Fire extinguishing system

A method for extinguishing fires in aircraft cargo spaces includes two pressure chambers separated by an annular boss which houses a restricting orifice and a check valve assembly. A lower chamber acts as a high rate discharge fire extinguisher and the upper chamber acts as a metering fire extinguisher. Upon receipt of an activation command from the cockpit, all the agent contained in the high rate discharge chamber is emptied within seconds. At the same time, the pressurized agent contained in the upper chamber pushes the check valve to a closed position and allows the agent in the metering chamber to flow through the orifice of the restrictor at a predetermined rate. With the properly sized orifice, the agent in the upper chamber will be emptied at a rate that lasts for the needed duration of the aircraft fire protection system.

FIELD OF THE INVENTION 
The invention relates to fire extinguishers, particularly for use in 
aircraft cargo compartments and the like. 
BACKGROUND OF THE INVENTION 
Generally, the cargo space in commercial aircraft is inaccessible during 
flight. For this reason, most commercial aircraft rely on automatic 
fire-extinguishing systems to extinguish fires which occur in the cargo 
space and to keep the fire suppressed for the duration of the flight. 
Most fire extinguishing systems for aircraft cargo spaces include two 
sources containing a fire extinguishing agent. The first source rapidly 
discharges the fire extinguishing agent to knock down the initial fire 
erupting within the cargo compartment. The second source releases the 
extinguishing agent at a much slower rate, and prevents fire from 
reigniting within the compartment. The rate of discharge is dependent on 
the size of the cargo space. Without the extended discharge, the 
concentration of the fire extinguishing agent in the cargo space could 
drop below what is necessary to keep the fire suppressed and embers could 
reignite the fire. 
Previous fire extinguishing systems, such as U.S. Pat. No. 5,183,116 by 
Fleming, U.S. Pat. No. 5,083,867 by Hindrichs et al., and U.S. Pat. No. 
4,643,260 by Miller, disclose the use of two independent fire 
extinguishers, consisting of two separate containers. Each container is 
equipped with its own charge valve, safety relief, pressure indicator, 
discharge outlet, explosive cartridge, rupture disc assembly, mounting 
lugs, and doublers. These types of systems take up excessive space, use 
longer piping connections, and require excessive time for installation 
onto the aircraft mounting platform. 
Another type of fire extinguishing system is the "Bottle Within a Bottle" 
designed and manufactured by the Pacific Scientific Company in 1982. This 
design used an outer container as the high rate discharge fire 
extinguisher and an inner container as the metering fire extinguisher. 
While this system had several advantages over two separate extinguishers, 
relatively complicated weld structure joined the outer container and the 
inner container together to form a single fire extinguisher. The 
disadvantages of this design include the difficulty in monitoring the 
pressure of the inner container, the dependence of the outer container 
size on the size of the inner container, and the cost and complication of 
the design. 
Thus, a need exists for a fire extinguishing system which not only is more 
compact, but also has fewer parts and increased reliability. 
SUMMARY OF THE INVENTION 
A dual chamber fire extinguisher system is provided with two pressure 
chambers joined together by a passage having a restricting orifice and 
preferably another passage controlled by a check valve assembly. One 
chamber acts as a high rate discharge fire extinguisher and the other 
chamber acts as a low rate discharge metering fire extinguisher. The dual 
fire extinguisher chambers are preferably joined by a suitable structure 
containing the passages. The chambers are normally stored in an upright 
position with the high rate chamber at the bottom and the metering chamber 
at the top, and with the fire-extinguishing agent stabilized between the 
two chambers. The size of the high rate discharge chamber is determined by 
the amount of fire extinguishing agent required to maintain a high agent 
concentration sufficient to knock down an initial fire erupting in a 
closed area such as an aircraft cargo compartment. The size of the 
metering chamber is determined by the duration required for maintaining a 
low agent concentration sufficient to prevent the fire from reigniting. 
This size is determined in part by the rate of the air leakage out of the 
cargo compartment. 
The check valve permits the chambers to be filled through an inlet into the 
high rate discharge chamber and through the check valve into the low rate 
chamber. Conveniently, the unit may be inverted during the fill operation. 
Upon receipt of an activation command signal from an aircraft cockpit, all 
the agent contained in the high rate discharge chamber is emptied through 
a suitable outlet within seconds. At the same time, the pressurized agent 
contained in the low rate chamber pushes the check valve to a closed 
position and allows the agent to flow through the orifice of a restrictor 
at a predetermined rate. With the properly sized orifice, the agent in the 
low rate chamber will be emptied at a rate that lasts for the entire 
duration of the needed fire protection. 
The use of a single pressure container with two separate chambers is 
compact, relatively light, economical, flexible in multiple aircraft 
applications, reliable, and able to withstand a high vibration environment 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, and particularly to FIG. 1, a 
fire-extinguisher of the invention, indicated generally by the numeral 10, 
includes an upper, low rate discharge pressure chamber 15 connected to a 
lower high rate discharge pressure chamber 20 by a generally circular 
flange or boss 35. Mounting lugs 25 are welded to the exterior of the 
upper pressure chamber and/or the lower chamber 20 for mounting the 
extinguisher 10 in an aircraft. A fill fitting 30 is attached to the 
exterior of the lower chamber 20. 
Referring to FIG. 2, a threaded bore 40 extends axially through the boss 
35. A tubular housing 45 extends through the bore 40 with its exterior 
threadably mating with the threaded bore 40 of the boss 35. An outwardly 
extending flange 50 of the housing 45 lies flush against the lower surface 
of the boss 35. An O-ring 55 is inserted into a circumferential groove 60 
formed in the housing 45 between the threaded portion of the housing 45 
and the flange 50, to prevent leakage of a fire-extinguishing agent 
between the bore 40 and the housing 45. An internal passageway 65 is 
formed inside the housing 45 in communication with at least one inlet hole 
70 extending through the side wall of the housing 45 beneath the flange 
50, and adjacent to the lower end of the housing 45 as viewed in FIG. 2. 
A tubular rod 75 extends through the passageway 65, protruding beyond the 
housing 45 at both the upper and lower ends. An outwardly extending flange 
80 on the upper end of the housing 45 has an outer diameter larger than 
the internal diameter of the housing 45 so that the flange 80 forms a 
valve member 83 which, in combination with the housing 45 end, forms a 
check valve. A seal gasket 100 surrounds the rod 75 adjacent the flange 80 
to complete the flange seal valve member 83 that seats against the end of 
the housing 45. The valve member 83 is shown in FIG. 2 in its open 
position. The gasket 100 is held in position by a sleeve 95 press-fit 
around the exterior of the rod 75. As can be seen, the outer diameter of 
the sleeve 95 is spaced from the inner diameter of the housing 45 so that 
fluid can flow through the open valve 83 passed the sleeve 95 into the 
remainder of the passageway 65. 
The lower end of the rod 75 slidably fits within a bore 103 formed in a 
lower end wall of the housing 45. A retaining washer 90 surrounds a 
reduced diameter portion of the rod 75 and is captured in that position by 
a swaged lower end 85 of the rod 75. The washer 90 engages the lower 
surface of the housing 45 and thus limits the upward movement of the rod 
75 to the valve 83 open condition illustrated in FIG. 2. 
A rod bore 105 extends axially through the tubular rod 75, and a restrictor 
110 is positioned in the bore 105. As seen, the upper portion of the 
restrictor 110 has a larger exterior diameter than the lower portion and 
it engages a shoulder 113 on the interior of the rod 75 formed by the 
upper portion of the rod bore 105 which has a larger inner diameter than 
does the lower portion. The restrictor 110 is tubular and includes a fixed 
metering orifice 120 and a filter 115 mounted on its lower end. 
Referring back to FIG. 1, a discharge head assembly 145 is positioned in 
the lower end of the high-rate discharge chamber 20. That assembly 
includes a tubular exhaust fitting 130 secured to the lower end of the 
chamber 20 and a frangible burst disk 125 (shown in the burst condition) 
secured around its outer periphery to the inside of the exhaust fitting 
130 by a threaded retainer 135. The discharge head assembly 145 includes a 
discharge head 147 which is sealed to the exterior of the fitting 130, 
being held in place by a nut 140. An explosive cartridge 150 is threaded 
into the lower end of the discharge head 147 and is connected to an 
electrical connector 155. The discharge head includes an outlet 148. 
The fire extinguisher is charged through the fill fitting 30, and is more 
conveniently operated with the fire extinguisher inverted from the 
position shown in FIG. 2. In either case, the fire extinguishing agent 
opens the check valve 83 formed by the rod flange 80, moving it to the 
open position illustrated in FIG. 2. Note that the stop washer 90 limits 
the opening travel of the rod 75. The extinguishing agent travels through 
inlets 70 and through the interior annular passageway 65 to open the valve 
83 and allow flow into the metering chamber 15. In this way, both the 
metering chamber 15 and the high-rate discharge chamber 20 are charged 
with the fire extinguisher agent. A commonly used agent is 
bromotrifluoromethane (Halon), being superpressurized to about 360 
P.S.I.A. at 70.degree. F. in both chambers utilizing nitrogen or some 
other suitable gas. 
When a fire is detected, the explosive cartridge 150 is remotely activated 
such as from the cockpit of an airplane, causing the burst disk 125 to 
rupture as shown in FIG. 2. Once the disc 125 is ruptured, the 
fire-extinguishing agent flows from the high-rate discharge chamber 20 and 
through the outlet 148 of the discharge head 147. The Halon agent from the 
high-rate discharge chamber 20 is rapidly discharged to ensure a minimum 
concentration in the aircraft cargo compartment of about 5% volume for an 
initial flame knockdown of a fire in the compartment. 
As the pressure in the high-rate discharge chamber 20 decreases, the 
pressurized agent in the metering pressure chamber 15 will push the valve 
member 83 downward into its closed position causing the seal 100 to engage 
the upper surface of housing 45. This prevents the fire extinguishing 
agent in the metering chamber 15 from traveling through passageway 65. The 
agent will, however, continue to flow through the orifice 120 of the 
restrictor 110 and the filter 115 at a predetermined rate to ensure 
approximately a 3% by volume extinguishing agent concentration for a 
predetermined time in the compartment to adequately control or extinguish 
a fire in the compartment. 
The fire extinguisher also has a safety relief valve and pressure gauge 
(not shown) associated with each pressure chamber.