GB2336409A - Transfer apparatus - Google Patents

Abstract

A transfer apparatus in which a carousel (1) carrying a series of sealable chambers (3) rotates inside a cylindrical housing (2). A plurality stations around the housing provide for the loading of materials, via an aperture in the wall of the housing (4), sequential treatment with a sterilising gas and sterile air (7,8,9,10), and unloading of materials into a segregated environment (13). Sliding seals (15) prevent the escape of gas to the segregated environment and to the outside environment. The cylindrical housing is likewise sealed and may be de-pressurised to prevent the escape of gas to the sealed environment and to the outside environment. The sterilising gas is introduced through pipe (7) whilst the sterile air is introduced through pipe (10). Items are introduced into the apparatus via a conveyor (5) and enter a segregated area via conveyor (6). The apparatus may be used in processes that are pharmaceutical, biotechnical or chemical in nature.

Description

r Transfer Apparatus This inventlon relates tc a transfer apparatus

usefull. as a transfer device through which objects iray be rove,--J between segregated envilror- nents.

1. Introduction.

Isolation technology is a relatively new branch of env--rci-j-,e:-,tal engineering concerned with the enclosure cf, various orocesses in closed chambers which are provided with specialised physical conditions, to suit the process.

7 ' L 1 1 -- - such processes are pharmaceutical, b--o-ecln'ca or cher-.a-7 na-ure. The chan-ber, or "Isolator," is fitted w_th a ventilation svs,-ei,. P--vd,g conditioned air or -ine--t gas, mans for the coe-rator carry ou- -:-?-ie pr-cess (such as gloves or hal."-su-is), instr-ineniation (such as that reiated to isolator at,-,oscll-lere pressure and air flow rate), and r,-.ea.-.s -crans-ler raw rnaterials into the isolator and -s-roducts ou-- of tre isolator. Isolation uechno-oT.Y, a ver-v scecilalised process env-Jrori-,en-- resulting i i=roved 3roduct cuality while at the same time safetv by the operator from what my be a -..azardous 2336409 technology may also cut the plant and ccs--s of n-r,-cesses to a s ign, i -PEi cant extent. TSO!ator tee'-lnclow,," is _being used increasingly in production and all-Jed to standard environmental for Processes. ZA. good exan-ple of such a critical process is ihe r-_rer)a--atio-, and filling of parenteral (inj ect- able,' drugs _ - -- C.

such as glass vials and ampoules. Such drjjs r-, s, c f be sierille, since they are d-irec-ilv i-L=_ bcj-,; --1'-e treatment.

housing has penetrations in the wall to to be loaded the se;-m-ab'le chambers on the roto-r, to acnil-- s- -'lising gas, to remove sterilisling gas and then to e 1 remove the =w sterile items from the sealable chamber and L i=o the iso-ator. Gas-tijht sliding sea's on Cle. front edges o each chamber work on -:i-,,e inner face cf the housing to ma-inta c",iar-,ber.

Stateme-i o-L: Invention.

in the inieurity of eac- The --'nvention,)rovil.4Aes an aparatus for the cont-inuous - 'Isaton, (-r decontarunat-4on, n the case c toxic s er:product and continuous oi _tems bo-_'n in-_o ojt o_ a bioloc-ca-',7!7 or sea"ed chanbe- , isolazo--, a carousel ca-r-,,7iJnc a seri es c-f sea ---=le WIbers i:-is-'de a housing, presentinj tu---. to a of stations for ial 1v loadling ng -,as ,e case of ox-c- prcj-t tire; cie-Qass--a-; unIcading r7aterial's fer -F-or,, the 4sola-or. seals provide for sea-linc i'-e sealable cha--be--s on the --oto--, the ca 2-ovij-,es a- r the c-oc)ara--.js the for of sterille air intended to f rther reduce the rsk of of any airborne contand-nation, to the interio-- o the isolator. This met.nod does however leave a direct Patn between the isolator atmosQhere and t-e outside a,imosphe-re, with the potential for atmosphere exchange and con--aination. Since this direct pathwav -n t-he d, aT-, m c rl,-usehole system, the isolator does not then fa-,-'.

To.-ithin Lne definition of a true isolator, in which the environment is seiDarated frorn the outs-'de env--ori,ent either by a physical wall or an absolute biolocical filter, at all times. Purthermore, the micusehole is d-.i;-,Li-t to validate, that is, to demonstrate Jts performance as a barrier to airborne contamination under all For these reasons, the dynamic mousehole is not pr-efer-red hy the 7K reclilatory authority, the Medicines Cc=rol (LMCA), and therefore it is otta-in a p_roduct licence 'Erorn the MICA, a -he sale o.-7 most cL-jQ;:)renarations in the UK.

7 7he Tn-,jen'or's Transfer Apparatus n-e --.-ie on- v device currently available f ,o,-, s 'nout and output fran an isolator is the c s e' c and since this device is difficui_t.7o --i,7ence, there is c-7--a-rly an urgent requirement for a device ca.- a r c.:i---s fUnction whilst maintaining.e zhe isolator. The invention meets t'--is need a.-otar-v trans:er apparatus as a meansc) and remove iteis frcrn both sterile isolators, without the pote.ntia-- fc- airborne material between the and tne r=r7,., on a continuous production bas-'s.

_Js a rotary transfer apparatus, and -4s --'-e rc--a-ing doors seen on public bu-J1c.-JL-as. de-,7-'.7e, a carouse- carries a series of sealable ---ambersin a cylindrical housing. The c- 71 -a- to sterile isolator, and so the carousel carries --'-e sealable cambers, within the cylindr'ca' to mat-ch each of the stations around the housling. 7-iese chambers are -jre.7e-rablv c.-lb-Jc in shape to p_romote Good gas circulation which would not be the case lif the cambers were an--- -a--row. cha.-rbe--s have eas--1v--"ie;nn--:-., we- rounjed edges and corners, and a polished interior to -crrp-, y w th Ck)od:,via-n.L:fact,,,ring Practce (GT, as reau--'red b,,,, 'the -Jnd,-,st-rv. The five stages take Q1.ace as the carousel rotates in one cL-rec,i--n, either -7'ock,ise or eit-her step-wise, or dv slow, - -inuo,,-,s rot-ation. i- be noted that tJ-ventlior -on - L - - -L -- --- cou-d be arranged to transfer materials to and from -core than one segregated enviJropip.ent, other --ran the outside In this case, the nunter of w--jld be cjr, plus the n,-LTber ted 10 ne L c-- segrega se----,,-iced. In the basic staaes are as oa.-n,,j Station.

exar-,ple with cla7be--s, s, su-tab wth --e-lerous -,v, arranaed spa7e-s- between all allo-w 117or free of the ster D1;-:ce(-i in the fi. -rs-- sea-'ai:)le _f Cutsi _e rcom --'-is can be -,-one patterns sho,-,!d be Subje= care ster"Sation under C=_ss use.

the is a i-a-.or advariage in , - t- - a -j,Ja- --a,je.

Gas ai- re-mo,jcz s s- -2-,;2-evo,-,s ioade-,; c.,i er -sened to a number of radially disposed chambers, each open at 4-ts distal end, which end is sealingly and slidably in conzact with -,he inside wall of the housing, wherein the openings in each of the chambers register with ports in the housing and are relatIvely sized such that the former seal around the ---ter:

means to rota--e the carousel between stations:

gas and output rreans at each of stations two and four, that gas may be supplied to, or withdrawn from, each chamber when c)os-i--ioned at each such station.

1hroujhout this account the term "sterilisat----n" -'s used as a convenience and aid to understanding. in -fa--.,- the ncroCess of cassinc cannot technically guarantee to achieve absolu--e condition of sterility given by autoclaving an_ -Irrad-a--ior., and so should correctly be re---erre,-- = as al "sanit--sa--io,-." c)rocess. This in no way detra=s the of the device described.

T ihe _4nliert-on can be built in a ranae of s_zes to co,;:)e wi -cads. At the research and p--,--,c-- scale -eve-, -,-ne d-aT.ete- of the carousel right be 5.IC -rn.

and sea-'ab-,.e chambers might be mteas,,re ISC ',6 square and 150 rrm (6 inches) high. At he end c-' --he scale, the carousel could be as as 1-0 r,).c-'.--es (33 -.;:--e+.-) across with chambers rneas:r-'--:, mtres (10 feet) ta7', r-,e--res -ei, scuare and 3 or The cha7-bers --a: be equipped with shelves, --a=s, ra,:.-s or -,.J-atever -'s -ecfui--ed to optimize the ant -J e s---2r- Satio- of th mate ials recruired;or the IC, r c 1E e S s.

!here are -n essence, five stages in the gas process, forrriin-: a for iteirts to be At t'-iS station the sealahle -hamber -'s coened --o a cop4-nus supp-', c: Cle dry, sier--'le filtered air, and thus purged of its isinQ Qas content, typicall, deAT. -1ejels _ess t-an 1 ppm of the gas. The gas is duczed to atmosphere, ncassed throujh a carbon filter or passed throu--h a catalytic con-jerter te render it ha-,-r-less. The c- amber be purged -h air down i-- d'naiever level of aas -'s known to be safe W orator e-,..posure, s7. nce e -rber w be oQ--n to Ln- --- pe- cha - so', a.---r rocin after the final cvcle. Note that if the s-- ato- is o--era inG _inder inert gas or any other atmosphere other tha- siandard air, --'ra'- gas be..iseci purge ou-- i 1 ne sterilisina gas, but that i:.rie ---iner7_ gas must be rec)'L7_-,,:ed by a--'r in a special 6th stage, before the -ha, ' - s o;:ened to the solac-- roor-,..

mbe- a- -_e sea- ab- e now o-cens to the solaicr env- r=nent and the ----ad is re-moved, eit her or aLlto,-nat-i-ca-', ---v 0-\; --he load cabe e4ec±ed n the centra a_ ---- - - - - - -- -L - of --'-e a ca be under the C =p = e -- ', -K- ',, _n c e -- a.: -i n j --'r- -- -i nven t i o -.

h-he a batch ef -OW be 1. oaded cha m., err from --he:i-,ie sea-ab-e ti -ore, pi,: ir the 1 The gas input and exhaust duct should be arranged to op.irnize the full penetration of the gas throughout the volume of the chamber, and indeed mixing fans may be provided to aid this process and to ensure that all items in the load are well exposed to fresh gas. Suitable gases for 7:his process aim hydrogen peroxide vapour, peracetic acid vapour, formaldehyde vapour, ethylene oxide, ozone and chlorine dioxide, though mixtures of these gases and of other gases may also be used. In larger installations of the device, a dedicated sterilising gas generator will be fitted to the system and its control integrated with that of the invention, PLC or PC based. Such gas generators are made by Steris Amsco (UP 1000), TPC Microflow (Citomat and Hperphase) and La Calhene (Sterivap). The gas injection phase may also include a pre-conditioning phase in which very dry air is introduced quickly, ready to accept a high burden of sterilising gas, short of the gas de-v,;-point at isolator temnerature.

iii. Lwell Station.

At this siation, the sterilising gas concentrat:---,-, is.Tain.ained at a high value (e.g. 1,000 to 2,OGO pp:7t ipically) to allow the gas sufficient time to kill any rn' cro-organisms present on the surface of the items inside the sealable chamber. The length of this dwell One will vary with --he size of the chamber and the nature of the load, for inscance, a large chamber will need a longer dwell time and a c,r.plex load containing many small items will also need a longer Jwell time for gas to penetrate and a= fully. in practice, the process will be fully validated during the cowrissioning of the complete system. M tem2erature of the chamber nay be optOmized durin this phase to suis the sterilising gas in use e.g. for hydroge: peroxide vapocr, the chamber trature should be in the region of 15-30 degrees C.

J7.7 of gas (and introduction of sterile a!

L 49 t'ne invention would a--',-L. --c release the contents Of one sealat,' e charber o the isolatcr ever-,; 2 4 The ppreference for _five chaT-bers a-d the of housing mean "in Isei =1 a _e -he ca- c--,! 1 n,- ca at t'- e - s, gn 7 of the inveni-ion Places five chambers p--riphe,, cIF the ex-Lending towards tne amls cl the carol-.se'L where the walls of -the ch,---rrbers meet, leaving a 2en-_aQonal free si3ace a-- the cen;-re of r-'.-ie carousel. This free space can be used:o house aio.r7ated r dlscharging and maybe also --o;-:ding, the se-alable chambers.

The carousel has a roof and a floor, forming he tops and bot-zorrLs of each sea,abe chamber. 7-e floc-r and ro---' ef the carousel are discs, -a:- the in7e-na e-F the cylin,--ir-ca' housing.

d. The housing is n-referabl-,7 sized tc acc-T7da--e -ihe cao--,se-: iave a floor and a abo-.7e the 71he c--i-,,7-e fo--:-e =v 2;ass the r-,c-, = floor of te or js-47j a iiahi shaft =spnere ci =e be a-- neaa--je 1---espe--- to - cress.-,re -,,,i -- - -- he -. -sc-atn-r -rwT,. room 53 -a' e nat;_-,,7 - b -as, Is, in r - L- -_.. - -eaka--e f--o.rr. -i'.,e chw ers u:-ide Qas 1 be away -tL7r-,r-. the h,-L-ran rcom.

Pressure be a fur,--'-,-r aid safetv ra-er-a-'s are be--::z handled.

the and -he C.aTbers t- Sma----er will e Ot once the sealable chamber has moved on to the startira ocsition once more, and is thus open to the isolatcr rocir, (the outside environment), 'he finished products be off-load-e. bv hand or they may be ejected by the sar-ne so= of mechan-ical system used to push materials out of the nt- he isolator.

hanber - t.

b. _As e-=-',a-i-ned, 'the carousel has five chambers, so that ead, of the f ive stages of sterilisation are taking. place at the same t-Te in one of the sealable chambers, within t-he c ind - - v ---i a j houlsing. The carousel is preferably moved round to the location of each stage by an electric under the command of a PLC which is also be used to monitor the cond--'t-ions in each chamber over time and to crovi,--e a record of the coeration of the apparatus for continuous validation purposes.

The carousel may be designed to turn in either direction, though in the accompanying drawings it turns when viewed from above. The 'Layout of the isolator system relative t-o the isolator room. may dictate one direction as convention the clockwise dl-rec-:-ion -'s chosen.

The turn-,-g of the carousel can be slow and continuous, the varlou,s stages of the transfer (loading, gassing, e-c.) iak-inG ulace as each sealable chamber nasses each stai-'cn.

The of the carousel can also be stepwise, fron. cne sia--.41-on to the next. The speed of stepping is as fast as ooss-'t-le to minimise the total cycle time, but not as fas- as to da:--PQe c-- the loads carried in the see--- ai each Station is defined b-,,, the sile cf the -a-rbers as noted, the nature and concentration cf the sterilising gas, the size, shape, number and of the items to be sterilised, and the S:er-i-,L-ty J',ssu-ance Level (SAL). BroadIv 12- oressure of in-f-lation being ad--js---d to give a gas-tight seal wit'n runin,n f--i-icn. insEr,=.en'--atJ.on of the seal -d provJde of the cond--'t-Jon of the pressure wou seals and warning of failure.

j. The ca- be constructed from a wi,-e va-r7. el,1 0 f -7aT-erals, thp very smal-est versons. ' j - -abiv being prefer, fabricated -f--cn, clear acrylic or PVC plast-ic. However, material of choice i- pha.-trtm-ceutical applications is stainless steel, ideally grade 316. This is fabricated to c)'-arrr.ace,j-.-Lcal standards, crevice-free w-T--h rounded corners, finished and polished to approximately C.50 RA.

ficiently rigid "rcughness average). The c-onstr"Lictiop is suf_ hold the dimensions =--nta,'-n gas-t-Jah-- of c'-,ar.bers the werational li-fe of ihe inven:io,--.

(2,1P reQ-jires t--ai -ihe c-..arrbe-s be cleaned, as well as sterilised, o- a eQ-jla-r basis, and thus i- the larger 1 al,7ers'-.ns cf the wi-I preferabl,' be fi-ed s an, sc--a, -1-a__1s or sparging bars:--c --he o-f t'l-e chambers and the hot,,;auer, by a warm air d,r-,,ing process. Tntesiggn an,--- of --'.-ie c--,ar-,bers also orc7.7-de for free drainage cl to a 1-aii--C:.1-" U.La_.

-r,v-' ces for t-ne -'L-so-"a-,cr for the b,,i -hal: a's-., for --emoval o' L since the chamber b.,',!-he cad 1ed o.jtQo-rg is no c_ finished carousel station and for the removal of gas and of air at the fourth carousel station. It- is convenient to orovide windows in the housing so that the contents of the sealable chambers may be observed at any time and Ehus lightincj be fitted also.

e. Since the sterilisation and transfer of material s be deemed a critical process in many cases, the operation of the invention will be monitored for performance by a series of measured oa-ra.-reters including, but not limited to, sealable chamber air/gas pressure, cylindrical housing air Dressure, gas flow rate, gas concentration -in the chamber, air flow rate, air/gas temperature, air-borne count and seal inflation pressure (see item a below). The readings from these instruments are continuous',-v logged or a cha recorded to glive data on the satisf ctorv _ransfer ---.L everv batch of material. Alarm, syst ms w11 provide warning of any system actual or Dol.--en--'al fa-ure.

C-lose cor,::rol, monlitoring and recording of critical processes is verv much a desirable feature for licensing "nder the K.A.

The sealable chambers are made gas-tight within ihe to housing by the use of sliding seals, the opening of each chamber. The operation of the sliding seals on the front of each sealable chamber is t-- cc)era'L-o-. o-.;7 the invention. These seals rr.-jsi s7--',je over the inner face of the and s--i---' a gas-tight seal at all times. It -d--LI be d-----f-cL-',-i to engineer a truly circular housi.ng, i- the larje- sizes of transfer apparatus, and so the sea - -:s must be designed to accorm.x)date some variation -- the between the front edges of the sealabc-,--rzers an- the inner wal I of --he cylindrical housing.

sea,s can provide tne degree of resilience the 14- v. of Again, this could be manual or automat-Lc. Once --he cnamber is unloaded, supplies of Tate--ia"i s ca-- be loaded for --ap.

in'-, -he iso7a-or.

k. It should be noted that the a s--'nQle it for --o:,,t-nuous inward and outward transfer o_ iteins - the op--ra--icn c'LE sterile or toxic conl--ain--,n--nt isolat-ors. The p-rincQa-", advantajes are:

Continuous ooeration ----F -solaT--or -ira:sfer, wir--'- no dire= pathway from the isolator atmose'-----e to --he isolator room a..-nn-sphere, thus t.--e -1so-"a--or can be cateaorised as ful--v sealed, making the task of.-:nde-- MICA/7"_-A muc- easler.

t.

j.

ices not take up---_ong spae, unlike transfer an-- i- one sinale c--'e--e of transfer eas, and to j a 3 allowed under 2,T and thus MCA regulations), since the incom.ina materiall, has been removed from. its sterilised chamber before the product is introduced.

Where the application is purely one of toxic contai.ment, the emphasis is different, and thus the chambers mLah-L accommodate the following stages:

i. Loading of product from within the -isolator.

Agai-11-, this might be manual in small-scale operations or fully automated in larger industrial scale operations.

ii. Decontar-Lination by washdown with deactivaiing agent.

This can be similar to the CIP process described above and would, either manually or automatically, clean cio,,,77 the contents of the sealable chamber so that they are safe to handle when +.-,ev emerge from the transfer aooaratus into so-'a--or room (the room in which the isolator s,,stE-r. is housed). As an example, many cytotoxic drugs (ar,-L--can--er) leave residues of active powders on the surface of the product. These can be removed and deactivated,,v aiDelication of a r.u.-,diy alkaline solution. --his --reatj-,en.:--- ihe Qrodu=s are safe to handle.

ii Dwel T--me for deactivating agent to t-ake effect -f the;3--od7--ct residues are parIticularly potenT-, tne de-a-t---,at--c agent may take some tire to act- --hjs a period of is required. A final rinse with high-purity water may -hen be required.

J---L- air 7curge.

; 7 iere, t'n- - - L -ox c cormonent is in powder form, or 0 aerosols of a -: i,-uid form, are possibly present, then --he air _n sealable chamber must be purged with clea a-'r befcre the can be opened to tIne --'so--a"zcr a=,.osohere. Prov--'s-on should be made for oue--a---3n.

1(0 -.c a pi;De cr duct (9) and air is introduced by a pipe or (1C). The wall of the searegated envi-rorL-nen-(iso--ator'i 1s show,- at (13), and the direction of rotatioo_ the carousel (in this example) is clock-olise (14). The seal s along the front edge of each cha-Tber are shown at F-'--,-Ire 2 shows a rnid-height cross-section of the to further I'llustrate the dispos-Ltion of the sealab-e chambers (3) on the carousel (1), the disoosition of the carousel (1) the cylindrical housing (2), the disposition Of the loading aperture (5), gas -Lr-,pu-r- and cutput pipes or ducts (7, 8, 9,10), the unloading aiDert,,ire (6) a-d the walls of the searecated. environment (isolator) (13).

i s TABLE OE' FIGURES An aTbodLment of the invention is now though by way of illustration only, with reference to the a--cc7,panying d-'i-agramw"--ic drawings in which:- Figure 1 is a perspective top view of the transfer apparatus with cutaways to show inner detail.

FJ1-gure 2 is a horizontal cross-section of the transfer ar-,a-ratus to show the disposition of the chambers v;-Jthin the hoi-,sing, and of the stations around the housinc.

7J- sh - - _L _cure ows a perspective top view o f t he nven-, on ,,;here-n the roof o_f the cylindrical housing, the wal- o_f the housing, the roof of one sealable and c the isolator have been parti a' 1,,7 - a w a-,,, details.

is can be seen from this figure, the rotary transIfer a2;Da--atus uses a carousel (1) with five sealable cha-rbers This carousel is mounted inside the c,,7", ca, The aperture in the housing (4 allows t---0a,d-J-a- ---,LO items (11) for transfer into the sec-egated en-17-4ron-r,eni (isolator) from a table or convevor (5). 1 t ei-..s --e-; .-,,e 7:-,e carousel to enter the isolator c- anc.-e-or --crjeyor (6).

S-Le-----'-s.nc cas is introduced to the sealable c:-iar7bers a or duct (7), and air is released from the c-arrbe.-s L-,' Pioe or duct (8). At the purging station, ga-s- -'s rele-ased L 7 ra-sf-r apparatus as claLimed in am; o_ the ore--edinQ air h- s, wnere-n the an,-u,ar dimension of each sta,,-,cn around the housing is t-hitv to dearees.

2 transfer aocara-us as -1a:i-..ed in anv of the preceding where-in the shape o_f the chai-bers -'s a cube.

A iransfer acoaratus as c-'ajired in any of the p-ecedJnci wherein each seals against ihe wa'l -f the 11 - - - - -- - - -o,js-'ng inflat-able elas:omer seals, seali-g around each correwonding aperture -'n the housing- wall.

7 transfer a;:). us as claimed in CIaLT. 1, wherein the para carousel is mounted on a shaft coaxial with the housinc, d-L -L A exte- ing outside the housing and be4ng drven by a- e 1. ectric Tret=.

-ransfer apparatus as -1a-,,-red whe-rein the cas and output mea-s is eac'r, a p r;--nsfer awaratus as claii-ed -in C-"a-T, 1, where-n the gas in-ui oioe and the aas output pipe are at s.:at-icns two and four are d-'-splaced as far apart as gas in.D..jt and cute,,-,t n-- those stations.

to the a-- -i(3. A -1ransfer a:)c)aratus as claimed' iln an.-,." of t'-e pre--edj-. nc and subs- ant all,,,- as descr-i'-e,-- herein L 1 MCLALM1 -lowing the transfer of mal:erials between Apparatus _for al segregated environments, the apparatus comprising:

a cy-',i,-idri--aL housing around which are a sequence of positions which constitute stations, at the first and last of which there are aiDertures in the housing walls forming ports for the transfer of materials into and out o_ the hous ne:

a carouse'L mounted co-axially within the housing, for rotation therein, the carousel comprising a corresponding number of radially disposed chambers, each open at its distal end, which end is sealingly and slidably in contaci with the inside wall of the housing, wherrein the openings In each o_f the chambers register with ports in the housing and are relat-"ve--.,, S171:1d such that the former seal around the,a'-te-r:

means to --otate the carousel between stations:

cas -'nout and ojk--nu-- means at each of stations two and _four, s ucl 7-hat gas mav be supplied to, or withdrawn, 10 r cm., e a c h hamber positioned at- each such statien.

Claims (1)

1. z trans' r anoaratus as claimed in Claim, 1, wher le i:ne housinG heicht

   and diameter are approxLT.af-e',-,; same A transfer apparatus as claimed in either of ihe claims, wherein the housing is eajijped f_ s-La,zie-s: stai-lons one and five are for the loadinj and of materials, stations two and f-'-,,,e are for the rDut and ou.put of aas, station three is a dwell s-.a---4Lon at- w,l-i the chamber reLTains sealed for the gas to take