US2580353A

US2580353A - Fluid pressure intensifier

Info

Publication number: US2580353A
Application number: US784839A
Authority: US
Inventors: Hunt Nathan Charles
Original assignee: C B Hunt & Son Inc
Current assignee: C B Hunt & Son Inc
Priority date: 1947-11-08
Filing date: 1947-11-08
Publication date: 1951-12-25
Anticipated expiration: 1968-12-25

Description

DeC- 25, 1951 N. c. HUNT FLUID PRESSURE INTENSIFIER 2 SHEETS-SHEET l Filed Nov. a, 1947 yar/MN Afa/v7' v A TTORWEX Dec. 25, 1951 N. c. HUNT 2,580,353

FLUID PRESSURE INTENSIFIER Filed Nov. s, 1947 f 2 SHEETS- SHEET 2 A TTO/VEX Y of my invention.

Patented Dec. 25, 1951 FLUID PRESSURE IN TENSIFIER Nathan Charles Hunt, Salem, Ohio, assignor .to

C. B'. Hunt & Son, Inc., Salem, Ohio, a corporation of Ohio Application November 8, 1947, Serial No. 784,839

(Cl. Gil-54.5)

14 Claims.

My invention relates to fluid pressure intensiers and to systems embodying uid pressure intensiers, and the principal object of my invention is to provide new and improved iiuid pressure intensiers and iiuid pressure systems.

In certain fluid systems, it is usual to utilize a pressure intensifier, so that relatively light pressure may be transformed to greater pressure to effect movement of the work-effecting mechanism. In such systems, the Work cycle usually comprises admission of fluid under pressure to the cylinder of the Work-effecting mechanism, to effect movement of its piston in one direction, and exhaust of such fluid under pressure to permit means (such as spring means) to return the piston to a predetermined position.

I have found that the usual system of the kind described above will become unreliable, inaccurate, and will lose effectiveness because of leakage, absorption, inclusion, and other reasons, and theA apparatus and system of my invention has been devised to overcome the disadvantages of the prior art apparatus and systems. Further,

the apparatus of my invention overcomes the disadvantages of the prior art Without the necessity of expensive additions to the intensifier and/or the system.

The apparatus of my invention also provides means whereby a constant pressure urges the intensifier parts to normal relation, thus providing exact and readily determinable relative movement of the intensiiier parts, and my invention further. provides means for readily indicating such relative movement. Further vand other novel features of my invention will be apparent from a reading of the followingdescription.

In the drawings accompanying this specification and forming a part of this application, there are shown, for purposes of illustration, various embodiments which my invention may assume, and in these drawings:

Figure 1 is a longitudinal sectional view through a pressure intensifier, showing a preferred embodiment of my invention,

Figure 2 is a fragmentary enlarged sectional View, showing parts of the intensifier in another position,

Figure 3 is a schematic representation of a system disclosing my invention,

Figure 4 discloses an electrical circuit which` may be used to control operation of the various parts of the system shown in Figure 3, and

Figure 5 is a longitudinal sectional view, with parts in elevation, showing another embodiment 'upper'portion working in the cylinder I5, an

Referring particularly to Figure 1, the intensier illustrated to show a preferred form of my invention comprises a body, including an open ended casing I0 providing a large cylinder Il. The open end of the casing I0 is closed bya block I2 which may be held in position by bolts I3. An inverted casing` I4,` providing a smaller cylinder I5 in alignment with the cylinder II, is held to the block I2, preferably by means of bolts I6 passing through apertures in' a ange I1 formed on the casing I4, the bolts being threaded into the block I2.

The bottom of the casing I0 is formed with an aperture I3, and an open ended casing I9 is secured to the casing I0, providing a small cylinder 20 in alignment with the cylinder II. A block 2I is interposed between a ange 22 of the casing I3 and the bottom of the casing Ill, and the component parts are held in assembled relation, preferably by means of bolts 23 passing through apertures in the flange 22 and the block 2 I, and threaded into the bottom of the casing I 0.

In the present embodiment, a piston rod 24, herein shown as a one-piece construction, has, referring to the relation of parts in Figure 1, an

intermediate porting working in the cylinder I I, and a lower portion working in the cylinder 20. The upper portion of the piston rod 24, in the construction shown, forms a piston which fits the cylinder I5, and this upper portion has a recess 25 and transversely extending ports 26 communicating with the recess 25.

The upper portion of the piston rod 24 works through spaced-apart -

seals

21, 28 respectively carried by the block I2 and casing I4, and the block I2 and aseal plate 29. The

seals

21, 28 are so constructed and arranged as to prevent leakage of fluid along the upper end of the piston rod in either movement of the rod. Intermediate the

seals

21, 28, the block l2 is formed with a transverse aperture 30 which leads from a threaded recess 3I at an exterior face of the block to a chamber 32 adapted to be in communication with the ports 26 in the upper end of the piston rod 24.

The intermediate portion of the pistonrod 24 carries a larger piston which comprises a backing plate 35 bearing against a shoulder 36 on the rod, a clamping plate 31 clamping a seal 38 between it and the backing plate 35. This piston construction is held assembled by a washer 39 and a nutv 43 threaded on a threaded portion of the piston rod 24. The clamping plate 31 is `Aformed with spaced lugs 4Il to prevent `the piston Vfrom completely vbottoming inthe cylinder ..II.

The lower end of the cylinder Il is formed with a recess #l2 for freely receiving the nut 40, this recess communicating with a transverse aperture 43 leading to a threaded opening i4 at an exterior face of the casing I.

The block 2| cooperates with the bottom of the casing ;I fand'thefiange kof the casing I9, to :support spaced-apart seals A5, .4.6 vwhich prevent leakage of uid along the piston rod in either movement of the rod. An aperture 50 extends transversely through -the Yflange 22, and establishes communication betweenthe interior of the cylinder 2B and -a threaded .opening 5l at an exterior face of theiflange.

The lower end of thefpiston rod 24 is reduced and threaded, vforming a shoulder against which bears an inverted cup-shaped vbacking member 52. A seal 53 is supported between the member 52 and a nut 54 threaded'on the reduced threaded `end..of` thev pistonrod, thisconstruction forming .-a piston .for cooperation -with :.the cylinder .25.- II-he Vbottom of fthe casing idlislformed .with .an aperture :.55 :to prevent yacuum or .-air pressure ffrom r.interfering with proper .operation of the fsmallpiston .inthe cylinder v20.

My invention includes the provision vof indi- -.cator:means,. so that'vthe -amountof piston travel iis readily visible at .all times. Asherein shown, :the :indicator means `comprises -a rod 'SE -supported jior movement Vwith `.the backing :plate 35 of the larger piston, the iupperend of the lrod 60 .being vformedwith graduations 'to show rany desired reading. The rod 4extends through fan.aperture 2-6! in the'block I2, and through Va bushing r6? in the Ailange Il v.of the :casing l. ffReadingsAnay `he `.taken by comparing the ieX- posed graduations .on kthe :rod T66 with .the ex- "terior lend voi rthe Vbushing 452.

Referring'particularly to Figure .3, the pres- Y :sure intensifier illustrated in l'igure 1 is .shown jconnected .to ia fluid .system Ain :accordance @with my invention. As shown, -the :outlet E3 of fthe small .cylinder :I5 is 4vconnected :to .the inlet Bil of a piston fand .cylinder `construction 55, this construction being adaptedntobe .combined rwith mechanism (not: shown) .to :perform 4.some -.usefu1 work. :Apressure gaugepG mayrbe interposedin :.the fline, so that pressure :readings are readily Avisible.

.A :service line :65, leading :from A:any 'suitable source .of:air, water, or Othersuitable fluidlunder substantially constant pressure, connected to ithe :inlet port l-'I .of a three-way fvalve 158 which fmay -be 10i any isuitable commercially available ftype. lIhe outletgpcrtf offthe valve'581is.ccn rnectedatotheopening -3l vin the block A2 andethe exhaust l0 :is :connected to an exhaust line fil. Aisolenoid :'12,.designatedas fNo. I solenoid, is Yaidaptedzto operatethe valve-:6850 that'its outlet port iBS :is .connected :either ,to the .inlet lport 161 ml'fthe exhaust port i0. .Aimetering valve 7-3, aofany suitable'nommercially available construcf-ti'on, is interposedin theline 56 Aleading to the inlet niort 6I,so`that :the-rate of viluid 'flow-may be controlled.

A tsecond fthree-:way `valve "l5, similar .to fthe avalve #58, vis aprovided, this .valve 'having .its 'inlet .r1.6 connected .to "the-service line "S6, ya pressure regulating lvalve :11 being Vpreferably interposed .1in theline, so that vluidf pressureto the'valve :may .be fadjusted "to any v.desired amount. The :outlet port 'I8 .'ofthecvalve T5 iis connected vto the .':openingr'l inthefcasingf, and the exhaust port '1.9 .fof the .valve 15 .Fis connected "to .the exhaust :line Ell. A solenoid x80, .designated :as No. '"2

ANo. ".relay32 designated as time delay-relay No. 2,

solenoid, is adapted to operate the valve 'I5 so that its outlet port I8 is connected either to the inlet port le orthe exhaust port i9. The opening 5I in the casing i9 is connected directly to the service line 68, by means of a conduit 8i.

Referring to the electrical circuit shown in Figure '4,1current is provided rthrough line wires .85, 8e which leadsto a suitablesource of;electrical energy. Branch conductors 8l, 88, and B are ,connected across the

lines

85, 86, and interposed .in the uconductor 81 are an electrical start switch 'ilfand a relay 9i designated as Relay I. interposed in the conductor 3S is a and also interposed in this line are contact points S3 which normally 4 prevent independent actuation of the relay '52. A conductor Sd connects `branch conductors 8l and 88.

A relay Q5, designated as relay No. 3, is inter- .pesedfin.thebranchconductor 89,;and ,aA relay 95,

designated .as time.delay-:relaylld d is.co n- .nected in parallel 4,With-relay r$5. Contact points .9?, undercontrol ,of relay .92, ,control ow .of

current through branch conductor 89.

Lineconductor 8.5 has yan interposed normally .closed switch 9E, .designated emergency `stop, :and interposed .normally closed `contact `points Iill which are under control of relay S5. Extend- .ingfromconductor 98 .to line conductor .18S are two lbranch conductors Iil,l |82 in which the coils vof solenoids -12 and 85.) areirespectively interposed, these. branch .conductors also having inter- ;posed contact points |03, 104, respectively under Acontrolioi .relays -Sl .fand 95.

In operatomand assuming theparts Hare in gpcsitionishown in Figures l through 4, `and fur- -ther Yassuming that all .fluid and electricalcon- 4nections .have been made, the operator closes start switch 99,'thus energizing relaysfl and e2. vllnergization of 'relay :SI closes contact points 1R13, 'to energize lthe fcoilsof solenoid l2, and .to consequently '.cause valve 'f 58 to connect inletV port 81 to outletportfi. .-Eluid'maythenflow through .opening 13|, .transversewaperture 39, to chamber '32,*from whenceit ows through ports `25,recess 25, opening G3 to the piston and cylinder construction 55, yat source pressure. This 'pressure `:may :or may not be suicient to move 'the piston in the construction 65, butrinanyevent,'the1uid :system is giventime tc ll completely.

After Ya certain interval following closing :of start switcli9ll, the :time delay'relaySBZ effects closing lof Contact pointsgSLso as'to eause'enerngization toi relays 95 and v95. Energization fof f Jrelay B5 causes closing of icontactpoints IM, 'so

that the coil of solenoid is energizedgandcon sequentlyrcause'valve v'l5 vtoconnect its inletand Voutletportsi, 13. 'Under these ccnditions,zreg ulated line *pressure .may :flow 'through ropening 144,transverse-aperture 33, to cylinder Vi I .beneath the large piston.

Since :the :large 'piston has .greater area than the smaller piston working in the cylinder `2i), the large piston 'andthe piston ro'd 24 Will be rcovedupivardly as viewed in .Figure 1. Sufficient/upwardirncvementwill cause the ports 2t to move out of communication with thechamber lilas seen `Airvigure, "theports 2% and 'the ladjacent parts of the block "i 2 forming valvemeans to automatically Aclose. o uid Isupply 'from 'the 'transverse aperture 30.

Because of'the'area 'difterential'between the pis'- 'tons working in 'the cylinders il 'and I5, .fluid pressure lwill befincreased in proportion to 'the difference in piston areas, andrthis increased -pressure is transmitted to the piston and cylinder construction 65. After a predetermined interval of time, relay '96 will operate to open the normally closed contact points IDB, breaking kthe complete electrical circuit, thus causing deenergization of all the relays in circuit. Valves 58 and 'I5 are returned (by springs or any other suitable means) to conerable, especially where heavy fluid pressures are used, since constant duid pressure opposing movement caused by the large piston will always produce a constant resultant pressure which eiects accurate movement of the large piston. However, in certain operations, for example light pressure operations, the small cylinder 2d and its piston may be omitted, and a spring or other resilient means may be used to return the parts to initial position.

Referring to Figure, a construction is shown wherein the air return is omitted, and a coil spring m5 surrounds the adjacent part of the piston rod 2da and is interposed between the block l2a and the backing plate 35a of the large piston. In this case, the aperture Il! of the con- ,A struction shown in Figure l is omitted; otherwise,

the remaining construction is the same, and like parts are identified by use of the same reference numerals, supplemented by the suffix ai From the foregoing, it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention, and it also will be apparent to those skilled in the art .that the embodiments herein described may be variously changed and modified, without departing from the spirit of the invention, and vthat the invention is capable of uses and has advantages not herein specifically described; hence it will be appreciated that the herein disclosed embodiments are illustrative only, and that my invention is not limited thereto.

,I claim:

l. A pressure intensifier for a fluid system, comprising: a body, providing a large cylinder and a small cylinder, the outlet of said small cylinder being connectable to said system; a large piston reciprccable in said large cylinder and having a piston rod the extremity of which forms a small .piston reciprocable in said small cylinder; a first conduit in said body, adapted for connection to a source of fluid under pressure; valve means, operable when said small piston is in its retracted position to provide for fluid communication between said small cylinder and said conduit; a second conduit, adapted to connect said large cylinder to said uid source, so that fluid pres- `sure may move said large piston and thus ex-- tend said small piston; said valve means being operable to interrupt fluid communication between said small cylinder and said first conduit when said small piston is moved toward its extended position.

2. A pressure intensifier for a fluid system, comprising: a body, providing large and small lcylinders; a large piston reciprocable in said 4large cylinder and having a piston rod the ex- 1 tremity of which forms a small piston reciprof cable in said small-cylinder, said small cylinder being connectable to said system, and said small piston having a recess extending inwardly from its working face and Atransverse port means establishing communication between said recess and its peripheral face; a first conduit in said body, adapted to connect a fluid source to said small cylinder; a second conduit adapted to connect said fluid source to said large cylinder to effect movement of both of said pistons; said transverse port means, when said small piston is in its retracted position, being in communication with said first conduit to provide fluid under pressure of said source to enter said system, said transverse port means being moved out of communication with said first conduit when said small piston is moved toward extended position by said large piston, to interrupt communication of said system with said source and to intensify pressure of fluid in said system.

3. A pressure intensifier for a fiuid system, comprising: a body, providing large and small cylinders; a large piston reciprocable in said large cylinder and having a piston rod the extremity of which forms a small piston reciprocable in said small cylinder, said small piston having a recess extending inwardly from its working face and transverse port means establishing communication between said recess and its peripheral face, said small cylinder being connectable to said system and having spaced-apart seals at its inner end; a first conduit in said body, adapted to connect a fluid source to said small cylinder at a point between said seals; a second conduit adapted to connect said fluid s ourceto said large cylinder to eifect movement of both of said pistons; said transverse port means, when said small piston is in its retracted position, being in communication with said rst conduit to provide fluid under pressure of said source to enter said system through said transverse port means, said recess, and said small cylinder, said transverse port means being moved out of communication with said first conduit when said small piston is moved toward extended position by said large pis-A with said source and to intensify pressure of fiuid `in said system.

a. In combination: a pressure intensifier coinrising: a cylinderthe outlet of which is connectable to a fluid system. and a piston operable in said cylinder; first valve means for admitting fiuid from a source to said fluid system; second valve means. for admitting fluid from said source to said intensifier for effecting movement ofv said piston; other valve means for interrupting fluid fiow from said first valve means to said'system when said piston is moved toy intensify pressure of uid in said system;vand time delay means, for effecting opening operation of said second valve means a predetermined time after thefiuid through said first valve means has been in communication with said system. K

5. In combination: a pressure intensifier comprsing unecual pistons working in respective cylinders, the outlet of the smaller cylinder being connectable to a fiuid system, resilient means for normally urging said pistons to retracted relation with respect to said cylinders, valve means in part carried by said small piston and in part carried by said small cylinder, said valve means being in open relation when said small piston is in retracted relation; first control valve means for admitting fiuid from a source under pressure through said valve means tosad system;

faraones "7 control valveimeansouadmitting 'fluid fromrsaid source lto the .largezcylinder for effecting moveine'nt of visaid pistons; Isaid 'valve `means .closing ywhen zsaid lsmall piston :is 174moved rtoward 4.its ex- @tended .p'osition, thereby interrupting Vcomrnunication -between :.'said source `and said :system: .fand 1time delay .means, for .effecting lopening op- .ferationfof saidsecond valve means a .predeterlfmined time :after the Isaid Asystem has been Vin operated means, constantly-connected to asource inf duid vunder `substantially *constant pressure, i'for urging said valve rmeans lto vposition wherein said 4system is 'in communication `with 'the fluid sourc'e.

'.'LA pressure '-'intensier for La iiuid 4system, I

:comprising: ra`body, Yproviding ja 'large Vcylinder 'and'smaller cylinders at either uaxial "end of lsaid large 'cylindenthe 'outlet of one o'f Isaid smaller cylinders -being connectable to said system; a 'largepis'ton Areciprocable 'in said large cylinder; Aa piston ^rod supporting said "large Vvpiston; and fsmaller pistons yonsaid piston'rod on opposite #sides 'of said :large piston and movable therewith, one of said smaller "pistonsfbeing' movable YWithin *said one smaller Icylinderto increase pressure in said system, and the other'smaller piston being movable Within-'the A'other smaller cylinder, said other smaller cylinder `being connectable to a source of uid underjpressure Tor normally urgvfing said piston rod'in one direction.

r`'8. A f'luidjpressure device, comprising: a block Ahaving an 'aperture therethrough, counterbores extending inwardly *from opposite surfaces of, said *block land 'a `passage Acommunicating with said aperture intermediate Ysaid counterbores; Vsealing means vdisposed vin each of .said counterbores; cap means fsecured to usaid block in'position .to hold one of said ,sealing means imposition, said cap means'providing apiston cylinder .axially aligned `vi'lithsaidaperture; 'and apiston Working through said l'aperture Yand into cylinder, saidpiston having'arecess entering fromits working face ,and opening fmeans :adapted to ,establish communi- `cation 4between 'said cylinder 4and said passage 'whensaidpiston is` in certain position .Within ,said

cylinder.

`9. A pressure intensifier 'for a ,fluid system,

' comprising: unequal pistons, connected together,

and'workinginrespective cylinders, the outlet of the cylinder 'for the 'smaller piston being connectable to saidsystem, and saidsmaller lpiston and a surface of its cylinder providing valve means Which Vis open `vvhensaidsmaller piston is 1in retracted position but which is closed when said .smaller .piston is. moved ,from retracted position; rst conduit means for connecting said valve means to-a source of fluid under pressure; :secondconduit means for 4connecting the cylinder :of 'the larger Fpiston to fthe fsame :source of fluid under pressuretoreiiect movement of said pistons vwhereby "said `valve means is closed and fluid 'pressurein said fsystem is intensified; fand addi- '.fti'onal ".valve :means operable 4a predetermined :timeafteresaid'systemhasfbeenin communication with said iiuid source, .to provide-'for gow-offluld through said second conduit.

10. .A viiuid system, comprising: a large cylinder containing ia large piston 'reciprocable therein;

-a .piston 'rod connected 'to vsaid large `pistonfand extending laterally therefrom; `a head closing usaid 'large :cylinder and 'having 'an 'aperture Cto pass said piston rod,:said aperture `beingformed Vwith counterbores 'extending inwardlyffrom opposite sides ci said head, and said head also having `a transverse passage communicating Withrsaid :aperture intermediate said counterbores; .sealing means disposed in each of `said counterbores; elongated cap means secured to Isaid headand providing asmall cylinder alignedwith said-aperture; and a "small piston .adjacent to "the 'end iof said piston rod and adaptedto'reciprocate within said-small cylinder, said small pistonhavingfa recess extending :inwardly "from its Working face and-also 'having fa plurality of radial ports ,com-

.municating Withfsaid recesszandadapted toxregisiter with said transversefpassage'When saidsmall piston is .in certain-position iwithinsaid cylinder.

.11. A pressure :intensifier for a fluid system, comprising: va body vproviding a Alarge cylinder, connectableat one end thereof to a'source 4ofifluid pressure; smaller cylinders at either axial fendfof "saidlarge cylinden'the outlet of one ofzsaid smalllsmaller cylinder'to increase pressure in 'saidrsystern when said pistons are movedin 'one direction and said Vother 'smaller piston'being movable in `said othersmallerfcylinder Vand normally forced in a direction to urge said pistons inzan opposite direction.

l12. A wpressure intensiier .for a iluid system, comprising: a Vbody providing a .large cylinder, connectable 'at 'one end thereof to a source of fluid pressure; smaller 'cylinders 'at :either 'axial endof said large cylinder, the 4outlet of one of said smaller cylinders being vconnectable Lto rsaid 'fluid system, the inlet of the other 'smaller cylinder being connectable to said source cf fluid pressure; a large piston reciprocable in fsaid large cylinder; 'a piston rod connectedto said'largepiston 'and projecting axially on both sides thereof, said piston rod having its one end adapted for use ras a small piston andhaving its other end formed to provide a piston rod for another "small piston, said one end of saidpiston frodbeing movable Within said one smaller cylinder to increase Ypressure'in said system when said pistons aremoved in one direction, `said other small pistonbeing movable Within 'said other smaller -cylinder Aand being normally urged to move'said pistons 'in lan opposite direction; and valve means comprising a recess extending inwardly from the Working `face of said one end of said piston rod, 'a plurality of radially disposed passages connecting #saidrecess with the peripheral surface of said piston rod, and passage means Within said body communicating with said source of'luid'pressure and 4said radially disposed passages when said one end of said piston rod is in position lnormally urged thereto by said other smallerp'iston.

13. A press reintensii'ler for a iluid system, comprising: a vbody providing a'large cylinder, Vconnectable at one end thereof to a source of -iiuid pressure; 'smaller cylinders-fat either axial endfo said large cylinder, the outlet of one of said smaller cylinders being connectable to said system, the other smaller cylinder being connectable to said source of uid pressure; a large piston reciprocable in said large cylinder; smaller pistons on opposite sides of said large piston and connected thereto for movement therewith, one of said smaller pistons being movable within said one smaller cylinder to increase pressure in said system when said pistons are moved in one direction, said other smaller piston being movable within said other smaller cylinder and being normally fluid-pressure biased to urge said pistons in an opposite direction; and valve means carried in part by said one smaller piston and in part by said body for establishing communication between said one smaller cylinder and said source of uid pressure when said one smaller piston is in position normally urged thereto by said other smaller piston.

14. A pressure intensifier comprising unequal pistons working in respective cylinders, the outlet of the smaller cylinder being connectable to a fluid system; means for normally urging said pistons to a retracted relation with respect to said cylinders, valve means in part carried by said smaller piston and in part carried by said small cylinder, said valve means being in open relation when said small piston is in retracted relation; first control valve means for admitting uid from a source under pressure through said valve means to said system; second control valve means for admitting iluid from said source to the large cylinder for eiecting movement of said pistons; said valve means closing when said small piston is moved from its retracted position, thereby in terrupting communication between said source 10 and said system; rst time delay means for e1- fecting opening operation of said second control valve means a predetermined time after said system has been in communication with said source; and second time delay means for effecting closing operation of said iirst control valve means and said second control valve means a predetermined time after said large cylinder.r has been in communication with said source.

NATHAN CHARLES HUNT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 715,598 Phillipp Dec. 9, 1902 777,008 Deries Dec. 6, 1904 1,865,561 Furgason July 5, 1932 2,032,185 Sciaky Feb. 25, 1936 2,058,377 Francis Oct. 20, 1936 2,075,235 Sciaky Mar. 30, 1937 2,126,490 Martin Aug. 9, 1938 2,231,680 Pfauser Feb. 11, 1941 2,289,043 Rockwell July 7, 1942 2,324,149 Gray July 13, 1943 2,334,841 Raiche Nov. 23, 1943 2,349,846 Corin May 30, 1944 2,403,912 Doll July 16, 1946 2,446,657 McLeod Aug. 10, 1948 FOREIGN PATENTS Number Country Date 26,933 France Dec. 6, 1923 (Addition to No.,539,14i