Патент USA US2119440код для вставки
Patented May 31, 1938 2,1 19,440 UNITED STATES PATENT OFFICE ’ 2,119,440 HYDRAULIC JACK Timothy C. Pomeroy, Long Beach, Calif. Application December 23, 1935, Serial No. 55,874 6 Claims. This invention relates to new and useful'im (Cl. 60-52) understood that the invention is not ‘con?ned to provements in- hydraulic jacks, generally, and . the exact features shown as various changes may more particularly to jacks of the general char be made within the scope of the claims which fol acter disclosed inmy Patent No. 1,744,673. low. An object of the present invention is to pro vide a simple and e?icient hydraulic jack which may safely be carried about in the tool box of a vehicle without danger of leakage, regardless of temperature changes, A ' jacks of this character, has been eliminated, and 3-3 of Figure 2; v A further object is to provide ahydrauiic jack provided with an expansion chamber secured di rectly to the body of the jack, and having its lower end communicating with the upper end of the jack cylinder, whereby ,a portion of the ?uidv contained in the expansion chamber is drawn into the jack cylinder, when the plunger is ele 5 2—2 of Figure 1, with some of the parts shown .in Figure 1 omitted; pressure medium thereof. ' the general construction of the jack; ‘ Figure 2 is a sectional plan view on the line A further object is to provide a hydraulic jack in which the usual breather duct, common to which is so constructed that when once ?lled‘with an ample supply of oil, or other suitable pressure 15 medium, it may be operated for a long period of time without having to replenish any of the '20 In the drawings: Figure 1 is a vertical sectional view showing ' ‘ ' Figure 3 is a€detail sectional view on the line 10' - Figure 4 isgan enlarged detail sectional view showing the normal shape of the sealing means provided at the upper end of the cylinder; Figure 5 is a/simil'ar view showing the sealing 15 means when under pressure; Figure 6 is a detail sectional view showing one of the metallic sealing members of the operating‘ ' handle, removed therefrom; and > Figure 7 is a top view of the jackon a smaller 20 scale, showing the lifting hanger disposed at an ' angle to the jack handle. - , In the selected embodiment of the invention vated, to thereby replace the ?uid, which is nor mally displaced by the operating parts within , here shown, there is illustrated in Figure 1, for 25 purposes of disclosure, a hydraulic jack of' the the cylinder. general character shown and described in my Other objects reside in thespeci?c construc patent, hereinbefore mentioned, comprising a tion of the sealing means for preventing leakage cylinder H mounted in-a suitable base l2. 30 between the cylinder and plunger at the upper A hollow plunger I4 is mounted within the cyl- 3o end of the jack, and in the‘operating handle; in inder and has its wall spaced from the wall the speci?c construction of the plunger head, of theI I cylinder to provide an annular fluid whereby it is practically impossible for any of the liquid to escape from beneath the plunger head chamber IS. The plunger is provided at its lower _ into the upper portion of the cylinder; in the end with a head, generally indicated by the nul6, and comprising a cap i1 having a re- 35 simpli?ed construction of the valve mechanism; meral duced portion I8 ?tting into the lower end of the in the particular manner of mounting the expan plunger as by sion tank directly upon, the body of the jack, welding. l4 and suitablysecured~ thereto, ‘ whereby-it becomes in effect an integral part A suitable lifting head I9 is secured to the up thereof; and, in the novel means detachably-se cured to the plunger for engaging the vehicle or per end of the plunger l4 and has a reduced por- 40 object to be lifted, which comprises a step tion 2| ?tting into the upper end of the plunger, as clearly illustrated in Figure 1. The head .19 mounted for vertical. adjustment, whereby it may is preferably secured to the plunger by welding be lowered to a position in close proximity to the in a manner similar to the lower head or cap l‘l. . ground for engaging a low object, and in'the piv and intake tubes 22 and 23, respective~ 45 otal mounting of said hanger upon the head of Discharge ly, are arranged in spaced relation within the the plunger whereby said hanger may be rotated plunger I4, and have their upper ends secured about a vertical axis with respect to the jack. 7 Other objects of the invention will appear from the following description and ' accompanying drawings and will be pointed out in the" annexed claims. ' In the accompanying drawings, there has 'been' disclosed a structure designed to carry out the various objects of the invention, but it is to be to the head l9 by suitable threads, as shown, or, if desired, they may be secured thereto by weld ing. The lower ends of the tubes 22 and 23 pass 50 through suitable apertures provided in the cap ,I‘I and extend below the latter, as clearly illus trated in Figure 1. - . ' ' p A feature of the invention resides in the con struction of the plunger head It, which, as best 55 > 2 2,119,440 a ' shown in Figure 1, comprises a suitable leather The guide ring or collar 35 is- welded in place, of the cap l1 and having aperturestherein for receiving the terminals of the tubes 22 and 23. 5 A plurality of resilient cup-shaped disks »25, of the cylinder | l, and is bored to receive the plunger l4, whereby it provides a guide for the plunger cup or packing 24, seated against the lower face - whereby it becomes, in effect, an integral part of ' a suitable material such as copper, are nested to gether and seated against the packing 24. A plate or washer 28 is seated directly against the in its up and down movement in the cylinder. The packing or sealing means, shown in Figures 4 and 5, is ?tted over the ‘plunger l4 and seated upon the upper face of the guide ring 36, and isv inner cup-shaped disk' 25, and has openings . retained thereon by a cap 38, preferably ‘received '10 therein for receiving the terminals of the tubes 22 and 23. The lower ends of the tubes project below the plate 26yand have suitable nuts or col lars 21 secured thereto, as by welding, whereby . inv threaded engagement with the upper end of 10 the cylinder II. This cap may, if desired, be welded directly to the wall of the cylinder. When means pf a suitable plug 28, preferably welded thereto. This plug is shown projecting below At the same time, the packing ring 32 is com the cap 38 is forced downwardly against. the , the leather cup or packing 24, cup-shaped disks packing 32, the convex portions 35 of the sealing _ rings 33 and 34 are engaged directly by the guide 15 25, and the plate 25 are suitably secured together ring 38 and cap 38, whereby they are compressed, to provide the plunger head l6. Before securing the nuts or collars 21 to the as shown in Figure 5. Where pressure is thus tubes 22 and 23, pressure is applied to the plate applied to the sealing rings 33 and 34, the axially 26 to thereby tightly compress the parts 24 and disposed ?anges thereof tend to spread in opposite directions, whereby the inner flanges will press 20 20 25 between it andv the cap l1, whereby a very substantial structure or plunger head is provided. against the wall of the plunger, and the outer The lower end of .the intake tube 23 is closed by flanges against the adjacent wall of the cap 38. the terminals of the tubes 22 and 23, whereby it may engage a plate 38 provided in the lower end . of the cylinder H, to thereby limit the down ward movement of the plunger in the cylinder. The cup-shaped disks 25 are shaped to constantly 30 exert an outward pressure against the annular ?ange of the packing 24 to thereby hold it in leak proof engagement with the wall of the cylinder, as will readily be understood by reference to Fig pressed between the sealing rings, whereby ‘por tions thereof will tend to bulge outwardly be tween the edges of the ?anges of the sealing‘rin'gs,‘ into engagement with the wall of the plunger 25 and the adjacent wall of the cap 38. When the above described sealing means is thus compressed, the liquid in the annular chamber I5 cannot es cape therefrom to the atmosphere, when the jack isv subjected to aheavy load. ‘ I . Figure 5 shows the positions which thepacking ring 32 and sealing rings 33 and 34 tend to assume, .7 Suitable openings. 29 and 3| are provided in ; when pressure is applied to the top and bottom ure 1. .35 the-tubes 23 and 22, respectively, adjacent to the .' thereof,_when positioned in the jack. When the plunger head I6, and are substantially hor'izon-_ sealing means is thus compressed, the ?anges of the sealing rings 33 and 34 are pressed into tally alined, as shown. The opening’ 3| estab _lishes communication ‘between the interior of-the 40 plunger l4 and the annular chamber IS in the cylinder above the plunger head ‘I 6; and the open ing 29 establishes communication between the interior of the plunger and the tube 23., Another feature of the invention resides in the 45 means provided at the upper end of the jack for closing the gap between thewall of the cylinder and the wall of the plunger. Hydraulic jacks of - leak-proof engagement with the walls of the - plunger l4 and cap 38, as clearly illustrated in 40 Figure 1. ‘ a - The lifting head'l8 is shown Ffcomprising a pair of check valves 39 and 4|, mounted in suitable valve chambers, 42 and 43, respectively. The valve 39 is normally held in engagement with a seat 44 by the action of a spring 45, retained in the valve chamber “by a suitable plug 45. the character herein disclosed, are often subjected ' The valve 4| is. normally ‘held in engagement to very'_high pressures, and meansmust there 50 fore be provided for positively preventing leakage with. avseat 41 by gravity. The valve chamber 42 is in direct communication with the discharge . tube 22 by means of “'a duct 48, and the valve chamber 43 communicates with the intake tube trouble in hydraulic jacks resides in the di?iculty 23 through a duct 49.- The valve chambers 42 experienced in preventing leakage of the oil or ' and 43 are in direct communication with each other through a port 5|. I Cl 01 liquid from the upper end of the cylinder, and to To operate the jack, the ?uid within the plunger eliminate .this difficulty, I employ a novel pack-E of the fluid from the jack while in operation and while supporting a load. A common source of ' ing or sealing means. for closing the gap between and in the‘ annular ?uid.;chamber I5, is pumped into the lower end of the cylinder below the plung er head l8, whereby the plunger is relatively moved upwardly in the cylinder. The means for thus 60 60 riated, even when the jack is supporting a heavy load for a long period of timel1 l ‘ "pumping the ?uid into the lower 'portion- of the This novel packing, as best ~ shown in. Figures '1, . cylinder is shown comprising a suitable displace 4, and 5, comprises a suitable annular packing ring ment rod 52, mounted in a tubular handlesecy the wall of the plunger and the upper end of the cylinder, whereby leakage is substantially elimi 32, of a suitable material such, for example, as vegetable rubber, which 'I have .found, does not tion 53 and having a head 54' ?tting the bore in the handle section 53._ The handle section 53 is 65 readily deteriorate when subjected to pressure liquids, such‘ as oil, commonly used in jacks of this general character.‘ The packing 32 is fitted by a suitable swivel joint, generally indicated by ' between two annular ‘metallic sealing ,members 70 33 and 34 of avsuitable spring metal, having con vex annular portions 35, as best shown in Figures pivotally connected to another handle section 55 the numeral 50, which is similar in construction tothe one disclosed 'in my patent, hereinbefore referred to. ' - 70 The handle. section 55 is pivotally connected to 4 and 5.‘ A guide ring 36 is ?tted into the upper I, the lifting head I9 by a suitable plug valve 58', v seated in a tapered bore 51, as best shown in .end of the cylinder II and has a beveled face 31 seated against ‘a correspondingly beveled face 75 provided on theupper end of the cylinder wall. Figure .2. The plug'valve 56v is retained in the , bore 51' by a suitable securing me'ans, generally 2,1 19,440 indicated by the numeral 58. This securing means is similar to that shown in my above mentioned patent, and automatically takes up wear in the valve to thereby prevent leakage. , The plug valve 56 has a peripheral groove 59, which is alined with a port 6| communicating with the valve chamber 43, as best shown in Figure 1. The plug valve 56 also has a ?uid circulating duct 62 which communicates at one w end with the peripheral groove 59 by means of .a port 63. ' The opposite end of the duct 62 is in direct communication with the interior of the handle section 55, whereby directv communi cation is established between the peripheral groove 59 and the interior of the handle section 53, as will be clearly understood by reference to Figuresil and 2. Another important feature of the invention resides in the means provided for preventing leakage of the oil or liquid from the. handle section 53 around the stem 62 of the displace ment rod 52. This stem, it will be noted by ref erence to Figure 1, is provided with a hand grip 65, whereby it may be conveniently reciprocated within the handle section 53 when the jack is manipulated. _ The novel means provided for preventing leak age of the oil around the displacement rod 62 is somewhat similar in construction to the seal ing means at the upper end of the cylinder, and comprises a suitable packing ring 66, interposed between two sealing rings 61 and ,68. The lower_ sealing ring 68 is seated upon a supporting mem ber 69 provided in the grip portion ‘H of the 3 with the thrust members 16 and 11, whereby the latter are actuated to unseat the valves 39 and M, as clearly illustrated in Figure 1. When the valves are thus positioned, direct communication is established between the in terior of the plunger I4 and the lower end of the cylinder, below the plunger head l6, where by the plunger may readily be lowered to its lowermost position, as shown in Figure 1. When the valves are so positioned, the oil or liquid 10 in the cylinder below the piston, and which is supporting the load, will ?ow upwardly through the discharge tube 22, through‘ the open valves 39 and 4|, thence downwardly through the in take tube 23, and through the opening 29 there of, and back to the interior of the plunger, there by permitting the plunger to descend into the cylinder. When the operating handle is swung outwardly to a position whereby the heads of the thrust members ‘I6 and 11 will engage the bottom of the peripheral groove 59 of the plug valve, and the displacement rod 52-is recipro cated within the handle section 53, the oil is drawn upwardly from the interior of the plunger through the tube 23, check valve 4|, thence ~ through the unseated valve 39, and downwardly through the tube 22 into the cylinder below the plunger head [6. Such circulation of the oil or liquid will cause the plunger to be elevated in the cylinder, as will readily be understood. Another important feature of this‘ invention resides in mounting directly upon the wall of the cylinder, an expansion tank 83, which con tains a reserve quantity of liquid to thereby posi handle section 53. A suitable collar or washer 72 engages the upper sealingring' 61, and is con tively prevent the jack from becoming inopera stantly pressed thereagainst by the action of a compression‘ spring 13, having one end‘engag sure liquid. ing the collar 12 and its opposite end the upper wall 14 of the grip portion ‘H of the handle sec tion 53. . ' The axial ?anges of the sealing rings 61 and 68 of the packing 66 are preferably provided with a plurality of small slits 15 '(see Figure 6), to thereby render said rings more ?exible and- re silient in operation, and whereby thr- actlon of the spring 13 may compress the packing 66 suf ?ciently to cause the ?anges 61 and 68 -to be constantly pressed against the walls oiv the dis placement rod 52. and the bore of the grip por— tion 1| . ' The means for unseating the valves 39 and tive, as a result of an insu?icient supply of pres The expansion tank 83 is best shown in Fig ure 1, and is hermetically sealed at its upper and lower ends by suitable caps 84‘ and 85, respec tively, which preferably are welded to the wall of the expansion tank. The tank, as a whole, is secured to the wall of the cylinder, preferably by welding. whereby it becomes, in effect, an integral part thereof. A small tube 86 is secured in piacc within the expansion chamber 81, de fined by the walls of the tank 83, and is shown having its upper end bent at right angles and passing through an opening in the wall of the expansion chamber and through an opening in . the wall of the cylinder, whereby the tube 86 4| is similar to that shown and described in my is in direct communication with the annular ?uid chamber I5 of the cylinder. The joints be previously mentioned patent, and brie?y con- . tween the tube 86 and the walls of the expan! sists of a pair of thrust members 16 and 11, sion chamber 31 and cylinder are hermetically I the former having one end adapted to engage sealed to prevent leakage therebetween. The the valve 39, and the latter having one end adapted to engage the valve M. The opposite other end of the tube 86 terminates adjacent to the bottom wall 65 of the expansion chamber ends of the thrust members 16 and I‘! are con stantly held in engagement with the periphery if the plug valve 56 by suitable compression ;prlngs ‘l8 and 19, respectively, as clearly illus ;rated in Figure 1. The thrust members 16 and 11 are arranged,' me over‘ the other, in the lifting head I9, and ire alincd with the peripheral groove.59 in the - alug valve 56. One end of the groove 59 ter ninates in cam faces 8| adapted to engage the thrust members 16 and 11 to thereby actuate and is preferably bent outwardly, as shown, al though it is to be understood that the lower 60 end of the tube 86 may be otherwise shaped, if desired. ' ' ‘ i One of the distinguishing features of the con- ' struction of- the expansion tank, herein disclosed, over structures of this general character now in 65 use, resides in the size of the expansion tank, whereby a relatively large chamber is provided above the level of the liquid therein,'as clearly illustrated in Figure 1. By enlarging the size of he latter. When the operating handle of the the expansion‘tank, as herein disclosed, I have ack, comprising the sections 53 and 55, is in ‘ found that the usual breather or vent hole, com 70 he position shown in Figure 1, that portion of monly provided in hydraulic jacks, may be dis he periphery of the plug valve 56 which is dis; pensed with, and I have also found that the nosed between the cam face 8| and the end usual ?ller plug may be eliminated or, if such a vall 82 of the groove 59, will be in‘ engagement plug is provided, it may be locked in sealing posi 75 4 2,1 19,440 tion so that it cannot readily be removed from the jack. ‘Because of the size of the expansion cham jack handle disposed at an angle to theaxle, whereby said handle may be conveniently op ber 81 above the level of the oil therein, when the _ erated without interference from the usual wheel jack is operated to lift a load, a portion of the fenders. Means is also provided within theplunger for oilin the expansion chamber may readily be drawn through the tube 86 into the cylinder to . preventing excessive pressures being developed supply the oil displaced by the wall of the plunger in the jack, when in operation, and consists‘of a .and the tubes 22 and‘23 in the plunger, When a relief valve, generally indicated by the numeral portion of the oilin the expansion chamber'is 10 thus drawn into the cylinder, a vacuum tends to 'develop in the expansion chamber 81, but, be cause of the size of this chamber, and further, be cause of the limited amount of oil withdrawn from the expansion chamber, the vacuum thus‘ 95, and provided in the plunger head l6. This relief valve has an operating stem v96, shown provided with a cross bar 91 having its terminals projecting outwardly through suitable elongated openings 98 in the wall of the plunger l4, whereby the terminals of the rod 91 will engage the guide ring 36, when the ‘plunger reaches a predeter developed is not suf?cient to interfere with the _ 15 mined elevation, thereby automatically opening operation of the jack. the relief valve 95. Such» opening of the relief Conversely, when the valves 39- and H are op erated to permit the fluid to return from below .valve 95 will permit the oil being pumped into the plunger 'head l5 'into the'upper portion of . the cylinder below the plunger head IE to by the cylinder, the surplus'oil is returned to the pass through the plunger head l6, back into the V20 expansion chamber, and may tend to create a interior of the plunger. The relief valve 95 is slight pressure therein, which pressure is not suf ?cient to prevent the plunger from being‘ lowered to its normal position, as shown in Figure 1. It 25 will thus be seen that by enlarging the size of ' \the expansion chamber 81, as herein stated, the jack, as a whole, is rendered far more ?exible in operation and’is more fool-proof in that itv cannot readily be overcharged with oil, which .30 might occur if an inexperienced person should introduce oil into the jack.. Also, by securing the expansion tank 83 directly to the cylinder, ‘it may be so ?xed thereto, that it cannot readily be jarred loose, which might cause leakage and thereby render the expansion tank inoperative. To secure the expansion tank directly-to the cyl inder, therefore, is an important" feature of the shown and described in detail in my Patent No. 1,699,917, and it is therefore thought unnecessary to further illustrate and describe the same .herein. The novel jack herein disclosed, has been found very e?lcient and practical in actual operation. Because of the unique construction 'of the plunger head I6 and also as _a result of the provision of the expansion tank 83, the jack may be ?lled with the necessary supply of oil or pressure liquid and suitably sealed, before leaving the factory, whereby it cannot be tampered with by inexperi enced persons. Thus, the manufacturer will‘be ' assured that the jack will always operate ef-, ?ciently. unless, of course, it should -' become damaged as a result of rough usage and handling, which might be of su?lcient scope to cause leakage. invention. 40 ' _ ' I . Means is also provided whereby the jack may _ The novel sealing means, shown inlFigures 4 and 5, so seals vthe jack against leakage, that it readily be used for lifting objects varying con siderably in height. Such means is clearly'illus-1 becomes substantially leak-proof, whereby all trated in Figure 1, and comprises a hanger 88 joints in the jack may‘ be welded, with the result ‘having its upper end portion 89 pivotally secured that the jack, as a whole, may be made from 45 means as a shouldered stud 9|. If necessary, the and plate steel, or any other suitable plate ma terial which is comparatively lighter in weight to the lifting head H. of the plunger, by such‘, lighter material such, for example, as tubular stud may be locked in place by a suitable pin 90. The hanger 88 is provided with suitable ratchet than cast metal. Because of the size of the teeth, generally indicated by the numeral .92,“ expansion chamber 81, the jack may also be used in extremely hot temperatures without ‘danger, adapted to be adjustably engaged by a step, gen 50 erally indicated by the numeral 93. This step is slidably mounted upon the upright portion of the hanger '88 and may readily be lvertically adjusted thereon by simply swinging the lower end thereof outwardly,v as indicated by the dotted lines in 55 Figure 1, whereby the step may be moved up or down, as desired. When the step is‘returned to its normal horizontal position, as shown in full - lines ‘inIFigure 1,_it lockingly engages the ratchet teeth 92, whereby it may be inserted under an object or a load to lift the latter when the jack is operated. The lower end of the hanger 88 is supported by a‘ suitable antifriction roller 94, .as the oil'or liquid has ample room to expand and contract without, in any way, jeopardizing the operation of the jack. _‘ I claim as my invention; . . ' - 1'. In a hydraulic jack, a cylinder, a hollow plunger therein having means ‘atits upper end for engaging an object to be lifted, a head at the lower end of the plunger engaging the wall of the cylinder, an inelastic ?uid in the cylinder and plunger, means for circulating said ?uid to operate the plunger,-.and an‘ expansion tank mounted in ?xed relation with respect to- the cylinder and having means for establishing com munication between‘ the lower end thereof and whichpreferably has a concaved' periphery; and 7 1 is adapted to roll directly upon the wall of the the upper portionof the cylinder. 2. In a hydraulic jack, a cylinder, a 110110“ cylinder, as clearly shown. A rib 80 is shown provided upon the hanger adjacent its upper end , ‘plunger therein having means at its upper end adapted to bear ‘against the wall of the plunger for engaging an object to be lifted, a head a1 . the lower end of the plunger engaging the wali thereby to further support vthe‘ hanger. By thus pivotally supporting the hanger upon of the cylinder, an'inelastic fluid in the cylindei 70 the plunger, it may be relatively rotated about and plunger, a valve mechanism in the uppei a vertical axis, with respect to the operating end of the plunger, a;pump.pivotally>connecteé handle 58-54, as illustrated vin Figure 7.‘- This to the plunger for operating said valve mecha nism to circulate thei?uld'between the plunge] is a very "desirable feature'as it makes it pos sible to insert the jack under an automobile axle and cylinder to thereby operate the plunger, a! in close proximitynto a wheel thereof, with the‘ ' expansiontank mounted in ?xed relation witl 5 2,119,440 respect to the cylinder, and a conduit connecting the interior of the lower end of the expansion tank with the upper portion 01' the cylinder. 3. In a hydraulic jack, a cylinder, a hollow plunger therein having a lifting head at its up per end for engaging an object to be ‘lifted, means at the lower end of the plunger engaging the wall of the cylinder in leak-tight relation, an expansion chamber of large- proportions dis posed in ?xed relation to the cylinder, said cham her being sealed to the atmosphere, and means establishing communication between the lower end'of the expansion chamber and the upper end of the cylinder whereby additional ?uid may be drawn into the cylinder from said chamber, when the plunger is operated, and said addi tional ?uid being returned to the expansion chamber when the plunger islowered to its nor mal position. 4. In a hydraulic jack, a cylinder, a hollow plunger therein having a lifting head at its up per end for engaging an object to be lifted, means at the lower end of the plunger engaging the wall of the cylinder in leak-tight relation, and in an expansion chamber disposed in ?xed relation to the-cylinder and having means establishing communication between the. lower end thereof and the upper end of the cylinder, said expan sion chamber containing an additional supply of ?uid, a portion of which is drawn into the cylinder when the plunger is elevated, and which ?uid is returned to the expansion chamber when the plunger is lowered to its normal position, said expansion chamber being sealed to the at mosphere and of such size that the vacuum and pressure created therein by the reciprocal move ,ment of the plunger in the cylinder, will not eifect the operation of the plunger, and whereby the jack will not require a breather or vent duct, thereby'preventing grit, dust, and moisture from ,being drawn into the jack when the latter is operated. ' 5. In a hydraulic jack, a cylinder, a plunger therein having means at its upper end for en gaging an object to be lifted, an inelastic ?uid in‘ the cylinder, means for circulating said ?uid to operate the plunger, an expansion tank mount 16 ed in ?xed relation with respect to‘the cylinder, and means for establishing communication be tween the lower end of the expansion tank and the upper portion of the cylinder. 6.‘ In a hydraulic jack, a cylinder, a plunger 20 therein having means’at its upper end for en gaging an object to be lifted, an inelastic ?uid in the cylinder, a valve mechanism in the upper end of ‘the plunger, a pump pivotally connected to the plunger for operating said valve mecha 25 nism to circulate the ?uid between the plunger and cylinder, thereby to operate the plunger, an expansion tank mounted in ?xed relation with respect to the cylinder, and a conduit connect ing the interior of the‘lower end of the expan--' sion tank with the upper portion of the cylinder. , TIMOTHY C.v POMEROY.