Pulse fog generator

In one embodiment of the present invention, a pulse fog generator powered by a resonant intermittent combustion device having a carburetor and a combustion antechamber, includes a starting air supply system for directing a flow of starting air into the antechamber, comprising an inlet/outlet ball check valve mounted over the discharge opening piston chamber within which a piston head is reciprocated by a connecting rod eccentrically mounted to an electric motor. A priming pump is mounted on the carburetor, and comprises a priming fuel chamber hydraulically communicating with the carburetor and a piston reciprocatable within the priming fuel chamber to draw fuel from a fuel tank into the priming fuel chamber and to discharge the fuel from the priming fuel chamber into the carburetor. In lieu of the reciprocatable piston, a resilient priming bulb and valve assembly can supply the priming fuel to the throat passage of the carburetor in another embodiment. An on-off control for the combustion device includes a shut-off plate, disposed over the air inlet of the carburetor, affixed to a slidably mounted plunger so that the shut-off plate can be moved between a position covering and a position displaced from the air inlet. The pulse fog generator has a pressure responsive formulation control apparatus inserted between a formulation tank and means for injecting formulation into the exhaust tube of the combustion device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention is in the field of fogging devices. In particular, 
the invention is directed toward fogging devices utilizing the pulse-jet, 
or resonant intermittent combustion, principle. 
2. Description of the Related Art: 
Fogging devices, used to generate an insecticide fog, for example, and 
utilizing the pulse-jet or resonant intermittent combustion principle, are 
well known in the prior art. An example of such devices is disclosed in 
Curtis, U.S. Pat. No. 3,993,582, Curtis U.S. Pat. No. 4,030,695, and 
Stevens et al., U.S. Pat. No. 4,343,719. Each of these patents discloses a 
fogging apparatus utilizing a resonant, intermittent combustion device, a 
fuel supply, a formulation supply, a formulation control device, and a 
starting device. In such prior art devices, the resonant intermittent 
combustion device is shut off by way of a valve located in the carburetor. 
One such prior art device is described in an operator's instruction manual 
for a pulse-fog generator manufactured by Curtis Dyna-Products Corporation 
of Westfield, Ind. The components of the pulse fog generator, as well as 
the operation of the device, is described for the GOLDEN EAGLE Model 2610. 
The apparatus of the present invention represents an improved version over 
these prior art devices. In particular, the present invention shows an 
improved starting system for the resonant intermittent combustion device, 
an improved combustion device shut off system, and an improved formulation 
control device. 
SUMMARY OF THE INVENTION 
A pulse fog generator powered by a resonant intermittent combustion device 
using a carburetor to feed an air-fuel mixture into a combustion 
antechamber, includes a starting air supply system for directing a flow of 
starting air into the antechamber, comprising an inlet/outlet check valve 
mounted over the discharge opening of a reciprocating piston assembly that 
is reciprocated by a connecting rod eccentrically mounted between the 
piston and an electric motor. The pulse fog generator further includes a 
priming pump for directing a quantity of starting fuel into the 
carburetor, comprising, in one aspect of the invention, a priming fuel 
chamber hydraulically communicating with the carburetor and a piston 
reciprocatable within the fuel chamber to draw fuel from a fuel tank into 
the priming fuel chamber and to discharge the fuel from the chamber into 
the carburetor. In another aspect of the invention, the priming pump 
includes a resilient primer bulb having an inlet for drawing fuel through 
the metering chamber of the carburetor, and an outlet for discharging fuel 
directly into the central throat passage of the carburetor. An on-off 
control system for the pulse fog generator comprises a shut-off plate 
disposed over the air inlet for the carburetor affixed to a slidably 
mounted plunger so that the shut-off plate can be moved between a position 
covering and a position displaced from the air inlet. In one aspect of the 
invention, a common valve body is provided to mount the priming pump and 
the on-off control system onto a retro-fitted carburetor.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated embodiment, and such further applications of the 
principles of the invention as illustrated therein being contemplated as 
would normally occur to one skilled in the art to which the invention 
relates. 
Referring first to FIG. 1, the various components of the pulse fog 
generator 10 of Applicants' preferred embodiment are schematically shown. 
The pulse fog generator 10 includes a resonant combustion device 11 
comprising an exhaust tube 12, communicating at one end with a combustion 
chamber 13, the combustion chamber 13 having a thermal glow coil 14 
functioning as a flame holder. 
Flow of fuel and air into a combustion antechamber 20 and thence into the 
combustion chamber is controlled by a fuel-air inlet valve 22, comprising 
a housing 23 which is transversely divided by a conventional petal-type 
check valve 24 into an upper chamber 25 and the combustion antechamber 20. 
The petal type check valve 24 is conventional and permits one-way 
introduction of a combustible fuel-air mixture into the combustion 
antechamber 20. An electrical spark generating system 30 has an electrode 
or spark plug 31 extending into the combustion antechamber and energized 
by a coil 32. The spark generating system is enabled by a first switch 33 
connected to a power supply 35 during starting of the engine. 
A carburetor 40 is disposed above the fuel-air inlet valve 22 and has a 
central throat passage 42. The carburetor 40 is a standard "pulse pump" 
type carburetor that has been modified for Applicants' invention as will 
be described herein. The central throat passage 42 extends through the 
carburetor and provides the primary air inlet into the carburetor and 
antechamber. 
A priming pump assembly 60 is mounted atop the carburetor 40 and disposed 
generally above the central throat passage 42. An on-off control valve 150 
is mounted on a mounting plate 152 that is affixed to a priming pump body 
61 of the priming pump assembly 60. The on-off control valve 150 comprises 
a shut-off plate 160 that is situated above the central throat passage 42 
and is adapted to cover the throat passage in order to terminate the flow 
of air into the carburetor when it is desired to shut the pulse fog 
generator 10 off. The priming pump 60 provides a means to inject fuel into 
the carburetor antechamber 20 during initial startup of the pulse fog 
generator. Once the generator is operating, a fuel delivery line 16 
continuously supplies fuel from the fuel tank 17 to the carburetor. 
A starting air supply system 80 injects air into the antechamber 20 during 
startup of the resonant combustion device 11. In one embodiment of the 
invention, the starting air supply system includes a bellows driven by a 
motor assembly, that intakes and expels air through an air pump body 
assembly 90 (FIG. 3) into the starting air line 81. The details of this 
bellows and pump body assembly 90 are discussed in the co pending parent 
application Ser. No. 53,826, at pages 7-8 and 10-12, which are 
incorporated herein by reference. 
In another embodiment, the starting air supply system 80 comprises a piston 
assembly 170, driven by a motor assembly 85, that intakes and expels air 
through an air pump body assembly 180 into a starting air line 81. The 
starting air line 81 communicates from the piston assembly 170 to the 
antechamber 20 to provide air to be mixed with fuel injected into the 
antechamber by the priming pump 60 during startup of the resonant 
combustion device 11. 
The pulse fog generator 10 further comprises a formulation tank 110 that 
stores the liquid mixture or formulation 111 to be vaporized in the 
exhaust tube 12 during operation of the generator. A formulation pressure 
line 113 communicates between the combustion antechamber 20 and the 
formulation tank 110, through a formulation tank pressurizing valve 114, 
in order to pressurize the formulation tank in response to the operation 
of the pulse fog generator. A formulation tank line 115 exits the 
formulation tank 110 as shown and passes through a formulation filter 116. 
The formulation tank line 115 communicates with a metering/shut-off valve 
assembly 120 which comprises a formulation shut-off assembly 126 having a 
shut-off valve 127 and a diaphragm actuator 135, a formulation metering 
valve 121, and a three-way valve 122. The design and operation of the 
shut-off valve 127 and the diaphragm actuator 135 will be explained 
further herein. 
The formulation metering valve 121 controls the rate of flow of formulation 
exiting the formulation tank line 115. The three-way valve 122 provides a 
means to flush the formulation lines once the fogging operation is 
complete. An outlet line 123 communicates from the three way valve 122 to 
the formulation injection nozzle 124 opening into the exhaust tube 12. A 
pressure line 125 extending from the antechamber to the three-way valve 
122 pressurizes the formulation flowing through the outlet line 123 to 
force the formulation through the formulation injection nozzle 124 into 
the exhaust tube 12. 
In the operation of the pulse fog generator 10, fuel and air are 
continuously drawn through the carburetor 40 and antechamber 20 into the 
combustion chamber 13. The thermal glow coil 14, when heated, causes the 
fuel-air mixture to burn, generating heated high velocity gases. The high 
velocity gases exit the combustion chamber 20 into the exhaust tube 12 
passing by the formulation injection nozzle 124. The venturi effect of the 
high velocity gases passing over the formulation injection nozzle 124, 
coupled with the pressurized formulation flowing through the outlet line 
123, causes the formulation to enter the exhaust tube 12 and the flow of 
high velocity gases. The formulation is vaporized in the exhaust tube, but 
is subsequently recondensed to a liquid fog shortly after exiting the 
exhaust tube 12. 
Having generally described the operation of the pulse fog generator, 
detailed description of Applicants' preferred embodiment will follow. In 
this embodiment, the starting system for the resonant combustion device 
11, described with reference to FIGS. 1 and 2, comprises the starting air 
supply system 80. The connecting rod 83 terminates at one end in a rod end 
84. The rod end 84 is eccentrically and pivotably mounted to an eccentric 
assembly 86. In this embodiment, the eccentric assembly 86 comprises a 
disc 87 having a pin 88 affixed thereon, as shown in FIG. 2. The pin 
extends through a bore (not shown) in the rod end 84. The pin 88 is 
mounted off center on the disc 87 so that, as the disc rotates, the rod 
end 84 moves in an eccentric fashion. The electric motor assembly 85 
includes a rotating output shaft 89. The disc is mounted at the end of a 
motor output shaft 89. Thus, the output shaft, and consequently the 
eccentric, rod end, and connecting rod are driven by the electric motor. 
Since the rod end 84 and connecting rod 83 are eccentrically mounted to 
the rotating eccentric assembly 86 and output shaft 89, the rotational 
motion of the output shaft is translated to a generally reciprocating 
motion of the connecting rod. 
The other end of the connecting rod 83 is suitably connected to a piston 
head 172. The piston head 172 is slidingly situated within a piston 
chamber 171. The reciprocating motion of the connecting rod 83, 
consequently, extends and retracts, or reciprocates, the piston head 172 
within the piston chamber 171. An air pump valve assembly 180 is situated 
at the open end of the piston chamber 171. The air pump valve assembly 180 
includes an inlet ball check valve 181 and an outlet ball check valve 182, 
each alternately operating as the piston head is reciprocated to draw 
atmospheric air into the pump chamber and expel air out along the starting 
air line 81. 
Referring to FIG. 1, the electric motor that drives the bellows is 
connected to the power supply 35 via a second switch 36. Thus, when the 
second switch 36 is depressed, electricity is provided to the electric 
motor, energizing the motor and starting the air pumping operation. The 
starting air supply system 80 works in cooperation with a spark generating 
system, in this case the coil 32 and spark plug 31 shown in FIG. 1, to 
comprise the starting system for the resonant combustion device. Fuel 
introduced into the antechamber mixes with the starting air and is ignited 
by the spark plug. 
The outlet ball check valve 182 in the air pump body assembly 180 prevents 
the heated gases resulting from the explosion in the antechamber from 
escaping through the starting air line 81 and starting air supply system 
80. However, the outlet ball check valve does not prevent air from being 
drawn into the antechamber by the vacuum resulting after the explosion, as 
the air pump valve assembly 180 operates essentially as an auxiliary air 
supply. During the vacuum pulse, the outlet ball check valve 182 of the 
check valve wafer is flexed, as well as the inlet ball check valve 181, so 
that air passes freely through the air pump valve assembly and into the 
starting air line to the antechamber. 
In one alternative to the present embodiment, the spark generating system 
30 and the starting air motor assembly 85 are wired in parallel, and the 
first and second switches 33 and 36 are combined into one switch. In this 
instance, depressing the single switch starts the electric motor which 
ultimately introduces starting air into the combustion antechamber, while 
also energizing the coil causing the spark plug to spark. 
The starting system of the present embodiment represents an improvement 
over the starting systems of the prior art that use a hand-operated air 
pump. Not only is operation of the hand pump to supply starting air to the 
antechamber cumbersome, it is also physically difficult for the operator. 
As the hand pump heats up, the piston expands, thereby increasing the 
force required to reciprocate the pump. In this embodiment, hand operation 
has been replaced by the electrical air supply system. 
The starting system for the resonant combustion device 11 of the pulse fog 
generator 10 in Applicants' preferred embodiment also comprises a priming 
pump assembly 60. As illustrated in FIG. 1, the priming pump assembly 60 
is mounted atop the carburetor 40 over the central throat passage 42. The 
details of one embodiment of the priming pump assembly will be illustrated 
with reference to FIG. 4. 
As background information, the relevant details of the carburetor will be 
first described. The carburetor 40 includes a fuel pump assembly 43, which 
comprises a fuel inlet orifice 44, a fuel inlet valve 45, a fuel pump 
diaphragm 46, a pressure/vacuum pulse inlet 47, and a fuel outlet valve 
48. Fuel from the fuel tank 17 (FIG. 1) passes through the fuel delivery 
line 16 to the fuel inlet orifice 44 of the carburetor 40. The fuel inlet 
valve 45 controls the flow of fuel into the carburetor, and prevents the 
backflow of fuel or air into the fuel delivery line 16. The fuel pump 
diaphragm 46 creates a vacuum when flexed which draws fuel into the 
carburetor through the fuel inlet valve 45. The fuel pump diaphragm 46 is 
flexed in response to the alternating pressure-vacuum pulses generated in 
the antechamber 20 by the operation of the resonant combustion device that 
are transmitted into the carburetor through the pressure/vacuum pulse 
inlet 47. The fuel inlet valve 45 is responsive to the flexing of the fuel 
pump diaphragm 46 so that it closes the fuel inlet orifice 44 when the 
diaphragm is flexed during the pressure pulse. The fuel inlet valve 45 is 
flexed to the open position when the diaphragm is retracted during the 
vacuum pulse. As the fuel pump diaphragm flexes, the fuel is pulled into 
the carburetor during the vacuum pulse, and pushed through the fuel outlet 
valve 48 during the pressure pulse. 
The fuel in the carburetor passes through a fuel filter 49 and a fuel 
passageway 52, past an inlet needle valve 50, and into a metering chamber 
51. Once in the metering chamber 51, the fuel is drawn into the central 
throat passage 42 of the carburetor by the venturi effect of air passing 
into the carburetor and through the central throat passage into the 
fuel/air inlet valve 22 and combustion antechamber 20. Once the engine is 
operating, air is constantly flowing through the carburetor and the 
central throat passage so that the fuel is automatically drawn into the 
carburetor and ultimately into the combustion antechamber. Furthermore, in 
an operating condition, the fuel pump is also operational. However, in a 
start up condition, the fuel pump is disabled, and no air is flowing into 
the carburetor sufficient to create a venturi effect to draw the fuel from 
the metering chamber into the carburetor. Consequently, the priming pump 
assembly is required to withdraw the fuel from the fuel tank and inject it 
directly into the carburetor so that an initial air and fuel mixture can 
be ignited. 
As previously noted, the priming pump assembly 60 of Applicants' invention 
is mounted directly on the carburetor 40. In this embodiment, an adaptor 
fitting bore 53 is drilled through the carburetor body 41 into the fuel 
passageway 52 directly adjacent the fuel filter 49. A pump adapter 63 is 
pressed into this bore, the pump adapter 63 having a pair of 
circumferentially sealing lands 64 and a central bore 65 communicating 
with the fuel passageway 52. A priming pump body 61, shown in detail in 
FIGS. 5a-5c, comprises a mounting surface 61a for mounting flush against a 
reciprocal mounting surface 41a on the carburetor body 41. A 
circumferential filter groove 61b receives an air intake screen or filter 
55 therein (FIG. 5c). A central air intake bore 66 extends through the 
priming pump body 61 to provide a flow path for atmosphere air into the 
central throat passage 42 of the carburetor 40. 
The priming pump body 61 further includes a priming fuel chamber 67 adapted 
to accept the circumferential sealing lands 64 of the pump adapter 63 in a 
press fit. The priming pump body is appropriately fixed on the carburetor, 
such as by bolts, so that the pump adapter is in simultaneous press-fit 
engagement in the adapter fitting bore 53 of the carburetor and in the 
priming fuel chamber 67 of the priming pump body 67. 
Referring again to FIG. 4, a priming piston assembly 70, having a piston 
head 71 with an O-ring groove 72 and an O-ring 73 resiliently mounted 
thereto, a piston rod 74 connected to the piston head, and a knob 75 
attached at the distal end of the piston rod 74, is situated in the 
priming fuel chamber 67 in the priming pump body 61. A retaining member 
76, such as a press fit hollow plug or a snap ring, located at the distal 
end of the chamber 67, prevents the piston head 71 from being completely 
withdrawn from the chamber. A biasing, or return, spring 77 situated 
between the retaining member 76 and the knob 75 biases the priming piston 
assembly 70 away from the carburetor and provides a return force against 
the knob 75 when the priming piston is pumped by the operator. 
In operation, the priming piston head 71 is withdrawn in the priming fuel 
chamber 67. As the piston head 71 is withdrawn, a vacuum forms in the 
priming fuel chamber 67 as well as in the fuel passageway 52 in the 
carburetor 40. This vacuum in turn opens the fuel inlet valve 45 and draws 
fuel from the fuel tank 17 into the carburetor 40, in a fashion similar to 
the operation of the fuel pump diaphragm previously described. Once the 
fuel is withdrawn from the fuel tank into the fuel passageway 52 of the 
carburetor, the piston head 71 is stroked back into the chamber 67. The 
piston head exerts a pressure against the fuel which closes the fuel inlet 
valve 45 and causes the fuel to flow through the fuel passageway 52 past 
the inlet needle valve 50 and into the metering chamber 51. Since the fuel 
withdrawn by the priming piston is being forced under pressure by the 
priming piston head, the fuel flows freely into central throat passage 42 
of the carburetor 40, without the necessity of the venturi effect created 
by air flowing through the central throat passageway. Thus, it can be seen 
that in the initial start up of the resonant combustion device of the 
pulse fog generator, fuel is injected into the combustion antechamber 20 
solely by manual operation of the priming piston, since the fuel pump 
diaphragm 46 and pressure/vacuum pulse inlet 47 are inactive. 
In starting the resonant combustion device using the starting system of 
Applicants' preferred embodiment, several strokes of the priming pump 
assembly may be necessary to inject a sufficient quantity of fuel into the 
antechamber. Air is also forced into the antechamber to mix with the fuel. 
The resulting fuel/air mixture is ignited by the spark generating system 
30 and the resonant combustion device becomes self-sustaining. Once the 
initial explosion of the fuel/air mixture has occurred, the starter system 
becomes redundant and is no longer operational. At this point, the priming 
pump is no longer needed to withdraw and pump fuel into the carburetor, as 
the fuel pump diaphragm 46 is now activated by the alternating 
pressure/vacuum pulses transmitted through the pulse inlet 47. The O-ring 
73 on the priming piston head 71 prevents any fuel from leaking from the 
priming fuel chamber 67. 
The starter system of the present embodiment comprising the primary pump 
assembly 60 represents an improvement over the priming systems of earlier 
devices. In earlier devices, the fuel priming function was performed by 
operation of a manual air pump used to temporarily pressurize the fuel 
tank, causing fuel to be injected from the fuel delivery line into the 
carburetor. As described above, use of the manual pump is cumbersome and 
physically difficult. The priming pump assembly is easier to operate, 
having a short stroke of 1 to 11/2 inches. Furthermore, there is no need 
to pressurize the fuel tank during the priming operation, which translates 
to a simplified fuel control system. The present embodiment of the priming 
pump assembly of Applicants' novel starting system allows for a minor 
modification to a stock pulse pump type carburetor and provides an 
improved fuel priming operation for the start up of the resonant 
combustion engine. 
The preferred embodiment of Applicants' invention includes an on/off 
control valve 150 mounted directly above the central throat passage 42 of 
the carburetor 40 to terminate the airflow through the carburetor to the 
antechamber 20. A mounting plate 152 is affixed to the distal surface 68 
of the priming pump body 61. Referring to FIG. 6, the mounting plate 152 
includes a first bore 153 through which a bushing 154 is pressed. The 
bushing 154 is elongated and extends below the bottom surface of the 
mounting plate 152, as shown in FIG. 6. A plunger assembly 156, comprising 
a plunger rod 158 and a shut-off plate 160, affixed at one end of the rod 
by way of a pin or screw, is slidably situated within the bushing 154. A 
knob 161 is pressed or threaded onto the other end of the rod 158. The rod 
also passes through a helical spring 162 which is situated between the 
bushing and the knob 161 so that the spring reacts against the knob 
tending to push the plunger assembly 156 away from the central throat 
passage 42. 
In the present embodiment, the priming pump body 61 described above further 
comprises a shut-off contact surface 69. The plunger rod 158 is of 
sufficient length that, when the rod is depressed, the shut-off plate 160 
contacts flush against the contact surface 69, covering the air intake 
bore 66 in the pump body and, consequently, the central throat passage 42. 
A recess 69a in the contact surface 69 is situated to receive the head of 
the pin or screw 159 to allow the shut-off plate 160 to completely seal 
off the air intake bore 66. 
The on/off control valve 150 of the present embodiment is used to prevent 
air from flowing into the carburetor, which starves the resonant 
combustion device 11 causing it to shut down. The on/Off control valve is 
operated by depressing the knob 161 and plunger rod 158 which, in turn, 
pushes the shut-off plate 160 down into contact with the contact surface 
69 of the pump body and covering the air intake bore 66 and central throat 
passage 42. Once the flow of air through the carburetor into the 
combustion antechamber is interrupted, the pressure/vacuum pulse cycle is 
terminated and the resonant combustion device 11 stops. Once the device 11 
stops, the plunger assembly 156 can be released, and the spring 162 
automatically retracts the plunger rod, and the shut-off plate, away from 
the air intake bore 66. The spring 162 also serves to keep the shut-off 
plate 160 away from the air intake bore 66 during operation of the engine. 
The on/off control valve 150 of this embodiment represents an improvement 
of shut-off systems in similar resonant combustion devices and pulse fog 
generators, in particular. In the prior system, the combustion device was 
shut-off by manipulation of a valve or vane in the carburetor itself to 
stop the flow of fuel and air into the combustion antechamber. Applicants' 
invention simplifies the shut-off mechanism since a valve interior of the 
carburetor, along with the requisite mechanical devices to manipulate the 
valve, is not required. In addition, Applicants' on/off control valve is 
biased to permit airflow, unlike most prior systems. 
In a different aspect of the invention, the priming pump assembly 60 of the 
previous embodiment is replaced by a priming bulb assembly 190, as 
illustrated in FIGS. 7a and 7b. The priming bulb assembly 190 is mounted 
on the a carburetor having the same features as the carburetor 40 
described above, with the exception that different fluid connections 
between the carburetor and the priming bulb assembly are required. The 
priming bulb assembly 190 includes a priming fuel inlet line 191 through 
which the priming fuel is drawn, and a priming fuel outlet line 192 that 
opens into the carburetor throat 42 at an outlet port 192a. The priming 
bulb assembly 190 is of a conventional design in which a flexible 
resilient bulb 193 is mounted on a priming valve body 194. A valve plate 
195 is mounted within the priming valve body 194 and includes an inlet 
valve 195a and an outlet valve 195b. The fuel inlet and outlet lines 191 
and 192, respectively, are appropriately connected to the priming valve 
body 194 to communicate with the proper valves. In this embodiment, the 
bulb 193 is transparent or translucent so that a visual indication is 
available that priming fuel is present in the bulb for injection into the 
carburetor. 
The priming bulb assembly 190 of this embodiment operates in a unique 
manner relative to the prior art devices. When the priming bulb 193 is 
initially depressed, air or fumes in the bulb are expelled from the bulb 
through outlet valve 195b and priming fuel outlet line 192 and outlet port 
192a into the carburetor. When the bulb resiliently returns to its 
pre-determined undeformed shape, a vacuum is formed inside the bulb that 
pulls the inlet needle valve 50 down and draws fuel from the fuel tank 
through the carburetor, through the priming fuel inlet line 191 and into 
the priming bulb 193. When the bulb is next depressed, the fuel within the 
bulb is expelled through the priming fuel outlet line 192 and outlet port 
192a into the carburetor throat 42. When the bulb is depressed, inlet 
valve 195a seats in its closed position, and when the bulb rebounds to its 
undeformed shape, the outlet valve 195b seats in its closed position. The 
resilience of the bulb 193 is sufficiently great to draw a vacuum in the 
metering chamber 51 sufficient to pull the metering needle valve 50 off 
its valve seat and to draw starting fuel from the fuel tank 17. 
With this embodiment, the priming fuel is injected directly into the 
carburetor throat, rather than through the metering chamber 51, as in the 
previous embodiment. In addition, the use of the priming bulb simplifies 
the connection between the priming bulb assembly 190 and the carburetor 
body to eliminate the pump adaptor 63 of the previous embodiment. On the 
other hand, the priming bulb assembly 195 requires valving separate from 
the carburetor valving, unlike the priming piston assembly 60 of the 
former embodiment. 
Applicants' preferred embodiment includes a formulation shut-off assembly 
126 interposed between the formulation tank outlet line 115 and the 
formulation metering valve 121. This formulation shut-off assembly 126 
terminates the flow of formulation into the exhaust tube 12 of the 
resonant combustion device 11 once the pressure/vacuum pulse cycle is 
interrupted in the operation of the device, such as would occur when the 
device 11 ran out of fuel. Although once the pressure/vacuum pulse cycle 
of the engine is interrupted, the engine has essentially come to a stop, 
residual fuel/air mixture in the combustion chamber 13, combined with the 
formulation mixture that may flow into the exhaust tube 12, may be ignited 
by the glow coil causing an explosion or fire. Furthermore, even in the 
absence of residual fuel/air mixture in the combustion chamber, the 
intense heat in the combustion chamber and exhaust tube can also cause the 
formulation mixture to explode or catch fire. This danger is greatly 
minimized if the flow formulation into the discharge tube is terminated 
immediately when the operation of the engine is terminated. The 
formulation shut-off assembly 126 performs this function. The function and 
structure of the formulation shut-off assembly of the invention is 
described in more detail in Applicants' co-pending parent application Ser. 
No. 53,826 at pp. 22-28, which is incorporated herein by reference. 
The formulation shut-off valve assembly 126 of Applicants' preferred 
embodiment represents an improvement over the "dead man" throttle of the 
prior art. The dead man throttle, such as the throttle described in the 
Curtis patent, U.S. Pat. No. 4,030,655, requires that the operator 
constantly press the throttle lever in order to maintain flow of the 
formulation into exhaust tube of the pulse fog generator. In order to shut 
off the flow of the formulation in an emergency situation, such as when 
the engine dies after having run out of fuel, it is incumbent upon the 
operator to quickly release the dead man throttle, thereby terminating 
flow of the formulation. The formulation shut-off valve assembly of 
Applicants' invention makes this safety feature entirely automatic and 
dependent only upon the continued operation of the resonant combustion 
device of the pulse fog generator. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.