U.S. patent application number 09/998495 was filed with the patent office on 2003-06-05 for disposable syringe and cartridge with pneumatic chamber.
Invention is credited to Ruben, Philip H..
Application Number | 20030105433 09/998495 |
Document ID | / |
Family ID | 25545285 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030105433 |
Kind Code |
A1 |
Ruben, Philip H. |
June 5, 2003 |
Disposable syringe and cartridge with pneumatic chamber
Abstract
A syringe or cartridge having a hollow barrel with an open end
and a second end suitable for attaching a needle assembly. A master
plunger assembly that includes a master plunger and a plunger
member is mounted in the barrel for longitudinal movement therein.
A slave plunger is mounted in the barrel for longitudinal movement
therein, and is located between the master plunger assembly and the
second barrel end so as to define two chambers. The first chamber a
liquid chamber and is between the slave plunger and the second
barrel end, and the second chamber is a pneumatic chamber and is
between the slave plunger and the master plunger assembly. The
liquid-containing chamber is suitable for containing a liquid to be
dispensed from the syringe, and the pneumatic chamber contains a
gas such as air. When the liquid-containing chamber contains a
liquid to be dispensed, a user applying selective pressure to the
plunger member will cause the master plunger assembly to slide
towards the slave plunger and compress the gas against the slave
plunger. The slave plunger will as a result of this pressure slide
towards the second barrel end as the gas decompresses and apply
pressure against the liquid as a result thereof. The liquid will
then be dispensed out of the syringe or cartridge via a needle
attached to the barrel end.
Inventors: |
Ruben, Philip H.; (Beverly
Hills, CA) |
Correspondence
Address: |
GREENBERG TRAURIG, LLP
21st Floor
885 Third Avenue
New York
NY
10022
US
|
Family ID: |
25545285 |
Appl. No.: |
09/998495 |
Filed: |
November 30, 2001 |
Current U.S.
Class: |
604/191 |
Current CPC
Class: |
A61M 5/484 20130101;
B01L 2400/0478 20130101; B01L 2400/0481 20130101; A61M 5/31513
20130101; B01L 3/0217 20130101; B01L 3/021 20130101 |
Class at
Publication: |
604/191 |
International
Class: |
A61M 005/00 |
Claims
What is claimed is:
1. A syringe comprising: a) a hollow barrel comprising a first
barrel end and a second barrel end, said first barrel end being
open and said second barrel end comprising means for allowing
attachment of a needle assembly; b) a master plunger assembly
mounted in said barrel for longitudinal movement therein, said
master plunger assembly comprising a master plunger and a plunger
member extending through said first barrel end for allowing a user
to apply pressure thereto; c) a slave plunger mounted in said
barrel for longitudinal movement therein, said slave plunger
located between said master plunger assembly and said second barrel
end so as to define a liquid chamber between said slave plunger and
said second barrel end, and to define a pneumatic chamber
containing a gas between said slave plunger and said master plunger
assembly; whereby, when said liquid chamber contains a liquid to be
dispensed from said syringe, a user applying selective pressure to
said plunger member will cause said master plunger assembly to
slide towards said slave plunger and compress said gas against said
slave plunger, said slave plunger will as a result of said pressure
slide towards said second barrel end as said gas decompresses and
apply pressure against said liquid as a result thereof, and said
liquid will be dispensed out of the syringe via the means for
allowing attachment of a needle assembly.
2. The syringe of claim 1 in which the gas substantially comprises
air.
3. The syringe of claim 1 in which the means for allowing
attachment of a needle assembly comprises an opening in said second
barrel end for coupling with a needle assembly.
4. The syringe of claim 1 in which the slave plunger and the master
plunger each are comprised of a rubber disc having at least one
ridge for making substantial contact with the barrel, said ridge
being suitable for sliding engagement with said barrel when
pressure is applied thereto.
5. The syringe of claim 1 wherein said plunger member comprises a
thumb engagement means at an end opposite the master plunger, said
thumb engagement means allowing a user to pull said plunger member
away from said syringe and cause a negative pressure on said master
plunger.
6. The syringe of claim 1 further comprising a flexible tether
connected between the master plunger and the slave plunger.
7. A cartridge comprising: a) a hollow barrel comprising a first
barrel end and a second barrel end, said first barrel end being
open and said second barrel end comprising means for allowing
penetration of a needle assembly; b) a master plunger mounted in
said barrel near said first barrel end for longitudinal movement
therein; c) a slave plunger mounted in said barrel for longitudinal
movement therein, said slave plunger located between said master
plunger and said second barrel end so as to define a liquid chamber
between said slave plunger and said second barrel end and a
pneumatic chamber between said slave plunger and said master
plunger; wherein said liquid chamber is filled with a liquid to be
dispensed from the cartridge via said second barrel end and said
pneumatic chamber is filled with a gas.
8. The cartridge of claim 7 in which the gas substantially
comprises air.
9. The cartridge of claim 7 in which the means for allowing
penetration of a needle assembly comprises a membrane disposed
across an opening in the second barrel end.
10. The cartridge of claim 7 in which the slave plunger and the
master plunger each are comprised of a rubber disc having at least
one ridge for making substantial contact with the barrel, said
ridge being suitable for sliding engagement with said barrel when
pressure is applied thereto.
11. The cartridge of claim 8 further comprising an aperture in said
barrel, said aperture disposed along said barrel so as to allow air
to flow to or from said pneumatic chamber.
12. The syringe of claim 7 further comprising a flexible tether
connected between the master plunger and the slave plunger.
13. A packaged cartridge combination comprising: i) a cartridge
comprising a) a hollow barrel comprising a first barrel end and a
second barrel end, said first barrel end being open and said second
barrel end comprising means for allowing penetration of a needle
assembly; b) a master plunger mounted in said barrel near said
first barrel end for longitudinal movement therein; c) a slave
plunger mounted in said barrel for longitudinal movement therein,
said slave plunger located between said master plunger and said
second barrel end so as to define a liquid chamber between said
slave plunger and said second barrel end and a pneumatic chamber
between said slave plunger and said master plunger; d) an aperture
in said barrel, said aperture disposed along said barrel so as to
allow air to flow to or from said pneumatic chamber; wherein said
liquid chamber is filled with a liquid to be dispensed from the
cartridge via said second barrel end; and ii) a cartridge packaging
hermetically sealed around said cartridge in which said cartridge
is vacuum sealed within said packaging; whereby as a result of said
vacuum sealing, the volume of space interior to said cartridge
packaging and said pneumatic chamber are substantially void of
air.
14. The packaged cartridge of claim 13 in which the means for
allowing penetration of a needle assembly comprises a membrane
disposed across an opening in the second barrel end.
15. The packaged cartridge of claim 13 in which the slave plunger
and the master plunger each are comprised of a rubber disc having
at least one ridge for making substantial contact with the barrel,
said ridge being suitable for sliding engagement with said barrel
when pressure is applied thereto.
16. A pipette comprising: a) a hollow barrel having a first
diameter and comprising a first barrel end and a second barrel end,
said first barrel end being open and said second barrel end
tapering from the first diameter to a second diameter, said second
diameter being substantially smaller than said first diameter, said
second barrel end being open at said second diameter; b) a master
plunger mounted in said barrel for longitudinal movement therein;
c) a slave plunger mounted in said barrel for longitudinal movement
therein, said slave plunger located between said master plunger
assembly and said second barrel end so as to define a liquid
chamber between said slave plunger and said second barrel end, and
to define a pneumatic chamber containing a gas between said slave
plunger and said master plunger assembly; d) a squeeze bulb mounted
on the first barrel end; and e) a flexible tether connected between
the master plunger and the slave plunger; whereby, when said liquid
chamber contains a liquid to be dispensed from said pipette, a user
applying selective pressure to said squeeze bulb will cause said
master plunger assembly to slide towards said slave plunger and
compress said gas against said slave plunger, said slave plunger
will as a result of said pressure slide towards said second barrel
end as said gas decompresses and apply pressure against said liquid
as a result thereof, and said liquid will be dispensed out of the
pipette via the second barrel end.
17. The pipette of claim 16 in which the slave plunger and the
master plunger each are comprised of a rubber disc having at least
one ridge for making substantial contact with the barrel, said
ridge being suitable for sliding engagement with said barrel when
pressure is applied thereto.
18. The pipette of claim 16 wherein the squeeze bulb further
comprises a release valve.
19. The pipette of claim 16 wherein the master plunger comprises a
threaded aperture suitable for receiving a mating threaded rod,
wherein when a mating threaded rod is engaged with said threaded
aperture, said mating threaded rod may be utilized to move the
master plunger along the pipette.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a disposable syringe or cartridge
for use with a syringe utilizing a pneumatic chamber for precisely
controlling the delivery of a liquid such as an anesthetic solution
to a patient.
BACKGROUND OF THE INVENTION
[0002] The standard delivery for local anesthesia use in dentistry
and medicine is with the anesthetic cartridges (carpules). In the
medical, dental and veterinary fields, cartridge ampoules of
injectable fluid are now commonly used in hypodermic syringes. Such
ampoules usually comprise a cylindrical container of glass or clear
plastic material, the forward end of which is sealed by a rubber
membrane and the rear end of which is sealed by a rubber piston
which is slideable within the container. They are manufactured
under rigid standards under which the anesthetic reaches the
dentist as sterile ampoules. In use, such cartridge ampoules are
positioned within the barrel of a syringe so that the membrane is
pierced by the rear end of a needle and the rubber piston is
advanced into the container by manual thumb force against a
thumb-operated plunger to inject the fluid through the needle into
the patient.
[0003] In addition to injecting the liquid into the patient, it is
important in many instances for the syringe to be used for
aspiration. Aspiration occurs when the doctor retracts the plunger
gently after the needle is inserted in the tissue to ensure that it
is not in a blood vessel. That is, if blood is aspired or drawn
back through the needle, the doctor will see this and remove the
needle from that location and attempt an injection in a different
location.
[0004] It is greatly desired when administering an anesthetic via a
syringe to be able to use precise control of the syringe so as not
to inject the anesthetic too quickly. Rapid injection may result in
tissue damage, or at least great discomfort to the patient. Thus, a
slow and precise control over the injection is required, wherein
excess pressure is avoided. It is generally very difficult to
control the flow of anesthetic, however, with a great degree of
accuracy and finesse. This is because the plunger pushes directly
on the rubber stopper within the cartridge. This creates a direct
hydraulic pressure on the liquid to be dispensed, which forces the
liquid out of the needle with excessive force. As a pocket of
anesthetic solution builds up within the tissue, it has nowhere to
go until it is absorbed in the surrounding tissues.
[0005] Disposable syringes are plastic syringes that have the
anesthetic liquid disposed directly in a dispensing chamber rather
than utilizing a separate cartridge. The principles of liquid
delivery and the need for precise control are the same as with the
cartridges described above.
[0006] It is therefore an object of the present invention to
provide an anesthetic cartridge or disposable syringe that
facilitates smoother and gentler delivery of its contents.
[0007] It is desired to be able to implement such precise control
of the delivery of anesthetics without requiring an excessive
number of parts, such as springs or valves, which would complicate
manufacturing.
[0008] It is further desired to provide a traditional anesthetic
cartridge or disposable syringe with the innovative modification
without compromising quality, safety or simplicity and would be
inexpensive to manufacture.
[0009] It is also desired to provide such a device that selectively
permits the plunger to engage the rubber stopper within the
cartridge to move longitudinally in either direction to inject or
aspirate in a normal fashion.
[0010] It is also an object of the present invention to provide a
means for the back-pressure that is created at the injection site
to be controlled, to cause as little pain or discomfort as
possible.
SUMMARY OF THE INVENTION
[0011] In a first aspect of the invention, a disposable syringe is
provided for dispensing an anesthetic solution and the like. The
syringe has a hollow barrel with a first barrel end that is open
and a second barrel end that has means for allowing attachment of a
needle assembly. The syringe also has a master plunger assembly
mounted in the barrel for longitudinal movement therein. The master
plunger assembly includes a master plunger and a plunger member
extending through the first barrel end for allowing a user to apply
pressure.
[0012] There is also a slave plunger mounted in the barrel for
longitudinal movement therein. The slave plunger is located between
the master plunger assembly and the second barrel end so as to
define two chambers. The first chamber is a liquid chamber and is
defined between the slave plunger and the second barrel end, and
the second chamber is a pneumatic chamber and is defined between
the slave plunger and the master plunger assembly. The first
chamber is suitable for containing a liquid to be dispensed from
the syringe, and the second chamber contains a gas such as air.
[0013] As a result of this syringe assembly, when the
liquid-containing chamber contains a liquid to be dispensed from
the syringe, a user applying selective pressure to the plunger
member will cause the master plunger assembly to slide towards the
slave plunger and compress the gas against the slave plunger. The
slave plunger will as a result of this pressure slide towards the
second barrel end as the gas decompresses and apply pressure
against the liquid as a result thereof. The liquid will then be
dispensed out of the syringe via a needle attached to the barrel
end.
[0014] In a second aspect of the present invention, a cartridge is
provided that operates on the same principle as the syringe. The
cartridge includes a hollow barrel with a first barrel end that is
open and a second barrel end that has means for allowing
penetration of a needle assembly. The cartridge also has a master
plunger mounted in the barrel for longitudinal movement therein.
There is also a slave plunger mounted in the barrel for
longitudinal movement therein. The slave plunger is located between
the master plunger and the second barrel end so as to define two
chambers. The first chamber is a liquid chamber between the slave
plunger and the second barrel end, and the second chamber is a
pneumatic chamber and is defined between the slave plunger and the
master plunger. The liquid chamber is filled with a liquid to be
dispensed from the cartridge via the second barrel end, and the
pneumatic chamber is filled with a gas such as air.
[0015] The means for allowing penetration of a needle assembly may
be a membrane disposed across an opening in the second barrel end.
When this cartridge assembly is inserted into a hypodermic syringe,
a user applying selective pressure to the plunger will cause it to
slide towards the slave plunger and compress the gas against the
slave plunger. The slave plunger will as a result of this pressure
slide towards the second barrel end as the gas decompresses and
apply pressure against the liquid as a result thereof. The liquid
will then be dispensed out of the syringe via a needle attached to
the barrel end.
[0016] The cartridge assembly may also be packaged in a
hermetically sealed vacuum package for shipping. In this
embodiment, an aperture is provided in the barrel so as to allow
air flow to or from the pneumatic chamber. This allows the
pneumatic chamber to be voided of air during the vacuum sealing
packaging process so that the master plunger will not be caused to
slide out of the barrel as a result of air pressure from the
pneumatic chamber.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 illustrates a standard aspirating anesthetic syringe
of the prior art;
[0018] FIG. 2 illustrates the syringe of FIG. 1 loaded with a
cartridge of the present invention;
[0019] FIG. 3 illustrates a standard harpoon type aspirating
plunger tip of the prior art;
[0020] FIG. 4 illustrates a standard anesthetic cartridge of the
prior art;
[0021] FIG. 5 shows a filled anesthetic cartridge of the present
invention;
[0022] FIG. 6 shows the cartridge of FIG. 5 after it has been
used;
[0023] FIGS. 7, 8, 9 and 10 shows the use of another embodiment of
the cartridge of the present invention in which an air escape hole
is provided for vacuum packaging;
[0024] FIG. 11 illustrates a disposable syringe of the present
invention prior to use;
[0025] FIG. 12 shows the syringe of FIG. 11 after it has been used;
and
[0026] FIG. 13 illustrates an alternative embodiment pipette in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] With reference to FIG. 1, a prior art re-usable syringe 2 is
provided. The syringe 2 in FIG. 1 is a breech-loading metal
cartridge syringe, in which a hermetically sealed glass cartridge
containing the anesthetic solution fits into the breech 4 of the
syringe. An example of a prior art cartridge 30 is shown in FIG. 4.
A disposable needle 8 is screwed into the front of the syringe. The
length of the needle 8, which extends into the breech, penetrates a
rubber membrane or metal cap and extends into the anesthetic
solution 34 in the glass cartridge 30. A plunger rod 11 is then
forced into the breech of the syringe against the plunger 32 at the
plunger end of the cartridge. Gentle pressure with the user's thumb
on the plunger rod then forces the rubber plug at the plunger end
of the cartridge to be passed into the glass cartridge, forcing the
liquid contents 34 to be expelled through the needle 8, which has
previously penetrated into the cartridge from the opposite end.
[0028] The preferred embodiment of the inventive cartridge 40 is
shown in FIG. 5. The cartridge 40 is the same shape and size as the
prior art cartridge 30, and is essentially a hollow barrel with a
first barrel end 42 that is open and a second barrel end 44 that
has a rubber membrane or the like for attaching the needle
assembly. There is also a master plunger 20 mounted in the barrel
in the same end position as the plunger 32 of the prior art
cartridge 30. A slave plunger 16 is disposed partway between the
master plunger 20 and the second barrel end 44. The exact location
of the slave plunger is not critical, but must allow for a
sufficient air cushion with respect to the master plunger 20 as
explained below.
[0029] The juxtaposition of the slave plunger 16 with respect to
the master plunger 20 and the second barrel end 44 forms two
chambers. The first chamber is a liquid chamber 34, similar to that
in the prior art cartridge 30 since it is filled with the liquid to
be dispensed from the cartridge in conjunction with the syringe.
The second chamber formed is a pneumatic chamber 18, which is
between the slave plunger 16 and the master plunger 20. This
pneumatic chamber 18 is filled with a compressible gas such as air,
forming an "air cushion" that allows for precise control of liquid
delivery in this invention.
[0030] FIG. 2 illustrates the cartridge 40 loaded into the syringe
2. In use, the operator applies pressure to the plunger rod 11,
which then causes the master plunger 20 to slide towards the slave
plunger 16. Since the gas in the pneumatic chamber 18 is more
compressible than the liquid being dispensed from the liquid
chamber 34, the slave plunger 16 will not immediately move to cause
the liquid to exit the needle 8. That is, a build-up of pressure in
the pneumatic chamber 18 is required before there will be enough
pressure to cause the slave plunger to begin to slide and push the
liquid out of the needle. As a result, there is not direct pressure
transferred from the user's thumb to the liquid in the liquid
chamber; the compressing of the air in the pneumatic chamber acts
as an "air cushion." This air cushion will slowly decompress once
the build up of pressure is enough to overcome the resistance
caused by the friction between the slave plunger and the inside
wall of the barrel and the resistance caused by the entry of the
liquid into the patient's body through the needle. This allows for
a more controlled injection of the liquid, since slight variations
in the pressure asserted by the user of the syringe will be
absorbed by the compressing/decompressing forces acting in concert
with the air cushion. Without the air cushion provided by this
invention, any such variations will be immediately transferred by
hydraulic pressure to the liquid being dispensed, resulting in an
uneven dispensing procedure and (likely) discomfort to the
patient.
[0031] As the plungers 16 and 20 are caused to slide along the
cartridge, the liquid is injected out of the cartridge and the
spent cartridge appears as in FIG. 6.
[0032] Although the introduction of the pneumatic chamber in this
invention causes a reduction of the volume of solution that is
available for injection (by about 20%, depending on where the slave
plunger is located), it is found that less anesthetic solution is
actually required to obtain the same results with this invention as
with the prior art.
[0033] It is often desired to be able to vacuum-pack the cartridges
in metal tins or other like packaging prior to shipment. However,
it has been found that the vacuum process may cause the master
plunger to slide out of the barrel due to the air pressure in the
pneumatic chamber with respect to the vacuum space outside the
cartridge. Thus, in another embodiment of this invention, an
aperture is provided in the barrel wall at some point along the
pneumatic chamber so that air can flow in or out of the pneumatic
chamber. In FIG. 7, aperture 50 is provided as shown. Preferably,
the aperture 50 is located about 4-6 mm from the barrel end 42 so
that it is just next to the master plunger 20. When the cartridge
is vacuum packed, the vacuum process will draw the air out of the
pneumatic chamber via the aperture. This will result in a desired
equilibrium between the pneumatic chamber and the outside of the
cartridge (within the vacuum packaging). As a result, there will be
no pressure on the master plunger 20 and it will remain in the
proper location in the barrel. When the user unpacks the cartridge,
air will be caused to re-enter the pneumatic chamber, and there
will again be a pressure equilibrium between the pneumatic chamber
and the outside of the cartridge.
[0034] When the user starts to apply pressure to the master plunger
in order to inject the patient, the master plunger will start to
slide towards the slave plunger as shown in FIG. 8. At first, the
compression will cause some of the air in the pneumatic chamber to
escape out of the barrel and into the outer surroundings, but as
long as the user applies enough pressure, the master plunger will
compress the air in the pneumatic chamber enough so that the slave
plunger will start to cause the liquid to be dispensed. The master
plunger will then start to slide and will quickly pass the
aperture, thus sealing the pneumatic chamber and allowing
controlled dispersion of the liquid in accordance with the
invention.
[0035] In another major embodiment of the invention, a disposable
syringe is provided with a pneumatic chamber that operates in
accordance with the principles discussed above. FIG. 11 illustrates
a disposable syringe 100, which is the same shape and size of a
conventional prior art disposable syringe and therefore may be
packaged and used in the same manner. The syringe 100 is a hollow
barrel 102 with a first barrel end 104 that is open and a second
barrel end 106 that has means for allowing attachment of a needle
assembly. The needle assembly attachment means 108 is well known in
the art and need not be discussed any further here.
[0036] There is also a master plunger assembly 112 mounted in the
barrel for longitudinal movement therein as shown in the Figure.
The master plunger assembly 112 includes a master plunger 114 and a
plunger member 116 that extends through the first barrel end 104
for allowing a user to apply pressure, typically with his or her
thumb. A slave plunger 118 is disposed partway between the master
plunger 114 and the second barrel end 106. As with the cartridge
described above, the exact location of the slave plunger is not
critical, but must allow for a sufficient air cushion with respect
to the master plunger 114.
[0037] The juxtaposition of the slave plunger 118 with respect to
the master plunger 114 and the second barrel end 106 forms two
chambers. The first chamber is a liquid chamber 120 which is filled
with liquid 124 to be dispensed from the cartridge in conjunction
with the syringe. The second chamber formed is a pneumatic chamber
122, which is between the slave plunger 118 and the master plunger
114. This pneumatic chamber 122 is filled with a compressible gas
such as air, forming an "air cushion" that allows for precise
control of liquid delivery in this invention.
[0038] In use, the operator applies pressure to the plunger member
116, which then causes the master plunger 114 to slide towards the
slave plunger 118. Since the gas in the pneumatic chamber 122 is
more compressible than the liquid 124 being dispensed from the
liquid chamber 120, the slave plunger will not immediately move to
cause the liquid to exit the needle 110. That is, a build-up of
pressure in the pneumatic chamber is required before there will be
enough pressure to cause the slave plunger to begin to slide and
push the liquid out of the needle. As a result, there is not direct
pressure transferred from the user's thumb to the liquid in the
liquid chamber; the compressing of the air in the pneumatic chamber
acts as an "air cushion." This air cushion will slowly decompress
once the build up of pressure is enough to overcome the resistance
caused by the friction between the slave plunger and the inside
wall of the barrel and the resistance caused by the entry of the
liquid into the patient's body through the needle. This allows for
a more controlled injection of the liquid, since slight variations
in the pressure asserted by the user of the syringe will be
absorbed by the compressing/decompressing forces acting in concert
with the air cushion.
[0039] As the plungers are caused to slide along the syringe, the
liquid is injected out of the needle and the spent syringe appears
as in FIG. 12.
[0040] Also shown in FIG. 12 is an additional feature that may be
utilized with the disposable syringe of the present invention. A
tether 130 is fixed between the master plunger 114 and the slave
plunger 118. The tether 130 allows a user to withdraw the master
plunger 114 from the syringe and extract the slave plunger as well.
The tether 130 also ensures that the slave plunger will be
withdrawn along the syringe during an aspiration.
[0041] In yet another embodiment of the invention, a pipette is
shown in FIG. 13 that utilizes the air cushion techniques described
above. The pipette 200 has a hollow barrel 202 having a first
diameter D1. There is a first barrel end 204 and a second barrel
end 206, with the first barrel end being open and the second barrel
end tapering from the first diameter D1 to a second diameter D2
that is substantially smaller than D1. The second barrel end 206 is
also open at the second diameter D2.
[0042] There is a master plunger 208 mounted in the barrel as shown
in the Figure as well as a slave plunger 210, which is mounted in
the barrel between the master plunger and the second barrel end. A
liquid chamber 214 is thus defined between the slave plunger and
the second barrel end, and a pneumatic chamber 218 is defined
between the slave plunger and the master plunger. In this
embodiment, the liquid chamber may be only partially filled with
liquid, and the liquid may be drawn in through the end 206 in an
aspirating manner.
[0043] A resilient squeeze bulb 220 having a release valve 222 is
mounted on the first barrel end as shown in the Figure.
Additionally, a flexible tether 218 is connected between the master
plunger and the slave plunger as shown. The tether allows a user to
withdraw the master plunger from the pipette and extract the slave
plunger as well. The tether also ensures that the slave plunger
will be withdrawn along the pipette during an aspiration.
[0044] Optionally, the master plunger may be provided with a
threaded aperture 230 suitable for receiving a setting tool, which
is a mated threaded rod 232 as shown in the Figure. When the
setting tool is engaged with the threaded aperture, it may be
utilized to move the master plunger along the pipette.
[0045] Details of the master plunger and the slave plunger are also
shown in FIG. 13. As seen in the Figure, each of the plungers
comprises three flexible rings that are located to enclose a pair
of internal grooves. Although this is the preferred embodiment of
the plunger since it provides a good deal of stability within the
barrel, other embodiments (such as the use of a single ring) may
also be utilized with this invention.
* * * * *