CA2384520A1 - Flow control elements for use in liquid dispensers - Google Patents

Abstract

A flow-control/flow-regulation element (314) improves the operation of a liquid dispenser. In some embodiments, the flow-regulation/flow-control element (314) comprises a flow restriction that is disposed in the conduit that delivers pressurized liquid to the dispensing valve (310). Since the fl ow restriction has an orifice (416) that is smaller than the orifice of the dispensing valve (310), liquid is re-supplied to the conduit more slowly tha n it is dispensed through the dispensing valve (310).

Description

2 CA 02384520 2002-03-11 pCT~JS00/25411 FLOW CONTROL ELEMENTS
FOR USE IN LIQUID DISPENSERS
Statement of Related Cases This case is related to U.S. Patent Application 09/395,363 filed September 14, 1999 and entitled "Article and Method for Flow Control in Liquid Dispensing Devices, and to U.S. Patent Application 09/494,387 filed January 31, 2000 and entitled "Article and Method for Predictable Dispensing of Small Liquid Volumes.
Both of these cases are incorporated herein by reference.
Field of the Invention The present invention relates to liquid dispensers. More particularly, the present invention relates to a method and apparatus that provides precise control and regulation over the delivery of micro-liter and sub-micro-liter volumes of liquid from liquid dispensers.
Background of the Invention Pharmaceutical, combinatorial chemistry, high-throughput screening, and medical diagnostics applications, to name a few, require dispensing very small volumes of liquid (i. e. , nano-liters to micro-liters) into a receiver such as a micro-titer plate. It is usually necessary to perform the dispensing operation without cross-contamination, which might occur, for example, if a reagent is being added to a receiver that already contains another reagent.
To substantially eliminate the incidence of cross-contamination, a "non-touch off' method of liquid dispensing is typically used. In this method, a droplet being dispensed does not contact the receiver (or liquid or other material in the receiver) until the droplet completely disengages from the tip of the dispenser. Non-touch-off dispensing requires supplying enough kinetic energy to a liquid droplet for it to overcome the surface tension of the dispensing tip and enough kinetic energy so that it can be accurately and reliably directed to a desired destination.

Non-touch off dispensing of liquid volumes between about 0.1 to about 5 micro-liters is performed using either shake-off methods or implemented with various valve mechanisms that apportion the dispensed volume. While the use of valves for this service is straightforward in principle, it is rather difficult to implement in practice, as discussed further below.
Some valve-based prior-art liquid dispensers use a pressurized reservoir, such liquid dispenser 100 depicted in FIG. 1. Dispenser 100 includes a reservoir 102 that is maintained under pressure by gas (e.g., nitrogen, etc.) supplied by gas supply line 104. Liquid 106 is provided to supply conduit 108 from reservoir 102. Conduit delivers liquid 106 to valve/nozzle 110 (hereinafter simply "valve 110") for dispensing through orifice 112.
Dispensers, such as dispenser 100, that provide a constant "re-supply" of liquid to replace dispensed liquid (e.g., those wherein the dispensing energy is provided by a pressurized reservoir, etc.) are prone to inaccuracy. Such inaccuracy is related to characteristics of the dispensing valve.
In particular, the amount of liquid dispensed from such dispensers is proportional to the amount of time that the dispensing valve is open (as well as pressure, fluid viscosity, etc.). The behavior of dispensing valves (e.g., valve 110) that are typically used in such dispensers is such that there is a rapid response to an impulse (e.g., voltage) to open, but the closure response tends to be less precise.
Reasons for such imprecision include, for example, variations in fluid parameters (e.g., viscosity), aging of the valve spring, contamination, and the like. By way of example, if a dispensing operation dispenses 1 micro-liter of liquid in 20 milliseconds, and there is a 2 millisecond delay on valve closure, then an error of 2/20 or IO percent in the amount of dispensed liquid has occurred (assuming no variation in fluid paramaters).
Other valve-based prior art liquid dispensers forgo the pressurized reservoir in favor of a "positive displacement" method. Positive-displacement type dispensers, such as dispenser 200 depicted in FIG. 2, use a fluid "pulse" having a calibrated volume in an attempt to avoid the problem described above. Such dispensers do not provide a continuous refill; rather, a discrete amount of liquid is metered towards a dispensing valve/nozzle in response to a compressive stroke of a pump.
Liquid dispenser 200 includes a reservoir 202 containing liquid 106, conduit 204 leading to positive-displacement pump 206, and conduit 208 leading to dispensing valve/nozzle 210 (hereinafter simply "valve 210"), arranged as shown. In operation, a volume of liquid 106 is drawn from reservoir 202 through conduit into pump 206. The advanced liquid is discharged into conduit 208 towards dispensing valve 210. Three-way valve 205 controls the flow into and out of positive-displacement pump 206.
Valve 210 opens to dispense the liquid through orifice 212 and thereafter closes. After the compressive stroke, pump 206 draws liquid from reservoir 202 for the next dispensing pulse. Liquid is not advanced towards dispensing valve 210 during this pump-charging operation. Since no "re-fill" liquid is present to be dispensed until the subsequent dispensing pulse, no "extra" liquid is dispensed if the closure of valve 210 is sluggish.
Although a discrete amount of liquid is advanced by pump 206 during the dispensing pulse, to actually dispense that amount of liquid from valve 210 is problematic.
In particular, as valve 210 opens to dispense the desired volume of liquid, the pressure rapidly drops. As the pressure nears ambient, the energy available for dispensing is insufficient to dispense the remaining liquid. Thus, the full volume of liquid that is advanced toward dispensing valve 210 during each dispensing pulse is not dispensed.
There is a need, therefore, for a liquid dispenser that is avoids the shortcomings of prior art liquid dispensers, as discussed above.
Summary of the Invention In accordance with some embodiments of the present invention, a liquid dispenser comprising one or more flow-control/flow-regulation elements that ameliorate some of the shortcomings of prior art liquid dispensers are disclosed.

WO 01/19432 cA o23e452o 2002-03-11 PCT/LTS00/25411 In a first embodiment, the flow-regulation/flow control element comprises a flow restriction that is disposed in the conduit that delivers pressurized liquid to the dispensing valve. The flow restriction restricts the flow of the pressurized liquid into the conduit.
The flow restriction, which in some embodiments is realized as a restriction orifice, has an orifice that is smaller than the orifice of the dispensing valve. As a result, liquid is re-supplied to the conduit more slowly than it is dispensed through the dispensing valve. Since the re-supply rate is less than the dispensing rate, a relatively smaller error results from delays in valve closing than would otherwise occur.
Furthermore, since flow is regularly re-supplied to the dispensing valve (unlike positive-displacement dispensers), sufficient pressure is available for dispensing liquid during the entire dispensing cycle.
In a second embodiment of the invention, the flow-control/flow regulation element comprises a dynamic pressure sensor that is operatively engaged to an elastic region of the conduit that delivers pressurized liquid to the dispensing valve. The dynamic pressure sensor senses pressure in conduit, which pressure can be correlated to the amount of liquid discharged from the dispenser. Variations in the measured pressure indicate an offset from baseline operation.
In a third embodiment of the invention, the flow-control/ flow regulation element comprises a resilience-adjustment element that is operatively engaged to an elastic region of the conduit. The resilience-adjustment element is operable to adjust the resilience or elasticity of the elastic portion of the conduit. This adjustment can compensate for changes in fluid characteristics (e.g., viscosity, etc.) as well as for changes in the elasticity of the conduit or in the mechanical operation of the dispensing valve. In one embodiment, resilience is adjusted by applying a pressure to the outside of the conduit. The pressure acts as a counter-force to a decrease in resilience.
In a fourth embodiment of the invention, the flow-control/flow-regulation element comprises a flow-blocking member and a measurement device or sensor that is operatively engaged to an elastic region of the conduit.

WO 01/19432 CA 02384520 2002-03-11 pCT/US00/25411 The flow-blocking member meters liquid into a chamber that is defined by the flow-blocking member at one end and the dispensing valve at the other end. The measurement device or sensor monitors changes in the size (e.g., diameter) and/or pressure of the chamber. Readings obtained from the measurement device or sensor are used to quantitatively evaluate the volume of liquid that is dispensed from the chamber through the dispensing valve. The dispensed volume is adjusted, as required, by adjusting the operation of the dispensing valve.
Brief Description of the Drawings FIG. 1 depicts a conventional "pressurized reservoir" fluid-dispensing device.
FIG. 2 depicts a conventional "positive displacement" fluid-dispensing device.
FIG. 3 depicts an improved dispenser comprising at least one flow-control/flow regulation-feature in accordance with the present teachings.
FIG. 4 depicts an improved dispenser in accordance with the present teachings wherein the flow-control/flow-regulation feature is a restriction orifice.
FIG. 5 depicts an improved dispenser in accordance with the present teachings wherein the flow-control/flow-regulation feature is a dynamic pressure sensor.
FIG. 6 depicts an improved dispenser in accordance with the present teachings wherein the flow-control/flow-regulation feature is a resilience-adjusting element.
FIG. 7 depicts an improved dispenser in accordance with the present teachings wherein the flow-control/flow-regulation feature is a flow blocking member and a measurement device.
FIG. 8 depicts a control system for providing automatic closed-loop control of the liquid dispenser of FIG. 7.
FIG. 9 depicts a plot of the pressure in the chamber formed between the flow blocking member and the dispensing valve.

WO 01/19432 cA o23e452o 2002-03-11 PCT/US00/25411 Detailed Descriution The flow control/flow regulations elements described herein are suitable for use with a wide variety of existing liquid dispensers. For instance, in some embodiments in accordance with the present teachings, the present flow-control/flow-regulation elements are integrated into conventional pressurized-reservoir-type liquid dispensers, like dispenser 100, to improve the operation thereof. And in other embodiments, the present flow-control/flow-regulation elements are integrated into conventional positive-displacement-type liquid dispensers, like dispenser 200.
FIG. 3 depicts a liquid dispenser 300 in accordance with the present teachings.
Liquid dispenser 300 includes pressurized liquid source 302, conduit 308, flow-control/flow-regulation element 314, dispensing valve/nozzle 310 (hereinafter simply "valve 310") and orifice 312, interrelated as shown.
As previously described, pressurized liquid source 302 can be, without limitation, a pressurized reservoir (see, e.g., reservoir 102 in FIG. 1) or a pump drawing liquid from a reservoir (see, e.g., reservoir 202 and pump 206 in FIG.
2).
Conduit 308 places pressurized liquid source 302 in fluid communication with dispensing valve 310. Regions that are described to be in "fluid communication"
with one another, as that phrase is used herein, are capable of transferring liquid to one another. Conduits 308 are suitably formed from tubing, such as TYGONTM
tubing, which is commercially available from Norton Performance Plastics, Akron, Ohio.
Dispensing valve 310 controls the release of liquid from dispenser 300.
Dispensing valve 310 is advantageously a "micro" valve, such as is used for print heads in ink jet printers. Micro-valves are capable of dispensing micro-volumes of fluid in the range of about 20 nano-liters to several micro-liters. Micro-valves are commercially available from The Lee Company of Essex, Connecticut, and others.
Liquid is dispensed through orifice 312 in the nozzle portion of dispensing valve 310. In the illustrated embodiments of the present invention, the nozzle is an integral portion of dispensing valve 310 (i.e., it is obtained from a supplier as a combined valve/nozzle). In other embodiments, a separate valve and nozzle is used.

WO 01/19432 cA o23e452o 2002-03-11 pCT~S00/25411 Flow-control/flow-regulation element 314, which is operatively engaged to conduit 308, improves the accuracy and/or reliability of the dispensing operation.
Several embodiments of a flow-control/flow-regulation element 314 in accordance with the present teachings are described below.
Flow Restriction With reference to FIG. 4, in one embodiment in accordance with the present teachings, flow-control/flow-regulation element 314 comprises a flow restriction, such as restriction orifice 416. Restriction orifice 416 has an outlet orifice 418 that is smaller than opening 312 of dispensing valve 310. As a result, liquid 106 is re-supplied to conduit 308 and dispensing valve 310 more slowly than it is dispensed therefrom. Since the re-supply rate is less than the dispensing rate, a relatively smaller error results from any delay in valve closing than would otherwise occur, while a continuous refill of conduit 308 is advantageously provided.
In the illustrative embodiment depicted in FIG. 4, conduit 308 is inelastic.
It should be understood, however, that in other embodiments of the present invention, a flow restriction is used in conjunction with a conduit having an elastic region.
Pressure Sensing FIG. 5 depicts a further embodiment, in accordance with the present teachings, of flow-control/flow-regulation element 314. In the embodiment depicted in FIG. 5, flow-control/flow-regulation element 314 comprises elastic region 516 of conduit 308, and a pressure sensor 518. Pressure sensor 518 is operable to sense pressure in elastic region 516. Leads 520 from sensor 518 connect to appropriate electronics (not depicted) for processing sensor data and displaying and/or recording such data.
Monitoring the pressure in conduit 308 as it falls and rises during respective dispensing and refilling cycles provides information that can be correlated to an amount of liquid dispensed and also can provide indications of operational problems (e.g., occlusions in the conduit 308 and/or valve 310).
Since conduit 308 advantageously incorporates elastic region 516, pressure sensor 518 can be a dynamic pressure sensor ((e.g., piezo-resistive sensors, etc.), which is disposed on region 516. A static pressure-measurement device is required when the liquid conduit (e.g., conduit 308) is inelastic and disposed in the channel as a "flow-through" sensor. Dynamic pressure sensors are much less expensive (i.e., about an order of magnitude) than static pressure sensors and do not require insertion into conduit 308. Such insertion usually creates a "dead volume" and presents the possibility for introducing contamination in conduit 308.
In some embodiments, data from pressure sensor 518 can be utilized in a control loop (not depicted) to adjust the operation of valve 310 for changing timing or to adjust the supply pressure to compensate for temperature variations, fluid parameters (e.g., viscosity), partial valve occlusion, and the like.
Resilience Adjustment FIG. 5 depicts an additional embodiment, in accordance with the present teachings, of flow-control/flow-regulation element 314. In the embodiment depicted in FIG. 6, flow-control/flow-regulation element 314 comprises elastic region 516 of conduit 308, and resilience-adjusting element 622 that is operable to adjust the "resilience" or "elasticity" of elastic region 516.
The ability to adjust the resilience of elastic region 516 of conduit 308 provides a further measure of control over the dispensing process. For example, resilience-adjusting element 622 provides a way to adjust for "aging" of the conduit material. In particular, if elastic region 516 loses resilience over time, the resilience-adjusting element can be used to return the liquid dispenser to a baseline operation.
Moreover, the resilience-adjusting element 622 provides a way to compensate for variations in fluid parameters (e.g., changes in viscosity, etc.) from a baseline condition, which variations would otherwise affect fluid dynamics within the dispenser, and, hence, the operation thereof. Thus, resilience-adjusting element 622 advantageously maintains a baseline operation for the dispenser notwithstanding changed system conditions.
In the embodiment depicted in FIG. 6, resilience-adjusting element 622 comprises an enclosure 624 that defines a pressure-tight chamber 626 surrounding at least a portion of elastic region 516, and a pressure-adjustment element. In some WO 01/19432 cA o23e452o 2002-03-11 pCT~S00/25411 embodiments, the pressure-adjustment element is realized by gas supply conduit that delivers gas (e.g., nitrogen, etc.) to chamber 626, and a pressure regulator 632.
Additionally, optional vacuum-flow conduit 634 is connected to a vacuum source (not shown).
Increasing the pressure within chamber 626 effectively increases the resilience of elastic region 516 (at least the externally pressurized portion thereof).
Conversely, decreasing pressure within chamber 626 decreases the resilience of elastic region 516.
If a vacuum source is not available, the reference or baseline conditions for the dispensing operation is advantageously set with an elevated pressure within chamber 626 (i.e., elevated above the operating pressure within conduit 308). Doing so provides an ability to decrease pressure (below the baseline pressure setting), hence decreasing the resilience of region 516, as required. If the baseline operation is set with only ambient pressure on the exterior of region 516, and a vacuum source is not available, then the ability to decrease resistance by lowering pressure is forfeited.
In further embodiments of the present invention, flow-control/flow-regulation element 314 comprises various combinations of the structures described above for improving the accuracy of the dispensing operation.
For example, in one embodiment, the present flow-control/flow-regulation element 314 comprises an elastic region, a dynamic pressure sensor, and a resilience-adjusting means. In another embodiment, the present flow-control/flow-regulation element 314 incorporates an elastic region, a dynamic pressure sensor, and a flow restriction. In a further embodiment, the present flow-control/flow-regulation element 314 comprises an elastic region, a resilience-adjusting means, and a flow restriction. And, in an additional embodiment, the present flow-control/flow-regulation element 314 comprises an elastic region, a dynamic pressure sensor, a resilience-adjusting means, and a flow restriction.
Metered Flow FIG. 7 depicts yet a further embodiment, in accordance with the present teachings, of flow-control/flow-regulation element 314. In the embodiment depicted WO 01/19432 CA 02384520 2002-03-11 pCT~JS00/25411 1~
in FIG. 7, flow-control/flow-regulation element 314 comprises elastic region 516 of conduit 308, and flow blocking member 736.
A chamber 738 is defined by flow blocking member 736 and dispensing valve 310. In accordance with the present teachings, chamber 738 receives a predetermined amount of liquid for dispensing.
Liquid is admitted to chamber 738 by flow blocking member 736. While flow blocking member 736 is advantageously realized as a valve, any arrangement operable to ( 1 ) meter a desired amount of liquid into chamber 738 and (2) block any more than the desired amount of liquid from entering chamber 738 may suitably be used. Dispensing valve 310 controls the flow of liquid out of chamber 738.
Flow-control/flow-regulation element 314 also includes a measurement device or sensor 740 (hereinafter simply "measurement device 740") that is operable to monitor changes in the size (e.g., diameter, etc.) and/or pressurization of chamber 738. Leads (not shown) from measurement device 740 connect to appropriate electronics or other mechanisms (not shown in FIG. 7; see, e.g., FIG. 8) for processing sensor data and displaying and/or recording such data.
In some embodiments, measurement device 740 is inserted within chamber 738, while in other embodiments, it is suitably engaged to the exterior of chamber 738. While either location may suitably be used, devices that are inserted within chamber 738 present a possibility for introducing contamination.
In one embodiment, measurement device 740 is a dynamic pressure sensor such as previously described. Again, the use of a dynamic pressure sensor, in contrast to a static pressure measurement device, is facilitated by the resilient and elastic nature of chamber 738.
As described in more detail later in this Specification, monitoring the pressure within, or the size of, chamber 738 as it falls and rises during respective dispensing and refilling cycles provides information that can be correlated to an amount of liquid dispensed. This information also provides an indication of operational problems (e.g., valve occlusions). The measurement data is advantageously used to adjust the "open"

WO 01/19432 cA o23e452o 2002-03-11 PCT/US00/25411 time of dispensing valve 310, which, in turn, adjusts the volume of the dispensed liquid.
The fast repetition of the dispense cycles constitutes a dynamic process of repetitive pressurization of chamber 738 through flow blocking member 736 and repetitive discharge of liquid from chamber 738 through dispensing valve 310.
The operation and fluid dynamics of this embodiment of flow-control/flow-regulation element 314 is now described in further detail.
The pressure PI that forces liquid 106 towards flow blocking member 736 is assumed to be controllable and constant. Initially, flow blocking member 736 and dispensing valve 310 are open to "prime" the chamber 738.
After priming, dispensing valve 310 closes. Flow blocking member 736 closes with a selected delay Tl. As a consequence of delay TI , chamber 738 is pressurized. The pressure P2 within chamber 734, and/or it's diameter D2, is a function of:
[ 1 ] (PI x TI )/R1, where: RI is the fluidic resistance of the resilient chamber 738.
Dispensing valve 310 opens for a time T2 to dispense liquid contained in chamber 738. Time T2 is controlled by the system, as described below.
Assuming that all system parameters (e.g, the flow toward flow blocking member 736, the viscosity of liquid 106, etc.) are stable, the volume of liquid dispensed per pulse is constant, as well. The liquid volume that enters and pressurizes chamber 738 varies as a function of viscosity/temperature, and upstream conditions (e.g., contamination of the conduit feeding flow blocking member 736, etc.).
All other parameters, including pressure Pl, and "open" time Tl and T2, are controllable.
Consequently, pressure P2 inside chamber 738, or the dimension D2 of chamber 738, depends on the liquid viscosity and other upstream parameters (primarily, the condition of the channel feeding flow blocking member 736).

WO 01/19432 CA 02384520 2002-03-11 pCT~JS00/25411 Based, therefore, on a reading of pressure P2 or dimension D2, the "open"
time T2 of dispensing valve 310 is suitably adjusted to adjust the volume of dispensed liquid. Closed loop control of the time T2 assures proper compensation for all system variations, since such variations occur "upstream" of dispensing valve 310.
Closed loop control can be manually implemented in response to measurement data, or, alternatively, the flow monitor/controller can be instrumented for automatic control.
FIG. 8 depicts automated control system 842 for use in conjunction with flow-control/flow-regulation element 314.
Signal ms from measurement device 740 is transmitted to controller C. As appropriate, transmission electronics (not shown) are suitably used to transduce/transmit the signal ms to controller C as is appropriate for the nature of that signal.
As previously indicated, conditions within chamber 738 are dependent on the viscosity/temperature of the dispensable liquid. As such, automated control system I S 842 includes lookup-table LT for providing the "set-point" sp for controller C as a function of liquid viscosity, temperature, etc.
Controller C measures the difference between set-point sp and measurement signal ms. That difference, the "error," is manipulated by controller C in well known fashion to provide the controller output, control signal cs. The control signal corrects the open time T2 of dispensing valve 310 to drive the error to zero.
It will be appreciated that automatic control of flow-control/flow-regulation element 314 can suitably be implemented in many different ways. It is within the capabilities of those skilled in the art to appropriately instrument and arrange flow-control/flow-regulation element 314 for automatic flow control.
The performance of dispensing valve 310 is monitored taking a follow-up reading of pressure P2 inside chamber 738 immediately after the dispensing pulse (i.e., at the end of time T2). The drop in pressure P2 should correlate with time T2.
Lack of correlation indicates a problem, as is addressed in more particularity in conjunction with FIG. 9.

WO 01/19432 CA 02384520 2002-03-11 pCT~S00/25411 FIG. 9 depicts a plot of pressure P2 within chamber 738 versus timing TI
(i.e., flow blocking member 736 open time) and T2 (i.e., dispensing valve 310 open time).
For clarity of presentation, times TI and T2 are shown as being equal. It will be appreciated that typically, time TI is different than time T2.
Dispensing cycles 1 and 2 are assumed to show the baseline or normal pressure changes during the dispensing cycle. In particular, cycle 1 shows pressure P2 dropping from an upper pressure level UL to a lower pressure level LL as dispensing valve 310 opens for time T2 to dispense liquid from chamber 738.
The upper level UL, which is the liquid supply pressure Pl, is assumed to be the "normal"
or baseline pressure for a fully charged chamber 738.
After dispensing valve 310 closes, chamber 738 is re-supplied by opening flow blocking member 736 for time Tl. The plot shows pressure P2 rising from lower pressure level LL to upper pressure level UL as flow blocking member 736 opens for time TI to admit liquid to chamber 738. The action of dispensing valve 310 I S is pulsed, which is the reason for the sequential pressuring to Pl.
Deviations from these baseline conditions are indicative of problems. For example, in cycle 3, pressure PZ does not fall to the baseline, such that there is an offset 03, between the prevailing pressure and lower pressure level LL. Offset 03 is indicative of a clog in dispensing valve 310 (or a nozzle on the outlet of dispensing valve 310). To compensate for such a problem, time T2 - the open time of dispensing valve 310 - is increased.
After cycle 4, pressure P2 does not reach the upper pressure level UL, as shown by offset 04. This is indicative of a clog upstream of arrange flow-control/flow-regulation element 314. To compensate for such a problem, time TI
the open time of the flow blocking member 736 - is increased.

Claims (16)

1. A liquid dispenser comprising:
a pressurized liquid source;
a dispensing valve;
a conduit that places said pressurized liquid source in fluid communication with said dispensing valve; and a flow-control/flow-regulation element that is operably engaged to said conduit, wherein said flow-control/flow-regulation element is operable to affect or monitor a flow of liquid through said conduit.

2. The liquid dispenser of claim 1 wherein said flow-control/flow-regulation element comprises a flow restriction that restricts said flow of liquid into said conduit, wherein:
said flow restriction has a first orifice;
said dispensing valve has a second orifice; and wherein said first orifice is smaller than said second orifice.

3. The liquid dispenser of claim 1, wherein at least a portion of said conduit is elastic.

4. The liquid dispenser of claim 3 wherein said flow-control/flow-regulationelement comprises a dynamic pressure sensor that is operable to sense pressure within said elastic portion of said conduit.

5. The liquid dispenser of claim 3 wherein said flow-control/flow regulation element comprises a resilience-adjusting element that is operable to adjust a resilience of said elastic portion of said conduit.

6. The liquid dispenser of claim 4 wherein said resilience-adjusting element comprises:
an enclosure that surrounds at least a part of said elastic portion, said enclosure and said part of said elastic portion defining a pressure-tight chamber; and a pressure-adjustment element operable to adjust pressure within said enclosure.

7. The liquid dispenser of claim 6 wherein said pressure-adjustment element comprises:
a gas-supply conduit in fluid communication with said pressure-tight chamber;
and a regulator operable to regulate pressure within said pressure-tight chamber.

8. The liquid dispenser of claim 3 wherein said flow-control/flow-regulation element comprises a flow blocking member and a measurement device, wherein:
a region of said conduit between said flow blocking member and said dispensing valve define a chamber for controllably retaining a volume of liquid;
said flow-blocking member is operable to admit liquid into said chamber;
said dispensing valve is operable to dispense liquid from said chamber; and said measuring device is is operably engaged to said chamber to obtain data pertaining to one or more system parameters that are indicative of an amount of said liquid discharge from said chamber.

9. The liquid dispenser of claim 8 wherein said measuring device is a dynamic pressure sensor.

10. The liquid dispenser of claim 9 wherein said dynamic pressure sensor engages an exterior surface of said chamber.

11. The liquid dispenser of claim 8 wherein said flow-control/flow-regulation element further comprises:
processing electronics for processing said data to determine a pressure within said chamber; and a display device for displaying said pressure.

12. The liquid dispenser of claim 11 wherein said flow-control/flow-regulation element further comprises an automated closed loop control system operable to adjust operation of said dispensing valve to control discharge of said liquid.

13. The liquid dispenser of claim 12 wherein said automated closed loop control system comprises a controller that is operable to:
receive said data obtained by said measurement device;
receive a set point;
determine an offset between said data and said set point; and generate a control signal for adjusting operation of said dispensing valve to reduce said offset.

14. The liquid dispenser of claim 13 wherein said automated closed loop control system further comprises a look-up table comprising temperature and viscosity data for said liquid.

15. The liquid dispenser of claim 13 wherein said controller is further operable to:
control operation of said flow blocking member; and adjust an upstream pressure of said liquid.

16. The liquid dispenser of claim 12 wherein said automated closed loop control system comprises Proportional-Integral-Derivative control.