US2540578A

US2540578A - Hydraulic internal locking jack

Info

Publication number: US2540578A
Application number: US618894A
Authority: US
Inventors: Stanley R Hall; Jelter Earl
Original assignee: Lockheed Aircraft Corp
Current assignee: Lockheed Corp
Priority date: 1945-09-27
Filing date: 1945-09-27
Publication date: 1951-02-06
Anticipated expiration: 1968-02-06

Description

Feb. 6, 1951 s. R. HALL r- -rAL HYDRAULIC INTERNAL LOCKING JACK 2 Sheets-Sheet 1 Filed Sept. 2'7, 1945 INVENTORS STANLEY R. HALL & EARL JE TER Agent Feb. 6, 1951 s. R. HALL ETAL HYDRAULIC INTERNAL LOCKING JACK 2 Sheets-Sheet 2 Filed Sept. 27, 1945 INVENTORJ STANLEY R. HALL & EARL JELTER Age nt Ulla/jig Patented Feh. 6,

UNITED STATES PATENT QFFICE 2,540,578 HYDRAULIC INTERNAL LOCKING JACK Stanley R. Hall, Burbank, and Earl Jelter, glen; dale, -Ca'lif.; assignors to Lockheed Aircraft Corporation,-Bi1rbank, Calif. Application September 27, 1945 Serial No. 61,84

Claims. 1

This invention relatesto jacks, and relates more particularly to hydraulic jacks; that is,

jacks operated by mild pressure.

Hydraulic jacks are employed extensively in many industries, being used in the aircraft industry, in railroading, in the automotive industry, etc. There is one feature of such jacks that has heretofore been the cause of considerable difficulty. In the event of fluid pressure leakage or failure with the jack rain in an extended position under load, the ram will retract with possibly serious consequences. This difficulty is also encountered in hydraulic rams and hoists employed to elevate automotive vehicles, etc. To insure against such accidental lowering of hydraulic jacks, it has been theprac'tice to thread the outer part of the ramand to provide a nut thereon which may be adjusted against the upper end of the jack barrel to retain the ram in the elevated position. .In other instances a pin is passed through one of several openings in the ram to engage the jack barrel and thus prevent collapsing of thejack. The thread, orthe openings in the ram, materially weaken the ram against lateral loading and carry moisture and dirt into the jack cylinder upon lowering of the ram so that the hydraulic fluid soon becomes contaminated. e

Other factors which have placed limitations upon the use of hydraulic jacks are the extensive cost of accurately machining both the internal surface of the cylinder and the external surface of the piston or ram, and the difficulty of main taining a fluid-tight seal around the ram in situations where the jack is subjected to lateral loading. I

It is an object of this invention to provide a hydraulic jack incorporating locking means for positively preventing accidental lowering or retraction of the ram in the event of fluid pressure failure or leakage, which locking me'ans isentirely contained. within the jack cylinder and remains therein throughout the full stroke of the jack. There are no elements of the locking means which extend from the cylinder to carry water or 'matically lock the ram in any selected or required position. It is unnecessary for the on r- A5 dirt back through the cylinder upon retraction of ator to thread a nut into position or to insert a safety pin. The only requirement is that the lock control lever be set in the locking position when the jackis put into operation.

Anotherobje'ct of the invention is to provide a jack of the character referred to in which the locking means cannot be accidentally released while the jack remains under load, and yet may be easily and quickly released when it is desired tolo'wer the ram and its load. Theloading 0f the jack resists manual operation of the control lever so long-as the jack remains under load, but when it is desired to lower the load, the introduction of a small amount of fluid under pressure frees the lock mechanifsm so that the lever may be readily moved to the released position with a minimum of effort. The introduction of the fluid pressure to the cylinder to free thelock mechanism for release further serves to insure that the cylinder contains sufficient fluid to prevent a sudden forceful retraction of the ram under load.

Another object of the invention is to provide a hydraulic jack in which it is unnecessary to grind, hone or specially finish the internal surface .of the cylinder 'toreceive a sealed piston. The

special accurate finishing of the jack cylinder has been a required item of cost in prior hydraulic jacks. In the "jack of the presentinvention, the

internal surface of the cylinder does not require careful or accurate machining, and the piston or ram carries no packing but merely moves through a suitable sealing means at the upper end of the cylinder. The positioning of the packing or sealing means at the upper end of the cylinder is especially advantageous because it is affected to a minimum extent by lateral loading and minor lateral displacement of the ram or piston with respect to the cylinder. Furthermore, the sealing means and wiping meansat the upper .end of the cylinder prevent the entranee of water into the cylinder.

Afu-rther .objectof the invention. is to provide .a locking hydraulic jack of the character above Figure 3 is an enlarged vertical detailed sectional view of the jack unit removed from the tripod;

Figure 4 is a transverse detailed sectional view taken as indicated by line 45 on Figure 3;

Figure 5 is a bottom view of the jack unit;

Figure 6 is an enlarged fragmentary sectional view taken substantially as indicated by line 6% on Figure 5;

Figure 7 is an enlarged bottom view of the release thrust Washer of the lock mechanism;

Figure 8 is a fragmentary sectional View of the ram limit mechanism showing the pawl carrier in the fully extended position; and

Figure 9 is a fragmentary transverse sectional View of the ram guiding means.

The jack mechanism of this invention is adapted for embodiment in hydraulic jacks, hoists and the like, for use in the various industries, and is capable of modification to suit it for use in devices of diflerent capacities and types. In the following description we will describe a typical form of the invention as embodied in a tripod jack useful in the aviation industry, it

being understood that this is not to be construed as limiting either the scope or applicability of the invention.

In Figure 1 we have shown a tripod T for operatively supporting the jack unit U. This tripod includes three inclined legs i0 secured at their upper ends in a central collar or carrier member H. Connecting braces l2 extend between the legs iii adjacent their lower ends and ground-engaging pads iii are secured to the lower ends of the legs by adjustable universal joints i l. Retractable casters are carried by brace members i3 extending inwardly from the lower parts of the legs it. We have shown a manually operable pump P supported in the lower portion of the tripod T for supplying the operative fluid pressure to the jack unit U. The conventional pump P illustrated has the usual operating levers lt-El and a release or return valve operated by a handle 8! to allow the return of the fluid to the pump or its reservoir when the load is to be lowered. It is to be understood that the jack means of the invention may be employed in connection with any other suitable source of actuating fluid pressure.

The cylinder ll of the jack unit U is provided at its upper end with a flanged head [8, (see Figure 3) by means of which the unit may be supported in the tripod T or other carrying structure. In Figure l iere is shown an extension for mounting the unit U in an elevated position on the tripod. This extension includes a lower ring l9 engaged on the carrier member II, and upper ring 2% and rods 2! extending between the two rings. The above mentioned head I8 of the jack cylinder i'l is supported in the upper ring to be some distance above the normal top of the tripod. In Figure 2 we have shown the flanged head 28 directly engaged on the carrier member H of the tripod. In this case any suitable form of fixture or extension 22 may be provided on the upper end of the jack piston or ram 23. It may be preferred to provide the tIiJDOd T with a collar 2% for encircling the lower portion of the jack cylinder H. The collar 24 is carried by suitable members 25 which extend inwardly from the legs ii. The lower supporting collar 25 assists in centering and steadying the jack unit U in the tripod.

The jack unit U of the invention includes the aforementioned cylinder I? and ram 23, and further includes means 26 for sealing the cylinder and ram, and a releasable locking means 21 for preventing accidental retraction of the ram.

It is a feature of the invention that the cylinder I'i may be a simple tubular member requiring a minimum of machining. A base or head 28 is suitably fixed and sealed in the lower end of the cylinder as by welding. The piston or ram 23 enters the upper end of the cylinder, and the cylinder and ram elements may be of approximately the same length. In accordance with'the invention, the outside diameter of the ram 23 is appreciably smaller than the inside diameter of the cylinder, and the only required means for sealing about the ram is located in the head i8 of the cylinder. This sealing means 25 may be in the nature of Chevron type packing engaged between a shoulder in the cylinder I! and a ring 3i secured to the flanged head 58 of the cylinder. A wiping ring 32 is recessed in the ring 3! to wipe the ram as it enters the cylinder and thus prevent the entrance of water and other foreign matter into the cylinder.

It will be observed that with the construction just described, it is unnecessary to accurately machine or finish the internal surface of the cylinder I1. However, the external surface of the ram 23 is machined or finished to properly cooperate with the sealing means 25. It is preferred to provide the ram with guide bushings 33 of brass, or the like, for cooperating with the cylinder ii. The guide bushings 33 are spaced apart on the lower portion of the ram 23 and are secured thereto by screws, or the like.

As will later become apparent, it is desirable to prevent rotation or angular displacement of the ram 23 with respect to the cylinder !1. The means for preventing such relative movement may take the form of a key 34 of square or rectangular transverse cross section engaged with a fiat or groove in the internal surface of the cylinder. The key 3 3 may be secured to the cylinder by spaced screws 3%, or the equivalent. The above mentioned guide bushings 33 of the ram 23 have gaps or openings 35 slidably receiving the key 34 and this cooperation prevents rota-.

tion of the ram 23 in the cylinder Ill. The key 34 may extend throughout substantially the entire length of the cylinder IT.

The ram 23 may be a simple tubular part closed at its upper end by a cap 56. A port normally closed by a screw or plug 3? is provided in the cap or head 36 to permit the bleeding of air from the interior of the ram. A similar port 38 is pro vided in the upper wall of the cylinder I l to communicate with the annular space between the cylinder I i and the ram 23. The port 33 may be employed to bleed air from the cylinder l1, and if desired, may be equipped with a pressure responsive safety valve. In the arrangement illustrated, the port 33 is normally closed by a screw or plug. A pressure and return line L eX- tends from the pump P. A line 39 communicates with a port it in the lower cylinder head 28 and a similar line leads from a second port 42 in said head. The lines 39 and ill are connected with the pump line L by a valve means to be later described. It will be observed that the cylinder and piston assembly of the jack unit U is of simple inexpensive construction.

The automatic locking means 27 is an important feature of the invention. The means 21 includes a rod or post 53 carried by the cylinder head 28 and extending vertically through the cylinder I i to have its upper end adjacent to thehead 36 of theta a- BE fli u l fi The 1 6st 43 issu 31 'rotatiohbihgp I U H a reduced stern '44 WE h rotatably passes through a semen seem; in the. head .221. The bearin er washennesns for, rot'atably supporting the post "43 on the head 28 willb'e later described; A are lever or cbht'rol 1evr 145 i secureqtotne lwer end (if the stem to be any aceessibre to the operator. The lever 45 is m "'b e through abiiut 90 to turn rh'eposjt et e its joperajitive and released pfisitiofis, paek m gland at is providedihjthe cy iiidi'. u zs rd the sjterht i, Th'p'ostfi h "of what anaem a; et t et' absences-r; 'i1lu'strated, ft r I t v these teeth In orme or; unmet sides of the post. '.'1he t" th '41 rupreaiy uirasgi em er of the post. As best figuratidn, and the co'r'res I 7 two series occupy co'rr spon'di g rizon't'al planes. The two "diametrically oppos te sides of the Ipost 43 which ar devoid of the teeth 11 are v preferably machined to present flat vertital surfaces. 1

The locking means 21 further includes a pa t1 assembly ashamed with the piston for rani 23 and cooperating'withthe teeth 4'! of the' p'ost'fl. This assembly comprises a 'pair 'of piawls 68 are a cageror the pa ls. The ,cagejhclhds and lower disc like mates '49 and secured in the lower portion of the tubular ram 23 by screws, or the like. Re se orcylindricalopenings 'st in the plates 4'9 and 5!) receivjeit he at sided po's't'43 in a manner to allow for the f ree circulation "of fluid into and out of the 'hbllow'ram 213. Two pairs of spaced vertical plates BjlfeXt'endbetween and are secured to the horizontal "plates!!! and 50 as by welding. As best shown inFi'gure 4, the plates 5| lie in parallel planeswhich'afe tangent to a circle concentric with the longitudinal axis of the jack. A vertical plate or backing member 52 extends between, and is secured to, the plates 5! of each pair of plates adjacent the 'wall of '5 the ram 23. It will be o bserved that the cage just described 'is fixed to the ram 23 totravel therewith.

The pawls 48 of the locking'meahs 21' are blocklike elements carried in the above describedcage to cooperate with the teeth of the post' 43. As illustrated in'Figuresfian'd "4, therfe are two opposing pawls, each having fiat vertical sides guided by the p1ates'5l and la flathori'zfintal lower surface riding on the plate '50. The inner or 'active sides of the pawls'48 havelser'rations 'or't'e'e'th 53 for engaging with the'te'th 41. Where the ratchet teeth 4'! are horizontal' as shown inthe drawings, the same teeth 53 "are cylindrically curved. and horizontal, and to have horizontal lower faces for cooperating with the upper faces ofth'e'teeth '41, and downwardly and inwardly inclined upper'faces foren'ga'girig with .Hthe lowersurf acs Qifthe 'Qte'ei h'ffl. As seen in 'Fig'iire "3, the teeth 41 "and aware 'cohplmeh'taiy aha-see 6 id have full mating enga ement. The teeth '53 are adapted toslide or ratchet past the teeth 41 when therai'n 23 moves upwardly, but lock with the teeth 41 to positively prevent downward movement of the ram. The upper cage plate 49 has downwardly and outwardlyinclined surfaces 56, and the tops of the pawls 48 have correspondingly sloping faces which cooperate with the surfaces 54 to urge the pawls inwardly when load is imposed on the pawl assembly. Spring means are provided to urge the pawls 38 into engagement with the teeth '4! of the post 43. Sets of spaced helical springs 55 are arranged under compression between the member 52 and the rear faces of the 'pawls to yieldingly urge the pawls inwardly. v V

The cylindrical curvature of the

teeth

41 and 53 allows the post 43 to be turned between the position where its teeth 41 are engaged by the pawl teeth '53 and the position where its flat faces oppose the pawls. The first named position of posted is the locking position where the pawls {l8 serve toprevent downward or retrograde movement of the ram and the second named position is the freleased position where the ram 23-is free to travel with respect to the cylinder l1 and post 43.

The invention includes means whereby the introduotion of fluid pressure into the cylinder Fl frees the post 43 for easy manual turning between the locking position and the released 'position, even though the jack may be under a heavy load. This means includes a bearing washer 5"! secured to a shoulder on the post 43 at the upper end of the stem 'M and'a bearing washer 58 engaged between the washer 51 and the upper face of the cylinder head 28.

The washer 5! is preferably of steel while the washer 58 is preferably of hard brass, or the like.

The above described port 4! which is of a smaller capacity than the port 52, discharges into the cylinder I! directly under the washer 58.

washer '58 is recessed or counterbored at this The point to allow the fluid to reach the stem at which "passes through the washer with some tolerance.

The lower face of the bearing Washer 57 has a "pattern of channels 59 shown in Figure 7, which allows thisiiuid under pressure to enter between the engaging faces of the two

washers

57 and 58. Assuming the jack to be under load, the sudden introduction of fluid pressure to the port Q9 results in the delivery of fluid pressure to the channels 59 so that a film of fluid is provided between the faces of the washers. This film of liquid ineiiect floats the post 43 "so that'it may be easily turnedto the released position. The

introduction of fluid under substantial pressure between the faces of the washers 5i and '52 raises the post is "to 're-establish lubricantbe'twe'en the washers and thus free the post for easy manual turning. In this connection, it is to be observed post l3, even though the jack is under a heavy load. it is to be un'cle'rstoodthatfthe construction and relation of the lever 'i5ari'd'the cylinder head 28 are suchthat the post is free for limited vertical movement so that the introduction of fluid under 'pressureto the cylinder il -frees the post as just described, and the introductionof jfiu id f or 'rhepurpose of operating'the jack is not unduly restricted.

Means "is provided "to assure diversion of the the port fluid pressure to the port 40 and thus facilitate easy turning of the post 43 as above described, while allowing the free rapid discharge of fluid from the cylinder ll when the jack is to be retracted. The above mentioned

lines

39 and 4|, leading from the ports it and &2, respectively, extend to a check valve which is at the end of the pump line L. The check valve has a through port 56 leading directly from the line L to the line 39 of the port at. A second port B of the check valve extends from the through port 60 to the terminal of line ii. A spring-urged ball 62 is arranged in the port 5! to cooperate with a seat therein and prevents pump pressure from flowing into the line ii and port :32. Accordingly, fluid pressure from the pump P is obliged to travel to However, upon release of the lock means 23 and retraction of the rain 23 the fluid pressure in the cylinder ii unseats the valve 62, and the fluid from the cylinder returns through the larger port :2 and line ii to the pump line L.

The invention includes a safety means for preventing over-travel of the ram 23. This safety or limit means includes a valve body 65 on the lower side of the cylinder head 28 and a line 5 extending from this body to the return side or reservoir of the pump P. The passage 65 of the valve body 65 contains ball El seating inwardly against a seat therein to normally prevent the outward flow fluid from the cylinder. A spring 68 is engaged between the ball 8'. and a guide nut 63 in the passage to urge the ball to the closed position. Ports E9 in the nut 58 maintain the passage in communication with the cylinder H. A limit rod it is secured to the ball El and extends upwardly through the nut 68 into the cylinder ii. We have shown the rod iii connected to the ball "Ti by a ball or universal joint so that the bail El is free to center itself on the seat. The rod iii slidably passes through openings ii in the cage plates 353 and 59, and is provided at its upper end with a nut 12. The nut 12 is located adjacent the upper end of the cylinder ii. In the event that the ram 23 is projected an excessive distance, that is, beyond the intended limit of its upward movement, the plate 49 engages the nut 32 lifts the rod iii to raise the ball 6? from its seat. This allows fluid under pressure to return from the cylinder i! to the pump or pump reservoir, and if the pump is further operated, the pumped fluid is merely bypassed through the passage and line 73 back to the pump reservoir. Upon lowering of the ram 23, the spring 63 recloses the limit valve 61 to condition the jack for further operation.

In describing the operation of the jack, it will be assumed that the pump P and the jack unit U have previously been primed and conditioned for operation. When it is desired to operate the jack to elevate a load, the lever 45 is swung to the lock position so that the teeth d7 of the post 43 are brought into engagement with the pawl teeth 53. The pump P is then operated to supply fluid under pressure to the lower end of the cylinder i! through the port it as above described. The introduction of this fluid displaces or forces the ram 23 upwardly and elevates the load. As the ram moves upwardly the teeth of the pawls 48 ratchet over the teeth il. When the desired height is reached, pump operation is terminated. The pawl teeth engaged with the teeth 41 positively prevent downward movement of the ram 23 and its load, even in the event of subsequent fluid pressure failure or leakage. Thus the lock means 21 automatically assures retention ,of the ram and its load in the elevated position. The lock means 21 also serves to prevent, sudden retraction of the load in the event of fluid pressure failure during operation of the pump and raising of the ram.

When it is desired to lower the ram 23 and its load, the pump P is put into operation for a short time, as by giving its operating lever a few strokes, to supply fluid pressure to the cylinder I! through the port 43. As above described, this fluid pressure is directed in such a manner as to provide a film of liquid between the washers 5'! and 5B. This renders manual turning of the post 43 easy. The operation of the pump P for a short period also assures the provision of fluid in the cylinder ['7 to replace any fluid that may have leaked out, thus avoiding the possibility that the ram 23 and its load may drop suddenly when the lock means 21 is released. Following or during the momentary operation of the pump P, the lever 45 is turned to the released position to move the teeth 47 out of engagement with the pawl teeth 53 and the handle 8| is operated to open the release or return valve of the pump P. This allows the ram 23 and its load to move downwardly and displace the fluid from the cylinder ll. The fluid is displaced through the port 42 and past the check valve E2 as above described, to return to the pump or its reservoir.

It will be seen that we have provided a simple dependable hydraulic jack embodying a lock means which is entirely contained within the jack cylinder to be permanently bathed in hydraulic fluid. There are no exposed lock parts subject to injury or maladjustment, and no lock parts which carr foreign matter into the jack cylinder. The lock means 2'! is simple and easy to operate, and is positive in its action. The control lever 25 of the lock means is conveniently located, and it is unnecessary for the operator to climb or reach a lock means at the top of the jack cylinder as he is obliged to do in conventional jacks.

Having described only a typical preferred embodiment of our invention, we do not wish to be limited to the specific details herein set forth, but wish to reserve to ourselves any features or modifications that ma fall within the scope of the following claims.

We claim:

1. In a hydraulic jack, or the like, two elements, one a cylinder, the other a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to cause one element to be moved to any one of a plurality of projected positions with respect to the other element, a member on one element having ratchet teeth, a pawl on the other element adapted to ratchet over said teeth during such projection of said projected eiement and cooperable with said teeth to prevent the return of projected element from its projected position, said member and pawl being arranged and related for relative turning movement, and means for effecting such relative turning movement to disengage said teeth and pawl and thereby allow the return of said projected element.

2. In a hydraulic jack, or the like, two elements, one a cylinder, the other a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to cause one element to be moved to any one of a plurality of projected positions with respect to the other element, a turnable member extending longitudinally of one element and having ratchet teeth,

a pawl on the other element cooperable with said teeth to prevent the return of said projected element from its projected position, and means for turning said member to disengage its teeth from the pawl and al.0w the return of said projected element.

3. A hydraulic jack, or like device, including a cylinder, a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to project the ram therefrom, a post turnably carried by the cylinder to extend longitudinally therein, ratchet teeth on the post, a pawl carried by the ram for cooperating with the teeth to retain the ram in a projected position, and means for turning the post to disengage its teeth from said pawl.

4. A hydraulic ack, or like device, including a cylinder, a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to project the ram therefrom, a post turnably carried by the cylinder to extend longitudinally therein, ratchet teeth on the post, a cage on the ram, a pawl having teeth and carried in the cage in a manner to have its teeth engage the teeth of the post to retain the ram in a projected position, and manual means for turning the post between a position where its teeth are engageable by the teeth of the pawl and a position where its teeth are clear of the pawl teeth.

5. A hydraulic jack, or like device, including a cylinder, a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to project the ram therefrom, a post turnably carried by the cylinder to extend longi tudinally therein, ratchet teeth on the post, a cage on the ram, a spring urged pawl in the cage for cooperating with the teeth of the post to prevent retraction of the ram from a projected position, the pawl being adapted to ratchet over the teeth of the post during projection of the ram, and means for turning the post between a position where its teeth cooperate with the pawl and a position where its teeth are clear of the pawl.

6. A hydraulic jack or like device comprising a cylinder, a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to project the ram therefrom including port means communicating with the cylinder, a longitudinally extending turnable post in the cylinder, ratchet teeth on the post, a pawl carried by the ram engageable with the teeth to retain the ram in a projected position, means for manually turning the post to release its teeth from the pawl and allow retraction of the ram, and means for facilitating such turning of the post when the jack is under load including two thrust bearing members having engaging faces which support the post for rotation, and means for directing fluid under pressure from said port means between said surfaces to provide a film therebetween.

'7. A hydraulic jack or like device comprising a cylinder, a ram operable in the cylinder, means for introducing fluid under pressure into the cylinder to project the ram therefrom including port means communicating with the cylinder, a longitudinally extending turnable post in the cylinder, ratchet teeth on the post, a pawl carried by the ram engageable with the teeth to retain the ram in a projected position, means for manually turning the post to release its teeth from the pawl and allow retraction of the ram,

and means for facilitating such turning of the post when the jack is under load including two thrust bearing members having engaging faces which support the post for rotation, at least one of said faces having fluid channels, and means for directing fluid under pressure from said port means to said channels to provide a lubricating film of fluid between said faces.

8. A hydraulic jack comprising a cylinder, head means on one end of the cylinder, a ram operable in the cylinder and projectable from its other end, a post rotatably secured to the head and extending axially into the cylinder, an axial row of ratchet teeth on the post, means for introducing fluid under pressure into the cylinder to project the ram, a pawl carried by the ram to ratchet past the teeth during such projection of the ram and cooperable with the teeth to prevent retraction of the ram, and means for turning the post to move said row of teeth out of cooperation with the pawl and thereby allow retraction of the ram.

9. A hydraulic mechanism comprising a cylinder, a head on one end of the cylinder, a ram operable in the cylinder and projectable from the other end thereof, a post turnably secured at the head and extending axially into the cylinder and ram, an axial row of ratchet teeth on the post, an axially extending untoothed surface on the post adjacent said row of teeth, means for introducing fiuid under pressure into the cylinder to project the ram, a pawl carried by the ram to cooperate with the teeth to prevent retraction of the ram, and means for turning the post to move said row of teeth out of engagement with the pawl and to move said surface into alignment with the pawl and thereby allow retraction of the ram.

10. A jack including a cylinder, head means at one end of the cylinder, a ram operable in the cylinder and adapted to extend from the other end thereof, means for introducing fluid under pressure into the cylinder to move the ram through said other end of the cylinder, a post carried by the head means for turning movement and extending axially into the cylinder, axially extending rows of ratchet teeth on opposite sides of the post, untoothed surfaces on the post between said rows, pawls on the ram cooperable with the rows of teeth to hold the ram in an extended position, and means for turning the post to move the rows of teeth out of engagement with pawl and to bring said surfaces into alignment with the pawls so the ram may retract.

STANLEY R. HALL. EARL JELTER.

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

UNITED STATES PATENTS Number Name Date 1,740,683 Gartin Dec. 24, 1929 1,962,459 Ostlund June 12, 1934 2,288,511 Bratz et al June 30, 1942 2,333, 74 Scannell Nov. 2, 1943 2,341,542 Grime Feb. 15, 1944 FOREIGN PATENTS Number Country Date 211,847 Germany July 13, 1909