Automatic Spray Dispenser For Pressurized Fluid

Abstract

A solenoid operated valve has a moveable armature piston restricting the flow of pressurized fluid introduced at the inlet end of a cylinder towards an outlet at its opposite end. A resilient closure member on the outlet end of the piston contacts a protruding outlet valve seat to maintain the valve closed until the solenoid coil is energized, at which time the outlet is opened momentarily to release a predetermined amount of pressurized fluid at the outlet end of the cylinder to a spray nozzle. The substantial flow impedance between the cylinder inlet and outlet results in a pressure differential between opposite ends of the piston that reseats and holds the closure member against the valve seat to prevent leakage.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to automatically timed pressurized fluid dispensers operated periodically to discharge a measured amount of pressurized fluid at predetermined intervals, and more particularly, to an improved dispenser of this type that prevents leakage of the pressurized fluid in the intermediate interval between the timed discharges.

2. Description of the Prior Art

Recently a variety of devices have been developed for automatically dispensing at predetermined periodic intervals measured amounts of pressurized fluids, such as insecticides, disinfectants, deodorants, respiratory decongestants, and similar materials commonly dispensed from aerosol spray containers. Initially electromechanical clockwork mechanisms were employed to operate a cam or linkage system, or to close a switch energizing a solenoid, that momentarily depressed the spring loaded valve stem on the conventional aerosol spray container. However, since considerable force is required to depress the valve stem of these containers, which are primarily designed for manual operation, electrical energy used for driving the clockwork mechanism and operating the solenoid had to be obtained from an AC outlet. Not only was the complex clockwork mechanism relatively expensive and fragile, but these devices could only be used where a convenient AC outlet was available.

More recently automatic dispensing devices have been developed that use a simple inexpensive electronic timer with a low power solenoid valve mechanism that could be operated over extended periods with conventional dry cell flashlight batteries. In these devices, instead of generating the considerable force necessary to depress the spring loaded valve stem on a conventional aerosol container, fluid within the container is applied directly to a simple solenoid valve either through an open access tube inserted into the container or through a special fitting that holds the container valve stem permanently depressed.

Typically such battery operated units had a valve arrangement with a resilient closure member attached to the solenoid armature to be held against an outlet valve seat until the solenoid coil is energized. The flux produced upon energization of the solenoid coil displaced the armature with its resilient closure member away from the valve seat to release the pressurized fluid through the open outlet to a spray nozzle. Unfortunately, with such valves, slow leakage of the pressurized fluid occurred during intervals between periodic sprays. Not only did this waste the fluid available for spraying from the container, but more importantly, the dripping of liquids, particularly such substances as strong disinfectants and insecticides, resulted in staining, paint removal or other damage to walls and other surfaces where the devices were commonly attached. Whereas positive valve closure to prevent leakage might be achieved using springs or heavy armatures to increase the force holding the resilient closure member against the valve seat, such expedients also required increased solenoid power to overcome this additional closure force, which correspondingly reducing the operating life of the batteries.

SUMMARY OF THE INVENTION

Automatic spray dispensers in accordance with this invention avoid leakage problems associated with the prior battery operated units by employing a unique solenoid valve arrangement wherein the occurrence of any leakage generates a force tending to push resilient closure member against the valve seat to stop leakage. In the preferred embodiment, the pressurized fluid to be sprayed is delivered to the inlet end of a cylinder containing the solenoid armature, which is located within a central opening of the solenoid coil. The solenoid armature made of a magnetic material forms an elongated piston that fits snugly for reciprocating movement within the cylinder. A resilient closure member attached to the adjacent end of the armature piston is normally held against a raised valve seat formed at the outlet end of the cylinder to maintain the valve closed preventing escape of the pressurized fluid until the solenoid coil is energized. Pressurized fluid introduced at the inlet end of the cylinder reaches the outlet end only through a relatively high impedance flow path, which in the preferred embodiment is defined by the small clearance between the inner diameter of the cylinder and outer diameter of the solenoid armature piston.

During the intervals between sprays the flow of pressurized fluid through this restricted path fills the annular space at the outlet end surrounding the raised valve seat to equalized the fluid pressures at opposite ends of the armature piston prior to solenoid energization. As the solenoid coil is energized by a current pulse, the resilient closure member momentarily lifts free of its valve seat allowing the pressurized fluid accumulated at the outlet end to be delivered in a short burst to the spray nozzle. As the fluid pressure at the outlet is released through the open outlet valve, a pressure drop is created between the inlet and outlet ends of the cylinder so that the greater force on the outlet end of the armature piston forces it downward against the valve seat. Since the high impedance flow path prevents rapid pressure equalization at opposite ends of the cylinder, any tendency for the closure member to lift from the valve seat to permit leakage in the interval between sprays is effectively counteracted, and since leakage would produce a pressure decrease at the outlet end, the resulting pressure differential would force the closure member against the valve seat.

In addition, by proper selection of the different force generating parameters, such as by having the force on the piston resulting from the pressure differential greater than the opening force applied by energization of the solenoid, the device may be made to prevent continuous release of the pressurized fluid in periodic sprays should the timer circuit malfunction in such a way that constant energizing current is supplied to the solenoid coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a preferred form of an improved automatic spray dispenser for pressurized fluids in accordance with the invention;

FIG. 2 is a top view of the device of FIG. 1 with the top cover removed;

FIG. 3 is a side sectional view of the automatic spray dispenser of FIG. 1 taken substantially along the line 3--3 of FIG. 2 showing its installation on a conventional aerosol container;

FIG. 4 is a schematic circuit diagram showing a preferred form of the timer circuit for periodically energizing the solenoid valve.

DETAILED DESCRIPTION

Referring now to FIG. 1, the improved spray dispenser 10 may employ a conventional aerosol container having a cylindrical can 12 with a cup shaped upper portion 14 containing an internal valve structure for dispensing the pressurized fluid contents. Typically the contents of the container 12 consist of a liquid mixture having an active liquid ingredient with a propellant, usually a halogenated hydrocarbon such as Freon, that has a high vapor pressure at atmospheric pressure and room temperature, so that the vapor pressure of the propellant expels the fluid mixture through a nozzle to produce a fine spray. An automatic spray dispenser mechanism in accordance with the invention is contained within a cylindrical housing 16 having a removable top cover 18 and a spray nozzle opening 20, and is removably attached as hereinafter described on the top portion 14 of the aerosol container 12.

Referring now to FIGS. 2 and 3, which illustrate the arrangement of components within the dispenser housing 16, the cup-shaped top portion 14 of the aerosol container 12 contains an upwardly projecting annular flange 22 with an inwardly projecting bead 24 surrounding an upright valve stem 26, which in the conventional aerosol can is adapted to be manually depressed to open the internal valve mechanism for releasing the pressurized fluid. A mounting partition 28 formed within the housing 16 contains a downwardly extending mating flange 30 with an outer annular groove for receiving the bead 24 so that the housing 16 is locked in position on the aerosol can 12 when the downwardly extending flange 30 is pushed into the upwardly extending flange 22. The flange 30 may contain narrow slots 32 spaced around the edge to provide the desired resiliency.

A vertical hole 34 extends through the center of the partition 28 and has a larger bore opening at its lower end for receiving the valve stem 26 to hold it depressed when the dispenser housing 16 is seated on the aerosol container 12, thus maintaining the internal valve arrangement open to release the pressurized fluid contents. One end of a tube 36 fits into an enlarged bore at the upper end of the hole 34 to deliver the pressurized fluid released from the aerosol container 12 to a solenoid 38 with a conventional annular coil winding 40 seated in an upright position within an annular depression in the upper surface of the partition 28. The solenoid coil 40 surrounds a cylindrical inner sleeve 42 that slideably receives an elongated cylindrical armature 44 of soft iron or other suitable magnetic material. The inside diameter of the sleeve 42 is only slightly larger of the outside diameter of the armature 44, which serves as a piston freely slideable within a vertical cylinder. A resilient closure member 46, preferably of hard synthetic rubber or an elastomeric plastic, is attached to the lower end of the armature 44 to contact a conically shaped valve seat formed at the tip of an upwardly extending protuberance 48 as an integral part of a cylindrical closure member 50 that is inserted into the lower or outlet end of the cylinder formed by the sleeve 42. An O-ring seal 52 to prevent fluid leakage from this end of the cylinder is carried in a groove around the closure member 50. Similarly a closure member 54 with an O-ring seal 56 seals the upper or inlet end of the cylinder formed by the sleeve 42, and both closure members 50 and 54 are held in place against opposite ends of the cylinder by a clamping arrangement consisting of an upper clamping plate 58 and a lower clamping plate 60 clamped together by elongated bolts 62 that extend through holes (not shown) provided in the partition 28 on opposite sides of the solenoid 38. The other end of the tube 36 is sealed in the upper portion of a hole 64 extending through the upper closure member 54 that defines an inlet passage into the upward or inlet end of the cylinder. Similarly a central hole extends through the lower closure member 50 from the conical valve seat at the tip of the protuberance 48 to define an outlet passage which has one end of an outlet tube 68 sealed in the enlarged bore at its lower end. The other end of the outlet tube 68 if formed as a spray nozzle with a reduced diameter to direct a spray through an opening formed in the dispenser housing 16 into the atmosphere.

Also contained within the housing is a small battery 72 that has its base removably inserted into an appropriately shaped depression formed in the partition 28 to hold it upright. A circuit board 74 secured by appropriate means to the upper surface of the housing partition 28 has various circuit elements as hereinafter described mounted thereon. A plastic covered terminal assembly 76 connects the battery terminals through insulated leads 78 to the circuit elements on the board 74 and insulated output leads 80 connect the circuit output terminals to supply periodic energizing current pulses to the solenoid coil windings 40.

Any suitable timing circuit or switching arrangement, preferably battery operated, may be employed for periodically energizing the solenoid, and a preferred form of such a timing circuit is illustrated and described in reference to FIG. 4. This particular circuit is both inexpensive and efficient since it employs only a small number of low cost circuit components and has very low operating power requirements. Generally the operation of such timer circuits are well known for light flasher applications where operating frequencies of approximately one cycle per second are employed.

The battery 72, typically a 9 -volt transistor radio battery, may be coupled through a manually operated switch 80 to deliver current pulses through a PNP-switching transistor 82 to energize the solenoid coil 40. An NPN-triggering transistor 84 has its collector terminal coupled through a resistor 86 to provide base current for periodically driving the switching transistor 82 into saturation so that an energizing current pulse is delivered from its collector terminal to the solenoid coil 40. The base terminal of the triggering transistor 84 is coupled to receive feedback signals through a capacitor 88 coupled in series with a resistor 90 from the collector of the switching transistor 82. The base of the triggering transistor 84 is also coupled to the emitter terminal of the transistor 82 through a large resistor 92 and its emitter is coupled to the negative terminal of the battery 72.

Upon closing the switch 80 to initiate operation of the timing circuit to produce periodic sprays from the dispenser, the voltage of the battery 72 is applied across the series circuit consisting of resistors 92 and 90, the capacitor 88 and the solenoid coil 40. With the emitter terminal of the NPN-triggering transistor 84 coupled to the negative battery terminal, the positive potential at the other battery terminal applied through the resistor 92, which for this application has a much greater resistance value than the resistor 90, initially results in a small positive potential at the base of the triggering transistor 84. This forward base-to-emitter bias causes the triggering transistor to begin conduction. With transistor 84 conducting its collector current is drawn through the resistor 86 from the base of the switching transistor 82 causing it to conduct, and current from its collector terminal divides to flow through the solenoid coil 40 and also through the series coupled capacitor 88 and the resistor 90 in the feedback path to add to the base current of the triggering transistor 84. The increased base current drives triggering transistor 84 further into conduction to increase the base current for the switching transistor 82 causing it also to conduct more heavily. With this regenerative effect, the switching transistor 82 is quickly driven to saturation to deliver full energizing current to the solenoid coil 40. However, after reaching saturation, the feedback current begins to decay exponentially as the capacitor 88 is charged at a rate determined by the RC time constant established by its capacitance value and the resistance value of the resistor 90. When this feedback current is reduced to a value at which the switching transistor 82 no longer conducts in saturation, its collector voltage decreases. This voltage change is feedback through the capacitor 88 in the feedback path to the base of the triggering transistor 84 to reduce its conduction, thereby further reducing the current flow through the switching transistor 82. This results in a reverse regenerative effect causing both transistors 82 and 84 to become nonconductive very quickly, thus terminating the energizing pulse to the solenoid coil 40. Thereafter, with the switching transistor 82 cut off, the charge remaining on the capacitor 88 holds the base of the transistor 84 negative while it is discharged by the battery 72 through the resistors 90 and 92. Both transistors 82 and 84 remain nonconductive until the capacitor 88 has discharged sufficiently to return the voltage at the base of the transistor 84 to a positive potential that again forward biases the base-to-emitter junction to initiate conduction, thus starting a new cycle.

For this application, wherein the desired interval between periodic sprays is relatively large, typically ranging from 15 seconds to as much as 15 minutes or more, the resistance value of the resistor 92 is much larger than that of the resistor 90. As should be apparent from the foregoing description of the operation, the pulse duration is primarily determined by the time constant of the feedback path as established by the values selected for the capacitor 88 and the resistor 90, whereas the interval between pulses is primarily determined by the time constant of the discharge path as established by the values selected for the capacitor 88 and the resistor 92. The time constant of the feedback path should be relatively low so that the pulse duration does not exceed the minimum interval required for the flow of pressurized fluid through the restricted path past the piston 44 to equalize the inlet and outlet pressures in the cylinder.

For example, in one practical version of the invention, wherein approximately a second is required for pressure equalization, the capacitor 88 has a value of 40 microfarads and the resistor 90 is 600-ohms. With the resistor 92 having a value of 1 megohm, the interval between pulses is approximately 28 seconds, and this interval can be increased without changing the pulse duration by employing larger resistance values for the resistor 92. In many cases, it may be desirable to use a variable resistance potentiometer for the resistor 92 so that the interval between pulses may be varied as desired by the operator. In this case, both the switch 80 and a thumb wheel for varying the value of the resistance 92 could be located to extend through appropriate openings in housings 16 so as to be readily accessible without removing the top cover 18. As to the other circuit values, with the battery 72 a conventional 9-volt transistor radio battery, transistors 82 and 84 may be of the type manufactured by Radio Corporation of America designated 40319 and 40320, respectively, the resistor 86 a value of 330 ohms, and the solenoid 40 a 32 ohm resistance. Of course, for longer delay intervals, it may be desirable to employ other types of timing devices such as low speed electrical motor arrangements or clockwork escapement mechanisms.

In operation, the dispenser housing 16 is snapped onto its mounting to be held securely to the top of the aerosol container 12. With the housing 16 in place, the depressed valve stem 26 opens the interior valve releasing the pressurized fluid contents from the aerosol container 12. This pressurized fluid is introduced through the tube 36 and the inlet passage hole 64 to the inlet end of the cylinder defined within the sleeve 42. With the solenoid coil not energized, the resilient closure member 46 at the bottom of the armature 44 contacts the conical valve seat on the protuberance 48 thus closing the outlet passage through the hole 66 in the lower closure member 50.

The snug fit of the piston armature 44 within the sleeve cylinder 42 restricts the flow of the pressurized fluid from the upper inlet end to the end of the cylinder producing a high flow impedance so that a substantial pressure drop results between the inlet and outlet ends during flow. Typically, the effective orifice should cause a pressure drop through the restricted flow path between the outer surface of the armature 44 and the inner surface of the sleeve 42 that is greater than the total upstream pressure drop of the flow path from the interior of the container 12 through the valve stem 26 and the tube 36 to the inlet end of the cylinder. For example, the orifice of the valve stem 26 for a conventional aerosol container has a diameter of approximately one-tenth inch, so that the cross-sectional area of the flow path to the inlet end of the cylinder is a little less than one one-hundredth square inch. With the armature 44 having a 3/8-inch diameter and a clearance of only one one-thousandth inch within the cylinder, the cross-sectional area of the flow path between the inlet and outlet ends of the cylinder is less than one one-thousandth of a square inch, thus providing a substantially greater flow resistance along the length of the armature.

Initially, pressurized fluid released from the aerosol container 12 flows slowly through the restricted flow path past the armature 44 to be released into the annular cavity surrounding the outlet protuberance 48 at the outlet end of the cylinder. This flow continues until the pressure at the bottom of the armature in the annular cavity adjacent the outlet valve seat equals the pressure at the inlet end of the cylinder. Until this happens, a pressure differential exists between the inlet and outlet ends tending to create a large net downward force on the armature 44 that forces the resilient closure member 46 downward onto the outlet valve seat to prevent the escape of pressurized fluid through the outlet passage to the outlet tube 68. However, when the pressures at the inlet and outlet ends to the cylinder equalize, only a slight net downward force on the armature 44 remains since the entire top surface area on the armature is exposed to the high pressure fluid whereas the bottom surface area has its center portion isolated from this high pressure by contact with the surrounding valve seat. If desired, a light spring 82 between the top of the armature 44 and the closure member 54 may be used at the top of the cylinder to supplement the small remaining net pressure force and the gravitational force on the armature 44 in order to maintain the closure member 46 firmly against the outlet valve seat when the inlet and outlet pressures are equalized. Although this additional spring force is not normally necessary in keeping the outlet closed to prevent leakage during normal operation, it is most advantageous in maintaining the closure member 46 against the valve seat when the dispenser housing 16 is not operatively mounted on an aerosol container, thus preventing foreign materials and deposits from entering or accumulating on the abutting valve surfaces which could interfere with complete closure during operation. For this purpose, the spring 82 should provide a force sufficient to overcome the weight of the piston 44 should the dispenser housing 16 be inverted when not in use.

With the pressure equalized at the outlet end of the cylinder during operation, an energizing pulse applied to the solenoid coil 40 supplies sufficient magnetic force to overcome the small remaining net downward forces so that the piston 44 moves upwards lifting the resilient closure member 46 off the valve seat to open the outlet passage through the hole 66 in the outlet closure member 50. With the conventional aerosol containers, the pressurized fluid is in the liquid state under the existing internal pressure within the container 12, which may be approximately fifty pounds per square inch above atmospheric. As the bottom of the piston lifts free, the aerosol fluid in the liquid state vaporizes and expands as it is discharged through the outlet passage to atmospheric pressure emerging as a spray through the nozzle on the end of the outlet tube 68. The sudden release of pressurized fluid at the outlet end of the cylinder causes a rapid drop in pressure to effect a substantial pressure differential at opposite ends of the armature 44. The much higher pressure at the inlet end of the cylinder quickly forces the armature 44 downward, easily overcoming the lifting force of the solenoid 38. To reseat the closure member 46 against the valve seat on the protuberance 48 and close the outlet valve to prevent further release of fluid. Subsequently after the outlet valve is closed, the fluid flows slowly through the high impedance flow path past the armature 44 to refill the annular space at the outlet end of the cylinder until the inlet and outlet pressures are again equalized, at which time the valve is again in a condition to be operated upon the next energization of the solenoid coil 40. Of course, the restricted flow path between the inlet and outlet ends of the cylinder should provide a flow rate sufficient to achieve pressure equalization within a time interval between the solenoid energizing pulses.

As may be evident, the automatic spray dispenser in accordance with this invention releases a measured constant amount of the pressurized fluid during each cycle of operation without accurate control of the energizing pulse width or use of a double valve arrangement. Typically the maximum lifting force provided by the solenoid 38 on its armature 44 in opening the outlet valve is in the order of several ounces, whereas the pressure differential force tending to reclose the outlet valve would reach a maximum of several pounds should the outlet be allowed to remain open. Not only does this feature avoid the need for a precision controlled pulse width control or double valving arrangements as employed in the prior art devices, but even should a short circuit or other malfunction result in a continuous flow of energizing current to the solenoid coil, the valving arrangement may continue to operate to provide periodic sprays but at much shorter intervals determined by the time necessary to equalize pressure at the outlet end of the cylinder. After opening, the valve is held closed by the differential pressure force until the restricted flow past the armature restores the outlet pressure so the magnetic force on the armature can again reopen the valve. Therefore, this arrangement prevents a circuit malfunction from holding the valve open continuously to discharge all of the pressurized fluid.

The valving arrangement of the invention also effectively prevents any appreciable leakage of pressurized fluid which was the most serious difficulty encountered in the prior art devices. During the period immediately following each energization of the solenoid 38, the pressure differential across the armature of 44 holds the resilient closure member 46 tightly against the outlet valve seat. Following the interval required for pressure equalization between the inlet and outlet ends of the cylinder, any tendency for the resilient closure member 46 to lift even partially from its contact with the outlet valve seat results in the high pressure being applied to the bottom area member 46 normally surrounded by the valve seat, thus forcing a larger opening. The resulting outlet flow would quickly reduce the pressure at the outlet end of the cylinder with the resulting differential pressure drop quickly forcing the armature 44 with its resilient closing member 46 down tightly against the valve seat to prevent further leakage. Thus, even a small leakage produces a pressure differential drop across the armature 44 that increases the downward pressure of the resilient closure member against the valve seat.

Although a preferred embodiment of the invention has been described herein with particular reference to its use in automatically dispensing pressurized sprays from aerosol containers the principles of the invention are generally adaptable for use in dispensing measured quantities of pressurized fluids in various other applications. For example, such a dispenser might be advantageously employed in automatically releasing measured quantities of a chemical agent into a process stream either at fixed intervals or at variable intervals in accordance with the timing of energizing pulses delivered to the solenoid 38. The frequency of energizing pulses might be automatically varied in accordance with a control signal generated by a sensor for maintaining a selected concentration of the ingredient being dispensed.

Claims

What is claimed is:

1. An automatic dispenser for discharging a measured quantity of pressurized fluid from a container at predetermined time intervals, comprising:

an elongated cylinder having a pressurized fluid inlet at one end and an outlet valve seat at the other end;

an elongated piston slidably moveable within said cylinder to provide a continuous high impedance flow path between opposite ends of the cylinder providing a flow resistance substantially greater than the total flow resistance from said container through said inlet into said one end of said cylinder, said piston including closure means at one end for engaging said outlet valve seat to prevent release of pressurized fluid and to define a space within said cylinder adjacent said valve seat;

conduit means for conveying said pressurized fluid from the interior of said container through the inlet to maintain the pressure at the inlet end of said cylinder at a maximum level of the pressurized fluid; and,

actuating means for applying a force for slidably moving said piston along said cylinder to displace said closure means momentarily from said valve seat after each said predetermined interval to release said fixed amount of pressurized fluid from said space adjacent said valve seat to decrease the pressure at said other end of the cylinder to a minimum level thus producing a pressure differential force on said piston to move said closure means back into contact with said valve seat to terminate the release of pressurized fluid, said high impedance flow path sufficiently restricting the flow of said pressurized fluid past said piston to increase the pressure at said other end of the cylinder gradually from said minimum to said maximum during a predetermined interval after said closure means has moved back into contact with said valve seat.

2. The dispenser of claim 1 wherein:

said piston is a magnetic solenoid armature; and

said actuating means comprises a solenoid coil adjacent said cylinder and a timing means for applying current pulses to said solenoid coil at fixed intervals to generate a magnetic force for displacing said armature along said cylinder.

3. The dispenser of claim 2 wherein:

said timing means further comprises a source of electric current and an interval timer circuit operable at said fixed intervals to send a pulse of current from said source through said solenoid coil.

4. The dispenser of claim 1 further comprising:

valve stem means on said container for releasing pressurized fluid contents when depressed;

mounting means releasably secured to said container for holding said valve stem depressed to release said pressurized fluid into said conduit means; and

spray nozzle means coupled to said outlet valve seat to receive the pressurized fluid released from said cylinder for spraying said predetermined amount during each energization of said actuating means.

5. The dispenser of claim 1 wherein:

said outlet valve seat is a protuberance having a conically shaped end portion surrounding an outlet orifice; and

said closure member has a resilient contact surface for contacting the conical portion of said protuberance to provide a seal surrounding said outlet aperture.

6. An automatic spray dispenser for dispensing measured quantities of a pressurized fluid from an aerosol container having a valve stem adapted to be depressed to open an internal valve for releasing the pressurized fluid contents, comprising:

a housing adapted to be removably mounted on said container for holding said valve stem depressed;

an annular solenoid coil mounted within said housing with a central cylindrical opening extending along the flux axis of said coil;

an elongated cylindrical sleeve mounted within said central cylindrical opening and having inlet and outlet end closures, said inlet end closure having a continuously open inlet port and said outlet end closure having a central protuberance surrounded by an annular open space extending into said cylindrical sleeve and formed with a valve seat at its end adjacent an outlet port;

a piston member including a solenoid armature of magnetic material slidably moveable with a snug fit within said cylinder for providing a high impedance flow path for the pressurized fluid between opposite ends of said cylindrical sleeve, said piston means having a valve closure member at one end for engaging said valve seat to prevent escape of pressurized fluid through said outlet port;

conduit means for conveying said pressurized fluid from said valve stem through the inlet port to maintain the interior of said cylindrical sleeve at the other end of said piston member continuously at a maximum level; and

electrical actuating means for periodically supplying a pulse of electrical current to said solenoid coil for moving said piston within said cylindrical sleeve to displace said valve closure member from said valve seat momentarily to permit escape of pressurized fluid through said outlet port from the open annular space surrounding said protuberance, thereby decreasing the pressure to a minimum level, and said high impedance flow path restricting flow of said pressurized fluid past said piston to delay the increase of pressure within said annular open space from said minimum to said maximum for an extended interval after said closure member has been moved back into engagement with said valve seat.

7. The automatic spray dispenser of claim 6 wherein said electrical actuating means comprises:

a battery;

a low powered timing circuit coupled to said battery and to said solenoid coil for periodically gating current pulses from said battery to energize said coil.

8. The automatic spray dispenser of claim 6 wherein:

said valve closure member comprises a resilient material mounted at one end of said piston for contacting said valve seat; and,

said valve seat comprises a conically shaped annular surface at the end of said protuberance.

9. The automatic dispenser of claim 6 wherein:

said restricted flow path is defined between the exterior surface of said piston member and the interior surface of said cylindrical sleeve to provide an effective orifice between the opposite ends of said piston for delaying the increase of the pressure in the space surrounding said protuberance to a level equal to the pressure at said inlet port for a period of time in excess of the duration of each energizing current pulse.

10. The automatic dispenser of claim 9 wherein:

the pressurized fluid within said container is maintained at a pressure substantially in excess of the pressure downstream from said outlet port and said piston member has a cross-sectional area sufficient to provide a differential pressure force on said piston member when said valve closure member is displaced from said valve seat in excess of the magnetic force applied to said armature during the flow of energizing current through said solenoid coil.