first holding projection deforms, elastically. Moreover, the needle holding tube 15 having a portion is placed in the cylinder 11 is fixedly secured to the inside of the cylinder 11 as the first holding step 15a forcibly passes through the first holding step 1 Ia in the cylinder 11.

[48] At the time the needle holding tube 15 is being placed into the cylinder 11, the first holding projection 15a is placed into the cylinder 11 smoothly following the guide surface 12a at the connection portion 12.

[49] In a state a needle holding portion of the needle holding tube 15 is exposed to an outside of the cylinder 11 in a state the needle holding tube 15 is secured to the connection portion 12 in the cylinder 11, and movement of the needle holding tube 15 toward a cylinder side is limited as the first holding projection 15a is supported on the inward flange 21 in the cylinder 11.

[50] Since there is a safety hazard caused by the needle 16 even if it is, not a manual assembly by an expert, but an automatic assembly with mechanical equipment in a state the needle holding portion of the needle holding tube 15 is exposed to the outside of the cylinder 11 and the needle holding tube 15 is secured to the inside of the connection portion 12 of the cylinder 11, it is preferable that the needle protection cap 17 is placed on the needle holding tube 15 for protection of the needle 16.

[51] Thus, once the needle holding tube 15 is placed in the cylinder 11, the inserting piece

20 is inserted in the inserting hole 18.

[52] In the meantime, if the inserting piece separation means is the gap 30 formed in a contact portion between the pushing rod 13 and the piston 14, and the close contact hole 31 in the center of the piston 14 formed such that the piston 14 is press fit in the front portion of the inserting piece 20, after placing a rear portion of the piston 14 in a front portion of the pushing rod 13, the rear portion of the inserting piece 20 is press fit into the close contact hole 31 in the piston 14 until the rear portion of the inserting piece 20 is placed in the inserting hole 18 in the pushing rod 13 fully, thereby putting the pushing rod 13, the piston 14, and the inserting piece 20, together.

[53] After placing the inserting piece 20 in the pushing rod 13, the pushing rod 13 is pushed into the space of the cylinder 11, to finish assembly of the disposable syringe of the present invention.

[54] A process for using the disposable syringe of the present invention will be described in detail.

[55] FIG. 5 illustrates a longitudinal section a disposable safety syringe in accordance with a preferred embodiment of the present invention, having the pushing rod 13 moved backward together with the piston 14 before injection. In this state, the injectable solution is drawn and filled in a left portion of the space of the cylinder 11 on the drawing with reference to the piston 14 on the pushing rod 13. Because a process for drawing and filling the injectable solution in the space of the cylinder 11 can be understandable once a process of the related art disposable syringe described already is referred to, the description of the process for drawing and filling the injectable solution will be omitted.

[56] In a state in FIG. 5, if a doctor or a nurse who is a user, holding the cylinder with one hand, moves the cylinder 11 toward a patient side, sticks the needle 16 held at the needle holding tube 15 into skin of the patient, and pushes the pushing rod 13 toward a needle holding tube 15 side which is a front side to move the piston 14 at the pushing rod 13 forward, compression force is applied to the left portion of the space in the cylinder 11 with reference to the piston 14 on the drawing. Since the needle holding tube 15 having the needle 16 fixed thereto is secured to the inside of the connection portion 12 of the cylinder 11, the injectable solution filled in the space of the cylinder 11 is kept injected into the skin of the patient through the needle 16, to make dispense of the indictable solution. FIG. 6 illustrates a state dispense of the injectable solution is finished.

[57] At the time the pushing rod 13 is pushed forward toward the needle holding tube 15 which is a front direction, the inserting piece 18 having closed the inserting hole 18 in a state a portion of the front portion is placed in the inserting hole 18 in the pushing rod 13 also moves together with the pushing rod 13.

[58] Accordingly, referring to FIG. 6, at the time the dispense is finished as the forward movement of the pushing rod 13 is finished, the inserting piece 20 is in a state a portion of the front portion thereof is placed in the needle holding tube 15.

[59] In the meantime, in above process, the second holding projection 20a at the inserting piece 20 interferes with the second holding step of the inward flange 21 in the cylinder 11, and passes through the second holding step 21a forcibly as the second holding projection 20a deforms for itself. After passed through the second holding step 21a forcibly, the second holding projection restores to an original shape to surround the inserting piece 20. Therefore, once the pushing rod 13 is moved toward the needle holding tube 15 fully to finish the dispense, backward movement of the pushing rod 13 is limited, because the second holding projection 20a on the inserting piece 20 is held at the second holding step 21a on the inward flange 21.

[60] After use of the disposable syringe of the present invention is finished, the needle 16 is pull out of the skin of the patient, the needle protection cap 17 is placed on the needle holding tube 15 having the needle 16 secured thereto for protecting the needle 16 with the needle protection cap 17, and, then, the disposable syringe is abandoned safely through a waste disposal expert company.

[61] In the meantime, in order to reuse the syringe, it is required for a re-user to draw the injectable solution into the space of the cylinder 11 in a state in FIG. 6, for which it is required to pull the pushing rod 13 having moved forward backward again in a direction opposite to the needle holding tube 15 which is a rear side as shown in FIG. 7. However, if the pushing rod 13 is moved backward, the disposable syringe of the present invention can not be used again after initial use of the disposable syringe, because suction force of the pushing rod 13 is not applied to the space of the cylinder 11 as the inserting hole 18 is separated from the pushing rod 13 by the inserting piece separation means.

[62] That is, if the inserting piece separation means is the communication hole 19 which makes the rear side space of the cylinder 11 with reference to the piston 14 on the pushing rod 13 and the inside of the inserting hole 18 in communication, since backward movement of the second holding projection 20a is limited as the second holding projection 20a is held at the second holding step 21a of the inward flange 21 if the pushing rod 13 is moved backward, the inserting piece 20, opening the communication hole 19, moves away from the inserting hole 18, at the end. If the communication hole 19 is opened, the suction force does not act on the space on a side of the needle holding tube 15 because a front side and a rear side of the cylinder with reference to the piston 14 is in communication even if the state of air tight contact is kept between the piston 14 and the cylinder 11 as before, failing suction of the injectable solution into the cylinder 11, the reuse of the syringe is not possible.

[63] When the pushing rod 13 is pulled backward, even though the suction force acts on the space of the cylinder 11 until the inserting piece 20 opens the communication hole 18, the injectable solution can not be drawn into the cylinder, because the second holding projection 20a on the inserting piece 20 is in air tight contact with the contact projection 15b in the needle holding tube 15, closing the inside of the needle holding tube 15 and the inside of the cylinder fully.

[64] On the other hand, referring to FIGS. 9 to 13, in a case the inserting piece separation means is the gap 30 formed in a contact portion between the pushing rod 13 and the piston 14, and the close contact hole 31 in the center of the piston 14 formed such that the piston 14 is press fit in the front portion of the inserting piece 20, if the pushing rod 13 is moved backward for reuse, the second holding projection 20a is held at the second holding step 21a of the inward flange 21, limiting rear direction movement of the pushing rod 13, only the pushing rod 13 having a close contact force weaker than the inserting piece 20 owing to the gap 30 moves backward.

[65] At the end, even if the pushing rod 13 is pulled backward for reuse of the syringe, since the pushing rod 13 moves backward in a state the pushing rod 13 is separated from the piston 14, failing to make the suction force of the piston to act on the cylinder 11 permitting no suction of the injectable solution into the cylinder 11, the reuse of the syringe is not possible.

[66]

[67]

Mode for the Invention

[68] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[69]

Industrial Applicability

[70] See advantageous effects.

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

Claims

[1] A disposable syringe comprising: a cylinder having a space therein with front and rear ends in communication with each other and a connection portion formed at a front as one unit therewith; a pushing rod movably placed in the space of the cylinder, the pushing rod having a piston mounted to a front side for providing compression force or suction force in a state the piston is in air tight contact with the cylinder; a needle holding tube placed in the connection portion and secured thereto in a hooked state, the needle holding tube having a needle secured to a front end; an inserting hole in a front of the pushing rod; an inserting piece detachably placed in the inserting hole in a state a portion of a front portion thereof is exposed to an outside of the inserting hole so that the portion of the front portion exposed to the outside of the inserting hole is placed in the needle holding tube to close a passage of the needle holding tube in a state the pushing rod is moved forward fully; inserting piece holding means for limiting movement of the inserting piece having closed the tube passage of the needle holding tube; and inserting piece separation means for separating the inserting piece having closed the tube passage of the needle holding tube from the inserting hole.

[2] . The disposable syringe as claimed in claim 1, further comprising: a first holding step formed in the cylinder along a circumference of the cylinder; and a first holding projection formed on an outside circumference of the needle holding tube along the outside circumference thereof such that the first holding projection can be held at the first holding step.

[3] The disposable syringe as claimed in claim 2, wherein the connection portion of the cylinder includes a front edge having an inwardly sloped guide surface in conformity with the first holding projection on the needle holding tube for smooth placing of the needle holding tube into the cylinder.

[4] The disposable syringe as claimed in claim 1, wherein the inserting piece holding means includes; an inward flange formed along a circumference of the cylinder, a second holding step of a cone shape formed at an edge of the inward flange having a diameter which becomes the smaller as it goes toward the needle holding tube the more, a plurality of cut away portions formed in the second holding step at regular intervals for improving elastic force of the second holding step itself, and a second holding projection formed on a front portion of the inserting piece along a circumference thereof such that the second holding projection is forcibly passed through the second holding step.

[5] . The disposable syringe as claimed in claim 4, wherein the needle holding tube includes a contact projection having a sharp edge formed along, and extended inwardly from, an inside circumference, so that the contact projection is in air tight contact with the second holding projection of the inserting piece in a state one portion of the front portion of the inserting piece is placed in the needle holding tube.

[6] . The disposable syringe as claimed in claim 1, wherein the inserting piece separation means includes a communication hole formed in the pushing rod for making a rear side space of the cylinder with reference to the piston on the pushing rod and the inside of the inserting hole in communication.

[7] The disposable syringe as claimed in claim 1, wherein the inserting piece separation means includes; a gap formed in a contact portion between the pushing rod and the piston, and a close contact hole formed in a center of the piston such that the piston is press fit to a front side of the inserting piece of the piston.