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Патент USA US2119440

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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.
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