Liquid-dispensing Device

Abstract

A device for repeatedly dispensing a predetermined quantity of liquid. A reciprocating piston pump has poppet-type intake and delivery valves which are actuated by the drive mechanism of the pump piston to open and close intake and delivery passages in synchronism with the pump strokes. An imperforate flexible diaphragm is interposed between the valve poppets and the valve seats to prevent the liquid from contacting the valve poppets. The piston drive mechanism includes a variable first lost-motion connection providing for an abrupt discontinuance of the pump strokes and a second lost-motion connection providing for a rest period of the pump piston at the end of the delivery stroke to permit the intake and delivery valves to be opened and closed with no flow taking place in the intake and delivery passages.

Description

This invention relates to a device for repeatedly dispensing a predetermined quantity of liquid and, more particularly, a liquid-dispensing device having a reciprocating piston pump including intake and delivery valves actuated by the drive means of the pump piston to open and close intake and delivery passages at the ends of the pump strokes. A prior art device of this character is described in British Pat. Specification No. 1,030,368.

An inconvenience of known dispensing devices of this character is the difficulty of providing for a sufficiently tight sealing of the valves so that the liquid is prevented from leaking out from the passages and fouling the adjacent portions of the device. Another inconvenience is that the delivery of the liquid is mostly discontinued only gradually. In a known embodiment the piston is reciprocated in the pump cylinder by a crank mechanism and accordingly it is moved very slowly at the ends of the strokes. As a consequence, after the delivery has been discontinued, a drop of the liquid often remains hanging for some time at the end of the delivery conduit connected to the delivery passage. If the dispensing device is used in an automatic analysis apparatus in which sample containers are advanced in succession past the delivery conduit to receive therefrom a predetermined quantity of a reagent, the hanging drops may fall by the side of the sample containers and foul the apparatus. A further inconvenience is the difficulty of providing for a simple and yet accurate and reliable adjustment of the dispensed liquid volume.

The principal object of the invention is to provide a liquid dispensing device of the character described in which provision is made to substantially eliminate fouling caused by leakage of the liquid from the valves or drops falling from the delivery conduit after the delivery stroke of the pump piston has been discontinued.

A more specific object in accordance with the foregoing principal object is to eliminate direct contact between the valve members of the intake and delivery valves and the liquid. Another specific object in accordance with the foregoing principal object is to provide means for effecting an abrupt discontinuance of the delivery stroke of the pump piston.

A further object of the invention is to provide a dispensing device of the character described in which any backlash in the drive means of the pump piston does not affect the length of the intake and delivery strokes.

The above and other objects, features and advantages of the invention will be more fully understood from the following description considered in connection with the accompanying drawing, in which:

FIG. 1 is a side elevational view, partly in section, of a preferred embodiment of the dispensing device with the intake valve in open position and the delivery valve in closed position;

FIG. 2 is a side elevational view corresponding to the upper portion of FIG. 1 with the valve positions reversed;

FIG. 3 is a front elevational view, taken on the line III-III of FIG. 1, of the valve actuating and piston drive mechanism of the dispensing device.

While only a certain preferred embodiment of the invention has been shown, it should be understood that various changes or modifications may be made within the scope of the appended claims without departing from the underlying idea or principles of the invention.

With reference to the drawing, the dispensing device shown therein has a pump cylinder 1 in which a pump piston 2 is reciprocable. A threaded piston rod 3 extends through a collar 4 secured to the lower end of the pump cylinder 1. The collar 4 serves as a stop which limits the downward or intake stroke of the piston 2 by engaging lower end of the piston, and the upward or delivery stroke by engaging an adjustable internally threaded collar 5 on the piston rod 3.

A valve assembly 6 mounted on the upper end of the pump cylinder 1 comprises a lower block 7, hereinafter referred to as the first valve block, which closes a variable volume pump chamber 8 defined by the bore of the pump cylinder above the piston 2. The first valve block 7 is provided with intake and delivery passages 9 and 10, respectively, which have a common portion 11 connecting them with the pump chamber 8 and are provided with intake and delivery valve seats 12 and 13, respectively. These valve seats are provided in the upper external surface 14 of the first valve block 7.

A flexible, imperforate diaphragm 15 is positioned on the upper surface 14 of the first valve block 7 to valve seats 12 and 13, and on the upper surface of the diaphragm 15 there is positioned another valve block 16, hereinafter referred to as the second valve block, which is clamped to the first valve block 7 by means not shown, such as screws, to keep the diaphragm 15 in tight sealing engagement with the portions of the upper surface 14 of the first valve block surrounding the valve seats 12 and 13. Poppet-type intake and delivery valve members 17 and 18 are mounted in the second valve block 16 in vertical register with the intake valve seat 12 and the delivery valve seat 13. Both valve members are movable up and down and the lower end of the intake valve member 17 is secured to the underlying diaphragm portion so that this portion is positively lifted from the valve seat 12 when the valve member 17 is lifted; this prevents the diaphragm from being drawn into engagement with the intake valve seat 12 under the influence of the reduced pressure existing on the downstream side of that seat during the intake stroke of the piston. The diaphragm portion underlying the delivery valve member 18 need not be secured to the valve member since it is lifted from the delivery valve seat 13 under the influence of the increased pressure existing on the upstream side of that valve seat during the delivery stroke. The stems of the valve members 17 and 18 are pivoted to a common valve-actuating lever 19 at spaced points 20 and 21. One end of the valve-actuating lever 19 is pivoted to a vertical push rod 22 which is biased downwardly by a spring 23. The force of the spring 23 and the lever ratios are such that the spring 23 always tends to maintain the intake valve member 17 in closed position and the delivery valve member 18 in open position in opposition to the action of a bias spring 24 mounted no the stem of the valve member 18.

The lower end 25 of the push rod 22 is adapted to screw as a cam follower and is maintained in sliding engagement with a cam disc 26 by the spring 23. The cam surface of the cam disc 26, which is rotated through 360.degree. for each dispensing cycle by a motor 27, comprises two substantially semicircular segments 28 and 29 having different radii (see FIG. 3). When the cam follower end 25 of the push rod 22 engages the cam segment 28 having the larger radius, the valve-actuating lever 19 is held in the position shown in FIG. 1 in which the intake valve member 17 is in the open position and the delivery valve member 18 is in the closed position, and when the cam follower end 25 engages the cam segment 29 having the smaller radius, the valve-actuating lever 19 is held in the position shown in FIG. 2 in which the positions of the valve members are reversed.

The cam disc 26 is provided with an eccentrically positioned pin 30 engaging in a horizontal slot 31 in a vertically movable slide plate 32 to move the slide plate up and down during the rotation of the cam disc. The slide plate 32 is guided vertically by grooved rollers 33 (FIG. 3) the grooves of which engage the lateral edges of the slide plate. The middle portion 34 of the upper edge 35 of the slot 31 is arcuate, the radius thereof being substantially equal to the distance between the axis of rotation of the cam disc 26 and the eccentric pin 30, and, accordingly, as the pin 30 traverses the arcuate portion 34, the slide plate 32 is held stationary for some time in its uppermost position; the purpose of this lost-motion connection between the cam disc and the slide plate will become apparent as the description proceeds.

The lower end of the slide plate 32 has a horizontal flange 36 to which a leaf spring 37 serving as a driver for the piston rod 3 is secured. The driver spring 37 straddles the piston rod 3 between the adjustable collar 5 and a fixed collar 38 on the lower end of the piston rod so that it can slide freely along the piston rod between the two collars. By screwing the adjustable collar 5 upwardly or downwardly on the threaded piston rod 3, the length of the stroke of the piston 2, and hence the volume of liquid dispensed during each dispensing cycle, may be varied; the length of the piston stroke is substantially equal to the fixed length of the stroke of the slide plate 32 minus the lost-motion distance corresponding to the setting of the adjustable collar 5.

The operation of the above-described embodiment of the dispensing device is as follows:

FIG. 1 shows the intake stroke. Thus, the eccentric pin 30 has passed its top dead center position and engages the lower edge of the slot 31 of the slide plate 32 to move the latter and, through the driver spring 37, the piston 2 and the piston rod 3 downwardly. During the intake stroke the cam follower end 25 of the push rod 22 engages the cam disc section 28 (FIG. 3) so that the valve-actuating lever 19 keeps the intake valve member 17 and the underlying portion of the diaphragm 15 lifted from the intake valve seat 12, while the delivery valve member 18 engages the diaphragm 15 under the influence of the spring 25 to press the underlying diaphragm portion into sealing engagement with the delivery valve seat 13 (FIG. 1). Thus, the intake passage 9 is open while the delivery passage 10 is closed, and liquid is drawn into the pump chamber 8 from a supply container (not shown) connected to the intake passage.

Shortly before the eccentric pin 30 and the slide plate 32 reach the bottom dead center position, the lower end of the piston 2 engages the upper end of the collar 4 so that the piston 2 and the piston rod 3 are arrested and the intake of liquid is discontinued. The slide plate 32 then continues its downward travel until it reaches the bottom dead center, the overtravel being accommodated by the driver spring 37. The overtravel ensures that the piston 2 is always arrested in an accurately defined bottom end position irrespective of any backlash in the connection between the cam disc 26 and the slide plate 32 and the piston rod 3. During the overtravel, when the piston 2 thus is held stationary, the cam follower 25 disengages the cam disc section 28 and engages the cam disc section 29 having the smaller radius. As a result, the valve-actuating lever 19 is pivoted in the anticlockwise direction (as seen in FIGS. 1 and 2) about the pivot 21 under the influence of the spring 23 until the intake valve member 17 has pressed the underlying diaphragm portion into sealing engagement with the intake valve seat 12 to close the intake passage 9. The valve-actuating lever 19 is then pivoted further in the anticlockwise direction about the pivot 20 by the spring 23 so that the delivery valve member 18 is lifted in opposition to the spring 24 to open the delivery passage 10.

When the eccentric pin 30 has passed its bottom dead center position and engages the upper edge 35 of the slot 31 to move the slide plate 32 upwardly, the driver spring 37 initially slides freely along the piston rod 3 whereupon it engages the collar 5 to drive the piston 2 and the piston rod 3 upwardly. Before the eccentric pin 30 and the slide plate 32 reach the top dead center position, the collar 5 engages the lower end of the collar 4 so that the upward movement of the piston 2 is discontinued. Since the piston 2 is still moving at some speed immediately before the collars 4 and 5 engage each other, the delivery of the liquid through the delivery passage 10 is discontinued abruptly and this minimizes the possibility that a drop of the liquid remains hanging at the outer end of the conduit (not shown) connected to the delivery passage.

After the piston 2 has been arrested, the slide plate 32 continues its upward travel until it reaches its top dead center when the eccentric pin 30 enters the arcuate portion 34 of the upper edge 35 of the slot 31. This overtravel is accommodated by the driver spring 37 and ensures that the piston is always arrested in an accurately defined upper end position irrespective of any backlash. Since both end positions of the piston are always accurately defined, an exact predetermined volume of liquid is dispensed during each dispensing cycle.

As the eccentric pin 30 traverses the arcuate edge portion 35, the cam follower 25 disengages the cam disc section 29 and engages the cam disc section 28 to cause the push rod 22 to pivot the cam-actuating lever 19 in the clockwise direction to permit the spring 24 to close the delivery valve 13, 18 and then to lift the intake valve body 17 and the underlying diaphragm portion from the intake valve seat 12 so that the intake passage 9 is opened and the next dispensing cycle may commence. Thus, the valve positions are reversed while the slide plate 32 and the piston 2 are held stationary.

Claims

We claim:

1. A device for repeatedly dispensing a predetermined quantity of liquid comprising: a reciprocating pump having a pump cylinder providing a variable volume pump chamber and a reciprocable piston in said pump cylinder; a first valve block having intake and delivery passages therein communicating with said pump chamber, said passages including intake and delivery valve seats provided in an external surface of said first valve block; a flexible imperforate diaphragm positioned on said external surface of said first valve block to overlie said valve seats and sealingly engage portions of said external surface surrounding said valve seats; a second valve block positioned on said flexible diaphragm; poppet-type intake and delivery valve members in said second valve block, said valve members being adapted to act on said flexible diaphragm on the side thereof facing said second valve block, thereby to cause said flexible diaphragm to engage said valve seats to close said passages; and valve-actuating means for displacing said valve members towards and away from said valve seats.

2. A device according to claim 1, wherein said intake valve member is secured to said flexible diaphragm.

3. A device according to claim 1, wherein said delivery valve member is biased towards said flexible diaphragm.

4. A device according to claim 3, including an actuating lever for said valve members, said actuating lever being pivoted to said valve members at spaced points and biased to keep said intake valve member in a closed position and said delivery valve member in an open position.

5. A device according to claim 4, including means for operatively connecting said actuating lever with a rotatable cam disc having an eccentrically positioned driver pin and a reciprocable slide operatively connected with said piston to reciprocate it in said pump cylinder, said slide having a slot-and-pin connection with said cam disc including a slot extending transversely of the direction of reciprocation of said slide and engaging over said driver pin.

6. A device according to claim 5, wherein means is provided for continuously rotating said cam disc and driver pin during the course of a dispensing cycle comprising an intake and a delivery stroke of said piston and wherein said slot-and-pin connection between said cam disc and said slide plate includes lost-motion means for effecting an abrupt discontinuance of said delivery stroke and a rest period of said piston between said delivery and said intake strokes.

7. A device according to claim 5, wherein said slide is operatively connected with said piston between two adjustably spaced abutments on a piston rod of said piston by lost-motion means permitting said slide to move relative to said piston a distance substantially corresponding to the spacing of said abutments.

8. A device according to claim 7, wherein said lost-motion means includes resilient means permitting slight overtravel of said slide past the end positions of said piston.

9. A device according to claim 8, wherein means is provided for continuously rotating said cam disc and driver pin during the course of a dispensing cycle comprising an intake and a delivery stroke of said piston and wherein said slot-and-pin connection between said cam disc and said slide plate includes second lost-motion means for effecting an abrupt discontinuance of the movement of said slide at the end of said delivery stroke.

10. A device according to claim 1, including drive means for reciprocating said piston and connected to actuate said valve-actuating means.

11. A device according to claim 1, in which said pump cylinder and said piston cooperate to provide said variable pump chamber.