US3051141A

US3051141A - Hydraulic lift

Info

Publication number: US3051141A
Application number: US33266A
Authority: US
Inventors: Ira A Weaver
Original assignee: Dura Corp
Current assignee: Dura Corp
Priority date: 1960-06-01
Filing date: 1960-06-01
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28

Description

` Aug. 28, 1962 l. A. WEAVER 3,051,141

HYDRAULIC LIFT Filed June l, 1960 2 Sheets-Sheet 1 l. A. WEAVER HYDRAULIC LIFT 2 Sheets-Sheet 2 Filed June l, 1960 HyVENToR. fr@ Weaver,

United States Patent O 3,051,141 HYDRAULIC LIFT Ira A. Weaver, Springfield, lll., assignor to Dura Corporation, Oak Park, Mich., a corporation of Michigan Filed June 1, 1960, Ser. No. 33,266 12 Claims. (Cl. 121-46) This invention relates, in general, to improvements in hydraulic lifting mechanisms, and has particular relation to an improved hydraulic lift for elevating motor vehicles, although the improved hydraulic lift according to the present invention may be used for other purposes.

The hydraulic lift of the present invention is of the type having a cylinder provided with a hollow piston containing hydraulic fluid, such as oil; also means for injecting compressed air on top of the oil to force the oil out of and under the piston to elevate the same; and means for positively locking the oil when the piston is elevated, even though the air pressure is exhausted from the piston.

Heretofore, units have been provided in which compressed air is delivered to the unit through a pipe on the outside of the cylinder. This pipe has delivered the air to the bottom of the cylinder from where the air has passed up through an oriiice in the bottom of the piston and through an upright tube at the axis of the piston to the interior of the piston above the level of the oil therein. The compressed air, by forcing the oil out of and under the piston has elevated the piston. The oil, upon being forced out of and under the piston, has passed through an opening in the bottom of the piston. This opening has been controlled by a valve in the lower head of the piston.

Lifts of the foregoing character, with the air pipe on the outside of the cylinder and buried in the ground, have the objection that there is danger of the pipe being broken, for example, by rough handling, and underground ruptures require expensive repairs.

Another objection is that where the oil lock valve is at the lower end of the piston, access to this position when repairs are necessary has been difficult, and a hollow enclosure has been required at the lower end of the piston.

Another objection to prior lifts of the character set forth is that when the piston is lowered under load, oil is `jetted upward and air mingles with the oil causing a mist lso that the oil level is continually lowered as oil s exy hausted with air. This misting will stain adjacent areas, as well as create an unpleasant odor.

Prior lifts of the character set forth have also lacked any provision for automatically removing any air that might accumulate in the upper end of the cylinder; also any provision for automatically discharging any accumulated liquid as the piston moves up and down.

In prior lifts having no valve to prevent the return of oil into the piston, the entire piston may be supported by air pressure. If the air pressure varies, the supported load will raise or lower. If any weight is removed, i.e., if the wheels or transmission are removed, the whole load will be elevated in heights corresponding to the weight removed.

Prior lifts of the type containing one piston approximately at the center of the lifting supports have the further objection that when the load is off center with regard to the superstructure, there is a binding action between vthe piston and the cylinder, so that when the air inlet is closed, if there is a leakage of air pressure, for example, through the packing or the valves, the piston may hang on the wall of the cylinder, especially if the oil has been forced out of the piston and air escapes through the lower orice in the piston bottom and accumulates around the packing at the top of the cylinder. It is possible for the entire piston to be suspended by skin friction, and a slight 3,5l,l4l Patented Aug. 28, 1962 ICC jar may cause the piston to drop. Such sudden drop may dislocate the vehicle on the suspension points and result in injury to workmen or damage to the vehicle.

One of the main objects of the present invention is to provide an improved hydraulic lift in which objectionable features of prior lifts, such as those above set forth, are eliminated.

Another object is to provide a lift in which the air is injected through the top of the piston to force the oil within the piston downwardly through a low level oil control valve attached to the lower end of a tube extending upwardly through the piston to a control valve and then downwardly inside the piston and outwardly through the side of the piston to the space between the piston and the cylinder, and thence beneath the lower end of the piston.

Another object is to provide a structure in which the oil discharge through the side of the piston is at a point slightly below packing between the piston and the cylinder when the piston is fully elevated. This will allow any air accumulating outside of the piston to be automatically discharged with each operation of the lift.

, Another object is to provide a low level oil lock near the bottom of the piston. This is provided by means of a low level oil pan submerged in oil. When the level of the oil drops to near or below the bottom of the pan, the weight of the oil in the pan causes the pan to lower and prevent further movement of oil or air through the piston. The pan is suspended above the valve by means of a weight, so that the weight of oil in the pan overcomes this weight and allows the pan to close the valve.

Another object is to provide an extreme height stop that may be readily disengaged from the piston in order that the piston may be withdrawn from the cylinder if necessary for service. It also provides means to restrict the oil flow from the piston into the casing before the stop or stops are reached. 'Ihis prevents abrupt stop of the piston, and cushions the impact.

A further object is to provide an inlet for the air to the piston and means comprising a short length of hose attached to the inlet and arranged so that when the hose is twisted or given a turning or rotary motion it will close the oil valve and lock the piston at any desired height when the air is exhausted.

The structure of the improved lift of the present application comprises a package that may be easily made and will withstand shipping and installation abuse. All moving or serviceable parts are readily accessible from above the oor and the top of the piston.

Further features and `advantages and adaptations of the invention will be apparent from the lfollowing detailed description taken in lconnection with the accompanying drawings, it being understood that the invention is limited only within the scope of the appended claims and not to the particular embodiments selected for illustration.

In the drawings:

FIGURE 1 is a vertical section taken axially through an improved hydraulic l-ift embodying the present inventlon;

FIGURE 2 is a fragmentary top plan view of the upper end of a frame contact and lift assembly, as illustrated in FIGURE 1 and Ishowing the valve operating mechanism therefor;

FIGURE 3 is a plan view of the low level oil lock valve; and

FIGURE 4 is a transverse sectional view taken along .the line 4 4 of FIGURE 1 showing the guide ring secured to the lower end of the piston; also the recessing of the guide ring for passage of oil to and from beneath the piston, and vertical guide means for preventing rotation of the piston.

Referring now to the drawings, in the embodiment of the invention `selected lfor illustration, the hydraulic lift has an external, upright, stationary cylinder 1i), closed at its bottom by an upwardly concave disc or plate 11, which may be welded peripherally at 12 to the flower end of the cylinder 18. The weld 12 seals the lower end of .the cylinder and is of strength suiiicient to lwithstand the internal pressures vto which Athe lift is subjected in the operation thereof.

'Y A hollow cylindrical piston` 13 is mounted co-axially withm the cylinder 10 for movement up and down vertically therein. Therlower end lof thepiston 13 is closed by la lower head, disc, or plate 14, which is illustrated as upwardly concave and as fitting peripherally within the lower end of ythe piston 13 and welded peripherally to the piston at 15.

The external diameter of the piston v13 is substantially less than the :internal diameter of the cylinder 18. A `guide ring 16 is secured around the lower end of the piston ,'13, for example, by welding to vthe piston 13 at 17. The external diameter of the ring 16 is sufiiciently smaller than `the internal diameter of the cylinder 10 to permit the piston and guide ring to slide freely up and down in the cylinder 1li. The guide ring 16 is preferably hardened, and is recessed on one or more sides as illustrated at 18 in Fl"- URE 4 to allow oil to pass `between the piston 13 and cylinder 10 to the lower end of the cylinder and beneath the lower head 14 of the piston 13. To prevent rotation of the piston 13, a vertical guide "19 is secured to the inner surface of the cylinder `10, for example, by drilling holes `20 through the cylinder 18 and welding the guide 119 securely to the cylinder, as illustrated at 21. The guide ring 116 has a recess 22 milled therein. The sides of this recess 22 slidingly cooperate with the sides of the vertical gu-ide '19. The vertical guide 19 is of an upright length slightly greater than the total height that the piston 13 Itravels in the cylinder 10.

As illustrated in FIGURBl, suitable packing 24 is provided between the cylinder 10 and piston 13, and a gland and guide rin-g is provided at 25, whereby the piston 13 may lmove vertically with relation to the cylinder 10 in pressure-tight manner. The packing Z4 has a support 26 which rests on a stop plunger 28. One or more suitable sealing rings, such as the 4sealingrring 30 disposed in a groove in the ring 25, cooperates with the outer surface of the piston 13.

The upward stroke of the piston 13 is stopped at the upper lim-it of vertical movement `of .the piston by engagement of a stop block 31 secured to the piston v13, for example, by welding, as shown at 311 in FIGURE 4, with the stop plunger 28. While only one stop plunger 28 is illustrated in the drawings, it is to be understood that more than `one such plunger may be employed.

The plunger 28, which is preferably cylindrical, operates in a cylindrical stop plunger housina 32.` The open inner end of the housing 32 is welded at 33 to the cylinder 110, and the outer end of the housing is closed at 34. The plunger 28 has a ilat portion 35, which is engaged by the stop block 31. On its upper surface, the plunger 28 is flat at 36, and has a cross slot 37 at right angles to the flattened surface 36. A pin 38 engages in slot 37. This pin -is secured off center in the lower end of a rotating release pin 40. The release pin 40 is disposed in a tube 41 welded at its lower end at 42 to the housing 32. The upper end of the tube 41 has a cap 44 removably screwed or threaded thereon at 45.

In inserting the piston 13 into or removing same from the cylinder 10, the cap 44 is removed Ifrom the tube 41 and the release pin `48 is turned or rotated by engagement of a suitable `tool in `the slot 46. Rotation of the pin 4l) withdraws the stop plunger 28 from the path of vertical movement of .the stop block 31. Upon inserting the piston 13 into the cylinder to position where the stop block 31 is below lthe plunger 28, the plunger 28 may be returned to stop position by turning or rotating the pin 40'.

The top of the hollow piston 13 is closed `by an upper head or top wall 48 recessed inwardly from the upper end of the wall of the piston 13,and welded peripherally thereto at 49. The wall of the pist-on 13 has an openinn-g 50 above the packing 24, so that as the piston v13 moves up above the guide ring 25 any accumulated liquid will drain out.

Disposed vertically at the axis of the piston 13 is an upright tube or pipe 52. The upper end of this ltube 52 opens through an axial opening 53 in the head 48, and is Welded to the head 48 at 54. Another shorter upright tube 55 opens through an opening 56 in the head 48 and is welded to the head 48 at 58. The lower end of vthe tube 52 is screwed or threaded at l59 into the upright portion of an elbow iitting 60. A tube 61 screwed or threaded at 62 into the horizon-tal portion of the elbow iitting 60 opens through )an opening 63 in the wall of the piston 13 and into the space between the outer surface of the piston 13 and the inner surface of the cylinder 18. The tube 61 is welded at 64 to the wall of the piston 13.

When the li-ft or piston 13 thereof reaches the upper end of its vertical movement, the discharge -tube 61 is Ilocated slightly below the packing 24 as illustrated in dotted lines at 65 in lFIGURE l. Thus, when the lift starts to lower, it will automatically remove any air that might accumulate in the upper end of the cylinder 10.

With the discharge tube 61 disposed as shown in dotted lines at 65, it will be noted that the tube 65 is opposite the adjacent end of `the stop plunger 28. The oil ow from the piston into the cylinder i-s thus restricted before the stop or stops 28 are reached, which prevents abrupt stop of the piston and cushions the imp-act.

A valve body 68 is secured to the top of the upper head or top wall 48 of the piston `13. This valve body has an opening 69 which registers with the opening 53 through the head 48 and therefore with the upper end of the tube 52; also another opening 70 which registers with the opening 56 and therefore with the upper end of the tube 55. The valve body 68 is pressure-sealed to the head 48 about the openings 69 and 70 by O-rings 71 and 72.

A rotating valve 73 having a lateral port 74 is rotatable in the valve body 68 for turning the port 74 into and out of register with the passage 75 in the valve body 68. When the port 74 is in register with the adjacent end of the passage 75, this passage places the tube 52 in communication with the tube 55 through the hollow interior 73 of the valve 73, the port 74 and the passage 75. The valve body 68 has a cap- 76 provided with sealing rings 77 and 78 coacting respectively with the `stem of the valve 73 and with the valve body 68.

The piston head 48 has ran opening 79 therethrough in registration with the openings 80 and 81 through the valve body 68 and a iiller litting 82, permitting introduction of oil into the inside of the piston 13. yThe upper end of the filler opening 81 through the tting 82 is closed by a removable filler plug 83 screwed or threaded into the litting 82. A sealing or O-ring is provided at 82.

An air inlet tube 84 has a reduced lower end fitting through an opening 85 through the piston head 48 and welded thereto at 86. A vehicle frame engaging superstructure or lframe contact lhaving contact plates 87 for contact, for example, with the frame of the vehicle to be lifted, has an air inlet passage 88 downturned at its inner end `and registering with the air inlet passage 89 in the tube 84 for yadmitting and exhausting compressed air o1 air under pressure into the hollow interior of the piston 13. v

The frame contact rests on the upper end of the piston 13, and is bolted thereto by bolts 90. The heads at the lower end of bolts 90 coact with one or more plates 91,

Y welded at 92 to the piston 13, and the upper ends of the bolts pass through plates 87 and have nuts 93 threaded thereonand into cooperation with the plates 87. lWhen the plates 87 `are installed, they seal on O-rings 94, one of which is shown in the upper end of the air inlet tube 84.

A bale plate 95 may, if desired, be welded at 96 to the wall of the piston 13 in spaced relation beneath the lower end of the air inlet tube 84.

As illustrated in FIGURE 2, the frame engaging superstructure may have an opening 97 in the top 98 thereof to give access for removing or servicing the valve assembly.

The air inlet passage 88 is drilled through the superstructure 37 and, as illustrated in FIGURES 1 and 2, an air inlet fitting 99 is secured to the side edge of the superstructure 87 by bolts 100 and is sealed by an O-ring 101. A short length of hose 102, preferably wire-wound or the like, is attached to a hollow rotating valve member 103 in the air inlet 104. As illustrated in FIGURES l and 2, a crank arm 105 is connected, for example, by a pivotal connection 105' to a link 106 for operating a connecting member 107. .The other end of the connecting member 107 is attached to a pin 103, which engages an arm 109 on the rotating valve 73 for the purpose of turning or rotating this valve by sliding movement of the member 107 on member 110 Welded at 111 to the super, structure 87.

It is, therefore, evident that if the hose '102, through which air passes to the hollow interior of the piston 13, is rotated, it will not aiect the passage of the air to the piston, but move the crank arm 105 and its connections as described to open and close the oil lock valve 73. The hose 102 is not necessarily wire-wound, but Wire-winding or other suitable provision is preferable to enable the hose to withstand the torque thus imposed thereon. The hose 102 is of comparatively short length, to which the regular air hose 112 may be attached when lifting a vehicle or other load. The air hose 112 may be provided with an air control valve illustrated more or less diagrammatically at 113 for delivering air under pressure into the interior of the piston 13, and for exhausting the air from the piston, as well understood in the art.

A low level oil pan 115 has a sleeve 116 which surrounds the tube 52 which guides the vertical movement of the pan 115. The low level oil valve 118, as illustrated in FIGURES l and 3, is a round structure having a center portion internally threaded at 119, and passages or conduits 120. The valve 11S is screwed or threaded onto the lower end of the tube 52. Seats 121 are formed on the valve 11S at the upper ends of the conduits 120 for la wafer valve 122, which is of annular form, and surrounds the tube 52.

A lifting support 124 is aihxed to the bottom of the pan 115, and coacts with the wafer valve 122 to hold this valve above its seats 121. The pan 115 and wafer valve 122 are held up with the -valve 122 above its seats 121 so that oil Imay enter the passages or conduits 120 from the bottom of the interior of the hollow piston 13 and pass up through the tube 52, as will be hereinafter described.

The pan 115 holds the valve 122 open by means of a weight 126 on an arm 127 pivoted at 128 to a lug or bracket 129 secured to the tube 52. The opposite end of the arm 127 is connected to a lifting arm or connection 130 connected at its upper end to the adjacent end of the arm 127, and at its lower end to a lug 132 on the pan sleeve 116.

The pan 115 has an upright sleeve portion 135 therein, which projects upwardly from the bottom wall of the pan. This sleeve portion 135 surrounds an upright tubular guide 136, which further guides and prevents undue turning of the pan 115 about its vertical axis. The upper end of the guide tube 136, which is welded at 137 to the bottom of the upper piston head 48, opens through the piston head 4S and has at its upper end a removable plug 140', as shown in FIGURE 2. When the plug 140 is removed from the upper end of the tube 136, a short length of hose may be attached so that when air is applied to the piston the water and sludge may be siphoned oi. In all lifts where 'air is applied to oil in large quantities, moisture in the pressurized air will be condensed and returned in oil as an emulsion. This emulsion will iinally separate into oil and water and will tarnish the piston and the presence of Water will decrease the life of the packing as well as other working parts of the piston. The lower end of the guide tube 136 projects downwardly through an opening in the lower piston head 14, and is welded thereto and sealed by the welding, as illustrated at 138.

In the use and operation of the hydraulic lift of the present invention, the hollow piston 13 is filled, through the iiller :fitting 82, with oil or other appropriate liquid to a height as indicated, for example, by the dot and dash line A in FIGURE l.

The pan is now full of oil, and is completely suspended in oil. At this time the value of the counterweight 126 is such that it more than balances the weight of the valve 122, the oil filled pan 115 and the lifting arm 130, and the valve 122 will be held in wide open position, thus admitting oil into the conduits or passages of the Valve 118 and into the tube 52 to the level of the oil in the piston 13.

The superstructure 87 is positioned beneath the appropriate parts of the vehicle to be lifted, or in any appropriate manner beneath any other load to be lifted.

When it is desired to lift or elevate the load by the ascent of the piston 13, the valve, lfor example, as shown more or less diagrammatically at 113 in the regular air hose 112, is opened, admitting air under appropriate pressure into the piston 13 above the oil level therein through the hose 122, air inlet passage 88, and air inlet tube 84.

Air hose 102 is then rotated, without aifecting the passage of air into the piston, to turn or rotate the valve 73 through the arm 109 to open position with its port 74 in register with the passage 75. Oil under pressure from the air pressure in the hollow piston 13 is then permitted to flow from the interior of the piston 13 through the open valve 122, passages or conduits 120, and up through the tube 52 through the hollow interior 73' of the Valve 73 and port 74, and down through the passage 75, tube 55, elbow fitting 60 and tube 61 into the space between the piston 13 and cylinder 10, and downwardly through this space to beneath the lower piston head 14.

The oil, as it passes under pressure from the air pressure in the hollow piston to beneath the piston head 14 causes the piston 13 to rise vertically from the cylinder, thereby elevating the vehicle, or other load, to which the lift is applied.

When it is desired to hold the piston 13 and the load on the superstructure 87 at any desired point of the upward travel of the piston, the air hose 102 is rotated, again without aiecting the passage of air into the piston, to turn or rotate the valve 73 through the arm 109 to closed position, with its port 74 out of register with the passage 75. This locks the lift against the return of oil from beneath the piston to the hollow interior of the piston, and thus holds the piston and the load at the desired position.

As previously referred to herein, the discharge from the tube 61 into the space between the piston 13 and the cylinder 10, is located at a position in the wall of the piston so that when the lift reaches its full height the discharge from tube 61 is located slightly below the packing 65, as illustrated in dotted lines at 65 in FIGURE 1. Thus, when the lift starts to lower, it will automatically remove any air that might accumulate in the upper end of the cylinder. In other words, any air which might accumulate outside the piston is allowed to be automatically discharged with each operation of the lift.

As previouslyset forth, the valve 122 is normally openV as long as it and'itslow level oil pan 115 are submerged in oil. Should the oil level in the interior of the piston 13 become too low for any reason, due, for example, to insufcient lling, leakage, or for any other reason, so that as the piston 13 rises the oil level therein descends to a point near or below the bottom of the pan 115, the pan 115 will descend, due to the lack of buoyant effect of surrounding oil. This descent of the pan 115 will thereby automatically close the valve 122, thus halting further ascent of the piston 13 and sealing the lift against passage of air through the valve 118 and beneath the piston 13.

The foregoing action is highly desirable, since if air were admitted to the space below the piston, its action would become erratic.k The piston would ascend or descend by jerks, instead of smoothly and evenly, as is the case where the piston is supported entirely on oil, the latter being practically non-compressible.

The automatic discharge of any air which may accumulate outside the piston is also high desirable, for the reasons herein set forth.

The lowering of the piston 13 and the load thereon is accomplished `by exhausting the air from the space above the oil in the piston by manipulation, for example, of the air control valve 113, leaving such space open to the atmosphere.

During the lowering of the piston 13 and the load thereon, the oil in the cylinder ilows back into the piston ready for the -next lifting operation. In other words, the operation of the crank arm 105, as previously described, opens the valve 73, permitting the oil to flow from the space beneath the piston in a reverse direction through the tube 61, elbow 60, tube 55, valve passage 75, port 74, tube 52 and valve passages or conduits 120 into the hollow interior of the piston 13.

If the valve 73 is closed during any movement of the piston, the piston travel is immediately terminated, and locked, regardless of whether the air pressure is on or oft. In other words, the valve 73 ymay be instantly closed at any point in the stroke of the piston 13 without exhausting the air pressure. This makes it possible to stop the piston movement at once, and not allow expanding air to continue to raise the piston when the air supply is shut oi.

One end of the air inlet hose 102 is attached to one end of the rotating valve member 103, as previously described. The other end of the hose 102 extends to position behind the side of the vehicle being elevated. The hose 102 may be laid in a groove in the oor 140, as shown fragmentarily and more or less diagrammatically at 141 in FIGURE 2, so that a vehicle wheel or wheels may pass over the hose without injurying the same. Y Alternatively, the hose 102 may be laid on the oor in an open metal shield to prevent injury to the hose.

It is customary to suspend the regular air hose 112 at one side of the vehicle, whereby it may be pulled down and connected with the short air inlet hose 102, so that when the hose 102 is twisted or turned it will operate the oil control valve 73 to closed and open positions for preventing and permitting movement of the piston 13.

iFrame engaging lift portions, such as illustrated at 87, usually have contact pads for coaction with the vehicle, and it is necessary for the operator to look under Ithe car while spotting them.

To make certain that the aforementioned adjustable pads make proper Contact to support the vehicle when:

elevated, it is necessary to admit air to the interior of the piston slowly, which is dificult, to prevent rapid raising until the piston is loaded. With the lift of the present invention, the oil control valve is closed, and an air valve,

which is usually placed in the floor adjacent to the lift,

is opened. 'Ihe air valve is then closed, trapping a comparatively small volume of compressed air within the piston above the oil, so that while the operator is still in a kneeling position, a slight twist or turning of the hose 102 will `open the oil lock valve 73 and the expansion of the air will cause the piston to slow down before the car or vehicle is contacted or engaged. A slight twist or turning of the air inlet Ihose 102 will again lock the oil valve, and the air can be exhausted, if desired. The lift can then be lowered without the supply hose being connected.

However, if the air supply hose is left attached, the lift can be stopped inV its downward movement by again injecting air into the piston, the operator standing in a safe position from the vehicle. This will allow inspection of the area below the vehicle to insure that all obstructions are removed, and the vehicle will not be thrown from the lift lbefore reaching the floor.

The embodiment of the invention disclosed in the drawings and the speciication is for illustrative purposes only, and it is to Ibe expressly understood that said `drawings and the specification are not to be construed as a definition of the limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim:

l. A hydraulic lift comprising, in combination, a cylinder, a hollow piston movable up and down in said cylinder, stop means for stopping the piston at the upper end of its movement, said stop means comprising at least one stop plunger disposed within a housing, a tube joined to said housing and terminating at approximately oor -level at its upper end, a rotating member within said tube and having an off center projection so that when rotated it will withdraw said stop plunger from piston stopping position, and a cap sealing said tube and removable for operating said rotating member.

2. A hydraulic lift comprising, in combination, a cylinder, a hollow piston movable up and down in said cylinder, and closed at its lower and upper ends, a valve near the upper end of the piston, an air inlet opening through the upper end of the piston and registering with an air supply conduit having a rotating sleeve so that the supply of air will not be `obstructed by rotation of said sleeve, `a connection between said sleeve and said valve for turning said valve to closed liquid locking position, and to open position by rotation of said sleeve, and a short length of hose attached to said rotating sleeve for actuating the valve by turning said hose.

3. A hydraulic lift comprising, in combination, a cylinder, a hollow piston movable u-p and down in said cylinder, said hollow piston being adapted to contain the working liquid and closed at -its lower and upper ends, la rst conduit extending downwardly from the top of the piston and terminating at its lower end near the bottom of said piston, la second conduit extending downwardly from the top of the piston and opening through the side wall of the piston into space between the piston land cylinder, said -space being .in communication with the lower end of the cylinder beneath the piston, a valve located near the upper end of the piston and having an open position allowing the liquid to be Vforced upwardly from the piston through said rst conduit 'and downwardly through said second conduit into said space, said valve being operable to closed position to prevent the return of liquid into said piston, whereby to hold the piston at any point in its upward travel, said iirst conduit near the bottom of the piston having a valve attached thereto, and an upwardly opening pan operable to hold said valve open yby gravity weight, so that when the liquid level in -the piston is diminished to a point where it is near the bottom of -said pan, the weight of liquid trapped -in said pan overcomes the gravity weight and closes said valve.

4. A hydraulic lift comprising, in combination, a cylinder, a hollow piston movable up and down in said cylinder, said hollow piston being adapted to contain the working liquid and having closure members at its lower and upper ends, a rst conduit extending downwardly from the top of the piston and terminating at its lower end near the bottom of the piston, a second conduit extending downwardly from the top of the piston and opening through a wall of the piston for delivery of liquid into the lower end of the cylinder beneath the piston, -a low level liquid control iirst valve attached to the lower end of said iirst conduit through which liquid is admitted into said -iir-st conduit to the level of the liquid within the piston and operable to closed position upon occurrence of an undesired lowering of the liquid level Within the piston, and Ia second valve located near the upper end of the piston and having an open position allowing the liquid to be forced upwardly from the piston through said Irst valve and said first conduit and downwardly through said second conduit into the cylinder, said second valve being operable to closed position to prevent return of liquid into said piston, whereby to hold the piston at any point in its upward travel.

5. A hydraulic lift according to claim 4, wherein there is packing between the cylinder near its upper end and the piston, the lower end of said second conduit being directed laterally and opening into the cylinder through the side Wall of Ithe piston at a position so that when the lift reaches its full height said opening is positioned slightly below said packing .so that when the lift starts to lower, air will be automatically removed from the upper end of the cylinder.

6. A hydraulic lift according to claim 4, wherein there is stop means for stopping the piston yat the upper end of its movement, the lower end of said second conduit being directed laterally and opening into the cylinder through the side wall of the pis-ton -at a position so that said opening is disposed in proximity lto said stop means to restrict the liquid flow into the cylinder before the stop means is reached, whereby to prevent abrupt stopping of the upward movement of the piston and to cushion the impact.

7. A hydraulic lift according to claim 4, wherein there is stop means for stopping the piston at the upper end of its movement, the lower end of said second conduit being directed laterally and opening into the cylinder through the side wall of the piston at a position so that said opening is disposed in proximity to said stop means to restrict the liquid ow into the cylinder before the stop means is reached, whereby to prevent abrupt stopping of the upward movement of the piston and to cushion the impact, said stop means being in the form of a laterally slidable plunger, and a release pin having an oi center portion engaging in a slot in said plunger for actuating said plunger into and out of stopping position by turning of said release pin.

8. A hydraulic lift according to claim 4, wherein there is a laterally slidable stop plunger for stopping the piston at the upper end of its movement, and a release pin having an ol center portion engaging in a slot in said plunger for actuating said plunger into and out of stopping position by turning of said release pin.

9. A hydraulic lift `according to claim 4, wherein there is packing 'between the cylinder and the piston and a guide ring above said packing, the Wall of the piston having an opening above said packing so that as the piston moves upwardly above said guide ring any liquid `will drain out.

l0. A hydraulic lift according to claim 4, wherein there is a load engaging superstructure extending over and directly supported on the upper end of the piston, said superstructure including a contact plate having an air inlet passage extending therethrough, and lan air inlet tube opening through the closure member at the upper end of the piston and communicating with said air inlet passage for delivering air into the piston above the level of the liquid therein.

11. A hydraulic lift according to claim 4, wherein there is a load engaging superstructure extending over and directly supported on the upper end of the piston, said superstructure including a contact plate having an air inlet passage extending therethrough, an air inlet tube opening through the closure member at the upper end of the piston and communicating with said air inlet passage for delivering air into the piston above the level of the liquid therein, an lair vsupply conduit for supplying air to said air inlet passage, said `air supply conduit including a rotating sleeve, and connection between said sleeve and the second valve for turning said valve to closed and open positions.

12. A hydraulic lift according to claim 4, wherein the closure member at the upper end of the piston is disposed below the upper end of the piston, a load engaging lsuperstructure extending over and directly supported on the upper end of the piston and an air inlet tube opening through the upper end of the piston, said air inlet tube and `the iirst valve being disposed between the closure member 4at the upper end of the piston and the load supporting superstructure and within the upper end of the piston.

References Cited in the iile of this patent UNITED STATES PATENTS 1,689,145 Lunati Oct. 23, 1928 2,085,961 Dorward July 6, 1937 2,471,989 Weaver May 31, 1949 2,637,302 Harrison et al May 5, 1953