ML20148H654

Forwards IE Circular 77-05, Fluid Entrapment in Valve Bonnets. No Response Required

ML20148H654
Person / Time
Site:	Yankee Rowe
Issue date:	03/29/1977
From:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:	Groce R YANKEE ATOMIC ELECTRIC CO.
References
NUDOCS 8011190456
Download: ML20148H654 (1)

Text

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( UNITED STATES NUCLEAR REGULATORY COMMIsslON E-.

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REGION 1 3?h

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if 631 PARK AVENUE hb I KING OF PRUSSI A, PENNSYLV ANI A 19406 hh

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March 29,1977 F

Docket No. 50-29 r 6

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Yankee Atomic Electric Company ATTN: Mr. Robert H. Groce b Licensing Engineer E E

20 Turnpike Road Westborough, Massachusetts 01581 b Gentlemen:

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The enclosed IE Circular, 77-05 is being distributed for information, in i the belief that the subject matter is of sufficient safety significance E to warrant your specific attention. No written response is required.

R Should you have any questions concerning this matter, please contact g this office. i (T;

.c Sincerely, p C. .

James P. O'Reilly I Director

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Enclosure:

IE Circular No. 77-05 "

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H. Autio, Plant Superintendent  %

i Donald G. Allen, President 3

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$k IE Mail & Files (For Appropriate Distribution)

Central Files [(

4 Public Document Room (PDR)

Local Public Document Room (LPDR) TH S DOCUMENT CONTAINS k' Nuclear Safety Information Center (NSIC) POOR QUAUTY PAGES y.

Technical Information Center (TIC) W REG:I Reading Room '

Commonwealth of Massachusetts @[

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NUCLEAR REGULATORY COMMISSION

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OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 b'.

IE CIRCULAR 77-05 Date: March 29,1977  ;.

Page 1 of 2 y

p FLUID ENTRAPMENT IN VALVE BONNETS DESCRIPTION OF CIRCUMSTANCES:

[t a Gate valves of the type known variously as " split-disc," " flexible- h j disc," " double-disc," etc., have the ability to seal against both 5 4

seats at the same time. Under certain circumstances, when the valve e is closed, fluid may be entrapped in the bonnet cavity, and if the -

system is then heated up, an uncontrollable rise in pressure in the bonnet cavity can result. The reported effects of such pressure il rise range from inability to open the valve, to structural failures i~

of internal parts of the valve or failure of the bonnet. Consequences range from loss of function of the valve to fluid escape and injury l= <

to personnel or damage to equipment in the vicinity. Detailed informa- -

tion is provided in the enclosure to this Circular.

p DISCUSSION:

The most common cause of fluid entrapment is the orientation of the '

valve. Valves in pipelines where the pipe is horizontal, or nearly so, and where the valve stem is oriented horizontal or below the horizontal, result in the bonnet cavity constituting a drain pocket, where process fluid or condensate can collect while the valve is open. If the valve is then closed the drainage is trapped. Valves are often installed in such positions for reasons of space or operator convenience. Other pipe and valve orientations can, under credible circumstances, entrap fl uid . An example is filling a section of steam line for hydrostatic test, draining the line without opening that particular valve, and then

, heating up the line with steam. A variety of actions have been proposed to alleviate the situation, including internal pressure relief passages. -

external pressure relief paths, and specially controlled procedures.

You may wish to alert your engineering, operating and maintenance 1 staff to the existence and characteristics of the subject of this 1

Circular, and to consider the potential of your facility (s) for I an occurrence of the type described. Depending on circumstances, .

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IE CIRCULAR 77-05 i Date: March 29, 1977 E-Page 2 of 2 [

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5 E-any of a variety of corrective actions may be appropriate. Most E of these are, however, susceptible to human error, gnd, to the  ?-

extent feasible, we suggest that valves be installed to minimize 5F the potential for entrapment of fluid. jF E

Enclosure:

E Ltr., dtd 2/24/76, P. H. Awtrey, i Walworth Co. , to J. H. Tillou, j NRC, w/ encl. y rr

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1 A* Walworth Company P.o. sex 1103.uf anna M

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. February 4 .7. .a

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United States Nuclear Regulatory Commission- jc pff%E0 2syg0 g; T.*h Region IV Gil Ryan Plaza Drive R l-Arlington, Texas 76012 33y 4 ,

Attention: Mr. J. H. Tillou, Chief

~

Licem:e Contractor and *

, Vender Inspection Program - '

Subject:

Pote.ntial Overpressurization- Problem in Valves .

J Gentlemen:. - E' ConfirmingourconversationofJant$ary 30, 1976, . . .

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this is to advise you of the possibility of an overpressuriza- '

tion that can happen in gate valves having flexible wedges or having discs with equivalent flexibility. Our particular

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concern is with Pressure Seal steel gate valvos having flexible wedges and being installed with the stems horizontal or below horizontal.

Overpressurization is covered in the following paragraphs from ANSI B31.1-1973, " Power Piping" and AttSI B16.5-1973, " Steel Pipe Flanges, Flanged Valves, and Fittings":

ANSI B31.1-1973, Page_26, Paraoraph 107.1C .

1 Where liquid tr:pped in.: closed valve c:n be bested, an uncontre!!able rise in pressure c:n re: ult, i (An exampfe mir.ht be a flexible wedge pte v:!ve,in..

stalled with the stem horizontal, having he:t front warm 4tp of the pipeline applied to IIquid from the' testing,cleanint,. or conder. sed fluid, such liquid bein;;

entrapped in the bonnet section of the clos:d valve.)

Where sucit a condition is possib!:. the Owner sh:Hl ,

provide means in desisn.instalbtion.snd/or operstion , -

to assure th:t the prenure In the vshe sh:ll not ex.  ;

.ceed that n!! owed by the Code for the strained t:m. I perature. Any resultir; penetration of the pressure I wsn of the valve shall meet the requirements of this Code and of drains in ANSI 1116.5. -

. 4 Volvet for Industry. .. overywhere .

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" United States iluelear February 24, 1976 "D 1

Regulatory C'ommission e.. j i

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ANSI B16.5-1973. Page 2, Paragraoh 2.2.3: il t ,

! Fluid Thermal Expansion. Certain double [;

seated vs,1ve designs :re c:pable of scaling simultane. '

ously assinst pressure differentisi from the bonnet

[.: l EJ j section to the adjacent pipe in both directions. In . E i

such valves, a circurnst:nce in which the bonnet #'

I section is filled with liquid :nd subjected to an in.

[j" crease in tempersture can result in build up of pres. ,I sure in the bonnet s:ction. Where such a condition l is possible, it .is the responsibility of the pur:h:ser *

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to provide or require to be provided means.in de.  :

sign, installation, and/or oper:tlen to assure that 2 the pressure in the vr.lve shn!! not exceed that al.

9

• lowed by this st:ndard for the attsined temperature.

• For discussions and recommendations concerning this subje-t in the aforementioned valves, please refer to attached E.:tibits A, B, and C.

We shall be available for discussion relating to this or shall try to supply further data if desired.

Yours very truly, P. H. Awt/ y Chie f Eng.fneer PHA:me .

Attachments -

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. P.S. Concerning the Exhibit A (BUSHIPS Instruction 9480.72 with its Enclosure 1), attached copies of letters of February 2 and 12 give permission to release this infort.1stion.

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February 2, 1976 i 4-

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Haval Ships Engineering Center . .' '

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i Hyattsville, Maryland 20732 -

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T Attention:

Mr. J. F. Conway, Section Head 3

1. Valves, Piping Ccmponents, and Structural Analysis Sectic t)

Code 6153E . . (# l 4's! .

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I Su bj ect : BUSHIPS 9480.72 .  :

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Ser 648A5-308 -

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18 June .1964 ', .

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Gentlemen: - - -

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Confirming our telephone conversation of today, t z.

o permission is requested for Walworth Company to submit a copy -

, of the subject letter, along with its Enclosure 1, to the United States Nuclear Regulatory Con 1 mission for use by it in dealing,with a possible problem in overpressurization of valves. ,

7j I have discussed with the ' Nuclear Regulatory Commission i j ...'the possiblity of overpressurization, especially as applied to i '

steel gate valves having flexible wedges and mounted with the '!

4

' stem horizontal or below horizontal, and would like to use the el idubj ect document as background material . * -

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% ;r If.you have any later material that could likewise -

d be used on this subject, I would appreciate receiving a copy (

.and permission to submit it to the Nuclear Regulatory C.cmmission.

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s Yours very truly,

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P. H. Aw - -

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Chief Eng'ney ineer  ?!

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• t J Valvorth Coc:pany P.O. Box 1103 Huff Avenue $l Greensburg, Pennsylvania 15601 {l1 g

IJ Attention Mr. P.H. /.wcrey T.

Chief Enginee: .

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Centlemen: ,

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Inclosure (1) is forwarded in response to your letter of 2 February 1976. E Please be advised that the Naval Ship Engineering Center has no objection  !

to enclosure (1) being used in any articles or conversations per:nining h p

to the subject in question. ,

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• As a matter of information, the pertinent centents of enclosure (1) now, C and have for sone years, for=cd an integral part of the overall steem @

y system design requirenents for Ships of the United States Navy. +

Sincerely yours, (ji; O .

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ser 648A5-30 of 18 June 1964

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DUS!!IPS 9180 72 Ser 64EA5-.;,03 1

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From: Chief, Bureau of Ships .

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Subj: Surface ship steam syste= vdves, opera $ ion of prior to vs.mup

%y Enc 1: (1) Requirements and Procedures for Modifying Stearn Systeci Fleaible g Cate Valves as Neccesary . < ' -

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A Pureose. To pre ulgate instructiens eenceming the operition of . .

valves prior to the adnission of steam to the systers. *-

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2. Scope. This instruction applica to all valves in surface ship ster.s . ** y syste=s of non-nuclear construction. It does not apply to nuclear con-

.structien for which separate requirements have been developed, yurth er, . ((

.- ,,g although specifically directed at protecting flexible wedge Ctte valves g.

. , frc:a overpressurizatien, this instruction c.pplies to all steam systes y

' valves due to the desirability of re=oving water from all components of  ?

st(xn systems prior to wamup.

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7 P2ek rroun d. The p.r. pose and pri ary reason for using flexible wedge p{

g..Le valves in steam syste=s is to prevent binding when the valv.e is in -

h the closed position. In bish pressure-te:perature stcean systems, pipe

- 9 line e:gansien produces stresses and strains at valve end connections which 'l tend to slightly distort the vdve bedies. If the valve wedge is solid, is

• this dictertien will enuse the valve seats to press against the solid wedge,

• fC and, in effect, cle.mp the valve shut. This problem is overec=e'with flexible

• vedges, which are best described as two circular plates attached to each y othe: by e.n integral hub in the center. h'ith this design, the wedge vill j n

flex as the valve seats press against it, thus avoiding the clamping effect.  ?

. , Because of this very desirable characteristic, the flavy, as well a.s industry,

• E tscs flexible wedge gate valves in all cases where piping systes e:gansion

• g is,a significant factor.

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4. Discussien. The necessity of draining steam syste=s pric> to putting . w gt.

eteam on the line is mentiened in several doctments, including the EUSHUS P.anual. Unfortunately, it is not adequately covere:1 in these documents and g 41

'. there have been instances where the pr pratory action of drainage p'rior to steam admissica has been overlooked. As a result, several isolated $

4 instances of sericus da= age to flexible vedge 6 ate valves have occurred. It j

~ is characteristic of ficxible wedge gate valves that if we.ter enters the body 4

. neck as a result of syste= hydr = static tests, or by ot.her means, while the . W valve is closed, it' vill be tr:pped, regardless of the valve position, unless 3 the valve is either opened or the water is rc=rved via a body neck drain. -

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Briefly, this is due to the fact that with the ve.1ve in the closed position g

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ani a differential press'ure across the wedge, the upstream side of the wedge  %

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permittinn Vate i as i.ne coc wev neerf.ro=

anc its .L:.ne seat prhesures equa_ Lane,r or the to enter precoure the. nc[.k 3 rapc.nd 2. . .  ?

l taken off the line, the upstrea= side o' the wedge = oves back agiinct its  ;

3 j ecat, sealihg off the body, neck and trapping any water which =ay have entered.

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If the water rc=ains in the body neck, as. it will if the valve is - a s..

not ' cycled er drained, and stean is put on the line,* a situation closely '

y nd ed to a boiler without a relief valve exists. The steam hav.4ng a higher Q pre:sure thin .the water in the neck, wC' prevent water frca flowing into the  ;

line even thcugh the upstream face = oves away from the seat. As the .  ?

pres:ure equalizes, the cycle whereby the water ir.iti,'1 7 became trapped, $

is repeated, caly this time the water has been heated by the inec=ing steam.l' 4 The stea=, however, continues to heat the' nter due to its slose

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. pro:drity and higher te=perature, causing the water to expand. .If the iritial

• cut .tity of trapped water was large enough, the initial tempeiature differ-

/'

ential between stea= cnd water great enough, and the heating cycle continues . .; .;'. -' - 7

"' ' uninterrupted, the end result is predictable. The water pressure will build "

.!J up, due to the water's e:gansion being restricted, u-til either the body neck ruptures, the bor. net lif ts off, or the seat rings collapse. * ,

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. s It cheuld be noted that this phenc=ena has been proven by calcula- '%

tiens and controlled tests, during which a press =re was generated in the {

body neck equal to ten times that which e:cicted in the line.- As far as actual

' installttions are concerned, there are caly two known cases where this over-pre:sur ;ati:n has resulted in darage on n'on-nuclear surface ships and both '.

l . cecur ances v:uld have been avoided h. d proper vamup procedures been employed,.

5* Aetien. -

a. 'rTa--no Precedu es. The following eteps should be incorporated inte t.11 cpera ,i.ng procce=res covering wart up of steam systems, .if they . .

already do not Ic= a part of sa=e, prior to the ad=icsien of stea=:

l (1) Cycle all valves to ascertain t' hat they are operational and -

r icave thc= in. the opeh position for at least ene =inute to per: it drainage ' *

• l l of the b dy into the line. .-

(2) Open m drains on the valve bodies and in the b.ne, '

i .

l (3) Line up the system for vamup in accordance v4th e:cisting . .

operating procedures. All vr.lve body' drains shculd be left open to permit '

drai . age thr:ughout tha va=up period, Other drhins cheuld be pocitioned

.fer e:::isting instructions. .

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(g) proceed with var =up epe[ation and c.'cae valve body drains .-

a,t the conclusion of camca ,

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b. Modi ficati ""' "yi 1 located $dt'h their stems below the '

hori: ental may rep,e ~ if~]on in addition to the requirments of i section 5.a to Protech thC" f#* +-

The r.edificationo and s..ow to pc..f"d $1;ibd'd 2neceseary, ty of overpressuri:stion. are given in 1

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enclosure (1). - Thess modific , are F.herally considered to be outside 5 c orc tii Therefore, they should be

((e d n a pyard o tenke~r av"e. , ,

d1;bility period.

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. syste:n drainage ar.d the subject v - a%c si cr b p 'iB

& Effective Date. Thi3 4 H8 e.e+*1on becemes effective upon receipt *

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Supply Dept., MA7SIA (W 8h Ccpy to *

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.. gl bf I EQ7IREC;D AND PROCEDUE3 FO?. MODIFYEG STE.G '

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• a, SYSTC Ft" ELE GATE VALVIS AS ECISSAE! -

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.lf a cate valve is installed with its stem located below the horizontal

• h and a drain i.s not located on the valv'e neck, there is no. means of remov-ing any vster nich r.dght be located therein er. cept by cycling the valve.

.* i The wedge or disc cntering the neck cavity will displace its volume of p

s Vater into the piping s/atem, where it ecn be dtained off.' Unfortunately, I the quantity of water removed by this action from the necks of fle.d.ble .

F

' wedge gate valves rsy not preve.nt ovsrp essuri:stion because the wedge '. .

only displaces about 30 p ireent of the neck cc.v'.ty, which is not enough. .. {i Additionally, there is no way of preventing some of the displaced water j

frem re. entering the neck cavity as the wedge is moved to the closed

. position. . . .

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. s . LL This being the case, udificatiens r.ay be necessary to all inverted flex ' .

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wedge gate valves in steam systems, if prevention of overpressurization C is to be guaranteed. If these valves already have body neck drains, no . .

7 m dificatiens are necc.sc r/. The required :.odifications'in turn are depen- .

dent upon whethcr a valve is considered as being a "one way" or ",two way"

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• Briefly, a cne wa7 valve is any valve which when closed, W1 realice

• c pres:ure differentic.1 fre.c only ene direction under any conditions. Any

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' valve sidered a tw way va.lve.

whose location falls outside of this limitation is, of necessity, con- '

. T g-There are valves which are borderline

• cases and/or can fall into eithe'r

• l category, particularly if an error in line up is made. Therefore, the .s; l .

following sketches and .or'e detailed description have been included to ,

[S clarify what determines whether a par:.ict'.ar v .lve is Hone Way" or newe ya.fn,

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! '. It should *oe noted t'.at these eraples. do not take operator error *

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I The "one way" valves b the above sketch, b7 the aformc*ntioned * =

.j definition, are 5, 6, 7, 0, 10. ,

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i "t a wayH valves in tMc above sketch, by tho aforementioned .

. definih , .. e 3, 4 and 9.

• The "sorderline" valves, depending upon a particular its 1k tion are f 1 and 2. . _

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.. . a Eased on the above sketch, the definition of a "one n7" valve can ~

i be expanded as follows: -

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a. Any valve locat.cd in a cystem after any cmss connections so f, that it cannot be pressuri:cf frem the direction ths.t is opposite to

. norr.al. Refer to valve numbers 5, 6, 7, 8, 10. -

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b. The last valve in any system. Refer to valve nu=bers 5, 8,10. ,  !

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e. 'Any valve located before any cross connection.: f:cm other 1 eystc=s,vhich has a valvo located between it an;t the c:rcss connection, . ,' y no that it can be ischted if the cmss-connect valve is open. For e::a=ple, f valves 1 and 2 can be isolated if the cross-connect valve 9 is opened, 4 by closir.g valves 3 and 4, respectively. Since these valved w-ill only +

yealize pressure

• frem the boiler side no= ally and can be ischted fres -

i other systems, they can be censidered as "ene way" valves, j i . . . s 4 l

Valves 1 and 2.therefore.are en=ples of the " border line" '

cases r.entioned chove. If valves 3.'end/or 4 were not present, then va1Yes $

1 c.nd/or 2 cust be considered es "tw my" valves since it would not be

• pessihlo to isohte thcs if valve.9 vere open. , .,, ,-

.. ~

, The derytien of 5t w way" valves een be expanded as follows: .

, y

a. Any valve which - 11 he pressurized

• in the direction " '

cpposite to ner 11 when crees connections are opened. Refer.to valve -

nusbers 3 and h sich are no:. 2.lly pressurized

• fre: the boiler side but if clesed and the cross--cennect valve is open (va.1ve 9), they would be _

pressurized frc= the opposite direction. .

. =

b. Any valves in brar.ch connectichs w.hich lead to a cocon header g; that e-nnet be ischted frc= the her. der b7 closure of a valve between the= y, tind the header. Refer to velve np._bers 3 and 4. If boiler "B" vas secured -

dI r.nd valves 2 and h closed to ischte it, then vs.17e A wuld he pressurl=ce $'

frc: the boiler "A" side, or opposits to nor=al. Reversal of this precedure [

v:uld then replace v1vo 4 with vs.17e 3. ,

g!

y eNCE: The te=s " pressurized", "rmH:e pressure", eteatera, refer to - -

• 4 the y.1ves being su.bjected to a pr' essure diffsrentd -' uen in the closed j icattL=ce .

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MiStfIPSI;r':T 91.RO.72 .

h-3 8 June 1964 I

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' * *X "here' is ene othirr ew::pic, which fonows, and which has beeh included '

X to de cnstre.te the care that :.:st be taken in detemining whether a valvo E

. . is "onen or etwi' vay an4 further, tno care which .~.t:t be taken in c.ater -

zdning tha corrent, rcdifica, tion. * *

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' The e*c'sa p.' p. int, is t conventiend reducing station, per the following

- sketch: '

- * {.

. .. 12. . -

._, .- o. - .

n

. .X. .

n.

=.

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sr

. . 0 ** Y, f; s.t.. \ t-.- Q ,

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• he valves to be censidered here are n,12' .tnd 13 g.

.. .'Q, Q

' '. Yalve n is ene way valve, when elesed, with steam pressure always *

. ecming frcm the "IN" side.

4

,L halve 12 is a throttle vdve, g, lobe or needle type, and is net

.: .inveved. . - - 4:

4 h .' . '

Ydve 13 is a one way valve EUT, it is a one nr valve in the direction I' V .

eer.es i t_.- to nor: s1. If valves n and 13 c.re closed to isolate valve 34, L j ;'

• e.nd 12 is opened for operatier.a1 purycscs, then valve 1? will be pressurized -

frem the do r.etrests side and it zust be =. edified accordin;;17 .

, }T m

With the e.bove er= :ples as a basis for detemining the type 'of valve, h

the : dificatiens to be applied are

<;l M

.a. Cr.e way vdve - Drill a hele in the upstresin =ide of the wedge.

. 3.l

~

j 'b. Two way valve - I.r.stan a drain to at=caphere in thn valys neck. ,

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MISSIPSI!!ST 94140.72 ,

7 j ja Juno 1964 3

m 2

A plate should be attached in a censpicuous location reading ( '

rentIs VALVI !!AS A 7'dT HCLI I; THI U.G'6C'.M SIDE OF 'D'E WEEGE.

1F WT.EGE - i Is pr.0VID mar.E SUP.E IT IS TtEPLACED '5G SA!G WAY." i r . .,, .. .

This modification for "one hr::.y" valves vill prevent over pressu~ization Z since the hole provides a constant vent to the upstrc= piping. The reason I.

.. for using this type of sodification for thoso valves is .to mini::ise the '

{

pg number of drains that must be installed. . .

g For "tw wy" valves, the drilled disc is unac eptabic since it would d

e valve when closed, and =te.s I m.Mr..A.cead.r.nh 1;c'<ar. _xd,h.i'h:cuch t.h. he drilled hole. Therefore, pressure is applied to the cide oppcsite t utwo way" valv,es with, the stc= located below horizontal must be provided . ,

. with body neck drains to at=omphere per the following: =

. &. s

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l

?

F I ... .-

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4 l  : .

~

S5 f M saber'C 't W- I w f," M yty l ** , f of tuca'p f s&&e/.a W l '? ' y ,.e , 9 w s ,y)

. Lt ,

Pse.w..Se J der-,,4 } a. .

AVoto u)!du, Gvoces_

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= . . .

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- . NOTES - - .

' 1. Iocatien of drain hole in the neck cheuld be close to the top of the . k

. neck Ta'JT care should be tden not to drill through the pressure seal region. * .."

Someplace between 1/3 to 1/2 down from the te; of the valve (looking at the i

! ,- p#

i valve in the upright posit.iori) should avod> the region, but this should be ,

.'i cheeked before any drilling. See M.oto 9 .

x@

l- 2. Pre-heating and stress relieving (as necessary) should be in accordance i

. vith HII STD-27.u.

?

+

\. . .

3. Drain valves per 1El V-220?L .

Q g

i L Welding per lEL-.3TD-27,8. ,- . ,

. $m i  ! 5. Drain holes into valve bodies shall be in 'accordance wi'th HIL STD 22A. @

I 6. Drain valves :nd piping shall be 1/4" Es. Ihterials same as gate valve body. b f rii

! 7 When drilling hole, drill f 4 eneush off center to avoid wedge guides -

M i,

. inside the va]ve body.

T >

I 8. 30 c.srefu'. to avoid valve ste if hole is drilled with the valve

. partially assembled.

y

[. 9. The pressure scal region is in the tcp of the valve body and is evidenced 6

by a stainless steel or stellited overls.y; hole should be drm ed belcw this 4p

. oYCrlay. .

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.- Fr.closuro .(1) .

. 4 *

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w- -- 4 . , . . . _

'QG $

y, c.

!.F ml

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SPECIAL l Af > '

3 - WAY gypA3 ,

PIPE AXIS IN .

, ~

', VA:.YE -

A!!Y ORIEllTATION <-

1NCLUDING -

(FOR EXAMPLE, VERTICAL

• SEE EXHIBIT C) -

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. e. B -)

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Body neck "C" should be vented to pipe' run "A" or "B" that is upstrea:n

.1.  ;.

' by seating or backseating bypass valve.

.. 2. With bypass valve in mid-position, bypass action will occur bottieen "A" .

and "B" with "C" vented to both.

2 i* '3. Piping and operation may vary with particular bypass valve used. Appro-priate tag describing cperatias shculd be attached in cor.spicucus location. .

4. ' Piping may be installed below main valve.

s MCDIFICATION OF A FLEXIBLE WEDGE GATE VALVE WHE.9E FLOW

. MAY BE IN EITHF.R DIRECTICM

- L.

. EX}lIBIT 8 '

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"BACX SEAT" .

_ l_ "IKLET" 2:

k 'W k% N k;-;. (CcHHECT b% i

[o 60bY "MlH SEAT" N N

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."BY-PASSFLOW.ialltSEATTHRUSACXSEAT i:!

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