Abstrict A disposable syringe for injections comprises a cylindrical housing
(1), which accommodates a piston (5) with a rod (6), and a needle
fixing device (4). The piston (5) and the rod (6) are mechanically
disengaged from each other, a flange (7) is provided at the end
of the rod (6), and a washer (8) is fitted on the rod (6) coaxially
therewith. The diameter of the hole in the washer (8) is smaller
than the diameter of the flange (7), while the outside diameter
of the washer (8) exceeds the inside diameter of the housing (1)
by such an amount that the force of friction between the outer surface
of the washer (8) and the inner surface of the housing (1) surpasses
the force exerted upon the washer (8) as a result of motion performed
by the housing (1), including as accelerated motion thereof. The
disposable syringe is equally applicable in any medical institution
and for individual use.
Claims What is claimed is:
1. A disposable syringe for injections, comprising:
a cylindrical housing having a forward end, a rearward end, and
an internal surface;
a needle fixing device extending forwardly from the forward end
of said cylinder;
a cover permanently fixed to the rearward end of said cylinder,
said cover including a central hole;
a rod slidingly received within the central hole, said rod having
a first end adapted for movement within said cylinder;
an end extension member fixed to said first end of said rod, said
end extension member having a forward surface and an external periphery
which is greater than an external periphery of the first end of
said rod;
a piston positioned within said cylinder housing between said needle
fixing device and said end extension member, said piston being in
frictional contact with the interior surface of said cylinder and
having a rearward surface juxtaposed to the forward surface of said
end extension member, the rearward surface of said piston and the
forward surface of said end extension member being dimensioned and
arranged such that said forward and rearward surfaces are mechanically
free of engagement when in abutting contact;
a washer having a central aperture, a front end, a rear end and
a peripheral edge, said washer being positioned rearward of said
end extension member and forward of said cover, the peripheral edge
of said washer being in frictional contact with the interior surface
of said cylinder, said central aperture being dimensioned so as
to receive said rod such that a portion of said rod positioned forward
to said washer is free to reciprocate in a forward to rearward direction
with respect to said washer, and said central aperture having a
periphery which is less than the external periphery of said end
extension member such that said end extension member seals said
aperture when said end extension member is placed in contact with
said washer.
2. A syringe as recited in claim 1 wherein said end extension
member is a flat disk attached to a forwardmost end of said rod,
and said flat disk having a planar forward surface.
3. A syringe as recited in claim 2 wherein said piston is a solid,
cylindrical body with a planar rear surface.
4. A syringe as recited in claim 1 wherein said cover is integral
with said cylinder housing so as to form a unitary housing and cover
combination.
5. A syringe as recited in claim 1 wherein said rod is a solid,
cylindrical rod.
Description TECHNICAL FIELD
This invention relates generally to medical engineering and, more
specifically, to disposable syringes applied for injections.
PRIOR ART
Some disposable syringes for injections known to be in widespread
use nowadays comprise a cylindrical housing, a piston with a rod
accommodated in said housing, and a needle fixing device (cf., e.g.,
disposable syringes available from Trumo Europe Co., Belgium). The
syringes in question differ very little from disposable syringes
now in extensive use in modern medical practice, the sole exception
residing in that they are made of a cheaper material (i.e., polymer)
and therefore are not subject to sterilization. This means that
the construction of the known disposable syringes enables one to
make repeated use of them, which may occur on account of inattentive
or unscrupulous action of medical staff, or when injections are
made by those who are in narcotic or alcoholic intoxication. All
situations stated above can prove to be of importance, since such
cases are fraught with a danger of infection with the virus of AIDS,
that of infectious hepatitis, and of some other diseases.
One more prior-art disposable syringe is known to comprise a cylindrical
housing accommodating a piston with a rod, and a needle fixing device
(EP, A, 0282097).
The syringe under discussion features its needle fixed in a washer
situated in the front portion of the syringe housing and capable
of reciprocating lengthwise the axis of the housing. The piston
disposed past the washer in the syringe housing and rigidly coupled
to the rod is not engaged with the washer but has catches adapted
for the piston to engage the washer when both of them interact with
each other through their end faces. At the end of the injection
when the piston and the washer get in contact with each other through
their end faces, the piston becomes engaged rigidly by means of
the catches, with the washer, wherein the needle is fixed, with
the result that any attempt to repeatedly draw a fresh portion of
injection substance in the syringe, the washer together with the
needle is entrained by the piston into the housing of the syringe.
As soon as the needle gets inside the housing it is offset with
respect to the axis of the housing so that any attempt to perform
an injection results in breakage of the injection needle.
However, the aforementioned construction leaves room for reusing
a syringe, since the piston gets engaged with the washer only when
in its fully extended position in the front portion of the housing.
This causes the needle to be retracted into the housing, whereby
the syringe gets unfit for further use. Should the piston be not
brought to the fully extended position during injection, the syringe
can be applied for making an unlimited number of injections involving
almost complete utilization of the holding capacity of its housing.
DISCLOSURE OF THE INVENTION
It is an object of the invention to provide such a construction
of a disposable syringe for injections that would prevent any possibility
of reusing such a syringe.
The essence of the invention resides in the fact that in a disposable
syringe for injections, comprising a cylindrical housing, which
accommodates a piston with a rod, and a needle fixing device, according
to the invention, the piston and the rod are mechanically disengaged
from each other, the rod diameter is smaller than the piston diameter
and the rod end facing the piston has a flange has a flange, a washer
being set on the rod coaxially therewith, the diameter of the hole
in said washer being smaller than the flange diameter, whereas the
outside diameter of the washer exceeds the inside diameter of the
housing to such an extent that the force of friction between the
inner surface of the washer and the inner surface of the housing
surpasses the force exerted on the washer as a result of motion
performed by the housing, including an accelerated motion thereof.
The disposable syringe for injection, according to the present
invention, makes impossible repeated injections, is simple to manufacture,
and reliable in operation. Production costs of such a disposable
syringe, according to the invention, do not practically exceed those
of the heretofore-known disposable syringes.
SUMMARY OF THE DRAWINGS
In what follows the invention will now be disclosed in a detailed
description of a specific exemplary embodiment thereof given by
way of illustration with reference to the accompanying drawings,
wherein:
FIGS. 1 2 3 4 present a perspective disassembled view of a disposable
syringe for injections, according to the invention;
FIG. 5 is a longitudinal sectional view of a disposable syringe
for injections, according to the invention, when in an assembled
state in the initial position before drawing-in an injection substance;
FIG. 6 is a view of the disposable syringe of FIG. 5 at the instant
when an injection substance is drawn in;
FIG. 7 is a view of the disposable syringe of FIG. 5 as shown after
injection; and
FIG. 8 is a view of the disposable syringe of FIG. 5 while an attempt
is made to repeatedly draw in an injection substance.
PREFERRED EMBODIMENT OF THE INVENTION
The disposable syringe for injections comprises a cylindrical housing
1 (FIGS 1 5) one of whose ends carries a cover 2 held to the housing
1 through an inseparable joint. The cover 2 has a central hole 3.
The opposite end of the housing 1 has a needle fixing device made
as a cannula 4. The housing 1 accommodates a piston 5 (FIGS. 2
5 to 8), which rightly closes the cross-sectional area of the cylindrical
housing 1.
A rod 6 (FIGS. 3 5 to 8) is accommodated in the housing 1 in tandem
with the piston 5. The rod 6 is mechanically disengaged from the
piston 5 and has the diameter smaller than the diameter of the piston
5 and then the diameter of the hole 3 so as to provide free motion
of the rod 6 inside the housing 1 through the hole 3 in the cover
2. A flange 7 is provided at the end of the rod 6 which faces the
piston 5 and a washer 8 (FIGS. 4 to 8) is fitted on the rod 6 coaxially
therewith.
The diameter of the hole in the washer 8 exceeds the diameter of
the rod 6 but is smaller than the diameter of the flange 7. The
outside diameter of the washer 8 surpasses the inside diameter of
the housing 1 to such an extent that the force of friction between
the outer side surface of the washer 8 and the inner surface of
the housing 1 exceeds the force applied to the washer 8 when the
housing 1 moves, including accelerated motions of the latter.
The disposable syringe for injections, according to the invention,
is applied as follows.
When in the initial position the piston 5 is situated in the front
end portion of the housing 1 of the syringe that carries the cannula
4 (FIG. 5). The rod 6 adjoins the piston 5 through the surface of
the flange 7 while the washer 8 rests against the flange 7. To
draw in an injection substance the rod 6 is extended from the housing
1 of the syringe through the hole 3. As a result, the flange 7 of
the rod 6 gets tightly pressed against the washer 8 thus hermetically
sealing the space confined within the rod 6 with the washer 8 on
the one side, and the piston 5 on the other side, which in turn
provides for travel of the piston 5 after the rod 6 and the washer
8 throughout the pathway of the rod 6 when drawing in an injection
substance (FIG. 6). To perform injection the rod 6 is to be moved
in a reverse direction, i.e., to be retracted into the housing 1
of the syringe, thereby causing the piston 5 (FIG. 7) to move towards
the front end of the housing 1. In this case the washer 8 remains
in the rear end portion of the housing 1 of the syringe, i.e., nearby
the cover 2 which is ensured by virtue of the force of friction
between the outer side surface of the washer 8 and the inner surface
of the syringe housing 1. The outside diameter of the washer 8 is
so selected that the force of friction between the outer side surface
of the washer 8 and the inner surface of the syringe housing 1 be
substantially in excess of the force exerted upon the washer 8 when
the syringe housing performs axial accelerated motions. This in
turn rules out a possibility of returning the washer 8 to the initial
position when the piston 5 travels towards the front end of the
housing 1. A mechanical return of the washer 8 to the initial position
is not practicable either, since the cover 2 is joined to the housing
1 through a permanent joint.
A repeated attempt to draw in an injection substance in the syringe
will be futile, since the rod 6 alone, devoid of the washer 8 is
incapable of establishing hermetic sealing and rarefaction, which
are indispensable for the piston 5 (FIG. 8) to travel.
Thus, only a single use of the syringe is possible, whereupon it
is to be discarded and is subject to reclamation.
Widespread application of the disposable syringe, according to
the invention, will help practically rule out patient's infection,
during injections, with the virus of AIDS, that of infectious hepatitis,
and of some other diseases communicable by parenteral administration
of medicinal agents.
INDUSTRIAL APPLICABILITY
The invention is applicable is any medical institution and for
individual use for subcutaneous, intramuscular and intravascular
injections. |