WO1988001540A1

WO1988001540A1 - Internal shut-off assembly for ultrasonic dispersion nozzle

Info

Publication number: WO1988001540A1
Application number: PCT/US1987/002159
Authority: WO
Inventors: Clem S. Mc Kown
Original assignee: M & T Chemicals, Inc.
Priority date: 1986-08-27
Filing date: 1987-08-27
Publication date: 1988-03-10
Also published as: CA1309122C

Abstract

An ultrasonic nozzle (10) includes an atomizing surface (26c) for producing an atomized liquid spray; a liquid feed passageway (12) having an inlet (60) supplied with a liquid and an outlet (26f) for supplying the liquid to the atomizing surface (26c) the passageway having a first section (28d) with a first diameter and a second fluidly connected section (28e) with a second, smaller diameter, with a shoulder (64) defined between the first (28d) and second sections (28e) of the passageway; characterized by including an internal shut-off assembly positioned within the passageway (28) and cooperating with the shoulder (64) for preventing the supply of liquid to the atomizing surface (26c) the shut-off assembly including a shut-off rod (62) positioned within the passageway (28), the shut-off rod (62) having an outer surface spaced from the inner surface of the passageway and a sealing end (62a) adapted to co-operate with the shoulder (64) to prevent the supply of liquid to the atomizing surface (26c) and a valve actuator (68) for moving the shut-off rod (62) in a longitudinal direction in the passageway between a first closed position in which the supply of liquid to the atomizing surface is prevented and a second open position in which the supply of liquid to the atomizing surface is permitted.

Description

INTERNAL SHUT-OFF ASSEMBLY FOR ULTRASONIC DISPERSION NOZZLE

The present invention relates generally to ultrasonic dispersion nozzles and, more particularly, is directed to an ultrasonic dispersion nozzle having a novel shut-off assembly.

Conventionally, spraying processes have used no zz le s that rely on pressure and high velocity fluid motion to atomize liquids. Generally, such nozzles are hydralic (pressure) operated in which pressurized liquid is forced through the orifice and liquid is sheared into droplets, or are of the two fluid air atomizing type in which high pressure air or gas mixes with liquid in the nozzle and the air imparts a velocity to the liquid, which is then ejected through an orifice. These nozzles are available in a wide variety of designs with numerous spray shape patterns and flow rate capacities. Examples of the latter type of nozzles are those sold by Spraying Systems Co., North Avenue at Schmale Road, Wheatpn, Illinois 60187 under the 1/4JAU Series. However, such nozzles have various shortcomings that can cause operational and reliability problems. For example, although a high velocity spray may be appropriate for some applications, it is undesirable in most because the droplets hit the surface to be coated so hard that some of the coating material bounces off. This overspray condition is not only wasteful, but in addition, this also results in the spray being dispersed into the environment, which can be hazardous.

Another persistent problem with such nozzles is clogging. Specifically, in order to achieve the high velocities required to break up the liquid, small diameter channels and outlet orifices are needed. Because of these small diameters, however, the passageways are prone to blockage. This occurs when the fluid material dries in the orifices after the nozzle is shut off, when suspended particles gradually deposit in the nozzle, and/or when foreign matter enters the fluid stream. In order to remedy the latter two causes, high quality filtration equipment is necessary. In order to remedy the first cause, the nozzle must be flushed af ter each use . It will b e appreciated that a completely blocked passageway results in total nozzle failure, while a partially blocked orifice or channel can cause a distorted spray pattern or produce coarse droplets or decreased flow rates.

Distortion in the spray pattern can also occur when passageways are eroded by abrasive particles suspended in the liquid. Because of the high pressures that are used, even the hardest nozzle materials are damaged within a relatively short period of time.

In view of these problems, various applications require the use of ultrasonic nozzles which avoid the aforementioned problems. Examples of such ultrasonic nozzles are those sold by Sono-Tek Corporation, 313 Main Mall, Poughkeepsie, New York 12601. Reference is also made to U.S. Patent Nos. 4,153,201; 4,301,968; 4,337,896; and 4,352,459, all having Sono-Tek Corpo-ration as the common assignee. With these nozzles, atomization is achieved by vibrating a metallic surface at frequencies in the ultrasonic range, that is, above 20 kHz. Specifically, liquid is delivered to the atomizing surface through an axial feed tube running the length of the nozzle, and for obtaining the necessary vibration, the nozzle incorporates piezoelectric transducers sandwiched between nozzle halves, whereby the vibrational motion is transmitted, amplified and concentrated at the atomizing surface.

As a result of such vibrations, there is a formation of a two-dimensional grid of capillary waves in a surface film, that is, in the liquid film on the atomizing surface of the nozzle. As the amplitude of the underlying vibration increases, the height of the surface wavelets also increases until a critical amplitude is reached. At such time, the wave peaks become unstable and separate from the bulk liquid, whereby the liquid dispersed from the nozzle's atomizing surface takes the form of drops smaller than or equal to the size of the wave crests on which they were formed. Since wavelength is inversely related to frequency, higher vibrational frequencies result in smaller d rop lets .

With such nozzles, since the atomization process is not pressurized, the diameter of the bore of the axial feed tube is unrestricted. Therefore, liquid emerges onto the atomizing surface at a low velocity and spreads out into a thin film, and is atomized as described above.

The ultrasonic nozzles therefore provide distinct advantages over conventional nozzle arrangements. Specifically, the unpressurized operation results in a soft spray, with spray velocities being less than those typically produced by conventional nozzles by at least a factor of ten. Thus, the bouncing off of the spray material from the surface to be coated is substantially avoided, along with the aforementioned overspray condition. As a result, there is a resultant saving of expensive materials. Further, because unpressurized liquid is used, ultrasonic nozzles consume a minimum amount of power, for example, up to 3/8 inch, there is effectively a clog-free operation, even at supply rates of 0.1 g/hr. Other advantages include the use of the same nozzle to achieve flow rates from near zero to the rated capacity, the capability of producing tiny droplets with median diameters as low as 20 microns, and the ability to entrain the spray in a moving gas stream to accurately define a desired spray pattern and provide uniform coverage of large surface areas.

With all of the above nozzles, it is often important that there be a sharp cessation of fluid flow when the coating operation is terminated. In the aforementioned two-fluid supply nozzles sold by Spraying Systems Co., an internal shut-off assembly is provided which functions to interrupt the liquid portion of the spray only. Specifically, a stainless steel shut-off needle is provided in the liquid feed tube, which is normally biased by a coil spring to close the liquid feed tube. An air operated cylinder is provided to retract the shut-off needle against the force of the coil spring in order to start spraying. Since such nozzles operate under a high pressure and velocity, the shut-off needle does not effectively interfere with the supply of liquid. In such nozzles, since only the liquid feed tube is closed, there is still an output from the high velocity atomizing air tube.

Prior to the present invention, an internal shut-off assembly has never been provided with an ultrasonic nozzle, possibly because it was believed that there would be interference between the shut-off needle and the wave peaks that are formed. Instead, in order to discontinue liquid feed to an ultrasonic nozzle, particularly during intermittent operations, Sono- Tek Corporation recommends that an automatic solenoid valve be installed in the liquid feed line upstream of the nozzle, and that the power supply for the piezoelectric transducers be equipped with an interlock that attenuates the vibrations when the nozzle is off.

However, in actual tests with a methanol liquid and with an organotin based coating formula containing butyltin trichloride, in which an interlock activated by a process timer was provided such that vibrations of the piezoelectric transducers were attenuated and with a twoway electric solenoid valve installed immediately upstream of the ultrasonic nozzle, it was found that liquid dripped from the nozzle's orifice outlet following discontinuation of the liquid feed. When the interlock was by-passed, liquid atomization continued from the nozzle tip for several seconds following discontinuation of the liquid feed. Such tests were performed with the ultrasonic nozzle mounted in a horizontal orientation and with a liquid feed duration of approximately 0.5 seconds, which are typical for commercial fluorescent bulb coating processes.

Failure to achieve a sharp cessation of liquid flow from the nozzle's orifice in such applications is believed to be a result of the low surface tension of the liquids tested. As a class, liquid coating formulations to be applied to hot glass surfaces for the pylolytic formation of an SNO₂ film thereon tend to have relatively low surface tensions. OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention, to provide an ultrasonic nozzle that avoids the above mentioned difficulties. It is another object of the present invention to provide an ultrasonic nozzle that provides automatic and immediate cessation of flow from the nozzle outlet when the nozzle is turned off.

It is another object of the present invention to provide an ultrasonic nozzle having an internal shut-off assembly.

In accordance with an aspect of the present invention, an ultrasonic nozzle includes an atomizing surface for producing an atomized liquid spray; a liquid feed passageway having an inlet supplied with a liquid and an outlet for supplying the liquid to the atomizing surface, the passageway having a first section with a first diameter and second sections of the passageway; vibration means for supplying vibrations to the atomizing surface at an ultrasonic frequency; and internal shut-off means positioned within the passageway and cooperating with the shoulder for preventing the supply of liquid to the atomizing surface.

In accordance with another aspect of the present invention, an internal shut-off assembly is provided for an ultrasonic nozzle of the type including an atomizing surface for producing an atomized liquid spray; a liquid feed passageway having an inlet supplied with a liquid and an outlet for supplying the liquid to the atomizing surface, the passageway having an inner surface, a first section with a first diameter and a second fluidly connected section with a second, smaller diameter, with a shoulder defined between the first and second sections of the passageway; and vibration means for supplying vibrations to the atomizing surface at an ultrasonic frequency; the internal shut-off assembly including a shutoff rod positioned within the passageway, the shut-off rod having an outer surface spaced from the inner surface of the passageway and a sealing end adapted to cooperate with the shoulder to prevent the supply of liquid to the atomizing surface; and actuator means for moving the shutoff rod in a longitudinal direction in the passageway between a first closed position in which the supply of liquid to the atomizing surface is prevented and a second open position in which the supply of liquid to the atomizing surface is permitted.

The above and other objects, features and advantages of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partial longitudinal cross-sectional view of an ultrasonic nozzle according to the present invention;

Fig. 2 is a side elevational view, in exploded form, of the internal shut-off assembly of the ultrasonic nozzle of Fig. 1; and

Fig. 3 is an enlarged perspective view of the sealing end of the rod of the internal shut-off assembly of Fig. 1 in assembled condition in the ultrasonic nozzle.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawings in detail, and initially to Fig . 1 thereof , an ultrasonic dispersion nozzle 10 according to the present invention generally includes a liquid feed passageway 12 having an inlet end 14 supplied with a liquid and an outlet end 16 with an atomizing surface for dispersing the liquid in an atomized state, vibration means 18 for vibrating the liquid passing through passageway 12 at an ultrasonic frequency, and an internal shut-off assembly 20 positioned within passageway 12 for preventing supply of the liquid from the passageway 12 to the atomizing surface.

Specifically, nozzle 10 includes a reflecting horn 22 with a central bore 24 constituting the inlet end 14 of passageway 12, and an adjacent atomizing horn 26 with a central bore 28 constituting the outlet end 16 of passageway 12. Preferably, reflecting horn 22 and atomizing horn 26 are made of titanium. A pair of annular piezoelectric disks 30 and 32 are sandwiched between reflecting horn 22 and atomizing horn 26, and a contact plane electrode 34 is, in turn, sandwiched between piezoelectric disks 30 and 32. A common body electrode 36 is connected to at least one bolt 38, a plurality of which connect reflecting horn 22, atomizing horn 26, piezoelectric disks 30 and 32, and contact plane electrode 34 in the aforementioned arrangement.

More particularly, atomizing horn 26 includes an annular flange 40 having a plurality of apertures 42 circumferentially spaced therearound, and reflecting horn 22 includes an annular flange 44 having a plurality of apertures 46 circumferentially spaced therearound with a similar spacing as apertures 42. Bolts 38 extend through apertures 42 and 46 and are screw-threadedly received in apertures 47 in flange back-up ring 45 to provide the above-described sandwiching connections. In addition, two sealing O-rings 48 and 50 are provided in surrounding relation to piezoelectric disks 30 and 32, respectively, on opposite sides of contact plane electrode 34 and provide a seal between the contact plane electrode 34 and atomizing horn 26. In general operation, an input AC electrical signal is applied between common plane electrode 34 and common body electrode 36, and because of the back-to -back orientation of piezoelectric disks 30 and 32, both disks will expand and contract simultaneously and equally at the frequency rate of the electrical signal. However, the. vibration amplitude generated by disks 30 and 32 themselves is insufficient for atomization. Accordingly, reflecting horn 22 and atomizing horn 26 amplify the vibrations to a sufficient extent to cause atomization. In this regard, reflecting horn 22 and atomizing horn 26 are preferably made of titanium, which has superior acoustical properties and excellent corrosion resistance.

When the input electrical signal is bipolar, travelling pressure waves with frequencies similar to those of the input electrical signal propagate in both directions. Pressure waves, like electromagnetic waves, are characterized by a frequency f and by a propagation velocity c. The wavelength is defined by c/f. When the total length from contact plane electrode 34 to one end of nozzle 10 is equal to an odd multiple of /4, the outgoing and incoming waves are in phase and appear to be standing still in space. A cross-sectional slice of a nozzle reveals a regularly repeating sinusoidal variation of motion, the maximum amplitude of which depends on where the slice is made. The energy in the wave is essentially trapped within the structure.

The contact plane electrode 34 is in a nodal plane since the amplitude of motion is always zero. A point /4 away is in an antinodal plane, that is, a plane of maximum amplitude. At points in between, the maximum amplitude varies sinusoidally with distance. Therefore, the atomizing surface must be in an antinodal plane where the amplitude is at a maximum. In this regard, the distance between the end of reflecting horn 22 and contact plane electrode 34 is designed to have a length equal to /4. In like manner, the atomizing horn 26 is designed to have a length equal to an odd integral multiple of /4.

The atomizing horn 26 provides the amplification required for atomization by virtue of a sharp transition in diameters between a large diameter section 26a and a small diameter section 26b at a point /2 from the contact plane electrode 34. The amplification or gain is equal to the ratio of the cross-sectional areas of the two sections 26a and 26b. Thus, the gain is increased either by increasing the diameter of section 26a or reducing the diameter of section 26b. Typically, gains of six to ten can be achieved, which is sufficient for atomization. Atomization takes place on an end or atomization surface 26c at the tip of small diameter section 26b.

As previously discussed, the liquid is supplied through a passageway 12 to end surface 26c. More particularly, a cylindrical guide 52 extends within central bores 24 and 28, and within annular piezoelectric elements 30 and 32. Cylindrical guide 52 has an outer diameter which varies in accordance with the variations in the diameters of central bores 24 and 28. For example, central bore 24 includes a first diameter section 24a and a second smaller diameter section 24b. Thus, guide 52 has a first cylindrical section 52a which fits within first diameter section 24a and a second smaller diameter section 52b which fits within smaller diameter section 24b. First cylindrical section 52a further includes a reduced diameter section 52a about which a sealing O-ring 54 is fit for sealing central bore 24.

Central bore 28 likewise includes different diameter sections 28a - 28e, each fluidly connected to the next, and each successive section having a smaller diameter than the previous section, the last section 28e terminating at end surface 26c. In addition, section 28b is provided with internal screw threads. Thus, guide 52 has a cylindrical section 52c which fits within section 28a and a screw threaded section 52d which is screw threadedly received in section 28b for securing guide 52 in nozzle 10.

Cylindrical section 52c further includes a reduced diameter section 52c' about which a sealing 0-ring 56 is fit for sealing central bore 28 to prevent fluid escape. A further cylindrical section 52e connects cylindrical sections 52b and 52c, and is positioned within piezoelectric disks 30 and 32. Thus, passageway 12 is sealed from the rear end of reflecting horn 22 to end surface 26c of atomizing horn 26.

Cylindrical guide 52 further includes a cylindrical section 52f extending from the rear end of cylindrical section 52a, with section 52f being coupled with a Swagelok coupling device 58. A nozzle feed opening 60 is provided for supplying liquid to section 52f, and then through the remainder of guide 52 and sections 28d-28g of atomizing horn 26, to end surface 26c thereof. In accordance with the present invention, in order to achieve a sharp cessation of liquid flow from the nozzle orifice 28f, particularly in those applications where low surface tension liquids are used, such as the use of SnO₂ in the commercial coating of fluorescent bulbs, nozzle 10 is provided with an internal shut-off assembly 20.

As shown in Figs. 1 and 2, internal shut-off assembly

20 includes a rigid shut-off rod 62 positioned within guide

52, feed tube 28d and passageway 12, extending through coupling device 58 at one end, and terminating at the opposite end thereof at the entrance to section 28e of bore 28. Shut-off rod 62 has an outer diameter which is smaller than the inner diameter of feed tube 28d, as shown in Fig. 3. For example, shut-off rod 62 can have an outside diameter of 0.046 inch with a length of approximately six inches. In this manner, shut-off rod 62 is spaced from feed tube 28d so as not to interfere with the waves set up by the vibrating nozzle during normal operation. Shut-off rod 62 should preferably be made of a material that is resistant to chemical attack by the liquid, and may, for example, be made of type 316 or 304 stainless steel, titanium, tantalum, Hastelloy B or C, nickel and/or Monel. Preferably, the forward tip or sealing end 62a of shut-off rod 62 seats against a gasket made of tetrafluoroethylene (TFE) or other appropriate material.

As shown in Figs. 1 and 3, a shoulder 64 is formed between sections 28d and 28e of bore 28, which sections have different bore diameters. Accordingly, the forward tip 62a of shut-off rod 62 cooperates with shoulder 64 at the area of bore reductions, to quickly and positively seal the nozzle so as to prevent the flow of liquid to atomizing end surface 26c in the closed position of shut-off rod 62. In order to aid in the sealing operation, forward tip 62a preferably has a substantially conical configuration, as shown in Fig. 3, and shoulder 64 likewise has a similar frusto-conical configuration, The shape of forward tip 62a, however, can be varied, such as with a hemispherical shape, as long as a sealing effect is achieved. In addition, a polymeric or the like seat 66 can be provided against shoulder 64 for ensuring a positive sealing operation, as shown in Fig. 3.

The opposite end of shut-off rod 62 is connected to a valve actuator 68, such as a Whitey "92" Series valve actuator, which also forms part of internal shut-off assembly 20. In such case, a Whitey SS-92S4 valve body 70 can be used to connect Swagelok coupling device 58 to valve actuator 68. However, any other suitable electrically or pneumatically actuated valves can be used, such as an angle pattern valve or the like, which can be connected to a tube or pipe fitting 71 on valve body 70. Further, the valve actuator is preferably a normally closed (NC) actuator, although a double acting (DA) actuator is acceptable. Thus, for a normally closed actuator, as is conventional, a spring is provided to normally move shut-off rod 62 to the left of Fig. 1 to a closed position. When it is desired to operate nozzle 10, air can be supplied from a control means 73 to move shut-off rod 62 to the right of Fig. 1 to an open position, whereby nozzle 10 produces an atomized spray.

More particularly, a screw 72 or the like is fixed on the opposite end of shut-off rod 62, and is screwed into a screw-threaded tap 74 in valve actuator 68 by means of a knurled finger nut 76, as shown in Fig. 2. In this regard, the opposite end of shut-off rod 62 extends through

Swagelok coupling device 58 and valve body 70. In order to provide a sealing of such opposite end of shut-off rod 62, an O-ring seal 78 is provided, as shown in Fig. 1.

Accordingly, with the present invention, internal shut-off assembly 20 provides a sharp cessation of liquid flow from the nozzle orifice 28f, particularly in those applications where low surface tension liquids are used, such as the use of SnO₂ in the commercial coating of fluorescent bulbs. Having described a preferred embodiment of the invention with reference to the accompanying drawings, it will be appreciated that the present invention is not limited to that precise embodiment and that various changes and modifications can be effected therein by one of ordinary skill in the art without departing from the scope or spirit of the invention as defined in the appended claims.

INTERNAL SHUT-OFF ASSEMBLY FOR ULTRASONIC DISPERSION NOZZLE

GLOSSARY

Reference Number Description

10 ultrasonic dispersion nozzle

12 liquid feed passageway

14 inlet end

16 outlet end

18 vibration means

20 shut-off assembly

22 reflecting horn

24 central bore

24a bore section

24b bore section

26 atomizing horn

26a large diameter section

26b small diameter section

26c end surface

28 central bore

28a-e bore sections

28f nozzle orifice

30 piezoelectric disk

32 piezoelectric disk

34 contact plane electrode

36 common body electrode

38 bolt

40 annular flange

42 apertures

44 annular flange

45 annular flange back-up ring

46 apertures

47 screw-threaded apertures

48 O-ring 50 O-ring

52 cylindrical guide

52a-f cylindrical guide sections

54 O-ring 56 O-ring 58 Swagelok coupling device 60 nozzle feed opening 61 feed tube 62 shut-off rod 64 shoulder 66 seat 68 valve actuator 70 valve body 71 pipe fitting 72 alien set screw 73 control means 74 screw-threaded tap 76 knurled finger nut 78 packing seal

Claims

WHAT IS CLAIMED IS: 1. An ultrasonic nozzle comprising: an atomizing surface for producing an atomized liquid spray; a liquid feed passageway having an inlet supplied with a liquid and an outlet for supplying said liquid to said atomizing surface, said passageway having a first section with a first diameter and a second fluidly connected section with a second, smaller diameter, with a shoulder defined between said first and second sections of said passageway; vibration means for supplying atomizing vibrations to said atomizing surface at an ultrasonic frequency; and internal shut-off means positioned within said passageway and cooperating with said shoulder for preventing said supply of liquid to said atomizing surface.

2. An ultrasonic nozzle according to Claim 1; wherein said passageway has an inner surface, and said internal shut-off means includes: a shut-off rod positioned within said passageway, said shut-off rod having an outer surface spaced from said inner surface of said passageway and a sealing end adapted to cooperate with said shoulder to prevent said supply of liquid to said atomizing surface; and actuator means for moving said shut-off in a longitudinal direction in said passageway between a first closed position in which said supply of liquid to said atomizing surface is prevented and a second open position in which said supply of liquid to said atomizing surface is permitted.

3. An ultrasonic nozzle according to Claim 2; further comprising control means for controlling said actuator means to move said shut-off rod between said closed position and said open position.

4. An ultrasonic nozzle according to Claim 2; wherein said shoulder has a substantially conical configuration, and said sealing end has a substantially conical configuration with a shape that conforms substantially to that of said shoulder.

5. An ultrasonic nozzle according to Claim 2; wherein said shoulder has a substantially conical configuration, and said sealing end has a substantially hemispherical configuration.

6. An ultrasonic nozzle according to Claim 2; further including seat means positioned against said shoulder for cooperating with said sealing end of said shut-off rod to prevent said supply of liquid to said atomizing surface in said closed position.

7. An ultrasonic nozzle according to Claim 2; further including feed tube means positioned in said passageway for supplying said liquid, to said atomizing surface; and wherein said shut-off rod is positioned in said feed tube means in spaced relation from an inner surface of said feed tube means for preventing said supply of liquid to said atomizing surface in said closed position.

8. An ultrasonic nozzle according to Claim 2; wherein said actuator means is one of electrically and pneumatically operated.

9 . An ultrasonic nozzle according to Claim 2; wherein said actuator means includes one of a normally closed actuator connected with said shut-off rod for normally moving said shut-off rod to said closed position, and a double acting actuator connected with said shut-off rod.

10. An ultrasonic nozzle according to Claim 1; wherein said vibration means includes piezoelectric means for producing vibrations at said ultrasonic frequency, and amplifying means for amplifying said vibrations and for supplying said amplified vibrations to atomizing surface.

11. An ultrasonic nozzle according to Claim 10; wherein said amplifying means includes a reflecting horn having a central bore therein defining a portion of said passageway and an adjacent atomizing horn having a central bore therein defining another portion of said passageway, and said piezoelectric means includes at least one piezoelectric plate sandwiched between said reflecting horn and said atomizing horn.

12. An ultrasonic nozzle according to Claim 11; wherein said atomizing horn includes a first section with a first outside dimension positioned adjacent said at least one piezoelectric plate, and a second section with a second, smaller diameter and an end surface of said second section forming said atomizing surface.

13. An internal shut-off assembly for an ultrasonic nozzle of the type including an atomizing surface for producing an atomized liquid spray; a liquid feed passageway having an inlet supplied with a liquid and an outlet for supplying said liquid to said atomizing surface, said passageway having an inner surface, a first section with a first diameter and a second fluidly connected section with a second, smaller diameter, with a shoulder defined between said first and second sections of said passageway; and vibration means for supplying atomizing vibrations to said atomizing surface at an ultrasonic frequency, said internal shut-off assembly comprising: ashut-off rod positioned within said passageway, said shut-off rod having an outer surface spaced from said inner surface of said passageway and a sealing end adapted to cooperate with said shoulder to prevent said supply of liquid to said atomizing surface; and actuator means for moving said shut-off rod in a longitudinal direction in said passageway between a first closed position in which said supply of liquid to said atomizing surface is prevented and a second open position in which said supply of liquid to said atomizing surface is permitted.

14. An internal shut-off assembly according to claim 13; further comprising control means for controlling said actuator means to move said shut-off rod between said closed position and said open position.

15. An internal shut-off assembly according to Claim 13; wherein said shoulder has a substantially conical configuration, and said sealing end has a substantially conical or hemispherical configuration with a shape that conforms substantially to that of said shoulder.

16. An internal shut-off assembly according to Claim 13; wherein said actuator means is one of electrically and pneumatically operated.

17. An internal shut-off assembly according to Claim 13; wherein said actuator means includes one of a normally closed actuator connected with said shut-off rod for normally moving said shut-off rod to said closed position, and a double acting actuator connected with said shut-off rod.