US3640434A

US3640434A - Variable capacity fluid-dispensing device

Info

Publication number: US3640434A
Application number: US37809A
Authority: US
Inventors: Clarence L Walker
Original assignee: Sherwood Medical Industries Inc
Current assignee: Sherwood Medical Co
Priority date: 1970-05-15
Filing date: 1970-05-15
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: CA963859A; BE767143A; DE2122014A1; GB1340113A

Abstract

A pipette or other device for measuring and dispensing liquids which includes an aligned series of decreasing diameter, stepped cylinder chambers, e.g., three, contained in a barrel with the three chambers serviced by a common stepped piston for emptying and filling a receiver or reservoir carried by the device in communication with the chambers. A chamber at one end of the array is maintained in unobstructed flow communication with the receiver or reservoir which may or may not be a removable tip or nozzle on the device. A vented passageway communicates with vent ports from each chamber. A valving member is provided in the passage for selectively venting one or more of the chambers or connecting them in flow communication with the receiver or reservoir. In a specific form, the passageway can be formed between the barrel and a sleeve or collar surrounding the barrel which is rotationally slidable on the barrel. The valving member can be in the form of an elliptical ring on the inner surface of the sleeve or collar in sealing sliding engagement with the barrel outer surface, the ports of two of the other chambers falling between the longitudinal extents of the elliptical ring; and the center of the elliptical ring being located between the two ports. Rotation of the sleeve to a position placing the ring between the port vents one port while placing the other in flow communication with the nozzle, and rotation of the sleeve 90* one way or the other vents both ports or places both in flow communication with the nozzle to increase or decrease the liquid handling capacity of the device depending on the direction of rotation.

Description

llnited Mates Patent Walker 3&4QA34 lFeb. d, i 972 VARIABLE CAPACKTY lFLlUlllD- DllSWlENSING DEVICE Clarence L. Walker, Webster Groves, Mo.

Sherwood Medical Industries Inc., St. Louis, Mo.

May 15, 1970 [72] Inventor:

[73] Assignee:

Filed:

Appl. No.:

11.8. CI ..222/ll44.5, 222/ I45 Int. Cl ..B67d 5/02 Field of Search ..222/309, 386, 387, 388, 336, 222/I37, 386.5, 206, i34, I35, I36, I45. 144.5; [28/218 P, 234, 235, DIG. 5

[56] References Cited UNITED STATES PATENTS 3,496,970 2/1970 Pontigny ..222/ 145 X 2,819,928 l/l958 Liedberg "222/134 X [57] ABSTRACT A pipette or other device for measuring and dispensing liquids which includes an aligned series of decreasing diameter, stepped cylinder chambers, e.g., three, contained in a barrel with the three chambers serviced by a common stepped piston for emptying and filling a receiver or reservoir carried by the device in communication with the chambers. A chamber at one end of the array is maintained in unobstructed flow communication with the receiver or reservoir which may or may not be a removable tip or nozzle on the device. A vented passageway communicates with vent ports from each chamber. A valving member is provided in the passage for selectively venting one or more of the chambers or connecting them in flow communication with the receiver or reservoir.

In a specific form, the passageway can be formed between the barrel and a sleeve or collar surrounding the barrel which is rotationally slidable on the barrel. The valving member can be in the form of an elliptical ring on the inner surface of the sleeve or collar in sealing sliding engagement with the barrel outer surface, the ports of two of the other chambers falling between the longitudinal extents of the elliptical ring; and the center of the elliptical ring being located between the two ports. Rotation of the sleeve to a position placing the ring between the port vents one port while placing the other in flow communication with the nozzle, and rotation of the sleeve 90 one way or the other vents both ports or places both in flow communication with the nozzle to increase or decrease the liquid handling capacity of the device depending on the direction of rotation.

19 Claims, 6 Drawing Figum mm g; 6? 3 INVENTOR ace Z. I 7 m-ronwzss M w W W Uwar 2 x w 9 x X z/Z @NEWED FEE 819?? VARIABLE CAPACITY FLUID-DISPENSING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to variable capacity liquid measuring and dispensing devices and more particularly to a new and improved variable capacity pipette.

2. Description of the Prior Art One type of prior variable capacity pipette utilizes an ad justable stroke, single piston to attain different capacities. However, when such a device is provided for measuring and dispensing three different volumes it can require a stroke change of up to 4 to l or to l and a hand operating device of such a stroke change can be quite uncomfortable to the operator. Variable stops are often employed in such devices but suffer from increased inaccuracy on use.

SUMMARY OF THE INVENTION The present invention provides a variable capacity liquid measuring and dispensing device which utilizes the same liquid delivery actuator, e.g., a common plunger, for each capacity handled. The device of the present invention has a common receiver or reservoir for receiving a plurality of different volumes loaded by operation of separate chambers with a separate port for each chamber which can be selectively communicated with the common receiver or reservoir for selective delivery of different volumes of liquid into the receiver or reservoir each time the actuator is operated.

While illustrative embodiments of the invention are shown in the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms, but it is to be understood that the present disclosure is used as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view of the device of this invention shown in use for drawing liquid from a container into the receiver or reservoir of the device;

FIGS. 2 and 3 are enlarged fragmentary longitudinal sections through the upper portion of the device of FIG. 1 showing the device with its plunger in retracted and depressed positions respectively;

FIGS. 4 and 5 are enlarged longitudinal sections through the lower portions of the device as seen in FIGS. 2 and 3 respectively; and

FIG. 6 is a fragmentary section through another device of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a pipette 10 as an embodiment of the present invention with a receiver or reservoir which may be either a fixed tip or nozzle, or as shown is a removable tip or nozzle 12 having its outlet end immersed in liquid 16 in a container 14, for drawing measured amounts of liquid into the tip or nozzle of the pipette.

As better seen in FIGS. 2 through 5, the pipette is of the type having a barrel 20 with a bore in which a reciprocal plunger 22 is slideably mounted. A knob 24 is provided at the upper end of the plunger for operating the plunger. The upper end of barrel 20 is closed by a retaining cap 26 through which the plunger 22 slidably projects. A return compression coil spring 28 surrounding the plunger 22 is supported by a spring support shoulder 32 within barrel 20 and extends upwardly and biases against a shoulder surface defined by an outwardly projecting flange on plunger 22. A special arrangement is provided whereby the cap 26 can be turned relative to the barrel 20 so as to lengthen or shorten the stroke of the plunger for varying the initial volume of material drawn into the nozzle or up.

An enlargement 34 is provided on plunger 22 for centering plunger 22 within the bore of the barrel 20 during its reciprocal stroke travel below shoulder 32. Enlargement 34 also functions as an element of a stroke-modifying system so that an extra length of thrust stroke can be given to plunger 22 during discharge of the device, compared with the stroke given to evacuate the device preparatory to filling. Accordingly, considering FIGS. 2 and 4 with the plunger in its retracted position, a compression spring 36, of greater strength than return compression spring 28, is provided around plunger 22 and is supported in a cup fitting 38 through the bottom of which plunger 22 slideably extends. Spring 36 is capped in a cap fitting 40 which is slideably received on plunger 22 and is axially slidable within the barrel 20.

The top of cap fitting 40 is spaced below enlargement 34, with the plunger in retracted position, a distance equal to the evacuation stroke for readying the device for drawing up liquid. Accordingly, to evacuate the device and prepare for drawing up liquid the knob 24 is urged downward until enlargement 34 seats against the upper surface of cap fitting 40 and the increased resistance of spring 36 is encountered by the user. The end of the tip or nozzle 12 seated on the end of the device is then placed beneath the level of the liquid and the pressure on knob 24 is released to permit spring 28 to return plunger 22 to the position shown in FIGS. 2 and 4. The nozzle or tip of the device is now filled with liquid. To discharge the liquid, the plunger 22 is again depressed and when the resistance of spring 36 is felt the plunger is depressed even further until the rim of cap fitting 40 engages the rim of cup fitting 38, spring 36 being compressed therebetween as shown in FIG. 5, thereby adding to the discharge stroke to assure complete discharge of all liquid in the nozzle or tip of the device. On release of pressure on knob 24, both springs 28 and 36 return to their normal or rest positions as in FIGS. 2 and 4 with the plunger 22 retracted.

As best seen in FIGS. 4 and 5 the liquid drawing system for the device includes a plurality of three axially aligned

cylindrical chambers

42, 44 and 46 of equal length and of decreasing diameter in linear order from top to bottom. The top of each chamber is sealed by a sealing ring or O-

ring

48, 50 or 52 of proper size sealing against the outer surface of the portion of plunger 22 to be used to displace the predetermined volume of air or fluid from the respective chamber. Each of

chambers

42, 44 and 46 is provided with a laterally extending

port

54, 56 and 58 through the sidewall of barrel 20 and in flow communication with an annular passage 60 defined between a reduced portion 62 in the outer surface of barrel 20 and a collar 64 slidably fitted in the reduced portion 62. The bottom end of passage 60 is sealed with a sealing O-ring 66 beyond the lowermost port 58 and the upper end of passage 60 is vented to atmosphere at 67.

An elliptical groove 68 receives and retains an elliptical sealing ring 70 at the inner surface of collar 64 with sealing ring 70 sealing against the outer surface of barrel 20 in reduced portion 62. Because of its elliptical shape the ring 70 extends in groove 68 along the length of reduced portion 62 from a position above port 54 on the right in FIGS. 4 and 5 to a position below port 56 on the left, shown (full lines) asposition A in FIGS. 4 and 5. With the sealing ring 70 in position A, both the

ports

54 and 56 are vented to the atmosphere by

passageway

60 and 67 thereby venting both of chambers 42 and 44 to the atmosphere.

Turning collar 64 in an amount of in one direction will cause the elliptical sealing ring to move to a position B (in phantom in FIGS. 4 and 5) lying between

ports

54 and 56 so that only port 54 is vented at 67 to atmosphere while port 56 communicates with the passageway 60 below the sealing ring 70 and is in air or fluid flow communication with port 58. Turning collar 64 in the same direction another 90 will move ring 70 to position C (again in phantom in FIGS. 4 and 5) blocking the passageway 60 above port 54 so that both

ports

54 and 56 are in air or fluid flow communication with port 58 and both are sealed against venting at 67 The plunger 22 is stepped at

shoulders

72 and 74 to provide reduced diameter piston portions 22a and 22b for operation in the decreased diameter chambers 44 and 46 respectively. Although the plunger 22 is continually sealed between

chambers

42, 44 and 46 by O-

rings

48, 50 and 52, the outer surface of the plunger does not seal against the interior of the cylinder walls of the

chamber

42, 44 and 46 during operation but rather rides closely spaced from the walls during both upward and downward movement.

During drawing of liquid into the receiver or reservoir which is shown as the nozzle or tip 12 of the device with the elliptical sealing ring 70 in position A (which is the minimum volume setting) as the plunger is retracted to fill the nozzle or tip with liquid, liquid is drawn up into the nozzle or tip in an amount equal to the maximum displacement of plunger 22 in chamber 46 during the downward or thrust stroke when the device is evacuated in preparation for filling. During the discharge stroke the nozzle or tip 12 is emptied. To increase the volume of the device the collar 64 is rotated 90 to place the sealing ring 70 in position B. Now when the plunger 22 is retracted during the filling operation, suction for drawing liquid into the nozzle or tip is also provided from passageway 60 and port 56 so that air or fluid flows from chamber 46 through port 58, passageway 60, and port 56 to fill the space between the inner walls of chamber 44 and the outer surface of piston portion 22!; providing a volume of liquid in the nozzle or tip equal to the sum of the displacements of plunger 22 in chambers 44 and 46 created during the filling stroke of plunger 22. During a discharge stroke the flow of liquid from the nozzle or tip is reversed and the new total volume is discharged.

In order to further increase the capacity of the device for drawing a still further increased total volume of liquid into the receiver or reservoir 12, the collar 64 is rotated another at to place sealing ring 70 in position C. It will be seen that now during a filling stroke air or fluid is drawn from passageway 60 through both of

ports

54 and 56 to fill the annular portions within chambers 42 and 44 surrounding plunger 22 while chamber 46 is also being filled, thereby giving a total volume of liquid drawn into the receiver or reservoir by the device equivalent to the sum of the displacements created by the plunger 22 in

chambers

42, 44 and 46 during the filling stroke. It will also be seen that al. all times while either or both of

ports

54 and 56 are not being used for liquid filling and liquid discharge purposes they are vented to atmosphere by the upper portion of passageway 60, above the position of ring 70, at 67 so that suction and compression forces are not built up within the vented portions of the device during its operation.

Fig. 1 shown collar 64 in a first position (position A) indicated by the numeral 1 for handling a predetermined amount of liquid and shows a second position (position B) indicated by the numeral 2 to which the volume indicator on collar 64 can be turned for changing the capacity of the device.

Turning now to FIG. 6, there is illustrated a modification of the device. This modification handles its smallest selectable volume as a difference in displacements between piston portions rather than directly from the displacement of the smallest piston portion. In this device the end of chamber 461: has been sealed as at 80 and the receiver or reservoir 12a is connected with an ofiset discharge portion 15 which is mounted on and forms a part of the rotatable collar 64a and has a passage 17 which communicates directly with the annular passage 60a. The annular passage 60a beyond the passage 17 of discharge portion 15 is sealed with an O-ring 66a, and port 54a from chamber 420 is provided adjacent discharge portion 15 and between O-ring 66a and the elliptical sealing ring 70. A vent 67a from passageway 60a is provided beyond sealing ring 70, this time at the bottom end of collar 64a. In this embodiment the elliptical sealing ring 70 is used to switch either or both of ports 56a and 58a from communication with either vent 67a or discharge portion 15 for changing the capacity of the device.

It will readily be seen that with ring 70 in position A in FIG. 6, all chambers will be filled during operation of plunger 22 and the device will draw the maximum amount of liquid into the nozzle or tip 12a during its intake and discharge cycles, i.e., an amount equal to the sum of the displacements of the plunger 22 in all three chambers during the evacuation thrust stroke in preparation for filling, less the displacement after filling. With ring 70 moved to position 8, port 580 and chamber 46a are vented and during the intake stroke a volume of air or fluid will be introduced into both of chambers 42a and 44a around plunger 22 so that the volume of liquid taken into the nozzle or tip 12a is approximately equal to the sum of the displacements of plunger 22 in chambers 42a and 44a during the evacuation stroke in preparation for filling, less the displacement of plunger 22 in these two chambers after filling. If the device is operated with ring 70 shifted to position C, then both of chambers 44a and 46a are vented to atmosphere and only the annular space around plunger 22 in chamber 42a is filled with an amount of air or fluid (which corresponds to the amount of liquid drawn into the nozzle) equal to the displacement of plunger 22 in chamber 42a created during the filling stroke of plunger 22.

Although the above specifically described embodiments use equal length cylinders or chambers of varying diameters which are selectively connected in flow communication with the nozzle or vented to atmosphere, it is apparent that a variety of different sizes and shapes of cylinders can be used. Additionally, although each embodiment uses a linear array of three coaxial cylinders with the sealing ring operating on the vents of two of the cylinders, it will be apparent that a larger number of cylinders or chambers can be provided in any one array and can be serviced by the same movable collar. For example, either of the devices illustrated above can be merely extended with additional chambers of decreasing diameter and additional lengths of appropriately stepped piston. The collar is correspondingly lengthened and one or more additional elliptical sealing rings are provided on the inside of the collar to operate in the same general manner with the outlet ports from the additional chambers as the collar is rotated. Such additional outlet ports may advantageously be in linear alignment with the other ports or may be spaced circumferentially therefrom.

Also, in the illustrated devices the ports in each pair operated by the elliptical ring are spaced lengthwise from each other. However, the ring can also operate to open and close circumferentially spaced ports as the ring is rotated, as will be evident to those skilled in the art. Additionally, the sealing ring need not be elliptical but can be circular or any other shape and can be mounted in a collar which is axially slidable on the barrel rather than rotatable thereon for selection of the variable capacities.

lclaim:

l. A variable capacity measuring and dispensing device for a liquid, comprising a body having a plurality of separate fluid holding chambers each having a port therein, reservoir means carried by said device and in communication with said chambers in said body for receiving and holding a measured volume of said liquid, a connecting passage having a vented end and connecting said ports in generally linear flow communication between the vented end and the reservoir means, means for selectively delivering fluid into and from each chamber, and operable means for selecting one or more chambers to be filled with said fluid and for selectively blocking the flow of said fluid to the nonselected chambers and for venting the nonselected chambers whereby only selected chambers are filled with said fluid which draws an equal measured volume of liquid into the reservoir means by operation of the delivering means, said operable means for blocking said fluid flow including a movable sealing member mounted for movement from a position sealing the vented end from all ports whereby all chambers are filled with said fluid which draws a measured volume of liquid into the reservoir means by said delivering means, to positions intermediate adjacent ports in said connecting passage whereby nonselected chambers are vented through said vented end and only selected chamber ports receive said fluid through said passage which draws an equal volume of said liquid into said reservoir means.

2. The device of claim 1 wherein said operable means includes means retaining said blocking means against movement to a position between the reservoir means and one of the chamber ports communicating with said passageway.

3. A variable capacity measuring and dispensing device for a liquid, comprising a stepped barrel having a plurality of separate fluid-holding cylinders approximately of equal length and formed as a linear array in order of decreasing diameter and volume in said barrel, means for selectively delivering fluid into and from each cylinder, including displacement means mounted for concurrent movement within said cylinders, said displacement means being in the form of a common stepped piston movable between a retracted position and a discharge position and having a discharge or displacement element properly sized for each cylinder with the discharge element for each cylinder positioned in the next larger cylinder while the piston is in a retracted position and including a port for each cylinder extending through the sidewall of the barrel, reservoir means carried by said device and in communication with said cylinders in said barrel, said reservoir means receiving and holding a measured volume of said liquid, and operable means including means for selecting one or more cylinders to be filled with said fluid and for selectively blocking the flow of said fluid to the nonselected cylinders and for venting the nonselected cylinders whereby only selected cylinders are filled with said fluid which draws an equal measured volume of liquid into said reservoir means by operation of the delivering means, and said operable means includes means for selectively connecting each of a plurality of said ports to said reservoir means or venting to atmosphere for varying the number of cylinders filled with fluid as said reservoir means is filled with an equal volume of liquid thereby varying the capacity of the device.

4. The device of claim 3 wherein said operable means comprises means mounted on the outer surface of the barrel for movement between a plurality of selectable positions, each representing a different volume or capacity for the device and including sealing means on the inner surface of said mounted means for sealing a different number of said ports upon movement to each selected position.

5. The device of claim 4, where said mounted means comprises a collar surrounding the barrel over said ports.

6. The device of claim 5, wherein said collar is mounted for rotary sliding movement of the outer surface of said barrel.

7. The device of claim 6, wherein the sealing means comprises an elliptical sealing ring secured to the inside of said collar in slidable sealing contact with the outer surface of said barrel and wherein two of said ports for two adjacent chambers are spaced from each other along the length of said barrel, the upper and lower expanse of said ring along the length of the barrel being above and below said two ports and the center of the extent of said ring along the length of the barrel being between said two ports, whereby rotation of the sleeve to position the center of the ring between the two ports communicates the upper port with the upper portion of the passageway between the collar and barrel and communicates the lower port with the lower portion of the passageway between the collar and barrel while rotation from said center position 90 in one direction communicates both ports with the lower portion of the passageway and rotation of the sleeve 90 from the center position in the other direction communicates both ports with the upper portion of the passageway.

8. The device of claim 7, wherein at least one of the plurality of chambers has its port disposed below the lowermost extend of the ring and said reservoir means is in direct flow communication with lower chamber.

9. The device of claim 7, wherein said reservoir means is a nozzle on said sleeve in flow communication with the passageway between the collar and barrel above the uppermost expanse of said sealing means, and said plurality of chambers includes a chamber having its port communicating with the passageway above the uppermost extent of said sealing ring and of larger volume than the next lower chamber, and means sealing the end of the passageway beyond the nozzle and chamberoutlet.

10. A variably capacity pipette for measuring and dispensing a liquid comprising a body having a plurality of fluid chambers therein, a movable plunger having a plurality of fluid displacement means respectively disposed for fluid displacement movement in said chambers, a reservoir for holding and dispensing said liquid, passage means for establishing fluid communication between said reservoir and said chambers, and selectively operable sealing means in said passage means, said sealing means being movable to a first position wherein one of said chambers is in fluid communication with said reservoir and a second position wherein plural chambers are in fluid communication with said reservoir thereby to selectively vary the effective number of said chambers in fluid communication with said reservoir to vary the volume of liquid drawn into and dispensed from said reservoir.

11. The pipette according to claim 10, wherein said plurality of chambers are disposed in a linear array and said displacement means are disposed in a linear array.

12. The pipette according to claim 11, wherein said displacement means are rigidly connected together.

13. The pipette according to claim 11, wherein said plurality of displacement means are of different fluid displacement sizes.

14. The pipette according to claim 11, wherein said displacement means comprises interconnected coaxial piston means of different diameters, and said fluid is air.

15. The pipette according to claim 14, wherein at least one of said piston means is movable in more than one of said chambers and all of said piston means are concurrently movable.

16. The pipette according to claim 15, wherein each of said chambers comprises a cylindrical bore having a stationary sealing ring for each of said pistons means.

17. The pipette according to claim 10, wherein said plunger is movable a predetermined distance to effect the drawing in of a predetermined volume of liquid into said reservoir when said sealing means is in said first position, and said plunger is movable said same predetermined distance when said sealing means is in said second position to effect the drawing in of a volume of liquid into said reservoir which is different than said predetermined volume, said fluid chambers are substantially coaxial, and said plurality of fluid displacement means are substantially coaxial.

18. The pipette according to claim 17, wherein said passage means has an end vented to atmosphere, said sealing means when in said first position venting to atmosphere and sealing from fluid communication with said reservoir all of said chambers except said one chamber, said seaiing means when in said second position sealing said plural chambers from atmosphere.

19. The pipette according to claim 18, wherein said chambers comprise a plurality of cylinders in a linear array, and said plurality of displacement means comprise a plurality of pistons of different sizes rigidly connected together in a linear array.

Claims

1. A variable capacity measuring and dispensing device for a liquid, comprising a body having a plurality of separate fluid holding chambers each having a port therein, reservoir means carried by said device and in communication with said chambers in said body for receiving and holding a measured volume of said liquid, a connecting passage having a vented end and connecting said ports in generally linear flow communication between the vented end and the reservoir means, means for selectively delivering fluid into and from each chamber, and operable means for selecting one or more chambers to be filled with said fluid and for selectively blocking the flow of said fluid to the nonselected chambers and for venting the nonselected chambers whereby only selected chambers are filled with said fluid which draws an equal measured volume of liquid into the reservoir means by operation of the delivering means, said operable means for blocking said fluid flow including a movable sealing member mounted for movement from a position sealing the vented end from all ports whereby all chambers are filled with said fluid which draws a measured volume of liquid into the reservoir means by said delivering means, to positions intermediate adjacent ports in said connecting passage whereby nonselected chambers are vented through said vented end and only selected chamber ports receive said fluid through said passage which draws an equal volume of said liquid into said reservoir means.

2. The device of claim 1, wherein said operable means includes means retaining said blocking means against movement to a position between the reservoir means and one of the chamber ports communicating with said passageway.

4. The device of claim 3, wherein said operable means comprises means mounted on the outer surface of the barrel for movement between a plurality of selectable positions, each representing a different volume or capacity for the device and including sealing means on the inner surface of said mounted means for sealing a different number of said ports upon movement to each selected position.

7. The device of claim 6, wherein the sealing means comprises an elliptical sealing ring secured to the inside of said collar in slidable sealing contact with the outer surface of said barrel and wherein two of said ports for two adjacent chambers are spaced from each other along the length of said barrel, the upper and lower expanse of said ring along the length of the barrel being above and below said two ports and the center of the extent of said ring along the length of the barrel being between said two ports, whereby rotation of the sleeve to position the center of the ring between the two ports communicates the upper port with the upper portion of the passageway between the collar and barrel and communicates the lower port with the lower portion of the passageway between the collar and barrel while rotation from said center position 90* in one direction communicates both ports with the lower portion of the passageway and rotation of the sleeve 90* from the center position in the other direction communicates both ports with the upper portion of the passageway.

8. The device of claim 7, wherein at least one of the plurality of chambers has its port disposed below the lowermost extend of the ring and said reservoir means is in direct flow communication with said lower chamber.

9. The device of claim 7, wherein said reservoir means is a nozzle on said sleeve in flow communication with the passageway between the collar and barrel above the uppermost expanse of said sealing means, and said plurality of chambers includes a chamber having its port communicating with the passageway above the uppermost extent of said sealing ring and of larger volume than the next lower chamber, and means sealing the end of the passageway beyond the nozzle and chamber outlet.

18. The pipette according to claim 17, wherein said passage means has an end vented to atmosphere, said sealing means when in said first position venting to atmosphere and sealing from fluid communication with said reservoir all of said chambers except said one chamber, said sealing means when in said second position sealing said plural chambers from atmosphere.