WO2007127389A2

WO2007127389A2 - Method and apparatus for controlling fluid flow

Info

Publication number: WO2007127389A2
Application number: PCT/US2007/010277
Authority: WO
Inventors: James W. Kenney
Original assignee: Drummond Scientific Company
Priority date: 2006-04-27
Filing date: 2007-04-27
Publication date: 2007-11-08
Also published as: EP2016286A2; JP5185256B2; WO2007127389A3; US20070253832A1; CN101443551B; JP2009535557A; EP2016286B1; CN101443551A; EP2016286A4

Abstract

A method and apparatus for controlling bi-directional fluid flow. The apparatus has a pump (20) that operates in a continuous pump cycle having a pressure phase and a vacuum phase. A conduit (19) connects a common pump port to a utility port (29). An electrically- controlled valve (22) regulates air flow through the conduit. The valve operates between a first position isolating the pump and the utility port, and a second position connecting the pump and the utility port in fluid communication. A detector (18) continuously detects and communicates a signal identifying whether the pump is operating in the pressure or vacuum phase of the pump cycle A controller (24) uses the detector signal to synchronize actuation of the valve with the pump cycle to generate either continuous positive or continuous negative pressure at the utility port

Description

Method and Apparatus for Controlling Fluid Flow

Field of the Invention

[0001] The present invention relates to an apparatus and method for controlling fluid flow.

Background of the Invention

[0002] Devices that control both negative (vacuum) and positive (pressure) fluid flow are known in the prior art. Such devices typically include a bi-directional pump, such as a diaphragm pump, having both a pressure port and a vacuum port. The pump includes a plurality of internal, mechanical valves (usually flap type) that cyclically open and close to create sustained negative fluid flow at the vacuum port and sustained positive fluid flow at the pressure port.

[0003] To control bi-directional fluid flow through a common utility port, it is known to connect the pressure and vacuum ports of the pump to a second mechanical valve, which selectively connects in fluid communication the common utility port with one of either the pressure or vacuum ports of the pump. The valve is controlled by an operator to selectively create either vacuum or pressure at a downstream utility port. An operator may control the valve by, for example, depressing one of either a positive or negative pressure trigger. An example of a bi-directional, fluid-flow device is a laboratory pipetting device that admits and emits fluid to a disposable pipette. Summary of the Invention

[0004] The present invention provides an apparatus for controlling fluid flow.

In a preferred embodiment, the invention controls bi-directional fluid flow through a utility port by synchronizing movement of a single, electrically-actuated control valve with the alternating phases of a pump. An embodiment of the invention comprises a pipetting device for admitting and emitting fluid from a disposable pipette. [0005] In one embodiment, the bi-directional, fluid-flow control device generally comprises a utility port, a bi-directional pump, an electrically-controlled valve, a detector, and a controller. The controller is connected to the detector and the valve. The user activates the device using a user interface connected to the controller. [0006] The pump produces bi-directional fluid flow at a common port and operates in a continuous pump cycle having a pressure phase and a vacuum phase. A conduit connects the common pump port to the utility port. In one embodiment, the pump includes a reciprocating volume-displacement element that creates positive air pressure during one half of the pump cycle and creates negative air pressure during the other half of the pump cycle.

[0007] The electrically-controlled valve regulates air flow through the conduit.

The valve operates between a first position isolating the pump and the utility port, and a second position connecting the pump and the utility port in fluid communication. In a preferred embodiment, the valve comprises a three-way solenoid valve having a common port connected to the pump, a normally-open (NO) port vented to the atmosphere, and a normally-closed (NC) port connected to the utility port. The valve connects the NC port and the common port in fluid communication in the second position and connects the NO port and the common port in fluid communication in the first position. In an alternative embodiment, the valve comprises a first, electrically- actuated, two-way valve controlling fluid flow through the conduit, and a second, electrically-actuated, two-way valve controlling fluid flow from the pump to the atmosphere.

[0008] The detector continuously detects and communicates a signal identifying whether the pump is operating in the pressure or vacuum phase of the pump cycle. For example, the detector may comprise a photosensor that detects movement of the volume-displacement element or other cyclically-moving element of the pump. Alternatively, the detector may comprise an ultrasonic sensor that detects movement of the volume-displacement element.

[0009] The controller uses the detector signal to synchronize actuation of the valve with the pump cycle to generate either continuous positive or continuous negative pressure at the utility port. Negative pressure is generated at the utility port by cyclically actuating the valve to the second position during the negative pressure phase and then actuating the valve back to the first position during the pressure phase. Positive pressure is generated at the utility port by cyclically actuating the valve to the second position during the pressure phase and then actuating the valve back to the first position during the vacuum phase of the pump cycle.

[00010] In a further embodiment of the invention, the device includes means for controlling the flow rate through the utility port. In this embodiment, the controller changes the length of time the valve is actuated to the second position during either phase of the pump cycle. [00011] In yet another embodiment of the invention, the device includes means for controlling the flow of a measured volume (V) of fluid through the utility port. In this embodiment, the volume displacement per stroke (DPS) of the pump is either calculated or experimentally determined and programmed into the controller. The controller calculates and operates the pump for a calculated number (N) of pump cycles based on the DPS of the pump. In this embodiment, the device may include a sensor that measures the head pressure at the utility port and communicates the head pressure to the controller. The controller uses the head pressure to calculate more accurately the number (N) of pump cycles needed to meet the predetermined required volume.

[00012] The invention also provides a method of controlling positive and negative fluid flow through a utility port. In accordance with the method, a fluid flow source is provided that cyclically produces positive and then negative fluid pressure during a pressure phase and then vacuum phase, respectively, of a repeating cycle. The source is continuously detected to determine whether the source is operating in the pressure phase or vacuum phase. To produce positive fluid flow through the utility port, the fluid flow source is connected in fluid communication with the utility port during the pressure phase and isolated from the utility port during the vacuum phase. To produce negative fluid flow through the utility port, the fluid flow source is connected in fluid communication with the utility port during the vacuum phase and isolated from the fluid flow source port during the pressure phase. [00013] In a further embodiment of the method of the invention, the flow rate through the utility port is controlled by changing the length of time the fluid flow source is connected in fluid communication with the utility port during either the pressure or vacuum phase of each cycle.

[00014] In an additional embodiment of the method of the invention, a predetermined, measured volume (V) of fluid is delivered through the utility port by calculating and operating the pump for a calculated number (N) of pump cycles based on the volume displacement per stroke (DPS) of the pump. In this embodiment, the head pressure at the utility port may be measured to more precisely calculate the number (N) of pump cycles, especially for controlling fluid flow of compressible fluids.

[00015] In an additional embodiment, the apparatus controls uni-directional fluid flow through the utility port by controlling actuation of an electrically-actuated control valve.

Brief Description of the Drawings

[00016] Fig. 1 is a schematic illustration of an apparatus for controlling fluid flow in accordance with an embodiment of the invention;

[00017] Fig. 2 is a schematic illustration of the diaphragm pump and detector shown in Fig. 1;

[00018] Figs. 3a— 3d are fragmentary schematic illustrations of a pump motor shaft and detector in accordance with alternative embodiments of the invention;

[00019] Fig. 4 is a schematic illustration of a diaphragm pump and detector in accordance with a further embodiment of the invention; [00020] Fig. 5 is a schematic illustration of an embodiment of an electrically- actuated valve shown in Fig. 1 ;

[00021] Fig. 6 is a graph illustrating the cyclical phases of the pump shown in Fig. 1;

[00022] Fig. 7 is a schematic illustration of an apparatus for controlling fluid flow having a head pressure detector in accordance with an additional embodiment of the invention;

[00023] Fig. 8 is a schematic illustration of an apparatus for controlling fluid flow having a pair of electrically-actuated, two-way valves in accordance with a further embodiment of the invention;

[00024] Fig. 9 is a schematic illustration of an apparatus for controlling unidirectional fluid flow in accordance with yet another embodiment of the invention; and,

[00025] Fig. 10 is a pipetting device in accordance with another embodiment of the invention.

Description of Preferred Embodiments

[00026] For the purpose of illustration, there is shown in the accompanying drawings several embodiments of the invention. However, it should be understood by those of ordinary skill in the art that the apparatus and method of the present invention are not limited to the precise arrangements and instrumentalities shown therein and described below. [00027] As used herein, the term "bi-directional pump" means a pump that alternately creates positive (pressure) and then negative (vacuum) displacement during a repeating pump cycle. The term "uni-directional pump" means a pump that creates only either positive or negative displacement.

[00028] A fluid flow device in accordance with a first embodiment of the present invention is shown in Fig. 1 and is designated generally by reference numeral 10. The fluid flow device 10 generally comprises a detector 18, a bi-directional pump 20, an electrically-controlled valve 22, and a controller 24, which are contained within a housing 28 having a single utility port 29. Depending on the direction of fluid flow, the utility port 29 acts as either an input or exit port. A fluid flow conduit 19 connects the pump 20 to the utility port 29. Preferably, the valve 22 is located intermediate the conduit 19. A user interface 25 is located outside the housing 28. The fluid flow device 10 selectively provides either continuous positive or continuous negative fluid flow at the utility port 29.

[00029] In a preferred embodiment, the pump 20 comprises a diaphragm pump having a housing 30, a single, common fluid flow port 46, and a flexible diaphragm 34 bifurcating the piston chamber 32 as seen in Fig. 2. The diaphragm 34 is attached by a yoke 36 to one end of a drive rod 38. The other end of the drive rod 38 is eccentrically connected to a flywheel 40, which is centrically connected to the shaft 42 of a motor (not shown). Rotation of the shaft 42 and flywheel 40 causes the drive rod 38 and diaphragm 34 to move upwardly and downwardly, thereby creating positive pressure at the common port 46 on the upstroke and negative or vacuum pressure at the common port 46 on the downstroke. The pump has no valving between the diaphragm 34 and the common port 46. The pump 20 alternately produces positive pressure and then negative pressure throughout the pump cycle, the duration of which is a single rotation of the motor shaft 42.

[00030] The detector 44 continuously monitors whether the pump 20 is operating in the positive pressure or negative pressure phase of the pump cycle. In a preferred embodiment, the detector 44 monitors the phase of the pump cycle by tracking movement of a cyclically-moving (either linear or rotational movement) element of the pump 20. In the embodiment shown in Fig. 2, the detector 44 comprises a photosensor, which is located within the pump housing 30, and which reflects light off the surface of the flywheel 40. To differentiate the phases of the pump cycle, one half 40a of the flywheel 40 has a dark, non-reflective surface (shown in cross hatch) and the other half 40b of the flywheel 40 has a light, reflective surface. In this embodiment, the detector 44 and flywheel 40 are synchronized so that the detector 44 reads the boundary between the reflective and non-reflective surfaces at the same time the pump 20 transitions from one phase of the pump cycle to the other. [00031] Additional embodiments of detector/flywheel arrangements are shown in Figs. 3a - 3d. In the embodiment shown in Fig. 3, the detector 144 emits and detects light reflected off the surface of the motor shaft 142. In this embodiment, the shaft has a dark, non-reflective band 142a (shown in cross hatch) extending 180 degrees around the radial surface of the shaft 142. The other 180 degree portion 142b of the shaft has a light, reflective surface. The detector 144 is axially aligned with the non-reflective band 142a of the shaft 142. In this embodiment, the detector 144 and shaft 142 are synchronized so that the detector 144 reads the boundary between the reflective and non-reflective surfaces at the same time the pump 20 transitions from one phase of the pump cycle to the other.

[00032] Tn the embodiment shown in Fig. 3b, the detector 244 comprises a Hall effect transducer that interacts with a magnetic encoder on the flywheel. To differentiate the phases of the pump cycle, the encoder on one half 240a of the flywheel 240 has an opposite polarity than the encoder on the other half 240b of the flywheel. The detector 244 and flywheel 240 are synchronized so that the detector 44 detects a change in polarity at the same time the pump 20 transitions from one phase of the pump cycle to the other.

[00033] In the embodiment shown in Fig. 3c, the detector 344 comprises a microswitch and cam-shaped flywheel 340. The microswitch includes a cam follower

347 that tracks the outer, irregularly-shaped periphery of the flywheel 340. The detector 344 and flywheel 340 are synchronized so that the microswitch is either opened or closed at the same time the pump 20 transitions from one phase of the pump cycle to the other.

[00034] In the embodiment shown in Fig. 3d, the detector 444 detects light directly emitted from a source 445. The flywheel 440 has an irregular shape that cyclically interrupts the line of sight between the light source 445 and the detector.

The detector 444 and flywheel 440 are synchronized so that the detector 444 detects an interruption and then resumption of the light source at the same time the pump 20 transitions from one phase of the pump cycle to the other.

[00035] In yet another embodiment shown in Fig. 4, the detector 544 comprises an ultrasonic sensor 544 mounted inside piston chamber 532. The ultrasonic sensor 544 emits sound waves towards the diaphragm 534 to continuously measure the distance between the detector 544 and the diaphragm 534. In this embodiment, a maximum or minimum distance reading between the detector 544 and the diaphragm 534 indicates a transition from one phase of the pump cycle to the other. Other types of detectors may be used so long as the detector is capable of continuously determining the phase in which the pump is operating and electronically transmitting a signal to the controller that identifies the phase.

[00036] The electrically-actuated valve 22 is located intermediate the conduit 19 connecting the pump 20 to the outlet port 29. In a preferred embodiment, the valve 22 comprises a three-way solenoid valve such as shown in Fig. 5. The solenoid valve 22 has a housing 52 with a normally-closed (NC) port 54, a common port 56, and a normally-open (NO) port 58. The NC port 54 is connected to the utility port 29 by a section 19b of the conduit 19. The common port 56 of the valve is connected to the common port 29 of the pump by a section 19a of the conduit 19. The NO port 58 vents to the atmosphere.

[00037] The solenoid valve has a ferrous reciprocating element 60, which has a valve head 61 at one end and a cylindrical base 63 at the other end. An induction coil 64 surrounds the base 63 while a compression spring 68 surrounds the head 61. First and second seals 70, 72 are seated on opposed ends of the head 61. The compression spring 68 normally biases the valve head 61 to a first position wherein the common port 56 is arranged in fluid connection with the NO port 58 and the NC 54 port is closed. In the first position, the internal conduit 19 between the pump 20 and the utility port 29 is closed. When the induction coil 64 is energized, a magnetic field urges the valve head 61 to a second position wherein the common port 56 is arranged in fluid connection with the NC 54 port 58 and the NO port 58 is closed. In the second position, the internal conduit 19 between the pump 20 and the utility port 29 is open.

[00038] In the embodiment shown Fig. 1, the user interface 26 comprises a first trigger 26, which activates the device in the positive pressure mode, and a second trigger 27, which activates the device in the negative pressure mode. In a preferred embodiment, the device 10 is inactive until one of the triggers is a depressed. Alternatively, other forms of input device such as pressure sensitive transducers, capacitance transducers, multi-directional joy stick, key pad, computer, or other electronic input devices may be connected to the controller 24. [00039] The valve 22, detector 44, and user interface 26 communicate with the controller 24. The detector 44 continuously transmits to the controller 24 a signal identifying the phase of the pump cycle in which the pump is operating. The controller 24 synchronizes actuation of the valve 22 with the cycle of the pump 20 to create a sustained flow of either positive or negative air flow to the utility port 29. If positive pressure is desired at the utility port 29, the solenoid is energized only during the positive pressure phase of the pump cycle, i.e., t=0 to t?=T/2. Then, from t=T/2 to t=T, the solenoid valve is de-energized. When the valve 22 is energized, it moves from the first position to the second position, described above. Conversely, if vacuum pressure is desired at the utility port 29, the solenoid valve 22 is energized only during the negative pressure phase of the pump cycle, i.e., t=T/2 to t=T. Because the detector 44 and solenoid valve 22 have very fast response times, the aforementioned cycle (either positive or negative pressure) can be repeated at a very high frequency to create a continuous, sustained flow of fluid either into or out of the utility port 29. [00040] If a digital detector is provided, such as the detector 44 of the embodiment shown in Fig. 2, the signal has the square wave illustrated in Fig. 6a, which illustrates voltage (v) as a function of the pump cycle. If an analog detector is provided, such as the detector 544 of the embodiment of Fig. 4, the signal has the sinusoidal shape shown in Fig. 6b, which illustrates distance (d) of the diaphragm from a neutral position as a function of the pump cycle.

[00041] In another embodiment of the invention, the device not only selectively creates negative or positive pressure at the utility port 29, but also controls additional fluid flow properties. For example, the flow rate through the utility port 29 can be varied by controlling the amount of time the valve 22 is energized during either phase of the pump cycle. Referring to Figs. 6a and 6b, the flow rate exiting the utility port 29, represented by cross hatch, is reduced by 50% if the valve is energized only during the time period t=0 to t=T/4, and then closed during the remainder of the positive pressure phase of the pump cycle, i.e., t=T/4 to t=T/2, and the entirety of the negative pressure phase of the pump cycle, i.e., t=T/2 to t=T.

[00042] To communicate the desired flow rate to the controller, the triggers 26,

27 may be connected to potentiometers. The user controls the volumetric flow rate by controlling the distance each trigger 26, 27 is depressed. Other known user interface devices such as described above could be substituted for the triggers 26, 27. [00043] In another embodiment of the invention shown in Fig. 7, the device 110 delivers a measured volume (V) of fluid through the utility port 129. In this embodiment, the volume displacement per unit stroke (DPS) of the pump 120 is programmed into the controller 124. The DPS may be calculated based on the dimensions of the pump 120 or experimentally calculated using a calibration scale. The controller 124 calculates and allows the pump 120 to operate for the requisite number (N) of strokes to deliver the desired volume (V) of fluid. Data from the detector 118 allows the controller 124 to count each stroke of the pump. [00044] In this embodiment, the user interface 125 may comprise a keypad or a computer. The keypad 125 may include a plurality of input keys 127 and an LCD 128, which displays a wide variety of additional control options that have been programmed into the controller.

[00045] In this embodiment, the device 110 includes a sensor 178 that measures the external pressure or head at the utility port 129. The pressure sensor 178 communicates the head pressure to the controller 124, which factors this value into the ideal gas equation of state (pV=nRT) and Boyle's law to more accurately calibrate the number (N) of strokes of the pump 20 required to deliver the specified volume (V) of fluid. The pressure sensor 78 is preferably provided if the device 110 is controlling the flow of a compressible fluid at constant temperature such as air, whose properties are governed by the equation

[00046] The aforementioned embodiments have been described with reference to a motor-driven diaphragm pump. However, it should be appreciated that other types of bi-directional pumps may be used without departing from the invention. For example, a solenoid-activated diaphragm pump, such as manufactured by MEDO U.S.A., Inc., may be used. Other types of bi-directional pump may be used so long as the detector can continuously determine the phase of the pump cycle in which the pump is operating.

[00047] Similarly, the aforementioned embodiments have been described with reference to a detector that continuously determines the phase in which the pump is operating by tracking movement of a cyclically-moving element of the pump. However, depending on the type of pump, other types of detectors may be used so long as it is capable of continuously determining the phase in which the pump is operating and electronically transmitting a signal to the controller that identifies the phase. For example, if a solenoid-activated pump is used, the detector may identify the transition from one phase to another by detecting a change in polarity created by the solenoid.

[00048] The aforementioned embodiments have been described with reference to an electrically-actuated, three-way solenoid valve. However, it should be appreciated that the three-way valve could be replaced by other arrangements of electrically- actuated valves such as shown in Fig. 8. In this embodiment, the device 210 includes a detector 218, bi-directional pump 220, controller 224, and user interface 225 that are similar in construction and arrangement as described above. However, in this embodiment, the three-way solenoid valve of the embodiment in Fig. 1 is replaced with a pair of electrically-actuated, two-way valves, 280, 281, each of which regulates fluid flow through one branch of a manifold 283 connected to the common port 246 of the pump 220. One valve 280 regulates fluid flow from the pump 220 to the utility port 229 via a fluid flow conduit 219. The other valve 281 regulates fluid flow from the pump 220 to an atmospheric vent 282. [00049] Using the input signal from the detector 218, the controller 224 selectively opens and closes the valves 280, 281 in synchronization with the phases of the pump cycle to create either positive or negative pressure at the utility port 229. In the embodiment shown in Fig. 8, the valves 280, 281 comprise Piezo ceramic element valves, which are known to have the fast response time required to synchronize with the changing phases of the pump 220.

[00050] The aforementioned embodiments have been described with reference to a bi-directional pump. However, in a further embodiment of the invention, the device controls uni -directional fluid flow. In this embodiment, the device 310 includes a unidirectional pump 385, controller 324, user interface 325, and electrically-actuated, three-way valve 322. The device 310 may also include a detector 318. In this embodiment, the valve 322 comprises a solenoid valve such as described above. Similar to the embodiments described above, the controller 324 selectively actuates the valve 322 to deliver fluid at preset intervals, controlled quantities, measured volumes (V)₅ defined flow rates, and other properties or steps. [00051] It should be appreciated by those of ordinary skill in the art that the above-described embodiments of the invention may be used to control the flow of both compressible and incompressible fluids in a wide variety of environments. By way of example only, one specific embodiment is described below. [00052] A pipetting device in accordance with a further embodiment of the present invention is shown in Fig. 10 and is designated generally by reference numeral 410. The pipetting device 410 is constructed to admit and emit fluid from a disposable pipette 406, which may vary in size and shape. [00053] In the embodiment shown in Fig. 10, the pipetting device 410 has the shape of a known "gun-type" pipettor, which is easily gripped by the user 408 (shown in phantom). However, the device 410 could be made in a variety of shapes and sizes. [00054] The housing 411 of the pipetting device 412 has a handle portion 414 and a barrel portion 415 oriented transversely to the handle portion 414. A nosepiece or pipette connector 416 is fixed to and oriented downwardly transverse to the barrel portion 415. The pipette connector 416 is constructed and arranged to removably attach pipettes 406 of various lengths and diameters. The pipette connector 16 may include a hydrophobic filter 417, which may be removed and replaced. The filter 417 prevents contamination of the pipetting device 410 in the event the pipette 18 is overadmitted with fluid.

[00055] The device 412 has a bi-directional pump 420, control valve 422, and controller 424. An internal conduit 419 connects the pump 420 to the pipette connector 416. The control valve comprises a three-way, electrically-actuated solenoid valve 422 and is located intermediate the internal conduit 419. A detector (not shown) is built into the pump 420. A positive air flow trigger 426 and negative air flow trigger 428 extend from the handle portion 414 and are connected to the controller 424.

[00056] In the manner described above, the controller 424 actuates the valve

422 in response to signals generated by depression of either the positive air flow trigger 426 or negative air flow trigger 428. Additionally, the pipetting device may be provided with a more sophisticated user interface, which would allow the user to control the wide variety of fluid flow properties described above.

Claims

1. A device for controlling bi-directional fluid flow, comprising: a) a utility port; b) a pump that produces bi-directional fluid flow at a common port and operates in a continuous pump cycle having a pressure phase and a vacuum phase; c) a conduit connecting said common pump port to said utility port; d) an electrically-controlled valve that regulates air flow through said conduit, said valve operating between a first position isolating said pump and said utility port, and a second position connecting said pump and said utility port in fluid communication; e) a detector that continuously detects and communicates a signal identifying whether said pump is operating in the pressure or vacuum phase of the pump cycle; and, f) controller connected to said detector and said valve, said controller using the detector signal to synchronize actuation of said valve with the pump cycle to generate either continuous positive or continuous negative pressure at said utility port.

2. The device recited in claim 1, wherein negative pressure is generated at said utility port by cyclically actuating said valve to the second position during the negative pressure phase and then actuating the valve back to the first position during the pressure phase, and positive pressure is generated at said utility port by cyclically actuating said valve to the second position during the pressure phase and then actuating the valve back to the first position during the vacuum phase of the pump cycle.

3. The device recited in claim 2, including means for controlling the flow rate through said utility port.

4. The device recited in claim 3, wherein said flow rate control means changes the length of time said valve is actuated to the second position during either phase of the pump cycle.

5. The device recited in claim 1, said pump including a reciprocating volume-displacement element that creates positive air pressure during one half of the pump cycle and creates negative air pressure during the other half of the pump cycle.

6. The device recited in claim 5, wherein said detector comprises a photosensor that detects movement of said volume-displacement element.

7. The device recited in claim 5, wherein said detector comprises an ultrasonic sensor that detects movement of said volume-displacement element,

8. The device recited in claim 1, including means for controlling the flow of a measured volume (V) of fluid through said utility port.

9. The device recited in claim 1, wherein said volumetric control means calculates and operates said pump for a calculated number (N) of pump cycles based on the volume displacement per stroke (DPS) of the pump.

10. The device recited in claim 1, wherein said valve comprises a three-way solenoid valve having a common port connected to said pump, a normally-open (NO) port vented to the atmosphere, and a normally-closed (NC) port connected to said utility port.

11. The device recited in claim 10, wherein said valve connects said NC port and said common port in fluid communication in the second position and connects said NO port and said common port in fluid communication in the first position.

12. The device recited in claim 1, wherein said valve comprises a first, electrically-actuated, two-way valve controlling fluid flow through said conduit, and a second, electrically-actuated, two-way valve controlling fluid flow from said pump to the atmosphere.

13. The device recited in claim 1, including a user interface connected to said controller.

14. The device recited in claim 9, including a sensor that measures the head pressure at said utility port and communicates the head pressure to said controller.

15. The device recited in claim 14, wherein said volumetric control means uses the head pressure to calculate the number (N) of pump cycles needed for the predetermined volumetric delivery.

16. A device for controlling bi-directional fluid flow, comprising: a) a utility port; b) a pump that produces bi-directional fluid flow at a common port and operates in a continuous pump cycle having a pressure phase and a vacuum phase; c) means for connecting said common port and said utility port in fluid communication; d) means for regulating air flow between said common port and said utility port, said regulating means operating between a first position isolating said common port and said utility port, and a second position connecting said common port and said utility port in fluid communication; e) means for continuously detecting whether said pump is operating in the pressure phase or vacuum phase of the pump cycle; and, f) control means connected to said detecting means and said regulating means, said control means synchronizing actuation of said regulating means with the pump cycle to generate either continuous positive or continuous negative pressure at said utility port.

17. The device recited in claim 16, including means for controlling the flow rate through said utility port.

18. The device recited in claim 16, including means for controlling the flow of measured volumes (V) of fluid through said utility port.

19. The device recited in claim 16, wherein said detecting means detects movement of a cyclically-moving element of said pump.

20. A method of controlling positive and negative fluid flow through a utility port, comprising the steps of: a) providing a fluid flow source that cyclically produces positive and then negative fluid pressure during the pressure phase and then vacuum phase, respectively, of a repeating cycle; b) continuously detecting whether said source is operating in the pressure phase or vacuum phase; c) producing positive fluid flow through the utility port by connecting said fluid flow source in fluid communication with said utility port during the pressure phase and isolating said fluid flow source from said utility port during the vacuum phase; d) producing negative fluid flow through the utility port by connecting said fluid flow source in fluid communication with said utility port during the vacuum phase and isolating said fluid flow source from said utility port during the pressure phase.

21. The method recited in claim 20, including the step of controlling the flow rate through the utility port.

22. The method recited in claim 20, including the step of delivering measured volumes of fluid through the utility port.

23. A pipetting device for admitting and emitting fluid from a disposable pipette, comprising: a) a housing having a hand grip portion, a pipette connector, and a user interface; b) a pump that produces bi-directional fluid flow at a common port and operates in a continuous pump cycle having a pressure phase and a vacuum phase; c) a conduit connecting said pump to said pipette connector; d) an electrically-controlled valve that regulates air flow through said conduit, said valve operating between a first position isolating said pump and said utility port, and a second position connecting said pump and said utility port in fluid communication; e) a detector that continuously detects and communicates a signal identifying whether said pump is operating in the pressure or vacuum phase of the pump cycle; f) controller connected to said detector and said valve, said controller using the detector signal to synchronize actuation of said valve with the pump cycle to generate either continuous positive or negative pressure at said pipette connector.

24. The device recited in claim 1, wherein fluid is admitted to the pipette by cyclically actuating said valve to the second position during the negative pressure phase and then actuating said valve back to the first position during the pressure phase, and fluid is emitted from the pipette by cyclically actuating said valve to the second position during the pressure phase and then actuating said valve back to the first position during the vacuum phase of the pump cycle.

25. The device recited in claim 23, including means for controlling the flow rate through the pipette.

26. The device recited in claim 23, including means for admitting or emitting measured volumes of fluid through the pipette.

27. The device recited in claim 23, including a sensor that measures the head pressure at said pipette connector.

28. The device recited in claim 23, said pump comprising a diaphragm pump having a motor with shaft, and a reciprocating volume-displacement element connected to said shaft, said element creating positive pressure during one half of the pump cycle and creating negative pressure during the other half of the pump cycle.

29. The device recited in claim 25, wherein reciprocation of said element through one complete pump cycle is synchronized with a single rotation of said shaft.

30. The device recited in claim 29, wherein said detector comprises a photosensor that measures the angular location of said pump shaft.

31. The device recited in claim 23, wherein said valve comprises a three- way solenoid valve having a common port connected to said pump, a normally-open (NO) port vented to the atmosphere, and a normally-closed (NC) port connected to said pipette connector.