Patent Publication Number: US-7584751-B1

Title: Adapter for protective mask testing apparatus

Description:
GOVERNMENTAL INTEREST 
   The invention described herein may be manufactured, used and licensed by or for the U.S. Government. 

   TECHNICAL FIELD 
   This invention relates to apparatus for testing protective masks, such as so-called gas masks. 
   BACKGROUND 
   There are a variety of protective masks or, colloquially, “gas masks,” to prevent users from inhaling toxic substances of all sorts. Such masks include negative pressure chemical, biological, radiological, and nuclear protective masks, known as CBRN protective masks in military parlance. The M45 joint service protective mask, part of the M40 series of masks, is among those in use by various branches of the United States Armed Services. 
   It is, of course, desirable to assure that the M45 masks and other protective masks in use by the military function and fit properly in order to protect the users from exposure to various toxins. In particular, the function of the outlet valve of the protective mask is often critical. Upon inhalation, the outlet valve must close to a sufficient degree to channel inhalation through the mask&#39;s canister without drawing in toxins from outside the mask. Conversely, upon exhalation, the outlet valve must open sufficiently to expel the breath, again without unacceptable leakage. 
   The outlet valve and other features of protective masks may be tested at the manufacturing facility. Factory tests of the outlet valves of protective masks often suffer from certain drawbacks and disadvantages. For example, operation of the outlet valve is generally tested by applying positive or negative pressure to the valve from inside of the mask. Such test results are often not acceptable to the armed services or other users. Such “inside” tests differ from testing the function of the valve from outside of the mask, and therefore such outside testing is generally preferred as an indication of serviceability and reliability. 
   The joint service mask leakage tester (JSMLT, in military parlance) is a portable testing device that has been developed for testing certain protective masks. However, the results obtained from the JSMLT are generally only as good as the connection between the JSMLT and the protective mask to be tested. In other words, unless the mask to be tested is properly secured or connected to the JSMLT, the test results related to function, serviceability, leakage, and proper fit of the mask may be inaccurate, producing either false positives or false negatives. In addition to the JSMLT, other portable testers are available for use and also require a secure connection between the mask being tested and the test device. Some of these devices include the TDA-99M Protective Mask Leakage Tester, which is the commercial equivalent of the JSMLT, and the TDA-99B which are both available commercially from Air Techniques International (ATI), of Owings Mills, Md. 
   The current connections between the JSMLT and masks to be tested suffer from various drawbacks and disadvantages, especially with regard to masks having outlet valves of irregular geometry, such as the M45. Current connections to the JSMLT sometimes may not create a sufficient seal with the outlet valve for accurate testing purposes. Establishing a suitable connection may be a cumbersome process at times, the ability to achieve the suitable connection may be inconsistent at other times, and the resulting connection may be unreliable at still other times. 
   There is thus a need to address the various drawbacks and disadvantages of the current apparatus for testing protective masks. 
   SUMMARY 
   An adapter is provided for testing an outlet valve of a gas mask with a mask leakage testing apparatus. In one implementation, part of the adapter is an overmold having a resiliently compressible surface which has been conformed so as to mate with the outlet valve. The adapter has an insert formed of a material which is more rigid than that of the overmold. The insert is secured to the overmold in such a way that a surface of the insert at least partly underlies the conformed surface of the overmold. In this way, the insert surface provides support to the resilient compression of the conformed surface of the overmold. Certain portions of the conformed surface engage corresponding locations of the housing of the valve in an interference fit. As a result, the valve portion is sufficiently isolated for testing purposes by the apparatus. 
   In certain implementations, the adapter is part of a joint service mask leakage tester. The adapter in such implementations includes portions which oppose an M45 mask outlet valve to be tested. The portions which oppose the valve to be tested include first and second notches configured to engage, respectively, a drink tube and microphone connection port associated with the housing of the valve. Other portions of the adapter include multiple walls which engage corresponding locations on the valve in an interference fit. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a testing apparatus, a mask to be tested, and an adapter for the apparatus; 
       FIG. 2  is an enlarged, perspective view of the apparatus of  FIG. 1 ; 
       FIG. 3  is a top plan view of the adapter of  FIGS. 1 and 2 ; 
       FIG. 4  is side elevational view along line  4 - 4  of the adapter shown in  FIG. 3 ; 
       FIG. 5  is an exploded perspective view of the adapter and valve housing of the preceding figures; 
       FIG. 6  is a partial, side elevational view of a portion of the adapter taken along line  6 - 6  of  FIG. 3 ; 
       FIG. 7  is a partial, top plan view of the adapter taken along line  7 - 7  of  FIG. 3 . 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   Referring now to the drawings and, in particular, to  FIG. 1 , one suitable apparatus for testing protective masks  25  is as a joint service mask leakage tester (JSMLT)  21 . The JSMLT tests a variety of functions and features of protective masks in order to determine mask serviceability, identify defective components, and perform quantitative factor tests. To test for outlet valve leakage and perform the other tests of interest, the JSMLT includes an aerosol generator assembly, control unit, power unit, head forms, an interface hose, a fit test module, and other components. The JSMLT is a military version of ATI&#39;s model number TDA-99M, which is described at ATI&#39;s website at www.atitest.com. 
   As seen in  FIGS. 1 and 2 , testing apparatus includes a testing port  23  through which positive or negative air pressure is delivered for performing outlet valve leakage testing in a manner appreciated by those skilled in the art. 
   A protective mask  25 , here shown as the M45 negative pressure mask, includes an outlet valve  27  to be tested with testing apparatus  21 . To accomplish such testing, outlet valve  27  must be operatively connected to testing port  23 . Such operative connection means that valve  27  is exposed to one or more tests through suitably isolated pneumatic communication with testing port  23 . 
   Adapter  29  facilitates the operative connection between outlet valve  27  and testing apparatus  21 . As seen in  FIG. 2 , adapter  29  includes a surface  31  which opposes valve  27 . Surface  31  has been conformed or otherwise configured to connect valve  27  to testing apparatus  21  in sufficient isolation to test valve operation. Adapter  29  also includes a suitable connector  33  which secures adapter  29  in pneumatic communication with testing port  23 . 
   As seen by reference to  FIGS. 1 and 5 , outlet valve  27  includes a valve housing  41 . Valve housing  41  has various non-uniform geometries or portions which pose challenges to suitably connecting it to testing equipment. In this example and implementation, the non-uniform portions of housing  41  include a drinking tube (and associated fitting)  43  and a microphone connection port  45 , both of which extend radially outwardly from a cylindrical sidewall  47  of housing  41 . The uniformity of cylindrical sidewall  47  itself is interrupted by two gaps or breaks  49  which extend over an arc of about 30° each. Between the two breaks  49  is an isolated section  51  of sidewall  47 , and a tab  53  (for securing a mask cover (not shown)). Tab  53  extends radially outwardly from section  51  and cylindrical sidewall  47 , forming another non-uniform portion of housing  41  of valve  27 . At the base of cylindrical sidewall  47  is a cylindrical wall  57  ( FIG. 5 ) having a smaller diameter of curvature than that of cylindrical sidewall  47 , thereby forming a detent  55  between walls  57 ,  47 . 
   Referring now again to adapter  29  and  FIGS. 2-4 , in this implementation, surface  31  has been conformed to include various features or portions which engage corresponding locations on valve  27  to form an interference fit sufficient to connect valve  27  to testing apparatus  21 . Surface  31  includes notches  35 ,  37  configured to engage drink tube  43  and microphone connection port  45 , respectively, in an interference fit. Surface  31  also includes multiple walls for engaging valve  27 . For example, two circumferential arcs  59 ,  61  are formed into surface  31  to mate with breaks  49  in housing  41  of the outlet valve  27 . The circumferential arcs  59 ,  61  terminate in wall ends  63  which engage opposing portions of cylindrical sidewall  47  of housing  41  to form interference fits. A third notch  65  is sized to receive tab  53  therein in an interference fit. 
   Notches  35 ,  37 , and  65  are defined in surface  67  of adapter  29 . When adapter  29  is installed on testing apparatus  21 , surface  67  faces outwardly from testing apparatus  21  and opposes mask  25  to be tested. Surface  67  thus is an upper or outer surface of adapter  29  as shown in the drawings of this implementation. Upper surface  67  is part of a generally cylindrical wall  69  which extends circumferentially at the perimeter of adapter  29 . Notches  35 ,  37 ,  65  are positioned at angles around circumferential wall  69  so as to correspond to angular locations of drinking tube  43 , microphone connection port  45 , and tab  53 , respectively, in outlet valve  27 . 
   Similarly, circumferential arcs  59 ,  61  are disposed inwardly and near circumferential wall  69  of adapter  29 , and at angular locations to mate with breaks or gaps  49  in sidewall  47  of valve housing  41 . 
   Adapter  29  has a circumferential lip  71  extending inwardly at or near upper surface  67 , and a circumferential crevice  73  at or near the base of cylindrical wall  69 . Lip  71  is sized to resiliently compress as cylindrical sidewall  47  of outlet housing  41  is inserted into adapter  29 . As best visualized by reference to  FIG. 5 , when housing  41  has been sufficiently advanced, lip  71  decompresses to engage detent  55  at the base of housing  41 . Engagement of lip  71  into detent  55  provides the operator of testing apparatus  21  with a “snap in” feel that outlet valve  27  has been fully received onto adapter  29 , as well as providing a sealing function. Crevice  73  receives therein an upper portion of cylindrical sidewall  47  in an interference fit. 
   Referring now more particularly to  FIGS. 3-5 , in this implementation, the various notches, walls, and other geometries of adapter  29  are defined by conforming an outer surface (corresponding to surface  31 ) of an overmold  75 . Overmold  75  is formed of a resiliently compressible, polymeric material, preferably rubber, SANTOPRENE, or a soft elastomer, although other materials are likewise suitable. The resilient compressibility of the material for overmold  75  can vary in durometer from 20 to 80, such as between 20 and 50. A durometer of about 30 has been found well suited for this implementation. Overmold  75  surrounds or encapsulates an insert  77 . Insert  77  is formed of a more rigid material than that used for overmold  75 , such as aluminum, although other materials, such as nylon, or a more rigid polymeric material, are also suitable. By virtue of the more rigid material used for insert  77 , it supports overmold  75  and aids the various features of conformed surface  31  in establishing the interference fit sufficient to isolate valve  27  for testing purposes. Thus, insert  77  has its own circumferential insert wall  79  with upper surface  81  underlying upper surface  67  formed in wall  67  of overmold  75 . Similarly, insert  77  has cut-outs  83 ,  85 , and  87  ( FIG. 5 ) extending into insert wall  79  at angular locations corresponding to notches  35 ,  37 , and  65 , respectively, defined in overmold  75 . Cut-outs  83 ,  85 , and  87  are sized and dimensioned to underlie notches  35 ,  37 ,  65  when insert  77  has been encapsulated by overmold  75 . 
   A plurality of pins  89  extend upwardly or outwardly (as shown in the drawings) from surface  81  of insert wall  79 . Pins  89 , when surrounded or encapsulated by overmold  75 , aid in maintaining the angular registration between overmold  75  and insert  77 . 
   To encapsulate insert  77 , it is placed into a cavity of the mold corresponding to the overmold. The polymeric material for the overmold is then introduced into the cavity, which is then filled so as to encapsulate the insert and create the overmold. 
   It will be appreciated that the interference fit around each of the non-uniform portions of valve  27  needs to be sufficient to seal valve  27  to testing apparatus  21  for testing purposes. In other words, the interference fits created by the features of conformed surface  31  must not “leak” during testing. The existence of multiple, non-uniform geometries in valve  27 , as well as the spacing of such non-uniformities at different angular locations around the circumference of housing  41 , complicate the creation of a suitable interference fit for a variety of reasons. To address these complexities, the durometer of surface  31  must be sufficiently hard to remain sealed when exposed to positive and negative pressures of testing, yet sufficiently soft to conform to the non-uniform or irregular geometries of valve  27 . 
   Once an appropriate durometer or range of durometer is selected, the presence of angles and edges in the geometry of valve  27  still may make the valve prone to leakage or other unsealing, as such angles and edges may create sufficient stress concentrations to separate opposing portions of adapter  29  from valve  27 —even when such opposing portions are made of resiliently compressible material. Furthermore, the creation of suitable interference fits with resiliently compressible material is generally accompanied by a certain amount of “push back” force caused by its compression. While such “push back” force is desirable for the purposes of forming the interference fit, if such forces are greater at one angular location around the circumference of adapter  29  than at other such locations, there is a possibility that adapter  29  will “rock” in response to such unbalanced force, causing a gap in certain interference fits and unacceptable leakage. 
   In view of the foregoing, notches  35 ,  37 , and  65 , the other features of adapter  29 , and the corresponding underlying portions of insert  77  have dimensions selected for this implementation to achieve the desired interference fit. For example, notch  35  has a width of about 0.4 inches at upper surface  67 , a maximum depth of about 0.5 inches, with a radius of about 0.2 inches at the bottommost extension of notch  35 . The corresponding cut-out  83  has a width of about 0.6 inches at upper surface  81 , a maximum depth of about 0.4 inches, and a radius of curvature of about 0.3 inches defining the bottom area of cut-out  83 . Upper surface  67  of overmold  75  is spaced from upper surface  81  of insert  77  by about 0.175 inches. 
   Notch  37  comprises a five-sided channel, as best seen in  FIG. 6 , with a width of about 0.47 inches at upper surface  67 , a maximum depth of about 0.54 inches, a pair of vertically oriented sidewalls extending about 0.34 inches from upper surface  67 , and a pair of sidewalls angled inwardly from such vertical sidewalls by about 30°. Cut-out  85  in insert  77  corresponds to notch  37  and likewise has a five-sided trough, with a width of about 0.67 inches, a maximum depth of about 0.42 inches, a pair of vertically descending sidewalls of about 0.15 inches, and a pair of sidewalls extending inwardly to the bottom of the trough from the vertical side walls at an angle of about 30°. 
   Referring now to  FIG. 7 , notch  65  comprises a T-shaped trough with a width of about 0.122 inches at the outer edge of cylindrical wall  69 , depth of about 0.198 inches, and two pairs of champhered surfaces restricting the width to about 0.12 inches near the inner edge of cylindrical wall  69 . Cut-out  87  in insert  77  corresponds to notch  65 , and comprises a channel having a similar or identical width and depth. 
   Of course, while these particular dimensions have been found suitable of this application, the invention is not limited to such dimensions nor this application, and other sizes, configurations, and applications are clearly contemplated. Connector  33  may assume any number of forms suitable to secure adapter  29  to testing apparatus  21 . In this implementation, connector  33  includes a disc  36  of rigid material seated or otherwise received within the space defined by cylindrical wall  69 . A threaded shank  34  extends longitudinally outwardly from the disc sufficiently to be received in a complementarily threaded bore in testing apparatus  21 . 
   Operation of testing apparatus  21  and associated adapter  29  is readily apparent from the foregoing description. Adapter  29  is suitably secured to testing apparatus  21  to be in operative association with test port  23 . Outlet valve  27  is positioned in front of adapter  29  and at an angular orientation to match up the radially extending, irregular geometries of valve  27  with corresponding notches  35 ,  37 , and  65  in adapter  29 . Mask  25  is manipulated to insert outlet valve  27  into adapter  29 . Valve  27  is advanced relative to cylindrical wall  69  and into adapter  29  until lip  71  of adapter  29  engages detent  55  of housing  41 , such engagement being generally physically perceptible to the user of testing apparatus  21  and overall seal. An interference fit is created by the engagement of valve  27  against corresponding, resiliently compressible portions of adapter  29 . Outlet valve  27  is then subjected to one or more tests which act on the valve portion of valve  27 . 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, while the adapter  29  in this implementation includes an overmold and an encapsulated insert, use of two pieces is not required. Alternately, the overmold and insert can be replaced with a single component, either machined, molded, or otherwise formed to include portions for opposing and engaging corresponding locations on the valve to be tested. 
   As a related alternative, there is no need for various portions of adapter  29  to be defined integrally in or on a surface, or, for that matter, to be defined by conforming a surface through molding or machining. In other words, portions for mating or engaging corresponding locations on valve  27  can be provided to adapter  29  by fastening one or more pieces to adapter  29  at the appropriate locations. Thus, adapter  29  can be provided with portions for engaging valve  27  by affixing one or more discrete geometries relative to each other at suitable locations. 
   Similarly, adapter  29  can be equipped with adjustable or variable portions which move relative to each other to provide the necessary engagement with valve  27 . It is likewise understood that the sizes and shapes of the portions of adapter  29  which engage corresponding locations on valve  27  can be varied to suit any number of outlet valves for any number of protective masks. Furthermore, although the portions of adapter  29  in the illustrated implementations include notches, surfaces, and walls, still other geometries may be appropriate and suitable to provide the necessary engagement and interference fit with corresponding locations of certain outlet valves. So, for example, bores, steps, teeth, tongues, or other extensions, depressions, or geometries can be arranged on the adapter in a way to oppose corresponding locations on the outlet valve and achieve the desired seal with such valve. 
   It is understood that still further variations and modifications may be made without departing from the spirit and scope of the invention, and that the implementations and alternatives presented herein are not intended to limit the inventions, the scope of which is set out in the following claims.