1.  The Field of the Invention
The present invention relates to an apparatus and method for delivering a fire retardant material.  More particularly, the invention relates to a fire retardant delivery device which delivers an aerated liquid or foam in a controlled manner. 
2.  The Relevant Technology
Apparatus for discharging fire retardants are well known in the art.  Typically, a fire retardant delivery device is activated by a signal from a detector or sensor that indicates that a quantity of retardant is needed due to the detection of smoke or increased temperature.  One type of fire retardant delivery device, is shown generally in FIG.  1 as reference number 10.  This fire retardant delivery device 10 utilizes a pressure generator 12 which causes the rapid creation of a pressurized gas. 
Once the pressurized gas is generated, it is forced through orifices 18 and 19 to push against the top of a piston 20 as depicted in FIG.  1.  Piston 20 is forced downward, as shown by arrows A, along a path defined by a tube 24.  As piston 20 is moved it compresses fire retardant material 22 which is contained within casing 26.  Simultaneously, a portion of the pressurized gas is also directed through hole 36 and through tube 24 to heat fire retardant 22 so as to aid in the vaporization thereof. 
As piston 20 is forced to compress fire retardant material 22, the pressure of fire retardant material 22 within chamber 14 increases until burst disks 28 and 30 rupture.  Once burst disks 28 and 30 rupture, fire retardant material 22 is forced out of casing 26, through exit orifices 32 and 34.  Thereafter fire retardant material 22 is expelled out of diffuser 38 by way of diffuser hole 40.  The high velocity at which fire retardant material 22 is forced from exit orifices 32 and 34 results in fire retardant material 22 becoming atomized. 
Fire retardant material 22 is also heated by the hot pressurized gas created by generator 12 and which exits tube 24.  The temperature of fire retardant material 22 is raised by the pressurized gases such that it is vaporized as it leaves diffuser holes 40.  The temperature is controlled by regulating the flow rate of the hot pressurized gas which exits tube 24.  The flow rate is adjusted to be the minimum rate which is necessary to insure the complete vaporization of fire retardant material 22 when it is discharged from diffuser holes 40 at the lowest expected environmental temperature. 
Current designs and technology of available fire retardant delivery devices, such as fire retardant delivery device 10, have several problems that adversely effect the performance of the delivery of a fire retardant.  One problem is that this type of fire retardant delivery device 10 only provides for the delivery of an atomized and vaporized fire retardant material 22.  In some situations it is necessary to use an aerated liquid or foam to combat a fire or explosion.  A fire retardant delivery device such as fire retardant delivery device 10, illustrated in FIG.  1, is not capable of delivering an aerated liquid or foam since the high temperatures introduced by the pressurized gas flowing through tube 24 causes vaporization of fire retardant material 22 rather than aeration.  Similarly, this type of fire retardant delivery device 10 is not capable of delivering fire retardant material 22 with a predetermined ratio of gas to liquid, since this type of device only delivers a vaporized fire retardant material 22 through diffuser holes 40 and not an aerated fire retardant material. 
Yet another problem with this type of fire retardant delivery device 10 is that there is no control over the discharge of fire retardant material 22 in relation to the discharge of pressurized gases through tube 24.  The rate at which pressurized gases are discharged through tube 24 is controlled to cause vaporization of fire retardant material 22.  There is no control which will prevent the exhaustion of pressurized gases prior to the complete delivery of fire retardant material 22.  This is a problem since it is necessary for substantially all of fire retardant material 22 to be discharged to combat a fire or explosion. 
Accordingly, there is a need to create a fire retardant delivery device which overcomes the foregoing disadvantages.  In addition, there is a need to improve fire retardant delivery devices such that there is greater control over the distribution of numerous types of fire retardant materials. 
It is an object of the present invention to provide a fire retardant delivery device which is capable of a controlled discharge of a fire retardant material. 
It is another object of the present invention to provide a fire retardant delivery device which is capable of discharging numerous types of fire retardant material. 
It is another object of the present invention to provide a fire retardant delivery device which will discharge an aerated liquid or foam with a predetermined ratio of gas to liquid. 
It is yet another object of the present invention to provide a fire retardant delivery device which will discharge substantially all of the fire retardant material before the exhaustion of the pressurized gas which is used to drive the fire retardant material. 
A further object of the present invention is to provide a fire retardant delivery device which will actuate on command. 
Yet another object of the present invention is to provide a fire retardant delivery device which is compact and portable. 
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a device for discharging a fire retardant material is provided that includes a housing capable of storing a fire retardant material.  The housing has an initiator attached to a first end, while a discharging port is attached at a second end.  Additionally, sealed within the housing is a driver which forces the fire retardant material towards the discharging port.  The driver follows a path defined by a bypass tube located centrally within the housing.  The driver is forced along the path by exit gases created by the initiator attached at the first end.  The housing also has a choke assembly located near to the second end thereof.  The choke assembly selectively controls the rate at which the fire retardant material and the pressurized gases exit through the discharging port.  The choke assembly includes a choke body with a first and second cavity.  The second cavity directs the exit gases towards an aperture which connects with the first cavity.  In turn, the first cavity is connected to the fire retardant material by passageways.  Furthermore, first cavity is configured to aid in mixing and distribution of the exit gases and the fire retardant material through the discharging port.  The choke assembly also creates a pressure differential which aids in the discharge of the fire retardant material.  The pressure differential exits between the first end and the second end of the housing such that the first end is at a higher pressure than the second end. 
When the initiator is activated, the exit gases flow through both side apertures and an exit hole located in the bypass tube.  As the exit gases flow through the side apertures they force the driver toward the second end of the housing and compress the fire retardant material within the housing.  Simultaneously, the exit gases flow toward the exit hole of the bypass tube.  Both the exit gases and the fire retardant material remain within the housing for a short period of time due to a number of burst disks attached to the choke assembly.  Once the pressure within the housing is sufficient, the burst disks rupture and allow fire retardant material and exit gases to flow through the choke assembly.  Specifically the exit gases pass through the exit hole and are controlled by both the second cavity and the aperture.  The aperture is in communication with the first cavity and further limits the flow of exit gases therethrough.  Passageways are also in communication with the first cavity and restrict the flow of fire retardant material.  Exit gases and fire retardant material are mixed in first cavity and then discharged through discharge port. 
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.