Patent Publication Number: US-9418527-B2

Title: Pneumatic detector switch having a single diaphragm for alarm and fault conditions

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. Provisional Patent Application No. 61/886,256 filed Oct. 3, 2013 which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates generally to a pneumatic switch for fire detection, and more particularly, to a pneumatic detector switch having a single deformable diaphragm for indicating alarm and fault conditions. 
     2. Description of Related Art 
     The reliable detection of fire in commercial and military vehicles and aircraft is a critical function. A well-known prior art fire detection system includes a titanium or vanadium wire contained in a pressurized sensor tube. During fabrication, the wire is exposed to high temperature and pressurized hydrogen gas, which it absorbs while cooling. The hydrogen saturated wire is inserted into a sensor tube, pressurized with an inert gas, and then sealed at both ends to form a pressure vessel. 
     One end of the pressure vessel is then incorporated into a housing that comprises a hermetically sealed and pressurized plenum, wherein pneumatic detector switches are located. When the sensor tube is exposed to high temperature, for example, in the event of a fire or overheat condition in the vehicle, the pressure inside the vessel will rise, impacting the pneumatic detector switches. 
     Typically, prior art fire alarm systems use two separate pneumatic detector switches, one for indicating an alarm condition and another for indicating a fault condition. The pneumatic detector switches are typically deformable metallic diaphragms that are adapted and configured to move between open and closed switch positions in response to variations in the background pressure within the plenum. 
     When a deformable diaphragm is employed as an alarm switch, the open switch condition corresponds to a low or normal pressure condition in the plenum, whereas the closed switch position corresponds to a high pressure condition in the plenum. In the open switch position, the diaphragm is not in electrical contact with the alarm circuit. Conversely, in the closed switch position, when there is a high pressure condition in the plenum resulting from a fire or an overheat condition, the diaphragm makes electrical contact with a circuit to activate an alarm. 
     When a diaphragm is employed as a fault or integrity switch, the closed switch position corresponds to a normal pressure condition in the plenum, whereas the open switch position corresponds to a low or below pressure condition in the plenum. In the closed switch position, the diaphragm makes electrical contact with the circuit to indicate system integrity. Conversely, in the open switch condition, the deformable diaphragm moves out of electrical contact with the fault circuit, indicting a fault condition or loss of pressure within the plenum. 
     To reduce the manufacturing cost and weight of a fire detection system used in vehicles and aircraft, it would be beneficial to provide a pneumatic detector switch having a single deformable diaphragm for indicating both alarm and fault conditions. 
     SUMMARY OF THE INVENTION 
     The subject invention is directed to a new and useful pneumatic pressure detector switch that utilizes a single diaphragm for indicating both alarm and fault conditions. 
     The detector switch includes a retainer assembly adapted to communicate with a source of pressure, a deformable diaphragm supported within the retainer assembly and movable in response to changes in pressure communicated to the retainer assembly, a fault contact element supported by the retainer assembly adjacent a first side surface of the diaphragm, and an alarm contact element supported by the retainer assembly adjacent a second side surface of the diaphragm. 
     Preferably, the fault contact element is a conduit providing communication between the source of pressure and the retainer assembly. The retainer assembly includes a fault retainer supporting the fault contact element and an alarm retainer supporting the alarm contact element. The diaphragm is supported between the fault retainer and the alarm retainer. 
     The diaphragm is insulated from the alarm retainer. In addition, the fault contact element is insulated from the fault retainer and the alarm contact element is insulated from the alarm retainer. 
     The first side surface of the diaphragm is spaced from the fault contact element and the second side surface of the diaphragm is spaced from the alarm contact element, when there is a normal pressure applied to the diaphragm. 
     The first side surface of the diaphragm contacts the fault contact element when there is a below normal pressure applied to the diaphragm. The second side surface of the diaphragm contacts the alarm fault contact element when there is an above normal pressure applied to the diaphragm. 
     The subject invention is also directed to a pneumatic pressure detector switch that includes a retainer assembly adapted to communicate with a source of pressure and defining an interior pressure chamber, a deformable diaphragm supported within the interior pressure chamber of the retainer assembly and movable therein in response to changes in pressure communicated to the pressure chamber of the retainer assembly, a fault contact pin supported by the retainer assembly and extending to the interior pressure chamber adjacent a first side surface of the diaphragm, and an alarm contact pin supported by the retainer assembly and extending to the interior pressure chamber adjacent a second side surface of the diaphragm. 
     Preferably, the fault contact pin is a conduit providing communication between the source of pressure and the interior pressure chamber of the retainer assembly. 
     The first side surface of the diaphragm is spaced from the fault contact pin and the second side surface of the diaphragm is spaced from the alarm contact pin, when there is a normal pressure applied to the diaphragm within the interior pressure chamber. The first side surface of the diaphragm contacts the fault contact pin when there is a below normal pressure applied to the diaphragm within the interior pressure chamber. The second side surface of the diaphragm contacts the alarm fault contact pin when there is an above normal pressure applied to the diaphragm within the interior pressure chamber. 
     The retainer assembly includes a fault retainer supporting the fault contact pin in an insulated manner and an alarm retainer supporting the alarm contact pin in an insulated manner, and wherein the diaphragm is supported between the fault retainer and the alarm retainer in an insulated manner. 
     These and other features of the pneumatic detection switch of the subject invention and the manner in which it is constructed and employed in a fire detection system will become more readily apparent to those having ordinary skill in the art from the following enabling description of the preferred embodiments of the subject invention taken in conjunction with the several drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art will readily understand how to make and use the pneumatic detector switch of the subject invention without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a cross-sectional view of a pneumatic detector switch having a single diaphragm for alarm and fault conditions, which is constructed in accordance with a preferred embodiment of the subject invention; 
         FIG. 2  is a cross-sectional view of the pneumatic detector switch of the subject invention under a normal pressure condition; 
         FIG. 3  is a cross-sectional view of the pneumatic detector switch of the subject invention under an above normal pressure condition; 
         FIG. 4  is a cross-sectional view of the pneumatic detector switch of the subject invention under a below normal or null pressure condition; 
         FIG. 5  is a schematic representation of an alarm circuit wherein the pneumatic detector switch of the subject invention is under a normal pressure condition as shown in  FIG. 2 ; 
         FIG. 6  is a schematic representation of an alarm circuit wherein the pneumatic detector switch of the subject invention is under an above normal pressure condition, as shown in  FIG. 3 ; and 
         FIG. 7  is a schematic representation of an alarm circuit wherein the pneumatic detector switch of the subject invention is under a below normal pressure condition, as shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is illustrated in  FIG. 1  a pneumatic pressure detector switch constructed in accordance with a preferred embodiment of the subject invention and designated generally by reference numeral  10 . Detector switch  10  includes a retainer assembly  12  adapted to communicate with a source of pressure and defining an interior plenum or pressure chamber  14 . 
     The pressure source with which the retainer assembly  12  of detector switch  10  communicates may be a sealed pressure vessel housing a hydrogen saturated wire inserted into a sensor tube and pressurized with an inert gas, as is well known in the art. The retainer assembly  12  may be constructed from a metallic material such as molybdenum or the like. 
     A deformable metallic diaphragm  16  is supported within the interior pressure chamber  14  of the retainer assembly  12 . The diaphragm  16  is preferably stamped from a flat metallic sheet and is pre-formed into the required shape prior to installation into the pressure chamber  14 . A metal alloy of titanium, zirconium and molybdenum (TZM) is often utilized to construct such diaphragms. 
     The peripheral edge of the shaped diaphragm  16  is preferably brazed to the retainer assembly  12  to form the gas-tight seal. The diaphragm  16  is movable within the pressure chamber  14  in response to changes or variations in the pressure communicated to or otherwise within the pressure chamber  14  of the retainer assembly  12 . 
     A fault contact pin  18  is supported by the retainer assembly  12  and it extends to the interior pressure chamber  14  adjacent a first side surface of the diaphragm  16 . An alarm contact pin  20  is supported by the retainer assembly  12  and it extends to the interior pressure chamber  14  adjacent a second side surface of the diaphragm  16 . The fault contact pin  18  includes a central conduit  18   a  providing communication between the source of pressure and the interior pressure chamber  14  of the retainer assembly  12 . 
     With continuing reference to  FIG. 1 , the retainer assembly  12  of detection switch  10  includes a fault retainer  22  supporting the fault contact pin  18  and an alarm retainer  24  supporting the alarm contact pin  20 . The diaphragm  16  is supported between the fault retainer  22  and the alarm retainer  24 . 
     The metallic diaphragm  16  is electrically insulated from the metallic alarm retainer  24  by an insulating washer  26 . In addition, the metallic fault contact pin  18  is electrically insulated from the metallic fault retainer  22  by an insulating tube  28  and the metallic alarm contact pin  20  is electrically insulated from the metallic alarm retainer  24  by an insulating tube  30 . The insulators may be made from a ceramic material or the like. 
     The diaphragm  16  should be designed to insure that electrical contact will be made when a predetermined threshold pressure is reached within the pressure chamber  14 , corresponding to a certain threshold temperature for a given condition and application. Those skilled in the art will readily appreciate that the degree to which the diaphragm  16  deforms will be dependent upon the thickness and diameter of the diaphragm as well as its material of construction. 
     Referring to  FIG. 2 , there is illustrated the pneumatic detector switch  10  of the subject invention under a normal pressure condition. In this condition, the diaphragm  16  is out of contact with the fault contact pin  18  and the alarm contact pin  20 . This corresponds to a normal condition in which there is no alarm or fault condition present. 
     Referring to  FIG. 3 , there is illustrated the pneumatic detector switch  10  of the subject invention under an above normal pressure condition. In this condition, the diaphragm  16  is out of contact with the fault contact pin  18  and it is in contact with the alarm contact pin  20 . Moreover, there is electrical continuity between the diaphragm  16  and the alarm contact pin  20 , and there is no electrical continuity between the diaphragm  16  and the fault contact pin  18 . This corresponds to the existence of an alarm condition, such as a fire or overheat condition. 
     Referring to  FIG. 4 , there is illustrated the pneumatic detector switch  10  of the subject invention under a below normal or null pressure condition. In this condition, the diaphragm  16  is in contact with the fault contact pin  18  and it is out of contact with the alarm contact pin  20 . Moreover, there is no electrical continuity between the diaphragm  16  and the alarm contact pin  20 , and there is electrical continuity between the diaphragm  16  and the fault contact pin  18 . This corresponds to the existence of a fault condition, such as a loss of pressure within the detection system itself. 
     Referring now to  FIG. 5 , there is illustrated a schematic representation of an alarm circuit  100  which includes the pneumatic detector switch  10  of the subject invention. The alarm circuit  100  includes a power source  110 , an alarm indication device  112  and a fault indication device  114 . The power source  110  is connected to the diaphragm  16 . The alarm indication device  112  is connected to the power source  110  and to the alarm contact pin  20 . The fault indication device  114  is connected to the power source  110  and to the fault contact pin  18 . 
     As shown in  FIG. 5 , the pneumatic detector switch  10  is receiving a normal pressure flow through the conduit  18   a  of fault contact pin  18 . The diaphragm  16  is therefore out of electrical contact with the fault contact pin  18  and the alarm contact pin  20 . Accordingly, the alarm indication device  112  and the fault indication device  114  are both inactive. This is the normal operation state for the detector switch  10 , with the lack of electrical continuity indicating the required minimal pressure resides within the switch. 
     Referring now to  FIG. 6 , the pneumatic detector switch  10  is receiving an above normal pressure flow through the conduit  18   a  of fault contact pin  18 . The diaphragm  16  is therefore moved further away from the fault contact pin  18  and into electrical contact with the alarm contact pin  20 . Accordingly, the alarm indication device  112  is active, while the fault indication device  114  is inactive. 
     Referring to  FIG. 7 , the pneumatic detector switch  10  is receiving a below normal pressure flow (or no pressure at all) through the conduit  18   a  of fault contact pin  18 . The diaphragm  16  is therefore moved into electrical contact with the fault contact pin  18  and displaced further away from the alarm contact pin  20 . Accordingly, the alarm indication device  112  is inactive, but the fault indication device  114  is active. 
     The minimum normal pressure within the chamber  14  of retainer assembly  12  is typically set at a pressure which is equivalent to the pressure at −65° F., but it can be lower or higher depending upon the specific application. In this condition, the pressure received by the switch  10  is not sufficient to keep the diaphragm  16  electrically separated from the fault contact pin  18 . 
     The use of a single diaphragm switch will reduce manufacturing cost and the overall weight of the fire detection system, which is a critical factor for modern aerospace applications. However, it is envisioned that two switches could still be used to provide a redundant system. For example, if two switches were used, the diaphragm  16  and the fault contact pin/tube  18  from each switch could be electrically connected in series so that if either of the two switches fell below the minimal normal pressure, a fault condition would be indicated. Similarly, the diaphragm  16  and the alarm contact pin  20  of each switch could be electrically connected in parallel so if either of the two switches experienced an above normal pressure condition, an alarm condition would be indicated. 
     While the subject invention has been shown and described with reference to a preferred embodiment, those skilled in the art will readily appreciate that various changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention as defined by the appended claims.