Abstract:
A method and apparatus are provided for pneumatically controlling the operation of a water cannon such that the need for electrically power in the immediate vicinity of the water cannon is substantially avoided.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to water cannons and, in particular, to a pneumatic control system for a water cannon.  
         BACKGROUND OF THE INVENTION  
         [0002]    The typical water cannon comprises a barrel assembly that has an opening or nozzle through which a body of water is driven by the application of a mechanical force. There are at least two types of barrel assemblies employed in water cannons. The first type includes a piston that is located within a barrel and used to apply a mechanical to a body of water located in the barrel. To elaborate, the operation of the piston involves: (a) positioning the piston at a location within the barrel that will allow the piston to be displaced such that water is forced through the opening; and (b) displacing the piston such that a mechanical force is applied to a body of water located between the piston and the opening so that the water is driven through the opening. An example of such a barrel assembly is illustrated in U.S. Pat. No. 6,119,955, which is incorporated herein by reference.  
           [0003]    The second type of barrel assembly utilizes a barrel with a nozzle through which a body of water is driven (i.e., the opening) and a second end that is in communication with a channel that extends towards the nozzle. Typically, the barrel, channel and communication path between the second end of the barrel and the channel have a U-shape. An example of such a barrel assembly is illustrated in U.S. Pat. No. 3,722,819, which is incorporated herein by reference. In operation, the channel is used to carry a pressurized gas (typically, air) that is used to drive a body of water held in the barrel out of the nozzle.  
           [0004]    The typical water cannon also comprises a control system that interfaces with the barrel assembly and operates: (a) to place the barrel assembly in a condition or state so a mechanical force can be applied to a body of water in the barrel of the cannon; and (b) to cause a mechanical force to be applied to the body of water that forces the body of water out of the opening of the barrel assembly. In many such control systems, electrical components are employed that are in the immediate vicinity of the water cannon and, as such, are subject to coming into contact with water. Such systems must typically employ a number of measures to prevent the electrical components of the control system from coming into contact with water and either becoming disabled or presenting a safety hazard to individuals in the vicinity of the water cannon.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is directed to a pneumatic control system for a water cannon that substantially avoids the need for electrical circuitry in the immediate vicinity of the cannon.  
           [0006]    Generally, the pneumatic control system is applicable to water cannons whose operation involves at least two steps, the first step being the priming of the cannon, which at least includes the loading of a body of water into the barrel of the cannon, and the second step involving the “firing” of the cannon such that the body of water is expelled from the barrel. One example of this type of water cannon is a cannon that employs a barrel assembly with a piston that is used to push a body of water out of the barrel of the cannon. With a piston-type of water cannon, the first step involves not only the loading of a body of water into the barrel of the cannon but also the positioning of the piston so that the piston can subsequently push the body of the water out of the cannon. The second step, with a piston-type of water cannon, involves moving the piston such that the body is pushed out of the barrel. Typically, the second step occurs in response to the actuation of a trigger. Another example of a water cannon whose operation involves at least two steps is the piston-less water cannon, an embodiment of which is shown in U.S. Pat. No. 3,722,819.  
           [0007]    In one embodiment, the pneumatic control system comprises a valve that interfaces with the barrel assembly and is used to apply a fluid-related force to a body of water in the barrel in response to a pneumatic “fire” signal. In the case of a pistonless water cannon, the fluid-related force is applied directly to the body of water and the fluid-related force is typically in the form of a gas (e.g., air). For a piston-type water cannon, the fluid-related force is indirectly applied to the body of water. Namely, the fluid-related force is applied to the piston and then the piston transmits the force to the body of water. In this case, the fluid-related force can take either the form of a gas (e.g., air) or a liquid (e.g., water).  
           [0008]    The control system further comprises a pneumatic trigger for producing the pneumatic “fire” signal that is applied to the valve. The pneumatic trigger is subject to a pneumatic enable/disable signal. To elaborate, when the pneumatic enable/disable signal is in the disable state, actuation of the pneumatic trigger does not cause the pneumatic “fire” signal to be produced. If, however, the enable/disable signal is in the enable state, actuation of the pneumatic trigger results in the production of the “fire” signal.  
           [0009]    The pneumatic control system further includes pneumatic logic that operates to: (a) produce a disable/enable signal in the disable state so that the pneumatic trigger cannot be fired by actuation of the pneumatic trigger when the cannon is being fired or when the cannon is being primed; (b) produce a disable/enable signal in the enable state so that the pneumatic trigger can be fired when the cannon is not already in the act of being fired and the cannon is primed to fire; and (c) cause the valve to transition from the “primed” state to the “fire” state in response to a “fire” signal from the pneumatic trigger.  
           [0010]    In one embodiment, the pneumatic logic includes at least three pneumatic devices that each have at least one input for receiving a pneumatic signal (i.e., a gas signal) and at least one output for providing a pneumatic signal. The first pneumatic device receives a pneumatic signal from a third pneumatic device that is indicative of the state of the water cannon, i.e., the cannon is either in the act of firing or in the act of being primed. The first pneumatic device provides a first “prime” signal a predetermined amount of time after receiving the signal from the third pneumatic device that indicates that the water cannon is in the act of firing. The predetermined amount of time being an amount of time for the cannon to sufficiently complete a firing. As a consequence, the first “prime” signal is an indication that priming of the water cannon can commence.  
           [0011]    The second pneumatic device receives a second “prime” signal that is produced by the third pneumatic device in response to the first “prime” signal. The second pneumatic device provides a pneumatic signal that is used to enable or disable the pneumatic trigger. The second pneumatic device operates so as to provide the pneumatic signal that shifts the trigger from a disabled state to an enabled state a predetermined amount of time after the second “prime” signal is received. Consequently, the second pneumatic device operates to produce a pneumatic signal that disables the trigger during priming of the water cannon and enables the trigger after priming of the water cannon is sufficiently complete.  
           [0012]    The third pneumatic device receives a stream of gas that is distributed throughout the pneumatic logic and provides the basis for each of the pneumatic signals produced by the pneumatic logic. Further, the third pneumatic device receives the first “prime” signal provided by the first pneumatic device and the “fire” signal provided by the pneumatic trigger. Operation of the third pneumatic device is according to exclusive-or logic, i.e., the device is only capable of responding to one of the first “prime” signal and the “fire” signal at any point in time. Stated differently, the third pneumatic device is not capable of responding to the first “prime” signal and the “fire” signal at the same time. In operation, the third pneumatic device responds to the first “prime” signal produced by the first pneumatic device by providing the second “prime” signal to the second pneumatic device. The third pneumatic device responds to the “fire” signal produced by the pneumatic trigger by providing a pneumatic signal that causes the valve to release a pressurized gas or liquid into the barrel of the cannon and thereby “fire” the cannon. This pneumatic signal is also provided to the first pneumatic device to indicate that the state of the water canon, namely, that the cannon is in the act of firing.  
           [0013]    In one embodiment, the first pneumatic device comprises a pneumatic timer that operates to produce the first “prime” signal at a predetermined amount of time after receiving a pneumatic signal indicating that the water cannon is in the act of firing. The predetermined amount of time being an amount of time for the water cannon to sufficiently complete a firing.  
           [0014]    In another embodiment, the first pneumatic device comprises a pneumatic sensor/gate assembly that operates to produce the first “prime” signal after a sufficiently complete firing of the water cannon is detected by sensing that the water in the barrel of the cannon is at or below a predetermined level. In the case of a piston-type cannon, a sufficiently complete firing is detected by either sensing that the water is at or below a predetermined level or that the piston has traveled to a predetermined location in the barrel. In any event, the pneumatic sensor/gate assembly operates such that the pneumatic signal that indicates that the water cannon is in the act of firing “sets” the gate, i.e., causes the first “prime” signal to become inactive. A pneumatic signal produced by the sensor indicating that a sufficiently complete firing has occurred is applied to the gate and causes the gate to “reset”, i.e., causes the first “prime” signal to become active.  
           [0015]    In yet a further embodiment, the second pneumatic device comprises a pneumatic timer that operates to produce the pneumatic signal that enables the trigger at a predetermined amount of time after receiving the second “prime” signal. In this case, the predetermined amount of time is an amount of time that is sufficient for the water cannon to have been primed.  
           [0016]    In another embodiment, the second pneumatic device comprises a pneumatic sensor/gate assembly that operates to produce the pneumatic signal that enables the trigger after a sufficiently complete priming of the water cannon is detected by sensing that the water in the barrel of the cannon is at or above a predetermined level. In the case of a piston-type cannon, a sufficiently complete priming is detected by sensing either that water in the barrel is at or above a predetermined level or that the piston is at a predetermined location in the barrel, i.e., a location from which the piston can be moved to cause a body of water to be ejected from the cannon. In any event, the pneumatic sensor/gate assembly operates such that the second “prime” signal “sets” the gate, i.e., causes the pneumatic signal that disables the trigger to issue. The receipt by the gate of a pneumatic signal from the sensor indicating that a sufficiently complete priming has occurred “resets” the gate, i.e., causes the pneumatic signal that enable the trigger to issue.  
           [0017]    Another embodiment of the pneumatic control system is applicable to water cannons in which a body of water is loaded before firing but that already have a pneumatic trigger and valve. In this case, the pneumatic control system comprises the pneumatic logic without the valve and pneumatic trigger, and the pneumatic logic is retrofitted to the cannon. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a cross-section of a barrel assembly for a typical piston-type water cannon;  
         [0019]    [0019]FIG. 2 is a cross-section of a barrel assembly for a typical pistonless-type water cannon;  
         [0020]    [0020]FIG. 3 is a schematic of a pneumatic control system for a typical piston-type water cannon; and  
         [0021]    FIGS.  4 A- 4 C respectively illustrate the states of the pneumatic control system while the piston-type water cannon is firing, after the cannon has fired and while priming of the cannon is taking place, and after priming has been complete but before the cannon is fired. 
     
    
     DETAILED DESCRIPTION  
       [0022]    The present invention is directed to a pneumatic control system for a water cannon whose operation involves the loading of a body of water into the barrel of the cannon and the subsequent application of a force to the body of water that drives the body of water out of the barrel.  
         [0023]    Before describing the pneumatic control system, two types of water cannons to which the pneumatic control system is applicable are described. The first type is a piston-type water cannon and the second type is a pistonless-type water cannon. Characteristic of both types of cannons is that a body of water is loaded into the barrel of the cannon and a force is then applied to the body of water that drives the body of water out of the cannon.  
         [0024]    [0024]FIG. 1 is a cross-sectional view of a barrel assembly  10  of a typical piston-type water cannon. Generally, the barrel assembly  10  includes a barrel  12  and a piston  14  that resides within the barrel  12 . The piston  14  comprises a first disk  16 , a second disk  18 , and a rod  20  that connects the first disk  16  and the second disk  18 . The barrel  12  includes a first chamber  22  that holds the first disk  16 . In addition, the first chamber  22  includes a nozzle  24 , a water inlet port  26  for loading water into the first chamber  22 , and a first air port  28  that allows air to move in and out of the first chamber  22  during movement of the piston  14  and thereby facilitate movement of the piston  14 . To elaborate, the first air port  28  allows air to enter the first chamber  22  during firing of the water cannon (i.e., during movement of the piston  14  towards the nozzle  24 ) to prevent a vacuum from forming between the first disk  16  and the bottom of the first chamber  22  that would impede the movement of the piston  14 . Similarly, the first air port  28  allows air to exit the first chamber  22  during retraction of the piston  16 . The barrel  12  also includes a second chamber  30  that holds the second disk  18  of the piston  14 . In addition, the second chamber  30  includes a second air port  32  for transmitting air into the second chamber  30  to facilitate movement of the piston  14  towards the nozzle  24  and transmitting air out of the second chamber  30  when the piston  14  is being moved away from the nozzle  24 . A third air port  34  is provided for use in transmitting air that is used to move the piston  14  away from the nozzle  24  and thereby position the piston  14  for subsequently moving towards the nozzle  24  to eject water in the first chamber  22  from the nozzle  24 . A wall  36  separates the first chamber  22  and the second chamber  30  from one another. A hole  38  in the wall  34  accommodates the rod  20  of the piston  14 .  
         [0025]    Operation of the barrel assembly  10  comprises priming the barrel assembly  10  by injecting water into the first chamber  22  via the water inlet port  26  and moving the piston  14  away from the nozzle  24  by injecting a gas into the second chamber  30  via the third air port  34 . In addition, air is allowed to escape from the first chamber  22  via the first air port  28 . Likewise, gas is allowed to escape from the second chamber  30  via the second air port  32 . The “firing” of the barrel assembly  10  (i.e., the ejection of a body of water located in the first chamber  22  through the nozzle  24 ) is accomplished by injecting pressurized air into the second chamber  30  via the second air port  32  to cause the piston  14  to move towards the nozzle  24  and thereby eject the body of water previously established in the first chamber  22 . Movement of the piston  14  is facilitated by allowing air to enter the first chamber  22  via the first air port  28  and air to escape from the second chamber  30  via the third air port  34 .  
         [0026]    [0026]FIG. 2 is a cross-sectional view of a barrel assembly  42  of a typical pistonless-type water cannon. Generally, the assembly  42  includes a chamber  44  for holding a body of water. The chamber  44  is substantially defined by an inner sleeve  46  and includes a closed end  48  and a nozzle  50 . A water inlet port  52  is utilized to load a body of water into the chamber  44 . An outer sleeve  54  is separated from the inner sleeve  46  and in conjunction with the inner sleeve  46  defines a gas channel  56 . A gas inlet port  58  is used to transmit a gas to the gas channel  56 .  
         [0027]    Operation of the barrel assembly  42  comprises priming the barrel assembly  42  by injecting water into the chamber  44  via the water inlet port  52 . Once a sufficient body of water has been loaded into the chamber  44 , a gas (e.g., air) is injected into the gas channel  56  via the gas inlet port  58 . The gas travels down the gas channel and, in so doing, drives the body of water in the chamber  44  out the nozzle  50 .  
         [0028]    With reference to FIG. 3, an embodiment of a pneumatic control system  62  that is applicable to a piston-type water cannon of the type illustrated in FIG. 2 is described. A barrel assembly  64  for the piston-type water cannon is illustrated with elements that correspond to the elements of barrel assembly  10  given the same reference numbers.  
         [0029]    The control system  62  generally comprises: (a) a pneumatic valve  66  for transmitting gas (e.g., air) to and from the second chamber  30  of the barrel  12 ; (b) a pneumatic trigger  68  for generating a pneumatic “fire” signal to cause the valve  66  to inject air into the second chamber  30  of the barrel  12  to move the piston  14  and thereby eject water from the first chamber  22  via the nozzle  24 ; (c) a first pneumatic timer  70  for providing a pneumatic signal after a sufficiently completed firing of the barrel assembly  64  that is used in priming the barrel assembly  64  for another firing; (d) a second pneumatic timer  72  for providing a pneumatic signal after the barrel assembly  64  has been sufficiently primed that enables the pneumatic trigger  68 ; and (e) a pneumatic exclusive-or valve  74  that responds to the pneumatic signal output by the first pneumatic timer  70  by providing a pneumatic signal to the second pneumatic timer  72  that causes the second pneumatic timer  72  to wait a sufficient amount of time for priming activities to be completed before providing a pneumatic signal that enables the pneumatic trigger  68  and by taking action to cause the piston  14  to be positioned for a firing The pneumatic exclusive-or valve  74  also responds to the pneumatic “fire” signal output by the pneumatic trigger by providing a pneumatic signal to the first pneumatic timer  70  that indicates that the barrel assembly  64  is either in the act of being fired or primed. The control system  62  further includes a quick exhaust valve  76  that directs air to the second port  34  to cause the piston  14  to retract during priming of the barrel assembly  64  and directs air from the second chamber  30  to the exterior environment during firing of the barrel assembly  64 . The control system  62  further comprises a shot counter  78  that provides a count of the number of firings of the barrel assembly  64 , which is useful for maintenance purposes and the like. Also included in the control system  62  is a pressure indicator  80  that provides a user with an indication of when the pneumatic trigger  68  is enabled and, as a consequence, when actuation of the pneumatic trigger  68  will result in the firing of the water cannon. An air filter  82  serves to filter the air that is used by the pneumatic components in the remainder of the control system  62 .  
         [0030]    The pneumatic valve  66  is a 3-way, air actuated valve that includes an inlet port  86  for receiving air from an air supply line  88 , a bi-directional port  90  for providing air to the second chamber  30  during firing of the barrel assembly  64  and receiving air from the second chamber  30  during priming of the barrel assembly  64 , and a second outlet port  92  for venting air received by the bi-directional port  90  during priming of the barrel assembly  64  to the exterior environment. A control port  94  is used to place the valve  66  in either a “fire” state or a “primed” state. In the “fire” state, the valve  66  allows air to pass from the inlet port  86  to the bi-directional port  90  and then into the second chamber  30  of the barrel assembly  64  to move the piston  14  and thereby eject a body of water in the first chamber  22  from the nozzle  24 . In the “primed” state, the valve  66  allows air from the second chamber  30  of the barrel assembly  64  to pass from the bi-directional port  90  to the output port  92  during priming and, more specifically, during retraction of the piston  14 . The control port  94  is responsive to a pneumatic firing/priming signal that is in either a “firing” state or a “priming” state and provided by the pneumatic exclusive-or valve  74 . When the firing/priming signal is in the “firing” state, the control port  94  places the valve in the “fire” state. Conversely, when the firing/priming signal is in the “priming” state, the control port  94  places the valve in the “primed” state.  
         [0031]    The pneumatic trigger  68  is a 3-way, manually activated valve that includes an outlet port  98  for providing a pneumatic “fire” signal, a trigger  100 , and a control port  102  that is used to place the trigger  68  in either a “disabled” state or an “enabled” state. In the “disabled” state, actuation of the trigger  100  has no effect, i.e., there is no “fire” signal produced at the outlet port  98 . In effect, the trigger  68  is in a “safetyon” condition in the “enabled” state, which is effectively a “safety-off” condition, actuation of the trigger  100  results in a “fire” signal being produced at the outlet port  98 . The control port  102  is responsive to a pneumatic disable/enable signal that is either in a “disable” state or an “enable” state and provided by the second pneumatic timer  72 . When the disable/enable signal is in the “disable” state, the control port  102  places the trigger  68  in the “disabled” state. Conversely, when the disable/enable signal is in the “enable” state, the control port  102  places the trigger  68  in the “enabled” state.  
         [0032]    The first pneumatic timer  70  includes an inlet port  106  for receiving a pneumatic firing/priming signal from the exclusive-or valve  74  and an outlet port for providing a pneumatic, first “prime” signal. When the timer  70  receives a firing/priming signal that is in a “firing” state (i.e., indicative of the barrel assembly  64  being fired), the timer  70  responds by providing the first “prime” signal at a predetermined amount of time after receiving the firing/priming signal in the “firing” state. The predetermined amount of time is at least the time required for a firing of the barrel assembly  64  to be sufficiently completed. Consequently, the first “prime” signal indicates that a firing of the barrel assembly  64  is at a point that priming operations can commence for a subsequent firing. When the timer  70  receives a firing/priming signal that is in the “priming” state (i.e., indicative of the barrel assembly  64  being primed for a firing), the first “prime” signal becomes inactive.  
         [0033]    The second pneumatic timer  72  includes an inlet port  112  for receiving a second “prime” signal from the exclusive-or valve  74  and an outlet port  114  for providing the pneumatic, disable/enable signal to the trigger  68 . When the timer  72  receives the second “prime” signal (i.e., indicative of the barrel assembly  64  being primed for another firing), the timer  72  responds by providing the disable/enable signal in the enabled state at a predetermined amount of time after receiving the second “prime” signal. The predetermined amount of time is at least the time required for a the barrel assembly  64  to be primed, i.e., the barrel  12  loaded with a body of water and the piston  14  positioned to apply a mechanical force to the body of water. Consequently, the providing of the disable/enable signal in the enable state indicates that the priming of the barrel assembly  64  is sufficiently complete. As a consequence, the pneumatic trigger  68  can be actuated and the barrel assembly fired. When the second “prime” signal is inactive (i.e., indicative of the barrel assembly  64  being fired), the timer  72  provides the disable/enable signal in the disable state, which renders any actuation of the pneumatic trigger  68  ineffective.  
         [0034]    The pneumatic exclusive-or valve  74  includes a gas port  118  for receiving air from the air supply line  88  that has been processed by the air filter  82 . The air received at the gas port  118  is distributed throughout the control system  62  and used by the components of the control system  62  to generate pneumatic signals. In addition, the air received at the gas port  118  is used to retract the piston  14  during priming of the barrel assembly  64 . The valve  74  further includes a first outlet port  120  for providing the second “prime” signal to the second pneumatic timer  72  and providing gas to the second port  34  to retract the piston  14  during priming of the barrel assembly  64 . A second outlet port  122  is used to provide the firing/priming signal. A first control port  124  receives the first “prime” signal provided by the first pneumatic timer  70 . Similarly, a second control port  126  receives the “fire” signal produced by the pneumatic trigger  68 . When the first “prime” signal is received at the first control port  124 , the valve  74  responds by providing the second “prime” signal to the second pneumatic timer  72 . In addition, the valve  74  provides gas to the second port of the barrel assembly  64  to facilitate the retraction of the piston  14 . The valve  74  further responds to the first “prime” signal by providing a firing/priming signal in the “priming” state at the second outlet port  122 . In contrast, when the “fire” signal is received at the second control port  126 , the valve responds by providing the firing/priming signal in the “firing” state at the second outlet port  122 . Further, the valve  74  causes the second “prime” signal at the first port  120  to go inactive, which is indicative of the barrel assembly  64  being fired. Additionally, the valve  74  terminates the provision of any air to the barrel  12  via the second port  34  that would inhibit the firing action of the piston  14 .  
         [0035]    The shot counter  78  is incremented every time the barrel assembly is fired. In the illustrated embodiment, the counter  78  is incremented every other transition between the “firing” and “priming” states of the firing/priming signal.  
         [0036]    The pressure indicator  80  indicator provides a visual indication to an operator that the disable/enable signal provided by the second pneumatic timer  72  is in the “enable” state, meaning that the operator can actuate the trigger  100  to effect the firing of the barrel assembly  64 .  
         [0037]    A pair of lubrication ports  130 A,  130 B allow lubricants to be injected into the control system  62  during servicing that extend the life of elastomeric seals and the like that are present in many of the components of the system.  
         [0038]    Generally, operation of a pneumatic control system  62  for the piston-type water cannon involves the steps of: (a) priming the water cannon, (i.e., loading a body of water into the barrel  12 , positioning the piston  14  for subsequently applying a force to the body of water; disabling the trigger  68 , and placing the valve  66  in the “priming” state); (b) enabling the trigger  68  after the priming step is sufficiently complete; and (c) firing the cannon (i.e., placing the valve  66  in the “firing” state and thereby causing the piston  14  to apply a mechanical force to the body of water in the barrel  12 ).  
         [0039]    With reference to FIG. 4A, the operation of the pneumatic control system  62  is described beginning with the firing step. The firing step commences with a user actuating the trigger  100  after the pneumatic trigger  68  has received a disable/enable signal in the enable state from the second pneumatic timer  72 . Actuation of the trigger  100  causes the pneumatic trigger  68  to provide the pneumatic “fire” signal to the second control port  126  of the exclusive-or valve  74 . In addition, actuation of the trigger  100  causes the pressure in the line extending between the second pneumatic timer  72  and the trigger  68  to decrease and thereby place the disable/enable signal in the “disable” state.  
         [0040]    The exclusive-or valve  74  responds to the “fire” signal from the trigger  68  by blocking the outlet port  120 , which causes pressure in the line between the valve  74  and the second pneumatic timer  72  to decrease and thereby reset or render inactive the second “prime” signal. Further, the valve  74  terminates the provision of air from the outlet port  120  to the third air port  34  associated with the barrel  12 . As a consequence, air is not being forced into the second chamber  30  of the barrel  12  that would inhibit the forward movement of the piston  14 . In addition, the forward movement of the piston  14  causes air that is in the second chamber and between the second disk  18  and the wall  36  to be forced out of the third air port  34 . The air is then directed by operation of the quick exhaust valve  76  to the exterior environment.  
         [0041]    The exclusive-or valve  74  also responds to the “fire” signal by providing the firing/priming signal in the “firing” state at the second outlet port  122 . The firing/priming signal in the “firing” state is conveyed to the control port  94  of the valve  66 , the shot counter  78 , and the inlet port  106  of the first pneumatic timer  70 . In response to the firing/priming signal in the “firing” state, the control port  94  places the valve in the “firing” state, which allows pressurized air from the air supply line  88  to pass from the inlet port  86  to the outlet port  92  and into the second chamber  30  of the barrel  12 . Assuming the barrel assembly  64  has been appropriately primed, the pressurized air then forces the piston  12  towards the nozzle  24  and in so doing forces at least a portion of the body of water in the first chamber  22  of the barrel out of the nozzle  24 . The shot counter  78  responds to the transition of the firing/priming signal from the “priming” state to the “firing” state by incrementing its counter. The first pneumatic timer  70  responds to the firing/priming signal in the “firing” state by implementing a “delay” whereby the first “prime” signal will be produced at a outlet port  108  at a predetermined amount of time after the firing/priming signal in the “firing” state is received. The predetermined amount of time being a time that allows for the sufficient completion of the firing step before beginning the priming step.  
         [0042]    With reference to FIG. 4B, the priming step commences with the first pneumatic timer  70  providing the first “prime” signal at the outlet port  108 . The first “prime” signal is applied to the first control port  124  of the exclusive-or valve  74 . In response, the exclusive-or valve  74  blocks the outlet port  122 , which causes pressure in the line between the valve  74  and the first pneumatic timer  72  to decrease and thereby place the firing/priming signal in the “priming” state.  
         [0043]    The valve  74  also responds to the first “prime” signal being applied to the first control port  124  by causing air to be conveyed from the first outlet port  120  to the quick exhaust valve  76 . In turn, the quick exhaust valve directs the air to the third air port  34 . This air is then used to push the piston  14  away from the nozzle  24  and thereby position the piston  14  for a subsequent firing. The first control port  124  also responds to the first “prime” signal by causing the second “prime” signal to be provided at the first outlet port  120 . The second “prime” signal is conveyed to the inlet port  112  of the second pneumatic timer  72 . The second pneumatic timer  72  responds to the second “prime” signal by implementing a “delay” such that a disable/enable signal in the “enable” state will be produced at a outlet port  114  at a predetermined amount of time after the second “prime” signal is received. The predetermined amount of time being an amount of time that allows for the sufficient completion of the priming step before beginning the enabling step.  
         [0044]    With reference to FIG. 4C, the enabling step (which can be considered to be the end of the priming step) involves the second pneumatic timer providing the disable/enable signal in the enable state at the outlet port  114 . The disable/enable signal in the enable state is conveyed to the pressure indicator  80  and the trigger  68 . The pressure indicator  80  responds to the disable/enable signal in the enable state by providing the user of the water cannon with an indication that the cannon is primed for firing and the trigger  68  is enabled, i.e., in a safety-off condition. The trigger  68  responds to the disable/enable signal in the enable state by becoming enabled, i.e., capable of generating the “fire” signal upon actuation of the trigger  100 .  
         [0045]    With reference to FIG. 3, it should be appreciated that the control system  62  is readily modified to operate with a pistonless-type water cannon, such as the cannon shown in FIG. 2. Namely, since there is no piston, the structure between the pneumatic exclusive-or valve  74  and the barrel assembly that is used to move the piston  14  away from the nozzle  24  is eliminated. In addition, the valve  66  is replaced with a valve that need only respond to the firing/priming signal in the “firing” state by allowing pressurized air to be transmitted from an input port that is in communication with the air supply line  88  to an outlet port that is in communication with the gas inlet port of the piston-less water cannon, e.g., the gas inlet port  58  of the barrel assembly  42  in FIG. 2. With the exception of piston related functions, operation of the pneumatic control system for a pistonless-type water cannon is substantially identical to that for the piston-type water cannon.  
         [0046]    A number of modifications to the control system  62  are also feasible. For instance, while the operation of the control system  62  has been described with the understanding that there is a substantially continuous flow of water into the barrel of the water cannon, i.e., water is allowed to flow into the barrel regardless of the state of the barrel assembly, there are applications in which it is desirable to only allow water to flow into the barrel during priming operations. For such applications, the flow of water is controlled by a valve that is turned “on” and “off” via pneumatic signals. To elaborate, the valve is turned “on” so that water flows into the barrel using either the first “prime” signal or the “second” prime signal. Consequently, water begins flowing into the barrel at the beginning of the priming period or some predetermined time thereafter. The valve is turned “off” to terminate the flow of water the barrel at a predetermined time after the first “prime” signal or second “prime” signal becomes active and at or before the time that the trigger  68  is enabled. In one embodiment, the disable/enable in the enable state is used to terminate the flow of water to the barrel. In any event, the flow of water to the barrel is terminated sometime during the priming of the barrel assembly.  
         [0047]    Another possible modification to the control system  62  is to replace one or both of the first pneumatic timer  70  and second pneumatic timer  72  with a pneumatic sensor/gate device. The pneumatic sensor portion of the device senses the level of the water within the barrel of the water cannon. In the case of a pneumatic sensor/gate that replaces the first pneumatic timer  70 , the sensor operates to output a pneumatic signal when the level of water in the barrel is at or below a predetermined point or level, indicating that the firing of the barrel assembly is sufficiently complete for priming to commence. The pneumatic signal is applied to the gate portion. In response, the gate portion outputs the first “prime” signal. Similarly, in the case of a pneumatic sensor/gate device that replaces the second pneumatic timer  72 , the sensor operates to output a pneumatic signal when the level of water in the barrel is at or above a predetermined point or level, indicating that priming of the barrel assembly is sufficiently complete and, as such, the trigger  68  can be enabled. The pneumatic signal is applied to the gate portion, which responds to the signal by outputting the disable/enable signal in the enable state. It should be appreciated that a pneumatic sensor/gate device that replaces either the first pneumatic timer  70  or the second pneumatic timer  72  in a pneumatic control system that is used to control a piston-type water cannon can sense the position of the piston rather than sensing the level of water.  
         [0048]    Another possible modification to the pneumatic control system  62  is to invert all or some of the logic signals. For example, the firing/priming signal has been described such that when the signal is in the “firing” state the line carrying the signal has a higher pressure than when the signal is in the “priming” state. The pneumatic control system  62  is equally adaptable or capable of utilizing a firing/priming signal in which the “firing” state has a lower pressure than the “priming” state.  
         [0049]    A further possible modification involves realizing the functionality of the pneumatic exclusive-or valve  74  with two or more discrete components.  
         [0050]    Yet a further modification to the pneumatic control system  62  to employ a gas other than air. Further, the system  62  is capable of being adapted so that a liquid is the transmission medium for all or some of the signals. Consequently, the term pneumatic herein embraces fluid based signals whether in gas form or a liquid form.