referring to fig1 , a module isolation device in accordance with one embodiment of this invention is illustrated at 10 . the module isolation device is employed to receive oxygen permeate from an ion transmission membrane ( itm ) oxygen module 12 . exemplary itm oxygen modules are disclosed in u . s . pat . no . 5 , 681 , 373 , the subject matter of which is hereby fully incorporated by reference . also , as discussed earlier , itm oxygen modules are described in taylor et al . u . s . pat . no . 5 , 681 , 373 . this latter patent previously has been incorporated by reference herein . the oxygen permeate from the itm oxygen module 12 is the purified oxygen removed from an oxygen - containing gas ( e . g ., air ) that initially is directed into passageways 14 provided between the membrane units 16 of the module . the membrane units 16 include a dense , mixed conducting oxide layer through which oxygen permeates . the oxygen permeate , i . e ., the purified oxygen , is directed out of the module 12 through ceramic stack manifold 18 and a ceramic to metal seal 20 into inlet 22 of the module isolation device 10 . still referring to fig1 , the module isolation device 10 includes an outlet passage 26 downstream of the inlet passage 22 for receiving the flow of permeate oxygen . optionally , the outlet passage 26 can include a flow restricting orifice 28 through which the oxygen passes prior to entering an oxygen collecting header or plenum 30 . the flow restricting orifice 28 , if needed , is designed to provide sufficient back pressure in the event of increased flow from the module 12 , such as from a leak , to increase the pressure acting on a rupture disk ( described in detail hereinafter ) to a value higher than the pressure encountered during normal operation of the module 12 . the higher pressure resulting from a malfunction of the itm oxygen module 12 will rupture the rupture disk to isolate the module , as will be discussed in detail later in this application . it should be understood that the oxygen collecting plenum 30 generally is associated with one or more additional itm oxygen modules that are arranged in series or parallel , such that the oxygen permeate from all of the modules flow into and through the common oxygen collecting plenum 30 . a unique feature of this invention resides in the construction and operation of a module isolation valve 40 forming part of the module isolation device 10 . the valve 40 is designed to permit the flow of oxygen permeate from the inlet passage 22 through the outlet passage 26 when in an opened condition and to prevent the flow of the oxygen permeate to the outlet passage when in a closed condition . the module isolation valve 40 includes a valve seat 42 , a valve stem 44 including a valve member 46 at one end thereof , and a rupture disk 48 having a first face 50 engaging an opposed end 52 of the valve stem 44 . the rupture disk 48 includes a second face 54 in flow communication with a low - pressure header 56 through a conduit 58 . if desired , heat insulation material 60 optionally can be provided around the valve stem 44 adjacent the rupture disk 48 . it should be noted that when insulation material 60 is employed it is a porous material , e . g . alumina fiber , to permit flow communication of the oxygen permeate flowing into the module isolation device 10 through the inlet 22 with the first face 50 of the rupture disk 48 when the module isolation valve 40 is in an opened condition . the flow of oxygen permeate is schematically indicated by the arrows depicted in fig1 . it should be noted that the specific construction of the ceramic to metal seal 20 does not constitute a limitation on the broadest aspects of this invention . exemplary ceramic to metal seals usable in this invention are described in u . s . pat . no . 6 , 302 , 402 , the subject matter of which is hereby incorporated by reference . in the illustrated embodiment , the valve member 46 is in the form of a globe valve , however , other types of linear - action valves , e . g ., gate valves , angled valves , etc ., would work equally well in the invention . exemplary types of valves usable in this invention are disclosed in standard references , such as perry &# 39 ; s handbook of chemical engineering , chapter 10 . it should be understood that the materials employed to construct the module isolation valve 40 need to be chosen to be compatible for service in the hot oxygen product stream . an exemplary material is a nickel superalloy , such as haynes 214 or haynes 230 , sold by haynes international of kokomo , ind . alternatively , parts of the valve could be constructed of structural ceramics such as alumina , silicon carbide or silicon nitride . the rupture disk 48 needs to be designed for proper operation at the temperature of use in the system . this disk 48 either can be exposed to the operating temperature of the oxygen process stream , or it can be insulated from the process stream , such as by employing insulation material 60 , and thereby operate at a lower temperature . having described the structural arrangement of elements in the module isolation device 10 , the manner in which the device functions to isolate the module 12 from other modules joined to the module isolation device 10 through one or more common headers ( e . g ., oxygen collecting plenum 30 ) will now be described . during an upset condition , such as when a large leak develops in the itm module 12 , the flow exiting the module into the inlet passage 22 of the module isolation device 10 will increase . due to the flow resistance of the module isolation device 10 and the oxygen collecting plenum or manifold 30 , the pressure inside the module 12 also will increase . if a flow restrictor is employed between the module 12 and the oxygen collecting plenum or header 30 , ( e . g ., flow restricting orifice 28 ) the pressure inside the module 12 will increase even further . this increase in pressure is transmitted through the isolation device 10 against the first face 50 of the rupture disk 48 . this pressure increase resulting in an overpressure condition for the rupture disk 48 will cause the disk to rupture , or burst . when the rupture disk ruptures it no longer supports the lower end 52 of valve stem 44 , and the stem will drop under the force of gravity , the pressure drop across the valve member , and the viscous drag of the gas around the valve member 46 in the case of certain types of valves , such as globe valves . in this latter position the valve member 46 seats against valve seat 42 to close valve 40 and stop the flow of gas exiting from the itm oxygen module 12 to the oxygen collecting plenum 30 . this causes the pressure on the upstream side of the valve member 46 to further increase to the pressure of the high - pressure gas , which further assists in maintaining a good seal between the valve member 46 and the valve seat 42 . once the valve member 46 seats against the valve seat 42 , the oxygen collecting plenum or header 30 is isolated from the leak , thereby preventing contamination of the purified oxygen from the failed module 12 . in the illustrated embodiment , wherein the low pressure header 56 is a separate header from the oxygen collecting plenum or header 30 , a check valve in the conduit 58 , schematically indicated at 62 , is desired to prevent a backflow of gas from the low pressure header 56 into the permeate oxygen plenum 30 after the rupture disk 48 fails . that is , the check valve 62 precludes low pressure gas from the header 56 from passing through the opening in the ruptured disk 48 and into the oxygen collecting plenum 30 through outlet passage 26 of the isolation device 10 . referring to fig2 , a module isolation device 100 is depicted , which includes a number of elements that are the same as the elements employed in the module isolation device 10 . the elements in the module isolation device 100 that are the same as elements in the module isolation device 10 are identified by the same numerals , but with a suffix “ a .” suffice it to state that the module isolation device 100 disclosed is fig2 functions to receive permeate oxygen from ion transport membrane module 12 a in the same manner as described above in connection with the module isolation device 10 disclosed in fig1 . the only difference between the module isolation device 100 and the module isolation device 10 is in the manner in which the low pressure header 56 a of the module isolation device 100 is provided to communicate with the second face 54 a of the rupture disk 48 a . specifically , in the module isolation device 100 the oxygen collecting plenum or header 30 a is placed in direct communication with the second face 54 a of the ruptured disk 48 a through a conduit 102 of any desired configuration , whereby the low pressure flow of oxygen into the plenum 30 a through flow restricting orifice 28 a also constitutes the low pressure gas communicating with the second face 54 a of the ruptured disk 48 a . thus , the oxygen collecting plenum 30 a actually functions as the low pressure header in the module isolation device 100 . by employing this latter arrangement the purity of the oxygen in the oxygen collecting plenum 30 a is ensured , and there is no need to provide a check valve , similar to the check valve 62 employed in the module isolation device 10 , in order to prevent the backflow of low pressure gas through the ruptured disk 48 a into the oxygen collecting plenum 30 a . such a check valve is not required because the gas that is capable of flowing through the ruptured disk 48 a in a reverse direction actually is the same purified oxygen that is collected in the oxygen collecting plenum 30 a . referring now to fig3 , a pair of module isolation devices 200 and 300 are connected with an itm syngas module 12 b on the airfeed line into the module and the spent air effluent from the module , respectively . components of module isolation devices 200 , 300 that operate in the same manner as components in the module isolation device 10 will be referred to by the same numerals , but with the suffixes “ b ” and “ c ,” respectively . the operation of itm syngas modules are well known in the art and the specific construction thereof does not constitute a limitation on the broadest aspects of this invention . during operation of an itm syngas module 12 b a high - pressure synthetic gas , e . g ., methane or other light hydrocarbon gas , is directed through passageways 14 b of the module 12 and into engagement with permeate oxygen extracted from air fed into the module to thereby form the syngas . in the discussion that follows the module isolation device 200 will sometimes be referred to as the “ fresh gas isolation device ,” “ fresh air isolation device ” or by words of similar import , and the module isolation device 300 will sometimes be referred to as the “ spent gas isolation device ,” “ spent air isolation device ,” “ effluent isolation device ” or by words of similar import . although the description that follows describes a preferred embodiment in which the fresh oxygen - containing gas is air , in accordance with the broadest aspects of this invention other oxygen - containing gases can be employed . in the illustrated embodiment , a fresh air feed header 202 receives fresh air to be directed into the itm syngas module 12 b . this fresh air feed is directed into the fresh air isolation device 200 through an optional flow - restricting orifice 204 , and then through outlet conduit 206 of the device . the outlet conduit 206 communicates with air feed inlet 208 of the module 12 b . the air feed inlet 208 is provided by a ceramic conduit or tube that is concentric with an outer ceramic conduit or tube 210 that is connected to a ceramic to metal seal 212 . it is through this outer conduit 210 that the spent gas ( e . g ., the gas from which oxygen ions have been removed in the itm syngas module 12 b ) is directed into the spent air isolation device 300 . it should be understood that the construction and operation of the spent air module isolation device 300 is identical to the construction and operation of the oxygen permeate isolation device 10 illustrated in fig1 , with the exception that the gas being isolated by the isolation device 300 is the spent air that gave up its oxygen to the synthetic gas , as opposed to pure oxygen removed from the air by the itm oxygen module 12 . however , the structural features and operation of the module isolation device 300 is otherwise identical to that described above in connection with the module isolation device 10 . as noted above , the air feed into module 12 b and the spent air effluent from that module are connected to the module through the concentric ceramic tubes 208 , 210 , respectively . each of these tubes is connected to metal piping through a ceramic to metal seal 212 . still referring to fig3 , the module isolation device 200 employs a module isolation valve 40 b upstream of the ceramic to metal seal 212 for the air feed leg . the module isolation device 300 employs a module isolation valve 40 c for the spent air effluent from the module 12 b , downstream of the ceramic to metal seal 212 for the spent air effluent leg . the flow of the fresh airfeed into the inner concentric tube 208 of the module 12 b is illustrated by arrows 214 , and the flow of spent effluent from the module 12 b is illustrated by arrows 216 . during normal operation , both of the module isolation valves 40 b , 40 c are opened . air feed passes from the airfeed header 202 through optional flow restricting orifice 204 , through the airfeed module isolation valve 40 b and through outlet conduit 206 communicating with the air feed inlet 208 into the itm syngas module 12 b . spent air exiting the module 12 b ( as depicted by arrows 216 ) passes through the spent air module isolation valve 40 c of the spent air isolation device 300 , through an optional flow - restricting orifice 28 c and into spent air header or plenum 30 c . the flow - restricting orifices 28 c , 204 , if needed , are designed to provide sufficient back pressure in the respective isolation devices 300 , 200 in the event of an increased flow from the module 12 b , such as from a leak , to thereby increase the pressure acting on the rupture disks 48 b , 48 c in both module isolation devices 200 , 300 to values sufficiently above the pressures normally encountered under steady state operating conditions . as in the embodiments illustrated in fig1 and 2 , the valve stems 44 b , 44 c of the module isolation valves 40 b , 40 c in the module isolation devices 200 , 300 are mechanically linked to the first face 50 b , 50 c of the rupture disks 48 b , and 48 c , respectively . in the illustrated embodiment , the mechanical linkage is created by the first face 50 b , 50 c of the rupture disks 48 b , 48 c actually supporting ends 52 b , 52 c of the valve stems 44 b , and 44 c , respectively . in the event of a malfunction of the module 12 b , resulting in the backflow of syngas through both the inner and outer concentric tubes 208 , 210 , respectively , the high pressure backflow causes the rupture disks 48 b , 48 c to rupture , resulting in a closure of the respective module isolation valves 40 b , 40 c in the module isolation devices 200 , 300 . this will prevent contamination of the spent air effluent and the fresh air infeed by the syngas . as in the earlier described embodiments , the second face 54 b , 54 c of the rupture disks 48 b , 48 c in the fresh air isolation device 200 and in the spent air isolation device 300 , respectively , are in full communication with respective low pressure headers 56 b , 56 c . in the embodiment illustrated in fig3 , the low pressure headers 56 b , 56 c are separate from the fresh air feed header 202 into the module isolation device 200 and the spent air or effluent collection plenum 30 c of the module isolation device 300 . in this arrangement , it is desirable to employ check valves 62 b , 62 c in conduits 58 b , 58 c that communicate the low pressure headers 56 b , 56 c with the second faces 54 b , 54 c of the rupture disks 48 b , 48 c , in the same manner as described above in connection with the module isolation device 10 illustrated in fig1 . specifically , these check valves 62 b , 62 c will prevent the flow of gas from the low pressure headers 56 b , 56 c into the airfeed header 202 of the fresh air isolation device 200 and into the spent air header 30 c of the spent air isolation device 300 , respectively . still referring to fig3 , in an alternative , and more preferred arrangement , the air feed header 202 is employed as the low pressure header in communication with the second face 54 b of the rupture disk 48 b in the fresh air module isolation device 200 , and the effluent plenum or header 30 c is employed as the low pressure header in communication with the second face 54 c of the rupture disk 48 c in the spent air isolation device 300 . this is achieved by providing conduits communicating the respective airfeed header 202 and the effluent air header 30 c with the region underlying the second faces 54 b , 54 c of the respective ruptured disks 48 b , 48 c , in the same manner that conduit 102 is employed in the module isolation device 100 illustrated in fig2 . in this latter arrangement there is no need for any check valves to prevent the flow of gas from the low pressure region underlying the rupture disks 48 b , 48 c into the air feed header 202 and spent air header 30 c of the module isolation devices 200 and 300 , respectively , since the low pressure region 56 b in the module isolation device 200 would contain the same air supply as in the air feed header 202 , and the low pressure region 56 c in the module isolation device 300 would contain the same effluent as in the spent air header 30 c of that module isolation device . by way of brief description , and still referring to fig3 , the backflow of syngas resulting from a malfunction of the module 12 b will cause a significant pressure increase in the module isolation devices 200 and 300 , to thereby cause the rupture disks 48 b , 48 c therein to rupture and the corresponding module isolation valves 40 b , 40 c to close , in a manner similar to that described in connection with the module isolation device 10 depicted in fig1 and the module isolation device 100 depicted in fig2 . the closing of valves 40 b , 40 c isolates the undesirable backflow of syngas from a damaged module 12 b into either the fresh air feed into isolation device 200 or the effluent out of the isolation device 300 . referring to fig4 - 6 , module isolation devices similar to module isolation devices 10 , 100 , 200 and 300 , respectively , are depicted . the embodiments depicted in fig4 - 6 represent the most preferred embodiments and overcome a problem that potentially exists with the embodiments illustrated in fig1 - 3 . specifically , in the embodiments depicted in fig1 - 3 , the ruptured disks constitute part of the described module isolation valves 40 , 40 a , 40 b and 40 c , and in the disclosed embodiments , actually engage the lower ends of their respective valve stems 44 , 44 a , 44 b and 44 c to normally bias the isolation valves into their opened condition . it was determined that during operation of the module isolation devices 10 , 100 and 300 , the flow of gas against the valve members ; particularly valve members 46 , 46 a and 46 c , during normal operation of the modules 12 , 12 a or 12 c caused the valve stems 44 , 44 a and 44 c to vibrate against the rupture disks 48 , 48 a , 48 c thereby creating the possibility of premature failure of those rupture disks . in other words , the vibration of the valve stems 44 , 44 a and 44 c against the rupture disks 48 , 48 a and 46 c , respectively , can cause those rupture disks to fail , and thereby cause the valve members 46 , 46 a and 46 c to seat against their respective valve seats 42 , 42 a and 42 c , even if no malfunction of the module 12 , 12 a or 12 c occurs . this clearly is undesirable . fig4 - 6 disclose module isolation devices that are identical to the module isolation devices 10 , 100 , 200 and 300 , respectively , except for the construction of the module isolation valves . specifically , wherein the module isolation valves 40 , 40 a , 40 b and 40 c employed in the embodiments illustrated in fig1 - 3 include respective ruptured disks 48 , 48 a , 48 b and 48 c as a component thereof , the module isolation valves employed in the embodiments illustrated in fig4 - 6 do not include the rupture disk as a component thereof . in fact , as will be explained hereinafter , the valve stem of the valve assemblies illustrated in the embodiments of fig4 - 6 do not engage the respective rupture disks at all , and actually are spaced from the rupture disks during movement between opened and closed conditions of the valves . referring specifically to fig4 , a module isolation device 400 is depicted for use in connection with an ion transport membrane oxygen module 12 d , in the same manner as the module isolation device 10 . components of the embodiment illustrated in fig4 that are identical to components of the embodiment illustrated in fig1 are identified by the same numerals , but with the suffix “ d ” and in many cases will not be discussed in detail herein , for purposes of brevity . the sole difference between the module isolation device 10 illustrated in fig1 and the module isolation device 400 illustrated in fig4 is that the preferred embodiment of the module isolation device 400 includes three additional elements ; namely , a stationary , perforated plate 402 connected to the module isolation device for supporting a crushable member 404 thereon , the crushable member 404 , preferably being a spring supported on the perforated plate 402 , and a stopper , or actuating member 406 affixed to the valve stem 44 d and movable with said valve stem . optionally a porous insulation member 60 d can be provided to insulate a downstream region of the isolation device 400 , if desired . as noted above , most preferably the crushable member 404 is a spring , which will not need to be replaced when the module isolation device 400 is repaired with a new rupture disk 48 d , after a rupture disk has ruptured because of a malfunction of module 12 d . specifically , when the module isolation device 400 is shut down for repair , the compressed spring 404 will return to its normal , uncompressed sate , and therefore does not need to be replaced . a preferred type of spring is a wave spring . it should be noted that in this embodiment the lower surface 52 d of the valve stem 44 d is maintained out of engagement with the upper face 50 d of the rupture disk 48 d while the crushable member 404 acts against the actuating member 406 that is attached to the valve stem to normally maintain module isolation valve 40 d in an opened condition . in the embodiment of the invention illustrated in fig4 , the module isolation valve 40 d includes valve seat 42 d , valve stem 44 d including a valve member 46 d at one thereof , and a crushable member 404 , e . g ., a spring , retained on the stationary , perforate plate 402 and being compressible by an actuating member 406 attached to the valve stem . still referring to fig4 , in the event of a malfunction of the module 12 d the pressure within the isolation device 400 will increase to an undesirable level , and the rupture disk 48 d is engineered to rupture at that level . subsequent to the rupturing of the disk 48 d the increased flow acting upon the valve member 46 d produces a pressure differential that forces the actuating member 406 against the spring 404 ( or other crushable member ), to thereby cause the valve member 46 d to seat against the valve seat 42 d while compressing the spring or other crushable member . in the preferred embodiment , the lower end 52 d of the valve stem 44 d is maintained in a position where it does not move through the plane occupied by the rupture disk 48 d . as should be apparent , in the module isolation device 400 illustrated in fig4 any vibration imposed upon the valve member 46 d by the flow of oxygen during normal operation of the itm oxygen module 12 d will not cause the valve stem 44 d to vibrate against the rupture disk 48 d to thereby possibly cause a premature failure , or rupture , of that disk . turning to fig5 , a module isolation device 500 substantially similar to the module isolation device 100 depicted in fig2 is shown . components of the module isolation device 500 depicted in fig5 that are identical to components of the module isolation device depicted in fig2 are identified by the same numerals , but with the suffix “ e .” these latter components will not be described in detail herein , for purposes of brevity . in fact , it should be apparent that the difference between the module isolation device 500 shown in fig5 and the module isolation device 100 shown in fig2 is that the module isolation valve assembly 40 e in the fig5 embodiment is modified to the preferred form 40 d employed in the module isolation device 400 shown in fig4 . accordingly , components of the module isolation valve 40 e in the module isolation device 500 depicted in fig5 that are identical to components of the module isolation valve , 40 d in the module isolation device 400 depicted in fig4 are identified by the same numerals , but with the suffix by way of brief explanation , in the event of a malfunction of the ion transport membrane oxygen module 12 e , resulting in an increased pressure within the module isolation device 500 , the increased pressure acts directly on the first face 50 e of the rupture disk 48 e to cause the rupture disk to rupture . thereafter , the increased flow of gas will act upon the valve member 46 e to move said valve member in a downward direction to seat the valve member against valve seat 42 e while compressing wave spring 404 e . as is described in connection with the module isolation device 400 disclosed in fig4 , in accordance with the broadest aspect of this embodiment of the invention the wave spring 404 e can be replaced with other types of crushable members , but most preferably the crushable member is in the form of a spring so that it will not need to be replaced when a module is repaired with a new rupture disk , after the original rupture disk fails due to a malfunction of the ion transport membrane module 12 e . turning to fig6 , module isolation devices 600 and 700 are depicted , which are similar to the module isolation devices 200 and 300 illustrated in fig3 , and provide exactly the same functions as these latter module isolation devices . moreover , the only difference between the module isolation devices depicted in fig3 and 6 is in connection with the construction of the module isolation valves employed in the isolation devices . components of module isolation devices 600 and 700 that are identical to components of module isolation devices 200 and 300 are designated by the same numerals , with the suffixes “ f ” and “ g ” respectively . components of the module isolation valves in the module isolation devices 600 and 700 that are identical to the components of the module isolation valve in the module isolation device 400 illustrated in fig4 are designated by the same numerals , also with the suffixes “ f ” and “ g ” respectively . suffice it to state , that the module isolation devices 600 , 700 employed in connection with an itm syngas module , as shown in fig6 , functions in the same manner as the module isolation devices 200 and 300 employed in the fig3 embodiment , with the exception of the structure and operation of the isolation valves . in particular , in the module isolation devices 600 and 700 the module isolation valves 40 f and 40 g are each constructed in the same manner as the module isolation valve 40 d employed in the module isolation device 400 , and move between opened and closed positions in the same manner as in the module isolation device 400 . thus , the module isolation valves 40 f and 40 g actually prevent their respective valve stems 44 f , 44 g from engaging the rupture disks 48 f , 48 g in the respective module isolation devices 600 and 700 , to thereby prevent premature failure of those rupture disks resulting from vibration of the valve stems against the respective rupture disks caused by the normal flow of gas in the respective module isolation devices 600 and 700 . the potential problem of premature rupturing of rupture disks , which is solved by the structure of the module isolation valves 40 f , 40 g in the module isolation devices 600 , 700 , respectively , is prevalent in a module isolation device intended to function in the manner of module isolation device 700 , wherein the flow of gas during normal operation of the itm module is in a direction against the rupture disk 48 g , which also is the direction tending to force or vibrate the valve stem against the rupture disk . it should be understood that the flow of fresh air and spent air through module isolation devices 600 and 700 is the same as the flow of fresh air and spent air through the module isolation devices 300 and 400 in the fig3 embodiment , with the module isolation valves 40 g and 40 h moving to a closed position after rupturing of rupture disks 48 f and 48 g , by the same mechanism that module isolation valve 40 d is moved into a closed position in the module isolation device 400 disclosed in fig4 . moreover , the low pressure headers 56 f and 56 g can be of the same construction and employed in the same manner as low pressure headers 56 c and 56 d in the module isolation devices 300 and 400 , respectively . alternatively , the low pressure region communicating with the lower faces 54 f , 54 g of rupture disk 48 f and 48 g can be provided by communicating the fresh air feed plenum 202 f with the lower surface of rupture disk 48 f through a connecting conduit , and by communicating the spent air plenum 30 g with the lower surface of rupture disk 48 g through a connecting conduit , essentially in the same manner as described in connection with the module isolation device 100 illustrated in fig2 and the modulation device 500 depicted in fig5 . when the fresh air feed is employed to provide the low pressure area behind rupture disk 48 f , and the spent air is employed to provide the low pressure area behind rupture disk 48 g , there is no need to provide check valves in the low pressure sections to prevent contamination of the fresh air feed in the air feed header 202 or contamination of the spent gas in the spent gas collecting plenum 30 g when rupture disks 48 f and 48 g , respectively , are ruptured . the reason why such check valves are not be required was explained earlier in connection with the isolation devices 200 , 300 ; modified to provide air feed plenum 202 as the low pressure area behind rupture disk 48 b and spent gas plenum 30 c as the low pressure area behind rupture disk 48 c . that explanation will not be repeated herein for purposes of brevity . although illustrated and described herein with reference to certain specific embodiments , the present invention is nevertheless not intended to be limited to the details shown . rather , various modifications may be made in the details within the scope and range of equivalence of the claims and without departing from the spirit of the invention .