US2815643A - Variable area nozzle - Google Patents

Description

F. L. GEARY ETAL 2,815,643

VARIABLE AREA NozzLE v 8 shets-sheet 1 Dec. l0, 1957 Filed June 29, 1951 Dec' lo 1957 F. L. GEARY ETA; 2,815,643

VARIABLE AREA NozzLE l'reemc L. Gear William 'rauvie 7b avx:

@'M ffl-M603 E Dec lo 1957 F. L GEARY ETAL- 2,815,643

VARIABLE vAmm NozzLE Filed June 29, 1951 8 sheets-sheet 3 WHY Iuvez'a rs Mdera'cc L. Gear NNY Nw 1 l um. Il l I Y @Q iis: .Essi

F. L. GEARY ETAL VARIABLE AREA N ozZLE 8 Sheets-Sheet 4 Filed June 29. 1951 Dec 10, 1957 F. L. GEARY ET AL v 2,815,643

VARIABLE AREA NOZZLE Filed June 29, 1951 8 sheets-sheet 5 E .10. /45 2 59 w U6 4 ('57 /50 Fifth/Pm NM/VI/ (gw .i

@im l Dec. 10, 1957 F` L. GEARY- ET AL VARIABLE AREA NOZZLE 8 Sheets-Sheet 6 Filed June 29, 1951 Maly-12v.

10, 1957 F. L. GEARY ET AL 2,815,643

VARIABLE AREA NozzLE Filed June 29. 1951 `8 Sheets-Sheet 7 Eaggla. K

lA L 'H Dec. 10, 1957 F. L. GEARY ETAL VARIABLE AREA NozzLE 8 SheetS-Sheej', 8

Filed June 29, 1951 Flai?. 0.

Iaaz'zeaz Zo afs F'aeflezac: William arm i l r United States arent VARIABLE AREA NOZZLE' Frederick L; Geary,` Springfield, Mass., andY William Granville4 Taylor, Jr., Glastonbury, Conn., assgnors-to United Aircraft. Corporation, East. Hartford, Conn., a corporation of Delaware Application June*29,11951,'SerialfNb. 234,228 l lClaim. (GS60-35.6)

This invention'relates toa rvariablewarea` propelling nozzle for a-.turbojet engine Anobjectof this .invention is to provide .a .variable area propelling nozzle of4 the type. whichican be positioned at any number ofposi-tions between .twolimitso Y A further object is .to provide a propellingnozzle which for each position Yof thenozzle will provide a substantially circular opening.

Another object is to prow/.idea nozzle for a turbojet .engine which-can 'be opened .and closed with aminimumload being placed on -the lactuating mechanism..

A. further object is to. provide a -nozzle .for .an .exhaust duct of a lturbojetengine whichfor each position .of the nozzle. will provide an. opening which. is ysubstantiallyin oneplane perpendicular -to .the .axis of .the duct.A

Another object is to provide afnozzle .having .la minimum of weight.

Fig. 1 is a diagrammatic view of a turbojet engine in partial cross section with `the nozzle .in.elevation.

Fig. .2 is an enlarged view of the .propelling nozzle shown `in Fig. .1. v

Fig. 3 is .an enlargedsectionalview vtaken."throughfone of the flaps of .the .propelling .nozzle in Figi.

Fig. 4 :is .a .sectional view .in .a plane .thronghtheline 4--4 ofFig. Al 4showing thepivotalmountingtof theactuating arms.

.Fig 5 is a view .partially in...seotion .ofiihex'ed ,hoop bracket between .the actuating arm and the hoop. i

Fig. .6 kisa view of .the lik.hoop .bracket between the actua-tingarmand the=hoop.

Fig. .8 -is .a side view oa selfealigning .bearing showing the ball .and .housing Fig. .9 .is .atop viewof a Aself-.aligning-.bearing mounted in a clevis.

Fig.` lis aperspective viewnof. apartofthepropelling nozzle showing the arrangement of the iiaps. V

Fig; lltisanenlarged view-ofafmodiiication .oftthegpmpellingnozzle. u

.Fig` 12i-isan enlarged sectionaltview .takenfon the line i12-roof' Fig. '11.; p

:.ig. l.3.is.an enlarged view-.ofanother modification of .thepropellingnozzle Fig.; 14 is a rear view of-a part o'f thepropelling nozzle in.Fig.. Y13 .showing .the arrangement :of the flaps .with a smallportionin Section. K i

li-g. lfSis a view taken longitheline 'I5-'15 in'Fig. '14 showingthe pivotalmountin'gof `,the.iiaps i Fig. .1'6Li'san endview showing atrac'kandplley wheel of the modification shown'inFig. 1'31 'Fig i17 isan elevational view of a track and pulley wheel showing the spring. i

Fig. `1"8 is-a view showing'the'bracketfo'r attachingthe .linkslto the'hoopj n iFig. I9 is an enlarged view of a modification `dfth'e propelling nozzle. l

pressor 4 which in the arrangement shown is a centrifugal type driven by a turbine 6. Combustion chambers 8 therebetween deliver air from the compressor to the turbine. Anafterburner 10 is attached at the turbine outlet to provide a means of increasing the thrust.

The engine 2 has two axially spaced annular intake openings 12 to direct the incoming air into the two oppositely facing annular compressor inlets. Compressed air discharged from the compressor 4 passes to the turbine through the combustion chambers 8 where it is mixed with fuel from fuel nozzles 14. These fuel nozzles 14 receive fuel through conduit 15. The fuel-air mixture is initially ignited within the combustion chambers 8 by spark igniter 16.

From the turbine, the gases pass `around .a cone l18 into the diiiuser section 19 of the afterburner. When the af-terburner is operating, fuel from a conduit20is .dis-

No. 2,780,055, issued February 5, 1957, to .Carlton W.

Briston, Jr. The burning Aot this combustible mixture is stabilized in `the afterburner .combustion chamber 27 by llameholders 3,0 and 3 2. The burned gases discharge from the engine through the nozzle 44 Whose area can .be

varied.

The nozzle .44 is the type which .cansbe positioned at any number of positions vbetween -two limits. Tghe -three nozzles herein disclosed .are shown in Eigs. V2, 1l and 13. A nozzle :actuating system similar vto `the .fone shown with this invention is shown and claimed .in copending application Serial No. 193,734, tiled November 2, 1.950, 110W Patent No. 2,714,285, issued to F.,L..Gea1jy onAugust 2, 19.5.5.. The .actuatingsystem `consists .of the vcylinder 130, piston 132, connecting controlrod 134, nozzlecontrol .rod 78,` pistonrod 138, car 140, and track Ymechanism 142 for said car.

Referring tolFig. 2, the nozzle shown consists of `four main parts, (l) the actuating arms 46and 48, (.2) .the hoop 5 0, V(3) the flap supporting vring 52 and (4) the aps 54. These four parts areclosely interconnected by linkages and pivots.

The actuating arms aovand 48 each consist of asemicircular half-hoop`56pivoted at two spaced .pointson the aftebu'rn'er 10. The adjacent ends of the :two actuating armsareconnected by sh0r t synchronizing,links 58 which are pivoted on the arms and which -provide .for-synchronization of the opening and closingof the 4nozzle and also permit both arms to be .moved in either direction by one actuating system. These links may ,beadjustable in length, as shown. A similar synchronizing Vsystem `is :used .with the twoTposition nozzle shown in copending application Serial No. 193,734, iiled NovembergZ, 11.9.5.0, .nowPatent No. 2,714,285, issued toF. L. Geary o nAugust 2, 1955, andis not of itself a part o'f the present invention.

The pivotalpoints for actuating'arms 46 vand 43each haveplates Which'house self-aligningbearings. Each ofthelpivotal points is supported between two brackets@ and 64. Bracket 62 is lixed to the afterburner and bracket '64 extends over `a pivotal point and .has arms 66 which extend around plates 60 and are fixed to the first bracket 62. A nozzle control rod bracket 68 is fixed on the middle of each actuatingarm to .receive one end 4of one ,of the nozzle control rods 78 which has a self-aligning *bearing 'The 'hoop 50 is a circular member locatedar'oundthe end of "the afterburner to the rear of the actuating arms 46 and 48 and connected to said arms to move therewith. Two fixed hoop brackets 70 on one side of the afterburner and two link brackets 108 on the other side connect hoop 50 to the actuating arms. The hoop brackets are constructed to support the hoop substantially concentrically to the afterburner. The two fixed hoop brackets 70 (see Fig. on one side of the afterburner are rigidly fixed at one end to the hoop 50 and pivotally connected at their other ends to arm brackets 72 which are fixed to the actuating arm 48.

The main body of these fixed hoop brackets 70 is formed from two U-shaped members 74 and 76. Each member has notch 80 through each arm of the U near one end thereof in which the hoop 50 ts when the two U-shaped members are placed together. The U-shaped member 74 is smaller in width than U-shaped member 76 and slides therein to form the rectangular bracket around the hoop. An outwardly extending flange 82 attached to the bottom of each notch rests on the hoop 50 and is fixed thereto (see Fig. 7). While the flange is shown welded to the hoop it may be fixed by any means desired.

The other end of the fixed hoop bracket 70 also has a notch 84 which extends through each arm of both of the U-shaped members 74 and 76. However, this notch 84 extends inwardly from the end of the bracket and receives upper and lower projections 86 of an insert 88 which is fxedly mounted in the end of the fixed hoop bracket 70 by bolts 90. Said insert has an internally threaded hole 92 which receives a bolt 94. A lock nut 96 holds the bolt 94 in place, thus providing for adjust-l ing the length of the connection. The free end of the bolt 94 carries a self-aligning bearing which consists of a ball shaped member 98 mounted in a housing 100 (see Figs. 8 and 9).

The arm brackets 72 have two flat projections 102 extending rearwardly from the arms forming a clevis 104. The projections 102 of the arm bracket extend horizontally therefrom, one over the other. The ball shaped member 98 of the self-aligning bearing of the fixed hoop bracket 70 is held in the clevis 104 by a vertically extending bolt 106.

The two link hoop brackets 108 on the other side of the afterburner provide flat projections 110 extending forwardly of the hoop forming a clevis 112. The projections 110 of the link hoop brackets extend horizontally therefrom, one over the other. The actuating arm 46 on this side of the afterburner has arm brackets 72 identical to the arm brackets on the actuating arm 48 on the other side of the afterburner. Mounted between the clevis 104 on the actuating arm 46 and the clevis 112 on the hoop 50 is an adjustable bolt 114.

The adjustable bolt 114, Fig. 6, has a self-aligning bearing on each end with the ball member of one bearing being held in the clevis 104 by a vertically extending bolt 116 and the ball member of the other bearing being held in the clevis 112 by a vertically extending bolt 118. This connection of the hoop to the actuating arms locates the complete hoop in position but does not interfere with the relative expansion of the afterburner, half hoops, complete hoop or other parts.

Referring to Fig. 3, the flap supporting ring 52 which is iixedly attached tothe afterburner consists of several parts. One part, the ring 120, is fixed to the afterburner and has a flange 122 at its free end. A second part, another ring 124, has a mating flange 126 which is bolted to ange 122 by bolts 128. This ring 124 has a curved Sealing portion 130 for a purpose to be described later. A third ring 132 is fixed to the outer periphery of said `sealing portion and carries the mounting brackets 134 for the flaps. Each bracket has two mounting bosses 136, Fig. 10, forthe flap between which each flap 54 is pivoted.

Each of the aps 54 has mounted thereon, as by bolts 2138, a boss 140 on which each flap pivots. This boss is 'placed near the center of the flap'to balance the loads 153 and 159 face each other but do not meet.

. this application there are twelve (12) aps.

imposed on e'ach end of the ap by the exhaust gases passing from the afterburner. A bolt 142 pivotally connects each boss 140 between mounting bosses 136 on each bracket. The boss 140 on the flaps has a projecting built-up arm 144 for actuating each ap (see Fig. 10). For each ap there is a connection on the hoop.

These connections consist of brackets 146, Figs. 2 and 3, which are formed from two sets of members, members 148 and 150 and members 149 and 151. These members 148 and 150 have projections 152 extending from one end and flanges 154 extending outwardly from the other end. One member 148 is placed on hoop 50 with its ange 154 fixed thereto and its projection 152 extending to the rear of the hoop. The member 150 is placed on the opposite side of hoop with its flange 154 fixed thereto and its projection 152 extending to the rear of the hoop and adjacent the projection 152 of member 148. These two projections are fixed together such as by welding. A small ange 153 extends along the top of the members 148 and 150 in a direction opposite to flange 154. Members 149 and 151 have projections 152 extending from one end and flanges 157 extending outwardly from the other end. One member 149 is placed on hoop 50 near member 148 with its flange 157 fixed thereto and its projection 152 extending to the rear of the hoop. The member 151 is placed on the opposite side of hoop 50 with its ange 157 fixed thereto and its projection 152 extending to the rear of the hoop and adjacent the projection 152 of member 149. These two projections are fixed together such as by welding. A small flange 159 extends along the tip of the members 149 and 151 in a direction opposite to ange 157. Flanges Members 149 and 148 are interchangeable, as are members 151 and 150.

The connections from the hoop to the flaps are equally spaced around the hoop. In the arrangement shown in Four (4) of these brackets fall at the same point on the hoop as the hoop brackets. In this case the ends of the two fixed hoop brackets 70 which extend rearwardly of the hoop are used in place of the brackets 146, and the brackets 146 are merely placed over the holding band of the link hoop brackets 108 for the other two points. Two brackets 146 are equally spaced between each of the points on the hoop at which the hoop brackets are xed. An adjustable link 156 having self-aligning bearing on `v each end extends between each connection on the hoop and the ends of each built-up arm 144 of each flap. The link 156 has the ball member of the self-aligning bearing of one end held in the bracket 146 on the hoop and the ball member of the self-aligning bearing of the other end held between the ends of the built-up arm 144 of the flap.

` The flap itself is a plate having end portions 162 and 164 angularly displaced inwardly from a center portion 166 (see Fig. 10) and is reinforced by a plate 168 on the center portion 166 and end portion 164. The end of the ap which mates with the sealing portion of ring 124 has a flange member 170 fixed thereto on the inner side in which a sealing strip 172 is mounted. Holes 174 'are placed in the ange 170 to allow pressure from the afterburner to act against one side of the sealing strip to press it against the sealing portion of ring 124. However, where the adjacent aps overlap, this flange is located on the outer side with the holes to allow pressure from the afterburner to act against the sealing strip being located in the flap.

Along the inner side of end portion 164 of each ap which carries part of the reinforcing plate there extends an overlapping plate 176 which is attached to said flap. The end portion 162 of the adjacent ap is received in the opening formed by the first mentioned flap and said :plate 176. This arrangement provides for sealing between the flaps themselves.

peiaton of the modfczion shown in Figs. 1-10 Assuming..the device to` bev4 in the ...position "shownein Fghl., whenv the piston 1321is movedeto then'ght,v or rear, `thisaction in turn movesY theconnecting kcontrol rods 134-in the same direction. L Each connecting control? rod.134.is connected to its associated car 140.on-its track mechanism 142 and moves the car tothe right. along the.

track.. The nozzle control rods 78= are pushed by'their respective cars :140' to the:right,. orrear, to pivot each= actuatingfarm around itsw'fpivotal point. moveshoop 50 throughtxedhoop'brackets 70 and link hoop brackets 108.1 VThis-movement of; the hoopin turn" pivots. each Hap. simultaneously through` built-upf'arms 144'on the `apsand the. connecting adjustable links- 156 between said arms and the fhoop. This t pivoting of the aps is in a closing direction thereby reducing the area of theexhaust nozzle. If the nozzle is to be opened the piston 132 is movedv to the left, or front,'and throughv a: sequence. of operation,. thereverse: of that, described-i above, the aps are moved in an opening direction..

Referring to Fig. 1l, the nozzle shown consists vof three mainparts, (l) the bell crank lever and flap supporting ring 200, (2) the bell cranklevers 202 and(3') the aps` 204. .These three parts are .closely interconnected by linkages and pivots.

Referring to Fig. 12, the flap supporting ring 200 which isv xedly attached to the afterburner. consists of sev-` eral parts. One part, `a ring 206, having `holes 208,` is lxed to the end of the afterburner and extends as a radial flange. the'afterburner `and has a curved `sealing portion 212' fora purposev to be described later." A thirdatring. 214 extends aroundthe afterburner and vis attached at` each side to the free end of the two rings 206. and 210 and supports the bell crank levers 202. A fourth builtup ring 216 is xed to said sealing ring and carries the mounting'brackets 218 for the. flaps.

The bell crank lever 202 consists of twov members 220 and 222 similarly shaped which are placed one over the other and pivoted between two brackets 224 and 22S by a'bolt 226. A spacer 228 is located around the bolt 226 between the members 220l and 222. These bell crank levers are mounted around the third ring 214. A spacer 229 is ixedly mounted between the members 220 and 222. They have two levers 230 and 232. Lever 230 is offset downward at its free end and is connected to each adjacent lever 230 by links 234 having a self-aligning bearing on each end. Each link 234 has the ball` member 236 of the self-aligning bearing of one end held between the free endsof the parts of the members 220 and 222 forming lever 230 of a bell crank lever and the ball member of the self-aligning bearing ofthe other end held between projections 239 extending from the free ends of the parts of the members 220 and 222 forming lever 230 of the adjacent bell crank lever.

Each of the aps 204 has mounted thereon a bracket 240 having a boss 242 at each end which is placed between two bosses 244 on the mounting brackets 218 on the flap supporting ring 200. Also mounted on the flap is a builtaup arm 246 which has a clevis 248 at its free end. An adjustable link 250 having a self-aligning bearing on each end is connected between the free end of each lever 232 of the bell crank levers 202 and the clevis of the built-up arm of the flap which it is to actuate. The link 250 has the ball member 252 of the self-aligning bearing of one end held between the ends of the parts of the members 220 and 222 forming lever 232 and the ball member of the self-aligning bearing of the other end held in the clevis 248 of the built-up arm 246 of the flap.

The bell crank lever on each side of the afterburner has an extension 254 on the lever 232 which permits the nozzle control rod 78 to be connected thereto to actuate the nozzle 44. The flaps themselves are formed in a manner similar to those shown in Fig. l0. A U-sliaped member 256 is xed on the end of the ap 204 which This action A second ring 210 extends similarly; from4 mates with the Sealing portion of ring 210 in whicha sealing strip- 2518 is mounted?A Like. the ilap shownin Fig". 3', Where adjacent flaps overlap' this U-shaped mem;

cranklever 202 is of a different' constructionl and.. is

mounted at an angle to. the centerlinerof the afterburner.

This bell crank lever V202 has two `levers 230 andi 232. Lever 230 extends in a manner similar, to lever 230`of the modification shown in Fig. ll, however, the links. 2314" are connected `to the lever 230 adjacent each other at' the end of the lever. Thisl end of the lever is. bifurcated and twisted so as to receive the ends of adjacentv links 234" at dilierentY anglesl Lever 232' extends.. in a manner similar to' '232 of the'modication shown.. in Fig.` ll and. is connected to a built-up arm .246" ofV a tlap 204, by' a link 250" to actuate the flap. The'center part of the bell" crank lever 202 has two bosses, 211 and 213-each having a. hole for` pivotally mounting said lever. between ring'2l4t. and flange 215" bya bolt 217. This pivotakmountingis arranged so that the axis of the bolt 217." is atan angle to the centerline of the` afterburner, the -endof thebolt nearest the afterburner being located forward of thev other end of the bolt. This arrangement maintainsjthe distance between the free ends of adjacent levers 230fsubstantially constant as the bell crank levers are rotated;

Operation of the mdjcatl'on Shownin Figs. 1'1, 12," 19 and 20 Assuming the nozzle to be in the: position shown in` Fig. .ll,. when `the nozzle control rodsgfS are.. moved: to the left, or front, the bell crank levers'202 connected; to said. control rods are moved about their pivots with: levers.230..moving the adjacent bell crank. levers through, links4 234. Each other bell crank. lever .202i is moved.: by its adjacent lever 230. The motion of the links iisv transferred to the flaps through links 250andvbuilt=up arms 246. .This pivoting of the tlapsis in an opening directionthereby increasing the areaA of the exhaustnozzle. If the .nozzle is to be closed, the nozzle control rods; 7S are moved to the. right, or. rear, and through asequencei of operation, the reverse of that describedabove, the flaps are moved in a closing direction..

Referring to Fig. 13, thenozzle shown. consists of four main parts, (l) the hoop 300, (2) the hoop tracks 302, (3) the flap supporting ring 304 and (4) the aps 306. Thesefour parts are closely interconnected by linkages and pivots.

Referring to Figs. 13, 14, 16, 17 and 18 the hoop 300 is a circular tube located around the end of the afterburner and mounted for axial movement on tracks 302. A plurality of these tracks 302 are mounted around the afterburner. They are formed from a plate and have a single rail with hanged out parts 308 being ixed to the afterburner. For each track 302 there is a bracket 310 located on the hoop on which there is mounted two pulley wheels 312. The bracket 310 consists of two plate members 314 xed to the hoop and extending front and rear thereof. A pulley wheel 312 is rotatably mounted on each end by a bolt 316. These wheels support the hoop 300 and permit axial movement.

The flap supporting ring 304 consists of two circular members 318 and 320 which are fixed to the end of the afterburner. Circular member 318 has a ange 322 which extends radially therefrom and circular member 320 has a similar hange 324 which extends radially therefrom. These two anges are located adjacent each other and form a single flange projecting radially from the afterburner. Brackets 326 are bolted to said flanges 322 and 324, by bolts 328. These brackets have a boss 330 on each end, each with a hole for pivotally mounting the flaps 306 in a manner to be hereinafter described. A plurality of these brackets 326 are located around the flap supporting ring 304.

The tlap itself is a plate 332 with a hinge plate 334 and sealing plate 336 fixed thereto. The hinge plate 334 s flanged up at 338 to strengthen the iiap and flanged up at 340 to provide hinge points for the ap 306. These flanged portions 340 are placed between the end bosses 330 of adjacent brackets 326. A bolt 342 extends through each hole in a hinge plate and its mating hole in the boss of the bracket 326.

Each ap has an arm 344 for actuating it. These arms 344 consist of two members 346 spaced apart and fixed to the flap by flanges 348. For each ap 306 there is a connection on the hoop 300.

These connections are brackets 350 fixed to the hoop. Each bracket consists of two rearwardly extending bosses 352 fixed to said hoop and having a hole through the outer ends thereof. These lbrackets 350 are equally spaced around the hoop. An adjustable link 354 having a self-aligning bearing on each end extends between each bracket 350 on the hoop and the end of the arms 344 of the flap which it actuates. The ball member of the self-aligning bearing of one end of a link 354 is held between the bosses of a bracket 350 by a clevis pin 353 and the ball member of the self-aligning bearing of the other end of the link is held between the free ends of the two members of an arm 344 by a clevis pin 355. On each side of the afterburner the bracket 350 has two forwardly extending lbosses 356. The end of the nozzle control rod 78 on each side of the afterburner is held between the bosses 356 located on that side.

A seal is formed between the afterburner and nozzle 44 by having a channel 357 extend around the end of the afterburner over the hinge points of the flaps 306. A

sealing member 358 is placed within said channel and extends around the afterburner. The part of plate 332, forming a part of the ap 306, which is located over thehinge points is bent at 360 to mate with the sealing member 358 as the flap moves to any position.

Brackets 362 on the hoop 300 are mounted on opposite brackets 364 on the ap supporting ring 304. A spring 366 is located between said brackets, one end of said spring being xed to bracket 362 and the other end of said spring being xed to bracket 364. This construction biases hoop 300 to the rear for a purpose to be described hereinafter.

I Operation of the modification shown in Figs. I3-18 Assuming the nozzle to be in the position shown in Fig. 13, when the nozzle control rods '78 are moved to the left, or front, the hoop 300 is moved in the same direction. This movement of the hoop in turn moves each link 354 to the left turning*aps'306-simultaneously by arms 344. This action is against lthe' forcel of spring 366 but with the aid of the" exhaust gas against the inner side vof the flaps. lf the nozzle*A is to be closed, the nozzle control rods 78^are moved to the right, or rear, and through a' sequence-of operation, reversel of that described above, the aps are moved in a closing direction.` It is to vbe notedthat in vclosing the aps the spring 366 is arranged so that its force aids in this movement, this is to counteract the force of the exhaust gases acting against the-inner side of the flaps.

Although specific embodiments have been shown andi described herein for the-purpose of illustration, it'will be evident to those skilled inlthe art that the invention is capable of various modifications and adaptations within the scope of the appended claim. Another variable area nozzle of themultiple'dlap type is shown and claimed in copending application Serial No. 234,256, led June 29, 1951. A

We claim:

In combination, a duct having an outlet, a plurality of flaps pivotally mounted to' vary the effective area of said outlet, said aps being spaced outwardly from said duct to form a space between the outlet of said duct and said aps, said tlaps having their pivots located inwardly from their ends, each tlap having a section projecting forwardly'of said pivot anda section projecting rearwardly of said pivot, sealing means extending around cation with said space and thereby with the outlet of said duct to receive pressure fluid therefrom.

References Cited in the .file of this patent UNITED STATES PATENTS 2,475,022 Gregg July 5, 1949 2,488,174 Clegern Nov. l5, 1949 2,523,842 Oulianoif Sept. 26, 1950 2,563,270 Price Aug. 7, 1951 2,565,854 Johnstone et al. ,Aug. 28, 1951 2,569,497 Schiesel Oct. 2, 1951 2,597,253 Melchior May 20, 1952 2,608,820 vBerliner Sept. 2, 1952 2,639,578 Pouchot May 26, 1953 2,693,078 Laucher Nov. 2, 1954 FOREIGN PATENTS 607,686 Great Britain Sept. 13, 1948

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