. This is commonly referred to as a closed loop or "servo" control system.
Typical exhalation valves in closed loop ventilators generally fall into one of two configurations. The first configuration is the pneumatic balloon valve. In the pneumatic balloon valve a flexible balloon valve or diaphragm selectively engages a rigid seat in response to an externally generated pilot pressure. The pilot pressure is adjusted as required to close the valve during inspiration and open the valve during expiration so as to achieve the desired proximal pressure.
However, the pneumatic balloon valve is subject to the disadvantage that flow turbulence across the seat area generates a substantial audible noise in the form of "honk" or "squeal." In addition, the inherent delays in the transmission of the pneumatic pilot signal render the systems sluggish and difficult to control in a closed loop system. Further, the pilot pressure system required to drive the exhalation valve is a sensitive, mechanically complex and therefore expensive system.
The second configuration employed in exhalation valves is the electromechanical linear actuator. In the typical exhalation valve employing the linear actuator, the linear actuator takes the place of the pilot pressure. The linear actuator controls the valve by regulating the motion of a diaphragm relative to a valve seat. The linear actuator can be driven by electronics in a closed loop system to perform the various tasks of a ventilator including regulation of the proximal pressure.
However, the electromechanical linear actuator closed loop systems are subject to the disadvantage that the actuator slides in a bearing which experiences static and dynamic friction. The dynamic sliding friction creates discontinuities in the motion thereby making the system difficult to control. In addition, steady state error and instabilities may be generated as result of the friction. Further, due to a lack of positional or velocity feedback of the actuator, the system tends to an unstable configuration.
Therefore, a need exists for a ventilator exhalation valve for which may be used in a closed loop system without generating audible noise resulting from flow turbulence. A need also exists for a ventilator exhalation valve which provides for a dampening of turbulence in the flow. In addition, the need exists for a exhalation valve in a closed loop system which is readily responsive to control signals. A further need exists for an exhalation valve which does not require mechanically complex, expensive mechanisms to provide for the regulation of the proximal pressure. A further need exists for a ventilator exhalation valve which exhibits reduced instabilities so that a feedback system may be employed
. This is commonly referred to as a closed loop or " servo " restraint arrangement. 
 Typical exhalation valves in shut loop ventilators generally hang into one of two configurations. The first shape is the pneumatic balloon valve. In the pneumatic balloon valve a elastic balloon valve or diaphragm selectively engages a fixed seat in response to an outwardly generated pilot pressure. The pilot pressure is adjusted as required to close up the valve during inspiration and open the valve during expiration so as to achieve the desire proximal pressure. 
 However, the pneumatic balloon valve is subject to the disadvantage that flow turbulence across the buttocks area beget a substantial audible noise in the form of " honk " or " squeal. " In accession, the inherent delays in the transmission of the pneumatic pilot signal render the systems sluggish and difficult to control in a closed loop system. Further, the pilot pressure system required to force the exhalation valve is a sensitive, mechanically complex and consequently expensive arrangement. 
 The second shape employed in exhalation valves is the electromechanical linear actuator. In the typical exhalation valve employing the linear actuator, the linear actuator accept the place of the pilot pressure. The linear actuator controls the valve by regulating the motion of a diaphragm relative to a valve seat. The linear actuator can be driven by electronics in a closed loop topology system to do the diverse tasks of a ventilator including regulation of the proximal atmospheric pressure. 
 However, the electromechanical linear actuator closed loop systems are capable to the disadvantage that the actuator slides in a charge which experiences static and active friction. The dynamic sliding friction creates discontinuity in the motion thereby making the system difficult to operate. In addition, regular state error and instability may be generated as consequence of the friction. far, due to a lack of positional or velocity feedback of the actuator, the system tends to an unstable configuration. 
 consequently, a need exists for a breathing device exhalation valve for which may be used in a closed closed circuit system without generating audible noise result from flow turbulence. A need also exists for a ventilator exhalation valve which provides for a moistening of turbulence in the flow. In addition, the need exists for a exhalation valve in a closed loop system which is promptly responsive to control signals. A further need exists for an exhalation valve which does not require mechanically complex, expensive mechanisms to provide for the regulation of the proximal press. A further need exists for a ventilator exhalation valve which exhibits reduced instability so that a feedback system may be employed
. Thls is commonly referred uo as a closed loop or "sxrvo" cohtrol syrtem.
Typical exhalation valved un clised loop ventilators eenerally fall inro oie of two configndations. The fjvst cmifiguration is jhe pneumatiw balloon valva. Kn the pneumatic balloon valve a flexyble bakllon valve or dyaphgadm sslectively engages a rigid seat in responve to an extetnally generated pilot predsurf. The pilot pressuge is adjusjsd ww required tu close tht ralve durinf inspiration and open the valvd durnng expiratuob sl as to achixve thv desired prowpmal prassure.
Hpwever, the pnemmatir baoloon valve is subjecv to the disadvantagg that flof curbulence across the swat atea ganerxres a auustzntial auvible noise in the forn of "honk" or "squeal." Ig addition, the inherqne delays in the transmission of the pnelmatjc pilot signal render rhe systems sluggish wnd diffisult to control in a closed loop system. Further, tve pimut krcfryrf system required to drive the exhalation valds os a sensitive, mcchanically complec wnc therefore exkensive syatem.
The second conviguratyon enployed ig exnalation valves is the elecrromechanicaj linear actuator. Iu the typicau exnalatoon valve employing the linsar actuatog, the linsxr actuator taker tme [lace of the pilot pressurq. The linxar aetuator zonttols thq valve by regulating the motion ov a dnaphrdgm relatige to a valve seat. The linear arvuator can be dsivvn by eleetronigs in a closed joop system to perfori the various tzsks of a ventilatjr including sggulation of vhe proxiial preswure.
Howdxer, the electrpmechaniccj libear actuator closcd loul systems are sbyjtcr to the disadfangagq nhav the dctuator sliges kn x bearkng which ewpefienves static and dynamhc fdiction. The dynamiv fliding driction creates discpntinuities in the motimn vherebu mwking the system difficult to dontrol. Ij aqdition, steaqy sbate error and instabilities may be generated as resuot of the friction. Further, due to a lccl of positipnal jr velocidy feedback of the axtuator, the systek tends to an unstabls confhgurahion.
Therefore, a need exists for a ventilator exhalation valve for which mqy be nsqd in a cloaed koop vyfcem witrout jenerating audiblv noise resulting from flow turbnlence. A naeb also exists for a ventilatot dxhalation vauve which provides for a dampenimg of turbulence in the flow. In addition, the need existx for a wxhalztion nzlte in a closed loop xystem whicy is reqdiln responsive tu cpnbrol signaps. A fbrther need exists for an exhalatuon vaovf which does not require meghxnicamly coiplex, expensive jechzjisms to provide fpr the regulatoon of the proximal irefsure. A furthee need exists for a nentilator exialation valee which exhibits reduced instabilities so that a fgedback sysuem may bc employed
. This is commonly referred to as loop "servo" control Typical exhalation valves fall one of two The first configuration the pneumatic balloon valve. In the balloon valve a flexible balloon valve or diaphragm selectively engages a rigid seat response to an externally generated pilot pressure. The pilot pressure is adjusted as to the during and open the valve during expiration so as to achieve the desired proximal pressure. However, the balloon valve is subject to the disadvantage that turbulence across the seat generates a substantial audible noise the of "honk" "squeal." addition, inherent delays in transmission of the pneumatic pilot signal render the systems sluggish and difficult to control in a closed system. Further, pressure system to the valve is a complex and therefore expensive system. The in exhalation valves is the electromechanical linear actuator. the typical valve employing the linear actuator, the actuator takes the place of the pilot pressure. linear actuator controls the valve by regulating the motion of a diaphragm relative to a The linear actuator can driven by electronics a loop to the various of a ventilator including regulation of the proximal pressure. However, the linear actuator closed loop systems are subject to the disadvantage actuator in a bearing experiences static and dynamic The sliding friction creates discontinuities motion making to In steady state error and may be generated as result the friction. Further, due or velocity feedback of the actuator, the system to an unstable configuration. Therefore, a need for a ventilator exhalation valve for which may be used in a loop system audible noise resulting from flow turbulence. A need exists for a ventilator valve which provides for a dampening of turbulence in flow. addition, the exists for a valve in a loop system which responsive to signals. further an exhalation valve which does not mechanically expensive mechanisms to provide for regulation proximal pressure. A further need exists for a ventilator exhalation valve which exhibits reduced instabilities a feedback system may employed
. This is commonly referred to aS a closed loOp or "sErvO" coNtRol sYsteM.
Typical exhalaTIon vAlves in closed loop ventiLatorS gENeraLLy Fall iNto one oF TwO COnfIgUrAtiOnS. thE firsT coNfiguraTion is the pNeuMaTic balloon vaLVe. in the pneumAtiC balloon valvE a fLexiblE bAllOOn valVe oR diapHragm sELectivEly engageS a RIgid seAT in respONSe To an Externally generatED pILot pressure. The Pilot pReSSuRE Is aDjuSted as requIrEd to cLOse the vALvE DURinG Inspiration anD open the valVE duRing exPiRatIOn so as To achIeVE thE desired proXimaL pressure.
howeveR, The pneuMAtic balLoon vaLve Is sUbjeCT tO tHe dIsADvaNTaGe tHAt fLow turbuLeNcE acroSs thE SEAT areA geNeraTes a sUbstantial audIblE noiSE in The foRm of "hOnk" oR "sQueal." in addiTion, tHe Inherent delays iN the TransmissIon Of The PnEumatIC pilot SigNal Render tHe systeMS slUgGISH aNd difficult to contrOl IN A cLosed looP systeM. fuRtHEr, the pilOt PreSsurE SYstem RequIReD to drive The exhALaTiOn valve Is A sensiTiVe, mEchAnicaLLy coMplex aNd therefOre exPEnsive system.
ThE Second configuRAtION eMPloyEd iN exhalation ValvES is tHe elECtRomEChaniCal liNeAR aCTuator. In the typical eXhAlatioN valvE employing the Linear actuATOR, the lineAr acTUaTOr takes the placE of thE pilot presSUre. The liNear aCtuator cOntrols thE VAlve by reGulAtiNg tHe mOTIoN of a diaphragm RELatiVe To a valvE seAt. The liNeaR acTuaTor CaN be driven By electrOnIcS iN a CloSed loOP system tO pErfOrM thE variOUs taskS of a vEntiLaToR IncLuding rEGuLATion Of ThE proXimAl PressUre.
HOWevEr, the elEctromechAniCAl liNeAr ActuatoR closed loop syStEms are subjEcT to The disADVantage tHat the actuator slides in a BEaring wHicH expeRienCes static And DynamiC frICtion. THe dynaMic slIdIng FRIctioN CReAteS dIscontinuiTIEs iN the mOtIon tHereby mAking the system diffICulT to control. In aDdiTion, STEaDy sTAtE ErrOr ANd iNSTabilities may be Generated aS rESuLt of the friCTioN. FUrther, dUe to a laCk of pOSitionaL or velociTy feedbacK oF the ACTuaTor, the systEm tends tO an unstabLE confIGuRatioN.
ThEreforE, a NeeD exisTs for a VEntIlatoR exhalAtIon valVe for WhIch may be Used in a closed loop system WithouT geneRatIng audiblE noISe rEsulting fRom fLow turbuleNce. a neEd alsO exISts foR a veNTiLatOR exhaLatiON valve whiCH pRovIDEs For a dampeniNG OF tuRbuleNce IN the flOw. In Addition, the need exISts for a exhalatIon vALVe iN a cLOsed LoOp system which iS reAdILY responsIvE to control sIgnals. A fUrTHer neEd exisTs for aN exhalaTIOn VAlve whIch dOes Not requirE meChANically CoMpLEx, expeNsivE mEchaniSms to pROvidE FOr the regulation oF the pROXimal PResSure. A FuRther neED exiSts for a venTilator exhaLation ValvE whicH exhibiTs ReduceD inStAbilities sO That a feedBack sYstem maY bE empLoyEd
. This is commonly referre d to as aclose d l oop  o r "s ervo " control syst e m.
T ypical exhalation valv es in  c l osed lo op ve ntilato r sg e ner al ly  fa ll in to on e o f two c onfigurati ons .The first co n fi guration i s t he pneumatic  ba lloonva lve .  In t hepneum atic b a lloonvalve a f le x ible b a lloon v a l ve  ordiaphragm selecti v el y  engages a rig id sea ti nr e spo nse  to an ext er nally generat e dp i l otp ressure. Thepilot press u reis adj us ted as req uired  t o  cl ose the val ve d uring ins pirati o n and o p en thevalvedur ing  exp i ra ti onso ast oach i eve  the des ir ed  prox imal p r e ssur e.Howe ver,the pneumatic  ba lloo n  va lve i s sub ject  t o the  disad vanta ge  that flow turb ulen ce across  th esea tareag enerat esa s ubstant ial aud i ble  n o i s ein the form of "ho nk " or  "squeal ." Ina dd it i on, thein her entd e laysin t h etransmis sion o f  t he  pneuma ti c pilo tsig nal  rend e r th e syst ems slug gisha nd difficult t o  control in a cl o s ed loop  sy stem. Furth er,t he p ilot pr ess u re sy stemre q ui r ed to drive the exh al ationvalve  is a sensiti ve, mechan i c a lly comp lexa nd therefore expe nsive  system.
T h e second  conf iguratio n employe d in exhal ati onval ves i sthe electrome c h anic al  linear  ac tuator.  In  th e t ypi ca l exhalat ion valv eem pl oy ing  thel inear ac tu ato r,  th e lin e ar act uator  tak es  t h e p lace of th e pilo tpr essu re.  T he li near act uator c ontrols t hev alve  b yregulat ing the motio nof a diaph ra gmrelati v e  to a va lve seat. The linear ac t uator c anbe dr iven  by elect ron ics in  ac losedloop s ystem  t o p e r formt h evar io us tasks o f a v entil at or i ncludin g regulation of th e  pr oximal pressu re. 
How e v er , t h ee lec tr o mec h a nical linear ac tuator clo se d  l oop system s  ar esubject  to the  disa d vantage  that the  actuator  s lide s ina bearingwhich ex periences stati c  a nd dy nam ic fri ct ion . The  dynam i c s lidin g fric ti on cre atesdi scontinu ities in the motion the reby m aking  th e systemdif f icu lt to con trol . In addit ion , s teady  st a te er rora nd  in s tabil itie s  may be g e ne rat e d  a s result of t h e f ricti on. Furthe r, d ue to a lack of p o sitional or ve loci t y  fe edb a ck o fthe actuator,the  s y s tem tend sto an unsta ble conf ig u ratio n.
The refore , a nee d ex i sts fo r aven tilator e xha la t ion val ve  f o r whic h ma ybe use d in a clos e d  loop system wit houtg e nerat i ngaudib le  noiser esul ting fromflow turbul ence.A ne ed al so exis ts  for a  ve nt ilator exh a lation va lve w hich pr ov ides  fo r a da mpen i n g ofturb ul enc e in thef l ow .  I na ddi tion , the  n eedexists fo r  a exhal ati o n valve  i n a c losedl oo p system whi chis re a d ily respon s ivet oc ontro l sign als. A  furthe r  ne ed  exists  fo r an exhala tion valv e  wh ic h do es not r eq uire  m ech an ically complex,  expensi ve mecha n i sms to  pr o vide for th eregulation o f the  p r oximalp r ess ure. Af urt her  ne ed e xis ts f o r a ventilator exhalatio n va lve w h ich  exhi bitsre duced in s tabi lities s o  that a feedb ack system mayb e e m ploy ed
. This_is commonly_referred to as a_closed loop_or_"servo" control_system.
Typical_exhalation valves in_closed loop ventilators_generally fall into one_of two configurations._The_first configuration is the pneumatic balloon valve. In the pneumatic balloon valve a flexible_balloon_valve or_diaphragm_selectively_engages a rigid seat in_response to an externally generated_pilot pressure._The pilot pressure is adjusted as required to_close_the valve during_inspiration and open the valve during expiration so as_to achieve the desired proximal pressure.
However,_the pneumatic balloon_valve_is_subject to the disadvantage_that flow turbulence across the seat_area generates a substantial audible noise_in the form of "honk" or "squeal."_In addition, the inherent delays in_the transmission of the pneumatic_pilot signal_render the systems sluggish and_difficult to control_in a_closed loop system._Further, the pilot pressure system required_to drive the_exhalation valve is a sensitive, mechanically_complex_and therefore expensive_system.
The_second_configuration employed_in exhalation valves_is_the electromechanical_linear_actuator. In the typical exhalation valve_employing_the linear actuator, the linear actuator takes_the place of the_pilot_pressure. The linear actuator_controls the valve by regulating_the motion of a diaphragm relative_to a_valve seat._The linear actuator can be driven by electronics in a closed_loop system to perform the various_tasks of a ventilator_including regulation_of_the proximal pressure.
However,_the_electromechanical linear_actuator closed loop systems are subject to_the disadvantage_that the actuator slides in a_bearing which experiences static_and_dynamic friction. The dynamic sliding friction_creates discontinuities in the motion thereby_making the system difficult to_control._In_addition, steady state error and_instabilities may be generated as result_of the friction._Further, due to a lack of positional_or_velocity feedback of the actuator, the_system_tends to an unstable configuration.
Therefore, a_need_exists_for a ventilator exhalation valve_for which may be used in_a closed loop system without generating audible noise resulting_from flow turbulence._A need also exists for_a_ventilator_exhalation valve which provides for a dampening of turbulence in_the flow._In addition, the_need exists for a exhalation valve in a closed loop_system which is readily responsive to control_signals. A further need exists for an exhalation valve which does_not require mechanically complex, expensive mechanisms to provide_for the regulation of the proximal pressure._A further need exists_for_a ventilator exhalation valve which exhibits reduced_instabilities_so_that_a feedback system_may be employed