US 3459339 A
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A 1969 L. G. DAMGAARD 3,459,339
. PIPEITE Filed March 24 1967 g 5 t .5 1
INVENT OR wan, an. M waw ATTORNEYS 5, 1969 I L. e. DAMGAARD 3,459,339
2 Sheets-Sheet 2 Filed March 24 1967 M E I INVNI'OR BY om-4M. m
ATTORNEYS United States Patent M Int. Cl: G01f 11/06 US. Cl. 222-309 7 Claims ABSTRACT OF THE DISCLOSURE A dispensing pipette having a glass barrel and a glass plunger movable forward by finger pressure and rearward by a retraction spring, the rearward movement being 11mited by the engagement of the plunger with a non-circular stop disc clampable in an adjustable position between two nuts on a screw-threaded column extending rearward from the barrel in a off-set position.
Background of the invention This invention relates to a pipette of the kind, in which a glass plunger in a glass barrel is retracted by means of a spring to fill the barrel and is advanced by means of a finger of the user to empty the barrel, the forward movement of the plunger being limited by the plunger engaglng the bottom of the barrel, adjustable stop means being provided for limiting the rearward movement of the plunger.
Pipettes of this kind are particularly used for the d1spensing of measured quantities of chemicals in the chemical laboratory, and to obtain satisfactory operation such pipettes will have to fulfil a number of requirements which have not been adequately met by the constructions so far known. For reasons of corrosion, the barrel and the plunger of such pipettes are made from glass. The stop means comprise cooperating metal parts clamped or cemented to the glass parts. The spring may be a compression spring surrounding the plunger, or a tension spring located in the extension of the axis of the plunger, or two tension or hair pin springs arranged symmetrically with respect to the axis may be used.
A further requirement is that the stop means should be capable of fine adjustment and that it should be pos= sible to remove the plunger from the barrel for cleaning purposes without loosing or disturbing the adjustment once made.
A still further requirement is that all parts should be resistant to most chemicals and also resistant to boiling, dry-sterilizing and autoclaving, and besides the apparatus should be mechanically strong so that the parts are not deformed or displaced during use.
The volume of liquid dispensed by means of the pipette should be independent of the finger pressure exerted on the plunger. The pipette should have a convenient and compact over-all configuration.
Moreover it is important that the glass parts may be replaced in case of breakage without the necessity of adaptation or accurate alignment of glass parts and metal parts relative to one another.
It is a drawback of previously known devices of this type that in order to permit removal of the plunger from the barrel without disturbing the adjustment of the stop means once made, it has been necessary to secure metal parts to the extending end of the plunger either by cementing or by fastening means. Cementing is disadvan tageous because cemented parts are not readily exchangeable, and besides knows cements are either brittle or poorly resistant to solvents or heat. Attachment by fastening 3,459,339 Patented Aug. 5, 1969 means is not satisfactory either, because any fastening operation involves a danger or breakage of glass parts when performed by unskilled persons for the purpose of replacement. Besides metal parts secured in this way are liable to be displaced during use because it is not possible to use a high fastening pressure, and if so displaced they will no longer cooperate correctly with the other parts of the device.
It is the object of the invention to provide a pipette which fulfils all the abovementioned requirements and does not suffer from the drawbacks referred to.
Summary of the invention According to the invention, in a pipette of the kind re ferred to, the stop means comprises a non-circular disc which is adjustably clamped between two nuts on a screw threaded column attached to the cylinder and extending backwards from the latter parallel to the cylinder axis, the shape of the disc being such that in one angular position of the disc it extends into the path of movement of the cylinder head while in another angular position it is lo cated entirely outside the said path of movement.
By this arrangement the desired possibility of removing the plunger from the barrel without disturbing the adjustment of the stop means has been obtained without the necessity of securing any metal parts to the plunger. In fact, the only metal part which comes into contact with the plunger at all, is the spring which is a loose and easily replaceable part.
Brief description of the drawings FIG. 1 is a side view of the rear portion of a pipette according to one embodiment of the invention,
FIG. 2 a top view of same in its normal working position,
FIG. 3 a similar view where the device is ready for removal or insertion of the plunger,
FIG. 4 the rear portion of a pipette according to an other embodiment of the invention in one phase of a diluting operation.
FIG. 5 a top view of same,
FIG. 6 the rear portion of the pipette of FIG. 4 in another phase of the diluting operation, in side view, and
FIG. 7 a top view corresponding to FIG. 6.
Description of the preferred embodiments In the drawings, 1 is a glass barrel, which is constructed at its rear end with a collar 2, while 3 is a glass plunger provided with a plunger head 4 at its rear end. The rear face of the collar 2 is plane-ground and a disc 5 having a hole for the passage of the plunger 3 is clamped against the plane-ground surface by means of a corresponding disc 6 placed below the collar 2, e.g. with the aid of screws extending through the disc 6 and screwed into threaded holes of the disc 5 The disc 5 carries a threaded column 7, on which an upper adjustment nut 8 and a lower adjustment nut 9 with locking nut 10 are arranged. A stop disc 11 is clamped between the nuts 8 and 9. The stop disc 11 is of circular shape except for a flattened edge 12. A compression spring 13 is arranged between the disc 5 and the plunger head 4.
When the stop disc 11 is in the position shown in FIGS. 1 and 2, it cooperates with the plunger head 4 to form a stop for the backward movement of the plunger under the influence of the spring 13. Preferably, the StOp disc 11 is made from an artificial resin such as tetra-fluorethylene so as to form a soft abutment for the plunger head.
During use of the pipette the plunger may rotate relative to the barrel. In order that such rotation should not result in inaccuracy of the volume of liquid dispensed, the rear face of the plunger head is preferably plane-ground perpendicularly to the axis of the plunger.
If the plunger is to be removed the nut 8 is loosened and the stop disc 11 is turned to the position shown in FIG. 3, where the flattened edge 12 faces the plunger head 4, thus allowing this to pass. When the plunger is again inserted into the barrel, the stop disc 11 is turned back to the position shown in FIG. 2, and the nut 8 is tightened. It will be realized that the adjustment of the pipette has not at all been disturbed by the fact that the plunger has been removed and reinstated.
It is not absolutely necessary to use a locking nut for the nut 9. Even without this it is possible, with sufficient care, to remove and reinsert the plunger without disturbing the adjustment of the pipette. If a locking nut is used, this may be used in cooperation with the upper adjustment nut 8 instead of the lower adjustment nut 9.
The illustrated form of the stop disc 11 is only an example. Any non-circular form may be used, which in one angular position extends into the path of movement of the plunger head 4 and in another angular position allows the plunger head 4 to pass.
In the embodiment illustrated in FIGS. 4-7, the adjustment nut 9 has a reduced neck portion 14 at its top on which an additional stop disc 15 is easily rotatably mounted The reduced neck portion 14 may, if desired, be replaced by a sleeve separate from the nut 9 and having a smaller diameter than the latter. The additional stop disc 15 is of substantially the same shape as the principal stop disc 11, but has been made a little larger so that it is easier to handle independently of the stop disc 11.
The additional stop disc 15 in the embodiment of FIGS. 4-6 is used for obtaining a dilution of a chemical in predetermined proportion. While the additional stop disc 15 is kept in the position shown in FIGS. 4 and 5 the pipette is first immersed into the dilution liquid to fill the pipette as far as the plunger goes before the plunger head 4 strikes the additional stop disc 15. The pipette is then immersed into the chemical to be diluted and the stop disc .15 is turned to the position shown in FIGS. 6 and 7 so that the plunger head 4 is now further retracted until striking the stop disc 11. As contrasted to the stop disc the stop disc 11 is not easily rotatably, but clamped between the nuts 8 and 9.
Removal and reinsertion of the plunger takes place in the same manner in the embodiment of FIGS. 4-7 as described with reference to the embodiment of FIGS. 1-3.
1. A pipette for dispensing measured quantities of liquids, comprising a glass barrel, a glass plunger slidable in said glass barrel, said plunger being constructed at its rear end with a plunger head engageable by a finger of the user to urge the plunger forwards, the forward stroke of the plunger being limited by the plunger engaging the bottom of the barrel, a collar integral with said barrel, a spring for retracting said plunger, a Screwthreaded column regidly attached to said collar and extending rearward from the latter parallel to the barrel axis the opposite end being unsupported, two adjustment nuts on said screw-threaded column, and a stop disc clampable between said two nuts, the shape of said stop disc being such that in one angular position of the disc it extends into the path of movement of the plunger head leaving the major portion of said plunger head free to be engaged by a finger while in another angular position it is located entirely outside the said path of movement.
2. A pipette as in claim 1, in which one of the two nuts is provided with a locking unit.
3. A pipette as in claim 1, in which the rear face of the plunger head is plane-ground.
4. A pipette as in claim 1, wherein the stop disc is made from an artificial resin.
5. A pipette as in claim 1, in which the frontmost adjustment nut is provided at its end facing the stop disc with a reduced neck portion, a second stop disc having substantially the same shape as the principal stop disc being easily rotatably mounted on said neck portion.
6. A pipette as in claim 1, in which the frontmost adjustment nut is supplemented at its end facing the stop disc with a separate sleeve having a smaller diameter than the nut, a second stop disc having substantially the same shape as the principal stop disc being easily rotatably mounted on said sleeve.
7. A pipette as in claim 1, in which the rear face of said collar is plane-ground.
References Cited UNITED STATES PATENTS 1,191,882 7/1916 Fairbanks 222-309 X 2,792,157 5/1957 Gilman 222309 3,119,524 1/1964 King et a1 222309 X 3,250,441 5/1966 Levowitz et a1. 222309 ROBERT B. REEVES, Primary Examiner FREDERICK R. HANDREN, Assistant Examiner US. Cl. X.R. 128-218