US2822670A - Perforated caisson jack assembly - Google Patents

Description

G. E. SUDEROW PERFORATED CAISSON JACKASSEMBLY Feb. 11, 1958 5 sheets-sheet 1' Filed Sept. -2, 1953 Feb. 11, 1958 G. E. suDERow v2,822,670

PERFORATED cAIssoN JACK ASSEMBLY v BYZ/ ATTORNEYS.

Feb. 11, 1958 Y 3.. E. sUDERow 2,822,676

PERFORATED cAIssoN'JAcK ASSEMBLY Filed Sept. 2, 1953 3 Sheets-Sheet 3 o r l 25 Fw 23 .f @v1 5% :Ff l\ ,16 67 El \38 I Il l f W15 21 q a HIV a4 l. 34 n 11 v as l 35 w/I////f//fU///l///// Z2 It 2 N .W IIIIIIHH MW eorgQEfSfudeov,

TTORNEYS PERFORATED CAISSON `ACK ASSEMBLY George E. Suderow, New York, N. Y., assig'nor to DeLong Corporation, a corporation of Delaware Application September 2, 1953, Serial No. 378,103

11 Claims. (Cl. (S1-46.5)

The present invention relates to an improved jack assembly for raising or lowering a supporting leg relative to a base or platform structure. vention relates to improvements in a jack assembly of the type disclosed in the patent to Pointer 2,775,869.

An important object consists in associating with a base such as the deck of a barge or the like, and a tubular member such as a caisson, an improved jack assembly including vertically spaced upper and lower concentric axially disposed gripper rings of such size and diameter as to loosely embrace the tubular member. Positioned between the rings are circumferentially disposed raising and lowering means for axially displacing the rings relative to each other. Associated with the r'ings are locking means for releasably connecting the tubular member to the base.

A further object consists in mounting a jack assembly von the deck of a barge or the like, by circumferentially fspaced tie rods, which extend through the upper and lower gripper rings so as to allow the rings to be movable relative thereto and which also operatively connect the upper Vring to the barge. Each of the tie rods has connected vthereto an axially adjustable locking or retaining member which when the barge is elevated to the desired height on the caisson, is arranged to engage the lower gripper ring so as to relieve the lifting jacks of the load.

Other objects and advantages of the invention will become apparent from the following description when taken in conjunction with the accompanying claims and drawings.

Referring to the drawings in which is shown a preferred kembodiment of the invention:

Fig. l is a sectional view taken substantially along the line 1 1 of Figure 3.

Fig. 2 is a detailed sectional plan view taken substantially along the line 2-2 of Figure 3.

Fig. 3 is a sectional view taken substantially along the line 3`3 of Figure 1.

Fig. 4 is a view similar to Figure 3 but showing the parts in diierent operating positions, and

Fig. 5 is a sectional view taken substantially along the line 5--5 of Fig. l.

Fig. 6 is a perspective view of the casing assembly.

Referring to the drawings, the improved jack assembly, which is generally indicated vby the numeral 10 (Fig. 6), is shown for the purpose of illustration, associated with a base or platform structure in the form ofthe deck 11 of the oating `drilling barge 12. The deck may be provided with one or more vertical openings 13, through each of which extends a tubular supporting column, such as the caisson 14 which has a plurality of circumferentially symmetrically disposed longitudinal rows of 'uniformly spaced slots or bolt-receiving apertures 21. The jack assembly 10 comprises an upper gripper ring or annular member 15 and a lower concentric ring 16 which are of such diameters as to loosely receive and embrace the caissons 14. Each ofthe rings 15 and 16 is preferably formed with a horizontal portion or ange 17 'and an More particularly, this in? l2,822,670 Patented Feb. A11, Y195,48

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angularly disposed collar or4 vertical flange 18, that ex- Y tend in opposite directions from the rings.

Each 'of vthe collars 18 has circumferentially spaced holes 19 (Figure 4), in which are mounted reciprocating locking pin's or bolts 20, which are arranged to register and extend into the slots or apertures 21 formed in the wall of the caisson 14. It will be seen that when the vpins 20 of the rings 15 or 16 extend into suchv slots 21, the corresponding ring is firmly locked to the caisson 14 against relative movement therebetween longitudinally of the caisson. In thisconnection, it is pointed out that although the caisson or supporting column 14 has been shown as being provided with bolt-receiving apertures which extend completely through the wall of the supporting column, it will be realized that other meanswhich arethe full equivalent of such aperturesmay be provided on the column for cooperation with the pins 20 to prevent movement of either of the rings of the jack assembly longitudinally of the column. Itis only essential that the interengaging surfaces between the pins and the supporting column extend substantially transversely of ythe latter so that Von the irnposition of loads on the pins longitudinallyrof the column, there will be no camming action between such lsurfaces that will `be effective to urge displacement of the' vpins transversely of the supporting column.v As shown, each of the reciprocating pins 20 is connectedto a-.piston rod 22 of a double-action fluid pressure motor 23 so vas 'to be operated by any suitable hydraulic or air pressure means from a main source of supply through the'ilexible inlet and exhaust tubes 24 and 2S. While each of'the rings is shown provided with three of the locking-pins' 20, circumferentially spacedthereon, it will be Inaiifest that any number may be employed, so as to insure the uniform locking of the caissonj14 to the jack assemblyvdulringrthe operation of the device.

vPositioned between upper ring 15 Aandithe lower ring 16 and circumferentially disposed, relative there-tmy are spaced lifting cylinders 26 in each of which-'is mounted a reciprocating piston 273 (Figure 4) thatfis` securedto the undersideof the ange 17 of the* upper ring -15sovas to raise or elevate' thesa'me. Fluid'such as oil, air or steam is introduced under pressure, in to each of the cylinders 26 beneath the pistons 2f7 ythrough Vaninlet 28 from a valve housing 29 that communicates with` ythe source oflluid through a pipe 3l?. As shown, a valve 31 is associated with cach ofthe housings 29 so as to provide auxiliary'manually operable meansfor controlling the ilow ofthe fluid underfpre'ssureto the cylinderv26. Y :The upper ends of each of the `cylinders 26 is connected't'o atmosphere through the outlet'32. Y j

The deck 11 adjacent each of the openings 13 is formed with circumferentially spaced apertures vorv holes. (Figure 6) through which extend-the -tie rods ,or tension bolts' 34. Each of the rods .34 `has an enlarged head 3 5 at the upper end'thereof and extends throughvertical aligned recesses 36 in the flanges 157 Yof the upper and lower ring, and is o f suchl a length as to project lasubstanti'al distance above the upper ring 15'. Each ofthe rods 34 intermediate its ends` has a threaded portion 37 positioned above the-lowerring 16 4and arrangedto receive a polygon-al lshaped tool receiving nut 318,` fora purpose subsequently described. The lower lend preach of the rodsV 34 is also threaded -as at 39 and has,I de tacbf ably connected thereto a retaining nut 40 that'engagesthe underside of the deck 11 so as to limit the,upward movement of the bolt (Figure 5) .l

Between the upperl ringlS and the lowerring,1j6- are positioned spaced single-acting retracting cylinderswfll, each having a reciprocating piston y42 (Fig. 5) `terminating in a bifurcated lug 43 piv'otally connected at 44 to a lug 45 that extends upwardly from the low-er ring'16. The'uppei' en'd of each cylinder '41- is pivotally connected by a link 46 and a pin 47 to a depending lug 48 on the ring 15. Fluid from the main source of supply is conducted into one end of each of the retracting cylinders '41 through a pipe 49 (Fig. 5) in order to retract the pistons 42 into the cylinders. The' other end of each cylinder is connected to atmosphere through a pipe 50. The rings 15 and 16 may be provided with the circumferentially spaced guide members 51, each of which has an inclined face 52 positioned so as to guide the caisson 14 into proper position relative to the opening 13 when the parts are being assembled or installed.

In operation of the mechanism embodying this invention, the jack iassemblies and their associated parts are initially mounted on the deck 11 about the openings 13 and secured to the barge 12 by the tie rods 34. It will be seen that the lower ring 16 of each assembly will then rest on the deck about the openings 13. With a jack assembly 10 in this position, a caisson 14 is inserted, as by 'a crane, through the assembly, with such insertion being facilitated by the inclined faces 52 of the guide members S1, and through the opening or well 13 in the barge 12.

During such insertion, care is taken to align the rseveral vertical rows of openings 21 in the caisson with the corresponding pins or bolts 20 in the jack assembly 10. With thercaisson being held in such inserted position as by a crane (not shown) or the like, the cylinders 26 may be operated to lift the upper ring 15 until the upper pins 20 become aligned horizontally with a corresponding series of apertures 21 in the caisson. At this time the fluid motors 23 of the upper ring 15 are operated to extend its pins into the caisson apertures, to thereby lock the ring 15 to the caisson. The caisson will thereby be supported by the jack assembly 10 and, if desired, pressure can be relieved slowly from the lifting cylinders 26 so that the upper ring 15 will slowly descend, carrying the caisson 10 with it, until the pistons 27 `are completely retracted. Thereupon, pressure fluid to the cylinders 26 can be shut ot and the entire weight of the caisson will be borne by the upper ring 15 and transmitted through the cylinders 26 and the lower ring 16 to the deck 11 of the barge.

Desirably, in this final barge-supported position of the caisson, the lower end thereof does not project appreciably below the bottom of the barge 12 so that the latter can be floated to an erection site, as by being towed by a tug (not shown), with a minimum of towing resistance.

At an erection site, all of the caissons of vthe barge are moved downwardly into engagement with the marine bottom by the following sequence of operations of each iack assembly 10. In the event that the pins 20 of the lower rings 16 are not aligned with la series of apertures 21 in the caisson, the lifting cylinders 26 are operated to liftjthe caisson, by the pins 20 of the upper ring 15, until a series of apertures 21 in the caisson become so aligned with the pins 20 in the lower ring 16. At such time, the motors 23 of the lower ring 16 are operated to extend their pins 20 through the aligned apertures 21 in the caisson 14. Thereupon, the lifting cylinders 26 are operated to lower the upper ring 15 slightly to transfer the load of the caisson 14from the upper pins 20 to the lower pins 20, so that the upper pins 20 can be Withdrawn from engagement with their corresponding apertures in the caisson.

After such withdrawal of the upper pins, the cylinders 26 are operated to extend their piston rods 27 and lift the upper ring 15 lsubstantially the full stroke of the lifting cylinders until the upper pins 20 become aligned with a higher series of apertures 21 in the caisson 14, wherelupon the motors 23 of the upper ring 15 are operated to extend their pins 20 through such apertures. The cylinders 26 are continued to be operated to raise the upper ring 15 slightly to transfer the load of the caisson 14 from the lower pins 20 to the upper, so that such lower pins can be withdrawn from the caisson. Fluid pressure is then slowly relieved from the lifting cylinders 26 to slowly lower the upper ring 15, and thereby slowly lower the caisson 14 a distance equal to substantially the full retracting stroke of the cylinders. Thereupon, the pins 20 of the lower ring 16 'will become realigned with a higher series of apertures 21 in the caisson 14 andere inserted thereinto. The lifting cylinders then continue 'to lower the caisson 14 slightly until the load of the latter is transferred from the upper pins 20 yto the lower pins 20 so that the upper pins 20 can be retracted or withdrawn from the caisson.

The foregoing cycle of operations of the jack assembly 10 is repeated until the caisson is in engagement with the marine bottom. At that time the jack assembly 10 is operated in the following sequence of operations in order to raise the barge 12 on the caisson 14. With all the pins 2t) retracted, the lifting cylinders 26 are operated to lift the upper ring 1S a distance substantially equal to the full extension stroke of the cylinders 26 until the upper pins 20 become aligned with a series of 4apertures 21 in the caisson. The motors 23 of the upper ring 15 are then operated to insert their pins 20 into such apertures in the caisson 14. With the lower pins 20 being withdrawn from the caisson, the retracting cylinders 41 are operatedAto pull the lower ring 16 upward while fluid pressure is relieved from the lifting cylinders 26, until the latter cylinders are substantially -completely retracted and the lower pins 20 become realigned with a higher series of apertures 21 in the caisson 14. Thereupon, the pins of the lower rings 16 are inserted into such apertures to thereby support the lower ring 16 on the caisson.

The upper pins 2t) are then withdrawn from the caisson and the lifting cylinders 26 operated to raise the upper ring 15. Such raising of the upper ring 15 will move the latter into engagement with the heads 35 on the tie rods or bolts 34 so that the latter will pull the entire barge 12 upwardly with the upper ring 15, Near the end of such lifting stroke of the cylinders 26 the upper pins 20 will become realigned with a higher series of apertures 21 in the caisson 14, and at such time are inserted into such apertures. Fluid pressure is then relieved in the lifting cylinders 26 so that the load of the barge is transferred from the lower pins 20 to the upper pins 20. Thereupon, the lower pins 20 can be withdrawn from the caisson 14 and the retracting cylinders 41 operated to lift the lower ring 16 in order to reecycle the jack assembly for another lifting stroke in accordance with the foregoing sequence of operations.

After the barge has been raised a predetermined or desired distance on the caissons, it will be seen that the upper pins 20 may not necessarily become aligned with a series of apertures 21 in the caisson 14, because the last step through which the barge is lifted may not be equal to the full stroke of the cylinders 26, so that the barge cannot be supported on the upper pins. Furthermore, it may be desirable to shut off the source of uid pressure to the lcylinders 26 while the barge is in such elevated position. Accordingly, while the load of the barge is on the lower pins 20 of the jack assembly, the nuts 38 on the tie rods 34 can be screwed downwardly until they engage with the upper surface of the lower ring 16. Thereupon, relief of the fluid pressure in the cylinders 26 Vwill allow the barge to settle slightly until the load of the barge is taken by such nuts, instead of by the headed ends 35 of the rods 34.

Of course, in the event that the pins 20 of the upper ring 15 are aligned with a series of apertures 21 in the caisson 14 when the barge is raised to its desired height on the caisson, the upper pins 20 can be inserted into such apertures so that the load of the barge can be borne by the upper pins 20 and through the heads 35 on the bolts rather than by the nuts 38.

When drilling operations, or the like, have been completed at such a marine site and it is desired to move the barge to another marine site, the following sequence of operations is performed to lower the barge back down into the water and to pull up the caissons 14 out of engagement with the marine bottom so that the barge can be towed to another marine site'.

Assuming rst that the load of the barge is` being borne by Ythe lower pins 20 and the nuts 38, the lifting cylinders 26 are first operated to lift the upper ring 15 until the load of the barge is taken by the heads 35 of the tie rods 34. Thereupon, the nuts 38 are screwed upwardly on the tie rods 34 so as not to interferewith normal operation of the jack assembly 10. Fluid pressure is then slowly bled from the lifting cylinders 26 to thereby lower the upper ring 15, and consequently the barge, until the pistons 27 of the cylinders 26 are substantially completely retracted and the upper pins are aligned with a lower series of apertures 21 in the caisson and areinserted thereinto.

Making the alternative assumption, namely, that the weight of the barge in its erected position is being borne by the upper pins 20, the lower pins are retracted, and that thetluid pressure in the cylinders 26 is relieved, it will be seen that the cylinders 26 by their own weight drop downwardly to the extent permitted by the full extension of the retracting cylinders 41; Consequently, the ii'st step in the lowering of the barge from this assumed position will be to operate the retracting cylinders 41 until the lower pins 20 become aligned with a series of apertures in the caisson and are thereupon inserted thereinto. The lifting cylinders 26 are thereupon operated to lift the upper ring 15 slightly and also the barge, to transfer the load of the latter from the upper to the lower pins. After such transfer has been accomplished, the upper pins 20 are withdrawn from their engagement with the caisson, and uid pressure is slowly bled from the lifting cylinders 26, to thereby lower the upper ring 15 together with the barge a distance substantially equal to the full retraction stroke of the cylinders 26. At or near the end of such stroke, the upper pins 2,0 will become aligned with a lower series of apertures 21 in the caisson 14 yand are inserted thereinto. This position of the parts now corresponds to that of the parts at the end of the cycle described above with reference to the first assumptlon.

Thereafter, continued bleeding of fluid from the cylinder's 26 transfers the load of the barge from the lower pins 20 to the upper pins 20. The lower pins'are thereupon withdrawn from the caisson 14, and the cylinders 26 will again descend by their own weight, as governed by bleeding fluid from the retracting cylinders 41, until the lower pins become realigned with a lower series' of apertures in the caisson and are inserted thereinto. Fluid pressure is then again applied to the cylinders 26 to transfer the load of the barge from the upper'pins 20' to the lower pins 20. The upper pins are thereuponwithdrawn and the huid pressure slowly relieved from the cylinders 26 to lower the barge another step.

The 'foregoing sequence of operations is repeated until the barge becomes afloat. The following sequence of operations is then performed in order'to raise the caissons olf the marine bottom for towing of the entirev structure to another site of operations.

Assuming that the lower pins 20 are in engagement with the caisson 14 when the barge becomes aoat, the first step will be to continue to bleed fluid from the lifting cylinders 26 until the upper pins 20 become aligned with a lower series of apertures in the caisson 14 and are inserted thereinto. The retracting cylinders 41 are then operated to lift the lower ring slightly to transfer` its weight off of the lower pins 20, so that they can be withdrawn from the caisson 14. Thereupon, uid pressure isf slowly relieved from the retracting cylinders 41 to lower the lower ring 16 until it rests on the deck 11 of the barge. The upperpins 20 are then .withdrawn from the caisson 14, if need be iirst taking the Weight of the upper ring olf the upper pins by operation of the lifting cylinders, and iiuid pressure slowly relieved froni'the cylinders 26 to lower the upper ring 15 until the upper pins 20 become realigned with aA lower series ofv` apertures` 21 in the caisson 14. The' upper pins 2'0` are their inserted into such'apertures, and the cylinders l26'cpera`td to lift the upper ring 15 and consequently the'caiss'on 14. Near the end of the liftingy stroke of the"eyli`nde1"s 26', a lower series of apertures 21 inthe caisson 14` will become aligned with the lower pins 20, and such pins are inserted into such apertures. The upper pins 2'0 are then withdrawn from the caisson, while the lo'a'd thereon is borne by the pins of the lower ring 16, and fluid pressure bled from the cylinders 26 to-low'er the upper ring 15 in preparation for an'other'lifting stroke, on 'which the upper pins will be reinserted into the caisson and the lower pins withdrawn. The foregoing sequence of operations is continued in order to lift the caissons` 14 until their lower ends are substantially flush with the bottom of the barge. The weight ofthe caissons' then can' be borne by the lower pins and the supp-1y of fluidipressure to the jack assembly 10'shut` olf during towage of the assembly to another marine site.

It will be manifest that the size and number of gripping pins and bolts, lifting cylinders, tie rods, as well as the overall arrangement of the jack assembly may be varied to suit the particular use to which the device is` applied.

' Moreover, the jack may be with equal facility used to elevate or lower various types of bothfland and marine supports, members or columns as particular operating conditions may require. It is to be understood that the for-m of the invention shown is merely illustrative and that such changes may be made as come within'the purview of the following claims.

I claim: A'

1. In combination with a iioating barge having spaced openings in the deck thereof, caissons extending int'o' said openings and provided with vertically spaced apertures, a jack assembly for releasably connecting the barge tov each of the caissons and providing means for moving the caisson relative to the barge and for movingv thebarge rel,- ative to the caisson, said jack assembly including axially displaceab'le upper and lower rings through which the caissons extend, said rings being independently movable relative to each other, means connecting. the upper ring to said barge, means for moving the upper ring andk barge relative to the lower ring, meansfor moving the lower ring relative to the upper ring, circumferentially spaced bolts extending upwardly from the deck and' loosely throu-gh said rings, means on the lower end of each boli: engaging the underside of the deck for limiting the upward movement of the bolt, means on the upper ends of the bolts for limiting the upward movement of theupper ring, reciprocating .locking pins on each of: the rings and arranged to engage apertures in the caissons when moved into registration therewith, and means for actuating said pins, each of said caissons arranged to be moved by the jack assembly into xed engagement with the marine ground, and said barge when the caissons are in engage ment with the ground being operable by the jack assembly to be raised above the water.

2. In combination with a tloating barge having spaced v openings in the deck thereof, caissons extending into said opening-s and providedwith vertically spaced apertures, a jacky assembly for releasably connecting the barge to each of the caissons and providing means for moving-the caisson relative to the barge and for moving 'the' barge" relative to the caisson, said jack assembly including axially displaceable upper and lowerrings through which the caisson extends, said rings being independently movable relative to each other, circumferential'ly spaced lifting cyl-- inders between said rings, pistons movable in said cyl-V inders, each of said lifting cylinders being'mounted` on the: lower ring and having its piston connected to the upper ring, retracting cylinders between said 'rings and'y having pistons reciprocally mountedtherein, means connecting each' retracting cylinder to one Vo'f the rings; meanscon'i necting each retracting piston to the other; of said rings,

crcumferentiallyspaced bolts extending upwardly from the deck in the barge and loosely through said rings, meansvorn the lower endof each bolt engaging the underside of the deck for limiting the upward movement of the bolt, reciprocating locking pins mounted on each of the rings and arranged to engage apertures in the caissons when moved into registration therewith, means for supplying fluid pressure to said cylinders to selectively actuate the same, means for selectively actuating said pins, each of said caissons arranged to be moved by the jack assembly into fixed engagement with the marine ground, and said barge when the caissons are in engagement with the ground being operable by the jack assembly to be raised above the water.

3. In combination witha floating barge as called for in claim 2 in which each of the bolts is provided with means arranged to engage the lower ring for transferring the load on the bolts from the lifting cylinders directly to the lower ring.

4. In combination with a lioating barge as called for in claim 2 in which each bolt is provided with an intermediate threaded portion, a nut threaded on said portion above the lower ring and arranged to engage the same to transfer the Weight of the load on the bolts from the lifting cylinders directly to the lower ring.

5. In apparatus for erecting an over-Water platform, the combination comprising: an elongated leg for supporting a platform-like body, said leg having at least two longitudinal rows of pairs of oppositely-facing abutment surfaces spaced apart longitudinally of said leg and extending generally transversely thereof, said rows being arranged symmetrically about said leg; jacking mechanism operable on said leg for effecting relative movement between said leg and the body in either direction longitudinally of said leg, said mechanism including a pair of rigid members surrounding said leg and movable relative thereto and to each other longitudinally of said leg, a pair of locking elements spaced along the length of said sup porting member in alignment with each of said rows, each of said elements having a pair of oppositely-facing abutment surfaces complementary to each pair of surfaces of the corresponding row, one of said elements of each pair being mounted on one of said rigid members and the other of said elements of each pair on the other of said rigid members and both of said elements of each pair being mounted for independent linear reciprocating movement generally transversely of said leg to project and withdraw the corresponding element pair of surfaces into and out of overlapping relation with a pair of row surfaces, when aligned therewith, in order to substantially lock the corresponding rigid member to said leg against said relative movement in either direction therebetween or permit said relative movement, respectively, all of said abutment surfaces being substantially planar, disposed substantially normal to the length of said leg, and free of camming action effective on the imposition of a load longitudinally of said leg through a complementary pair of overlapped and mutually engaged abutment surfaces to urge a said element to withdraw its surfaces from a pair of row surfaces when overlapped therewith, and a plurality of reciprocating liuid motor means operatively connected to said rigid members for selectively effecting or restraining said relative movement therebetween in either direction, said motor means being arranged symmetrically about said leg and with respect to each of said elements and the connection of at least certain of said motor means with one of said members being disposed closely adjacent said elements thereon with less than 90 spacing, circumferentially of said one member, between each said connection and the nearest element in order to minimize bending stresses in said one member; and means mounting said mechanism to a platform-like body in order to operate the mechanism to lower said leg down 8 v i into engagement with a marine bottom, raise the bodyy and support it at least partially on said leg, lower the body back down' untilit is no longer supported on said leg, and pull said Vleg up out of engagement with the marine bottom for movement of the body, together with said leg and mechanism to another erection site, said one member, when said mechanism is being operated to raise or lower the body on said leg, being locked to the leg and the other member being unlocked therefrom, and said mounting means being connected to said other member and arranged symmetrically thereabout and with respect to each element thereon, said mounting means connections being disposed closely adjacent said other member elements to minimize bending stresses in said other member when the latter is locked to the leg and supporting the weight of the platform.

6. The structure defined in claim 5 in which each pair of surfaces of a row is defined by portions of the edges of an aperture and each pair of surfaces of an element is defined by portions of a locking bolt receivable in a said aperture when aligned therewith.

7. The structure defined in claim 5 including poweroperated means connected to each of the locking elements for selectively projecting or withdrawing the latter.

8. The structure defined in claim 5 in which the motor means are arranged to raise the said other member relative to the said one member by extension of said motor means when said one member is locked to and said other member is unlocked from the leg.

9. The structure defined in claim 5 in which the extent of the element abutment surfaces in the direction of their movement and engageable with the leg abutment surfaces is less than the transverse dimension of the leg in' said directions, whereby the extent of locking and unlock-j ing movements of the elements is less than said leg transverse dimension.

10. The structure defined in claim 5 in which the means mounting the mechanism includes a tension element secured to the other rigid member and securable to the body for lifting the latter when said other rigid member is unlocked from said leg, the one rigid member is locked thereto, andthe motor means are operated to effect upward movement of said other rigid member relative to the other, and including relatively-vertically-adjustable, interengageable abutment means on said tension element and on said one rigid member to support the body on said one rigid member independently of said motor means when the latter are rendered ineffective.

1l. The structure defined in claim 5 including an adjustable disengageable mechanical supporting connection extending between the said one member and the body for supporting the latter on the leg independently of said motor means, whereby after elevation of the body on the leg by operation of said motor means to an elevation whereat the element pair of surfaces on the other mem ber are not in alignment with a pair of row surfaces on the leg so that said other member cannot be locked to said leg, said mechanical connection can be engaged and the pressure in said motor means can be released.

References Cited in the tile of this patent UNITED STATES PATENTS OTHER REFERENCES Pages 44-45 of Engineering News Record of May 29, 1952.

Samuelson Mar. l1, 1952 U. S. DEPRMENT OF COMMERCE PATENT OFFICE CETIFICATE OF CORRECTION Patent Noo 2,822,670 February ll, 1958 George E. Suderow It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let sers Patent should read as corrected below.

Column 8, list of references cited, after line 69, add the following:

FOREIGN PATENTS LOUQ'YA France ===Jun 25, 1952 Signed and sealed this 29th Clay of April 1958.

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Comnssioner of Patents Attesting Officer

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