Liquid Metering Device With Concentric Pistons And Unidirectional Liquid Flow

Abstract

A liquid metering device is provided for transferring a measured batch of liquid from a supply container. The device includes an outer casing and an inner casing located within the outer casing and defining an annulus therebetween. A first piston is located in the annulus for sliding movement therein in response to fluid flow in and out of the annulus. A spring is provided within the outer casing for urging the first piston into an upper position, means is provided for directing fluid flow into the annulus to actuate the first piston into a lower position in opposition to the spring. A second piston is located within the inner casing for sliding movement therein, and is secured at its lower end to the first piston so that the first and second pistons move within their respective casings in unison. The second piston and inner casing define therebetween a liquid chamber in communication with a liquid outlet. Liquid communication means is provided between the liquid supply container and the liquid chamber. Upon actuation of means provided for terminating fluid flow into the annulus and for venting fluid contained therein to atmosphere, the pistons are moved to an upper position in response to the spring so that liquid is discharged from the liquid chamber into the liquid outlet.

Description

DESCRIPTION OF THE INVENTION

The present invention relates generally to a liquid pumping device, and more particularly to such a device for pumping adjustably metered batch quantities of liquid.

The device of the present invention is particularly useful for pumping metered batch quantities of various liquids used in apparatus for the preparation of samples for radioactive isotope tracer studies. Such liquids include liquid scintillators and liquid trapping agents for carbon dioxide. A sample preparation apparatus with which the liquid metering devices of the present invention are particularly useful is described and illustrated in pending Kaartinen Applications Ser. No. 242,481 filed April 10, 1972.

It is a primary object of the present invention to provide an improved liquid metering device which efficiently pumps batch quantities of liquids of pre-selected size, even when the liquid quantities amount to only a few milliliters or less. A related object is to provide such a liquid metering device which is operable when fully submerged within the liquid to be pumped.

Another object is to provide a liquid metering device which is compact, has few moving parts, and is easily operated automatically.

Other objects and advantages of the invention will become apparent from the following detailed description and upon reference to the accompanying drawings, in which:

FIG. 1 is a perspective view, partly cutaway, showing a liquid metering device illustrative of the present invention disposed within a typical liquid supply container or tank.

FIG. 2 is an elevational view of the illustrative liquid metering device.

FIGS. 3 and 4 are elevational views, partly in section, showing liquid unloaded (FIG. 3) and liquid fully loaded (FIG. 4) positions of the illustrative liquid metering device.

FIG. 5 is a sectional view taken along the line 5--5 in FIG. 2.

FIG. 6 is a sectional view taken along the line 6--6 in FIG. 2.

FIG. 7 is an exploded, perspective view showing the component parts of the illustrative liquid metering device.

While the invention will be described in connection with certain preferred embodiments, it will be understood that it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, an illustrative liquid metering device 10 is shown in FIG. 1 disposed in a typical supply container or tank 11 containing liquid to be metered and pumped to another location. The fully enclosed type supply tank 11 shown has an opening defined by a flange 12 in the top for receiving the liquid metering device 10, and is provided with a liquid fill inlet 13 closed by a suitable cap.

As will be seen, the liquid metering device 10 includes a generally cylindrically shaped pump assembly 14 mounted between rectangular base and top plates 15 and 16, respectively, by means of vertical supports 17 (four as shown). Also mounted between the plates 15 and 16, and located alongside the pump assembly 14, is a metering assembly 18 which functions to adjustably set the volume of liquid to be metered and pumped by the device 10.

The top plate 16 of the liquid metering device 10 is provided with holes 16a for alignment with corresponding holes (not shown) in the tank flange 12 and for receiving suitable fasteners (not shown) for securing the metering device 10 within the tank 11. The plate 16 also includes holes 16b for receiving the upper ends of the vertical mounting supports 17 and fasteners (not shown) therefore (corresponding holes 15a are provided in the base plate 15 for the lower ends of the supports 17).

For receiving a suitable pressurized gas (e.g. 25 psi. pressure), such as air or an inert gas such as nitrogen, the top plate 16 is provided with a gas inlet 19 having an on-off switch type valve 20. The valve 20 includes a vent (not shown) for releasing the gas pressure when desired (i.e. to discharge liquid from the pump when it is loaded, as described below). The top plate 16 is also provided with a liquid outlet 21 which directs the metered liquid to its ultimate destination. Mounted above the top plate 16 is a dial 22 associated with the metering assembly 18 to permit manual adjustment of the pumping volume (as described in more detail below).

Directing attention now to the pump assembly 14, as shown in the drawings it includes a large cylindrical piston 23 disposed within an outer cylindrical casing 24, and a small cylindrical piston 25 removably secured within a recess 26 provided in the center of the large piston. The small piston 25 moves up and down within an inner casing 27 which is secured to and extends part way down from the top plate 16 into an annular space provided between the small piston 25 and the recess 26 in which it is housed. The two pistons 23 and 25, which are secured together through a threaded connection 28, move up and down together at all times. In order to permit alignment of the small piston 25 within its casing 27, the connection 28 between the pistons 23 and 25 includes a wave washer 29a which produces spring tension between the two pistons, a lock washer 29b, and an intermediate regular washer 29c. As shown, the small piston 25, which may advantageously be formed of teflon or similar corrosion resistant, low-friction material, presents a round piston face 25a facing upwardly toward the top cover plate 16. Annular seals 25b are provided around the periphery of the piston 25 to assure liquid-tight sealing engagement between the piston and its casing 27.

Like the small piston 25, the large piston 23 also presents an upwardly facing piston face 23a, in this instance annularly shaped to fit between the outer 24 and inner 27 casings. Once more the piston 23 may be formed of teflon or the like, and includes an annular seal 23b held in place by a suitable seal retaining ring 23c.

To facilitate sliding movement of the pistons 23, 25 within their respective casings 24, 27, it may be advantageous to construct the casings of metal having an interior coating of low friction material such as teflon or the like. Such a coating may also desirably be resistant to corrosion by the liquid being pumped.

For urging the two pistons 23 and 25 normally upwardly and into an unloaded (with liquid) position (see FIG. 3), a coil spring 30 is located inside the lower portion of the outer casing 24 interposed between tue bottom support plate 15 and the underside of the piston 23. The position of the coil spring 30 when fully compressed (see description below) is shown in FIG. 4.

Communicating passages for the liquid passing through the liquid metering device 10 are provided as follows. Liquid enters the device 10 through a submerged suction inlet 31 provided in the bottom of the base plate 15. The inlet 31 is covered by a protective screen 32 supported between a shoulder 15b defining the inlet 31 and a dished upper retaining cup member 33 against which the coil spring 30 rests. Liquid entering the inlet 31 passes upwardly into the underside of the dished member 33 and into a flexible tubing 34, which may also be formed of teflon or the like. The tubing 34 is suitably secured at one end to a central opening 33a provided in the dished member 33, and at the other end to an internal channel 35 which runs longitudinally through the small piston 25. As will be seen, the channel 35 communicates between the flexible tubing 34 and an inner chamber 36 located adjacent the operating face 25a of the small piston. The upper end of the chamber 36 opens into the liquid outlet passage 21 provided in the top plate 16. For preventing backward flow of liquid through the pump, a pair of one-way (up and out only) check valves 37 and 38 are provided in the channel 35 and outlet 21, respectively.

Liquid flowing through the metering device 10 thus enters at the inlet 31, passes through the screen 32 (to filter out any particles of foreign matter that may be present), into the dished member 33 and thence through the tubing 34, the channel 35, check valve 37 and into the pumping chamber 36 from which it is ejected (as will be described below) through the liquid outlet 21.

On the pressurized gas side of the device 10, gas entering through the gas inlet 19 impinges on the piston face 23a and thereby forces both pistons 23 and 25 downwardly against the bias of the coil spring 30. As this occurs, the entering gas passes into and occupies an annular chamber 39 formed between the inner 27 and outer 24 casings. As the pistons 23 and 25 move downwardly, a vacuum is created within the smaller chamber 36; this vacuum draws the liquid upwardly from the tank 11 through the liquid inlet 31 and into the chamber 36 as previously described. When the entering gas supply is terminated by shutting off the valve 20, the trapped pressurized gases in the chamber 39 are vented through the valve and the pistons 23 and 25 return to their upper position in response to the urging of the coil spring 30.

For limiting the extent of downward movement of the unitary pistons 23, 25, the lower portion of the piston 23 carries a stop pin 40 (shown threaded into the piston body) which extends through a vertical slot 24a provided in the casing 24 and is adapted to cooperate with the metering assembly 18, as will now be described. The assembly 18 includes a stepped drum 41 fixedly mounted by means of a set screw 42 onto a vertical spindle 43 extending between a collar 44 carried by the base plate 15 and an opening 16c provided in the top plate 16. The upper end of the spindle 43 extends through the opening 16c where the manually operable dial 22 is affixed to it by means of a set screw 45. A seal ring 46 and retaining collar 47 are fixed to the spindle 43 (by set screw 48) just beneath the top plate 16.

Thus, the operator of the liquid metering device may adjust the batch volume of liquid to be pumped by simply turning the dial 22 until the desired step 41a is located adjacent the casing slot 24a. The downward stroke of the pistons 23, 25 then will continue only until the stop 40 carried by the pistons engages the selected step 41a, at which time the pressurized gas valve 20 may be actuated to release the gas pressure and thereby cause ejection of the measured quantity of liquid from the chamber 36 into the outlet line 21. The number and spacing of the steps 41a may be varied as desired to provide the necessary liquid batch sizes for each particular application. e

One of the features of the illustrative device resides in the provision therein of means for preventing liquid leakage into the pressurized gas chambers. To this end a porous washer 49, preferably formed of teflon felt or like material, is provided within the recess 26 at the base of the small piston 25. In the event of liquid seepage past the piston seals 25b and into the recess 26, the pressurized gas in the recess 26 forces such liquid through the porous washer 49 and back into the tank 11.

Another feature of the illustrative arrangement resides in the manner in which provision is made for the pistons 23, 25 to move downwardly in the casing 24 and compress the spring 30, without at the same time pinching or otherwise restricting flow of liquid through the tubing 34. As will be seen from the drawings, the tubing 34 is provided with a loose knot which, because of the flexibility of the tubing, is capable of self loosening during downward piston travel (see FIG. 4) and self-tightening during upward piston travel (see FIG. 3). It has been found that pinching of the tubing 34 is avoided if the mean slope of the knot is arranged opposite to the spiral of the spring 30, as shown in the drawings.

Claims

I claim as my invention:

1. A device for transferring a metered batch of liquid from a supply container comprising, in combination, an outer casing, an inner casing located within the outer casing and defining an annulus therebetween, a first piston located in the annulus for sliding movement therein in response to fluid flow in and out of the annulus, spring means within the outer casing for urging the first piston into an advanced position, means for providing fluid flow into the annulus to move the first piston into a retracted position in opposition to said spring means, a second piston located within the inner casing for sliding movement therein and secured at one end to the first piston so that the first and second pistons move within their respective casings in unison, said second piston and inner casing defining therebetween a liquid chamber in communication with a liquid outlet, liquid communication means extending between the liquid supply container and the liquid chamber, a first check valve between said liquid supply container and said liquid chamber for passing liquid from said supply container to said chamber during retracting movement of said pistons and for blocking the flow of liquid from said chamber to said supply container during advancing movement of said pistons, a second check valve connected to said liquid outlet for passing liquid discharged from said liquid chamber via said outlet during advancing movement of said pistons and for blocking the flow of liquid into said chamber via said outlet during retracting movement of said pistons, and means for terminating fluid flow into the annulus and venting fluid contained therein to atmosphere whereby the pistons are moved to an advanced position in response to the spring means so that liquid is discharged from the liquid chamber into the liquid outlet.

2. The device of claim 1 in which the liquid communication means includes a flexible tube located within the spring means and provided with a loose knot having the mean slope of the knot arranged opposite to the spiral of the spring.

3. The device of claim 1 in which means is provided for adjustably limiting the stroke of the pistons to thereby limit the volume of liquid transferred to a predetermined volume.

4. A device for transferring a metered batch of liquid from a supply container comprising, in combination, an outer casing, an inner casing located within the outer casing and defining an annulus therebetween, a first piston located in the annulus for sliding movement therein in response to fluid flow in and out of the annulus, spiral spring means within the outer casing for urging the first piston into an upper position means for providing fluid flow into the annulus to actuate the first piston into a lower position in opposition to said spring means, a second piston located within the inner casing for sliding movement therein and secured at its lower end to the first piston so that the first and second pistons move within their respective casings in unison, said second piston and inner casing defining therebetween a liquid chamber in communication with a liquid outlet, liquid communication means extending between the liquid supply container and the liquid chamber, said liquid communication means including a flexible tube located within the spring means and provided with a loose knot having the mean slope of the knot arranged opposite to the spiral of the spring means and means for terminating fluid flow into the annulus and venting fluid contained therein to atmosphere whereby the pistons are moved to an upper position in response to the spring means so that liquid is discharged from the liquid chamber into the liquid outlet.