U.S. patent number 3,807,694 [Application Number 05/231,881] was granted by the patent office on 1974-04-30 for vehicle service jack.
This patent grant is currently assigned to Applied Power Industries, Inc.. Invention is credited to John R. Butorac.
United States Patent |
3,807,694 |
Butorac |
April 30, 1974 |
VEHICLE SERVICE JACK
Abstract
Apparatus for engaging a portion of a vehicle to lift the
vehicle for servicing. The lift or jack includes a wheeled frame
supporting a fluid powered actuator or motor adapted to actuate a
hydraulic cylinder power unit to raise the load at a substantially
constant rate. Mechanical linkage is provided to manually actuate
the hydraulic cylinder to lift the load where a pressurized air
supply is unavailable. A mechanical linkage including a pivotal
lifting arm is operatively connected to the fluid powered hydraulic
cylinder unit to lift a vehicle upon the preselected operational
mode of said unit.
Inventors: |
Butorac; John R. (Hales
Corners, WI) |
Assignee: |
Applied Power Industries, Inc.
(Milwaukee, WI)
|
Family
ID: |
22870988 |
Appl.
No.: |
05/231,881 |
Filed: |
March 6, 1972 |
Current U.S.
Class: |
254/8B; 60/404;
60/386; 254/93R |
Current CPC
Class: |
B66F
5/04 (20130101) |
Current International
Class: |
B66F
5/04 (20060101); B66F 5/00 (20060101); B60p
001/48 (); B66f 003/24 () |
Field of
Search: |
;254/2B,2R,2C
;60/8R,8B,8C,93R,93L,386,404 ;91/4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simpson; Othell M.
Attorney, Agent or Firm: Petherbridge; Roy E. Lindgren;
Robert L. Gilhooly; Edward D.
Claims
What is claimed is:
1. A vehicle service jack comprising
a frame having spaced side plates carrying a pair of rotatable
wheels at one end thereof and a handle assembly at the opposite
end,
a pair of caster rollers supported by and spaced from said frame by
bracket means secured to said side plates such that said caster
rollers are freely pivotal about said bracket means,
a lift mechanism pivotally secured to said side plates between said
wheels and said caster rollers,
hydraulic pump means coupled to said lift mechanism for effecting a
pivotal lifting movement thereof upon the actuation of said pump
means,
an air motor carried between said side plates and adapted to be
connected to a source of pressurized air,
said air motor being operatively connected to said hydraulic pump
means for actuating said pump means upon introduction of
pressurized air to said motor, and
linkage means carried between said side plates and connecting said
handle assembly and said hydraulic pump means such that movement of
said handle assembly actuates said pump means to effect pivotal
lifting of said lift mechanism.
2. The apparatus of claim 1 further including valve means
selectively operable to actuate said hydraulic pump means upon
acutation of said air motor and said likage means separately or
simultaneously.
3. The apparatus of claim 1 further including release means carried
by said hydraulic pump means for pivotally retracting said lift
mechanism.
4. The apparatus of claim 1 wherein said lift mechanism comprises a
lift plate having depending side portions connected to a portion of
the hydraulic pump means to form a bell crank mechanism for
elevating a vehicle.
5. The apparatus of claim 4 wherein said lift mechanism further
includes a lift platform and a pair of head erecting bars supported
at one end from said frame side plates and connected at the
opposite end to said lift platform for maintaining said platform in
a horizontal position throughout the pivoted movement of said lift
mechanism.
6. The aparatus of claim 1 further including spring means coupled
to said lift mechanism and said frame to effect a retracting force
on said lift mechanism in a direction opposite to the pivotal
lifting mechanism thereof.
7. The apparatus of claim 1 wherein said hydraulic pump unit is
carried by said frame between said side plates.
8. The apparatus of claim 7 wherein said hydraulic pump unit is
pivotally supported from said side plates.
9. The apparatus of claim 1 wherein said air motor is supported
from said hydraulic pump unit.
10. Te apparatus of claim 1 wherein said hydraulic pump unit
includes a pump cylinder assembly actuable solely by said linkage
means to effect pivoted lifting of said lift mechanism.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to vehicle lifting apparatus and,
in particular, to an improved lifting jack operable manually,
through a pressurized air supply, or both modes of operation
simultaneously.
In the servicing of automotive vehicles, whether they are at a
location such as an automotive repair garage or along a roadway, it
is quite frequently necessary to elevate the vehicle in order to
work on portions of the engine, power train, or undercarriage. The
lifting jack which is operable by means of a source of pressurized
air is much more convenient for a mechanic in that it permits him
to elevate the vehicle with a minimum of manual labor; it is more
time saving and provides a rapid lifting of the vehicle. In
addition, the lifting jack which is operable by means of a
pressurized air supply can be actuated from a remote location such
that the mechanic can more closely inspect the car during the
lifting process. However, the source of pressurized air is not
always conveniently available in a repair garage and obviously is
unavailable when servicing a vehicle on a roadway. Therefore, the
lifting jack must be capable of elevating the vehicle through
manual operation of a handle.
While in many applications the lifting jack can be operated
manually to elevate a vehicle, it has been found in substantial
number of instances, due to the space required to operate the
handle, that the mechanical actuation of a jack is extremely time
consuming and in some instances it is impossible to apply the
lifting force in the exact position desired due to space
restrictions which interfere with the arc of the handle movement.
Therefore, the actuation of the jack through a pressurized air
supply is very desirable.
In the instant invention, both modes of operation are combined such
that the lifting jack may be operated manually or through a source
of pressurized air and therefore the advantages of each system are
combined into one device. In addition, to further increase the
speed of operation the lifting jack may be operated through the
application of pressurized air during actuation of the handle
mechanism.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to improve lifting
jacks.
Another object of this invention is to selectively actuate the
lifting mechanism manually through the use of a hand operated
hydraulic pump or by a pressurized air actuated fluid motor.
A further object of this invention is to provide an improved
lifting mechanism for selective actuation of the lift through the
use of a pressurized air fluid motor or manual operation.
Still another object of this invention is to actuate the lifting
mechanism through the use of a hand operated hydraulic pump and a
pressurized air actuated fluid motor simultaneously.
These and other objects are attained in accordance with the present
invention wherein there is provided a lifting jack with a rigid
frame or base having a plurality of rollers attached thereto for
permitting the jack to be rolled upon a surface to any desired
position beneath the vehicle. A lifting arm is pivotally connected
to the frame or base and actuated by means of a hydraulic fluid
cylinder selectively operated through the use of a fluid motor
driven by a pressurized air supply or manually through operation of
a handle mechanism.
DESCRIPTION OF THE DRAWINGS
Further objects of the invention, together with additional features
contributing thereto and advantages accruing therefrom, will be
apparent from the following description of one embodiment of the
invention when read in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a perspective view of the portable lifting jack;
FIG. 2 is a side elevation view of the lifting jack with portions
removed to better illustrate the internal elements thereof;
FIG. 3 is a plan view of the lifting jack with portions broken away
to better illustrate the internal structure thereof;
FIG. 4 is a detailed sectional view showing the hydraulic cylinder
power unit used to raise the lift elements;
FIG. 5 is a detailed sectional view of the valve arrangement used
in conjunction with the air motor;
FIG. 6 is a detailed sectional view of the air motor used to
actuate the hydraulic cylinder; and
FIG. 7 is a sectional view of the hydraulic cylinder power unit of
FIG. 4 taken along lines 7--7 and reduced in size.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to FIGS. 1 and 2, there is shown a portable lifting
jack 100 including a lifting mechanism 20, a hydraulic power unit
30 for elevating the lifting elements, an air motor 60 and a
mechanical linkage 40, for actuating the hydraulic pump thereby
raising the lifting elements. The lifting mechanism 20 is pivotally
supported between a pair of chassis side plates 1 and 2 which are
preferably made from steel plate of appropriate thickness and held
in parallel, spaced relationship with respect to each other by
means of a forward spacer 3 and rearward spacer 4 secured to the
side plate by any suitable means.
The forward portion of the chassis side plates 1 and 2 rotatably
support an axle 6 to which is secured a pair of wheels 7 for moving
the portable lift apparatus beneath a portion of a vehicle to be
elevated. The wheels 7 are secured to axle 6 by means of retaining
rings 8 in the conventional manner. Axle 6 is supported in the side
chassis plates by conventional bearings. Brackets 9 are secured to
the chassis side plates and each bracket carries a caster assembly
11 appropriately secured thereto to facilitate the positioning of
the jack assembly beneath a vehicle. The brackets 9 space the
caster assemblies 11 a sufficient distance from the side plates 1
and 2 to permit the caster roller to pivot completely about the
connection point.
As best shown in FIGS. 2 and 3, the lift arm assembly 20 comprises
a lift plate 21 having depending side portions 22 which extend in
parallel, spaced relationship with respect to each other and are
supported in the chassis side plate 1 and 2 for pivotal movement
such that the depending side portions move in a plane parallel to
that of the side plates. The lift arm assembly is supported between
the chassis side plates 1 and 2 by means of a tubular lift bearing
assembly 23 which is secured between the side plate to permit the
pivoting of the lift arm assembly thereabout. A portion of each
depending side plate is formed with an aperture which carries the
tubular lift bearing assembly 23. The lift mechanism 20 is pivoted
with respect to the side plates 1 and 2 to elevate a vehicle upon
actuation of the hydraulic power unit 30. The depending side plates
22 are formed with apertures which support the bell crank shaft 28.
The roll pin 29 mechanically secures a rod 31 of the hydraulic pump
unit 30 to the lifting mechanism 20 such that upon extension of the
rod 31 from the hydraulic pump unit the lifting mechanism 20,
acting as a bell crank, will pivot upward effecting a lifting
force.
A lift head or saddle 24 is carried by the lift arm assembly 20 and
comprises a head platform 25 and a pair of parallel, platform
support legs 26 depending therefrom and secured to opposed portions
of the sides 22 of the lift arm 21 by a suitable bearing to allow
the lift head to pivot relative to the lift arm assembly. The
platform support legs 26 have a pair of aligned openings adjacent
to their lower extremities to which a pair of head erecting
parallel link bars 27 are pivotally connected. The opposite end of
the head erecting bars 27 are each pivotally supported (12) to the
chassis side plates 1 and 2 such that the lift head 24 will be
continuously held erect throughout all positions of normal
operation of the lift arm mechanism thereby maintaining the
platform 25 in a continuous horizontal orientation. Tthe movement
of the head erecting bars 27 is parallel to the chassis side plates
1 and 2 and the path of the lift arm assembly 20 when actuated by
means of the hydraulic power unit 30. A tension spring 13 is
secured at one end to a connecting rod 14 (joining the pair of head
erecting bars 27) and to the forward spacer rod 3 at its other end
to provide a retracting force on the lift arm mechanism 20 to
facilitate lowering of the lift mechanism after an elevated vehicle
has been lowered to its original position.
The hydraulic power unit 30 is pivotally supported between the
chassis side plates 1 and 2 by means of suitable bearings or
bushings supported through the chassis side plates and engaging a
portion of the hydraulic pump unit. Actuation of the hydraulic
power unit is effected by means of either an air motor 60 or
through a mechanical linkage assembly 40 which act to drive a
piston carried within the hydraulic power unit effecting the
extension of the connecting rod or plunger 31 which is coupled to
the lift arm assembly 20. The reciprocating, hydraulic power unit
is carried between the chassis side plates and operatively
connected with the air motor 60 and mechanical linkage system as
best shown in FIGS 4, 5 and 6.
The hydraulic power unit 30 (shown in sectional detail in FIG. 4)
includes a valve housing 110, secured to one end of a hydraulic
cylinder 115 the other end of which is closed by a top cap 120 to
form a sealed chamber. A hydraulic fluid reservoir 116 is formed
between the outer wall of the hydraulic cylinder 115, the top cap
120 and valve housing 110 by a reservoir plate 117 forming a closed
chamber with ports 118 which function in a manner to be hereinafter
described. The hydraulic fluid reservoir is of a size sufficient to
contain a quantity of hydraulic fluid for use in actuating the
plunger rod 31 to effect elevation of the lifting mechanism 20.
Positioned within the hydraulic cylinder 115 is a plunger-piston
assembly 130. The plunger rod 31, which is secured to the lift arm
assembly 20, is formed with a reduced end portion 131 carrying a
piston or plunger cup 140 and comprises an extension of the
assembly 130.
The plunger cup 140 is utilized to effect a hydraulic seal on the
plunger 31 and the resultant force is used to elevate the lifting
mechanism 20. To that end, a support disc 141 is carried on the
reduced end portion 131 of the plunger abutting the shoulder formed
thereby. The plunger cup or piston 140 is supported by the disc
with a suitable back-up washer 142 and held thereto by means of a
nut and washer assembly 144 threaded onto the reduced end portion
of the rod 131. The plunger-piston assembly 130 thereby forms a
hydraulically sealed piston whose movement is dependent upon the
hydraulic pressure forces exerted against the face of the plunger
cup 140.
Positioned within the hydraulic chamber 150 is a high limit stop
mechanism 170 which functions to prevent the hydraulic
plunger-piston assembly 130 from being driven out of the chamber
and thereby reduces the structural strength requirement of the top
cap 120. The plunger rod 31 is formed with an orifice (176) passing
through the reduced end portion (which carries the plunger cup 140)
with the orifice forming a connecting fluid conduit from hydraulic
chamber portions 150 a to 150 b by means of the fluid communication
of the chamber 176 with a connecting conduit in which is supported
a stop pin 171.
The connecting conduit 176 is normally sealed to prevent hydraulic
fluid flow therethrough by means of a ball check valve 173 in place
by a spring 174 suitably positioned by a hollow retaining ring 175
threaded into the reduced end portion of the plunger 31. In
operation, as the plunger is extended to the left at its
furthermost position (FIG. 4), the stop rod 171 will engage the
inner face 120 a of the top cap moving the stop rod slightly to the
right in the enlarged opening in which it is carried. This movement
of the limit stop rod mechanically unseats the ball check valve 173
from its valve seat by means of the connecting linkage 172. The
fluid in the chamber 150 a is therefore metered through the conduit
176 at a controlled rate into the portion 150 b of the hydraulic
chamber. This metered flow of hydraulic fluid through the orifice
connecting these two portions of the chamber prevents an extensive
pressure build-up in chamber 150 a which would tend to drive the
piston-plunger assembly 130 out through the top cap 120, but
maintains sufficient pressure to hold a vehicle in the lifted
position. The fluid passing from chamber 150 a to 150 b passes out
through the ports 118 into the intake tube 111 through the
connecting conduit 113, all check valves 122 and 124, through
conduit 123 and is returned to the portion 150 a of the hydraulic
cylinder chamber.
As previously stated, the hydraulic power unit 30 may be actuated
by means of an air motor 60 or manually through pivotal movement of
the handle 5 which is connected to a mechanical linkage assembly 40
to effect the desired lifting movement of the lift arm mechanism
20. The air motor 60 (shown in sectional detail in FIG. 6 of the
drawings) is coupled to the hydraulic power unit 30 in a manner
shown in FIG. 5. The air motor 60 is actuated to elevate the
lifting mechanism by means of a pressurized air source supplied
through conduit (shown in FIG. 2 with the air line 61 and control
valve 59 rotated 90.degree. to better illustrate these
elements).
The air motor 60 comprises a valve housing 62 with a cylindrical
displacement chamber 64 extending from one end thereof. The chamber
is formed by a cylindrical wall 66. Reciprocally received in this
displacement chamber 64 is a piston 68. Piston 68 is provided with
a suitable sealing ring or packing 69 to form a fluid-tight seal.
As shown in FIG. 6, the sealing means is accomplished by a sealing
ring confined in an annular groove and slidably coacts with the
inner surface of wall 66. The piston 68 is biased toward the valve
housing 62 by a compression spring 63 which is seated between the
reverse face of the piston 68 and an end plate 81 secured to the
cylinder wall 66.
A hydraulic pump assembly 85 is secured to the end plate 81 in
fluid communication with the displacement chamber 64. A piston rod
84 carried at one end by the piston 68 is axially aligned with an
internal chamber or bore formed in the plunger body 86 and
appropriately sealed by an "O" ring to form a hydraulic or
fluid-tight seal thereabout. The end of the plunger body 86 remote
from the piston 84 is formed to threadingly engage a manifold 96
which is coupled to a suitable passage or port of the hydraulic
power unit 30 such that actuation of the air motor 60 will result
in the displacement of the plunger-piston assembly 130 of the
hydraulic power unit as will be hereinafter described in
detail.
The valve housing 62 of the air motor 60 is formed with a
cylindrical chamber 70. Chamber 70 is enlarged at surface 71.
Reciprocally received within the chamber 70 is poppet member 72
having a valve 74 at one end thereof and a piston portion 76 at the
other end. The piston 76 has a first periphery 77 closely received
by the inner surface of the chamber 70 and a second periphery 79
closely received by the surface 71. A differential pressure chamber
80 is thus formed between the walls of the chamber and the exterior
walls of the piston. The stem portion of the poppet 72 reciprocally
movable within these chambers is formed to receive a spring biased
(75) rod 78 which acts to control the actuation of a ball check
valve 92.
The end 60 a of the valve housing removed from the cylinder 66 is
formed with an air inlet 90 which is reduced at 92 to form a valve
seat for a spring biased (93) ball check valve 94. As the rod 78
moves to the right (referring to FIG. 6) it unseats the ball 94 for
a purpose to be hereinafter described. The poppet 72 carries an
elastomeric grommet 73 which closes an opening 67 when the poppet
72 is moved to the right and opens the opening as the poppet moves
to the left. Te grommet is elastomeric so as to reduce chattering
and to absorb the shock of the piston operating in its cycle.
In operation, a source of pressurized air is supplied to the inlet
90 with the ball valve initially unseated. As the air bypasses
check ball 94, it simultaneously enters passageways (not shown)
which communicate with the differential pressure area 80 creating a
resultant net force to the right (FIG. 6). The effect of this force
is to move poppet 72 and the rod 78 to the right to thereby
maintain the check ball 94 away from its valve seat 92. During this
same interval, air is delivered to the expansion chamber 64 which
moves the piston 68 to the left.
When piston ring 69 passes servo-valve port 57 in chamber 66, air
is conducted to chamber 71 through passages (not shown) creating
the differential pressure needed to drive poppet 72 to the left.
This opens valve opening 67 and allows rod 78 to move to the left.
Spring 93 and air line pressure closes ball check valve 92. In
order to prevent poppet 72 from attaining a balanced or hydraulic
dead center position with the valve opening 67 being open and the
inlet valve 92 being open, the spring 75 biases the poppet away
from ball check valve 92 which is, therefore, closed by the biasing
action of spring 93.
As grommet 73 is moved to the left, the air within the expansion
chamber 70 is permitted to escape through an outlet not shown.
Since the ball 94 is seated, incoming air is stopped during the
exhaust of the air from chamber 70 through the outlet. With the
decay of air pressure in chamber 70, the biasing spring 63 returns
the piston 68 toward the valve housing 62. As the piston 68
approaches the poppet, the ball 94 is again moved from the seat 92
by rod 78 and the cycle again repeated.
The cyclic operation of the air motor reciprocates piston 68 back
and forth in the displacement chamber 64 thereby reciprocating the
piston 84 of the hydraulic plunger assembly 85 and creating a force
on the plunger-piston assembly 130 of the hydraulic power unit 30
extending the plunger 31 affecting a lifting movement of the lift
arm mechanism 20.
As previously discussed, the air motor 60 is actuated through a
source of pressurized air 61 controlled by a valve 59 secured to
the handle 5. A source of air pressure (not shown) is coupled to
the valve 59 and upon actuation of the lever 58 the pressurized air
flows through the supply line 61 into the fluid motor to effect
reciprocation of the piston 68 and, thereby, the plunger 84
actuating the hydraulic power unit 30 elevating the lift mechanism
20.
Referring again to the hydraulic power unit 30, reciprocation of
the plunger 84 of the air motor 60 withdraws hydraulic fluid from
the hydraulic fluid reservoir 116 through the intake tube 111 as
the plunger is withdrawn towards the right (as seen in FIG. 5)
thereby unseating the ball check valve 112 from its valve seat
drawing the hydraulic fluid through fluid conduit 113. Upon
reciprocation of the air motor, the plunger 84 is moved to the left
and the valve 112 is again seated and ball check valve 114 is
opened to allow the hydraulic fluid to be conveyed into portion
150a of the hydraulic chamber 150 via passage not shown moving the
piston-plunger assembly to the left as shown in FIG. 4 for raising
the lifting mechanism 20. As the actuation of the air motor 60 is
repeated, hydraulic fluid is continually withdrawn from the fluid
reservoir 116, or the portion 150 b of the hydraulic chamber 150,
and passed into the portion 150 a of the chamber 150 affecting
movement of the piston-plunger assembly 130 to the left.
As stated, the hydraulic power unit 30 may be actuated by manual
manipulation of a pivotal lever or handle 5. To this end, a pump
cylinder 160 is secured into the valve housing 110. The pump
cylinder includes a speed pump plunger 162 slidably carried within
the pump cylinder and mechanically coupled to the linkage mechanism
40. The speed pump plunger 162 is concentrically positioned about a
power pump plunger 164 secured into the valve housing 110 and
having a passageway defined therethrough in fluid communication
with the passageways 113 and 213 (FIGsS. 4 and 7) at a point
between the ball check valves 122-124 and 222-224. Suitable seals
and packings such as O-rings provide a fluid-tight seal between the
plunger 162 and the power pump plunger 164. Due to the positioning
of the valves in the housing 110, valves and ports 122, 124 and 113
are shown in FIG. 4 only and valves and ports 222, 224 and 213 are
shown in FIG. 7 only.
As the plunger 162 is moved outwardly (referring to FIG. 4) by
means of the mechanical linkage system, the plunger withdraws
liquid from the hydraulic reservoir 116 and the area 150 b of the
hydraulic chamber through the intake tube 111, passageways 113 and
213, unseating the ball check valves 122 and 222, and withdrawing
the hydraulic fluid into the passageway 163 and the internal bore
portion of the plunger. At this time, ball check valves 124 and 224
are drawn downward against their respective valve seats. Upon the
plunger 162 being operated in the reverse direction (to the left as
shown in FIG. 4) the ball check valves 122 and 222 are firmly
seated against their valve seat and the hydraulic fluid in the
passageway 163 is passed through ball check valves 124 and 224,
which are lifted from their valve seats, through passageways 123
and 256 into the chamber 150a of the hydraulic chamber 150. As the
plunger 162 is cyclically operated, additional quantities of
hydraulic fluid are passed in this manner resulting in the piston
plunger assembly 130 moving outwardly to the left raising the
lifting elements or mechanism 20.
The hydraulic fluid continues to be passed through this dual
conduit (123,256) system into the chamber 150 a until the pressure
reaches approximately 200 psi. This dual conduit flow raises the
lifting elements very quickly until the load or vehicle is engaged
creating the pressure rise.
Upon the pressure increasing, pressure relief valve 180 is
actuated, dumping the fluid heretofore passing through ball check
valve 224 and conduit 256, through conduits 182 and 183 back into
the reservoir 116 thereby decreasing the force required to operate
the plunger 162.
The plunger 162 is connected to the mechanical linkage system 40
for effecting reciprocation thereof. A handle 5 extends from a yoke
41 which is pivotally secured between frame plates 1 and 2 by any
suitable means such as shaft 42. The yoke 41 is linked to and
coacts with segment 44 mounted on shaft 42 between the outer ends
of the yoke 41. The pivotal lever arm or segment 44 is formed with
a bifurcated portion such that each portion of the bifurcated
segment is appropriately connected to a power link bar 45 extending
from each of the bifurcated segments and pinned at the opposite end
to the end of the plunger 162. Movement of the handle 5 causes the
yoke 41 to move the power link 45 to reciprocate the plunger 162 of
the pump cylinder 160 thereby effecting lifting of the lift
mechanism 20. A suitable stop 43 is provided to limit the travel
arc of the handle.
After the lift mechanism 20 has been elevated raising the vehicle
or load, when it is desired to return the load to its initial
position and remove the jack, the release assembly 50 is actuated
by rotating knob 51 positioned at the top of the handle 5. Rotation
of knob 51 rotates a rod 52 passing through the center of the
handle 5 and connected to a pivot or universal assembly 53 to
effect rotational movement of release valve link 54 coupled to the
release valve plunger 55. Movement of the release valve plunger 55
outward (as seen in FIG. 4) unseats a ball check valve 56 from its
valve seat allowing the force of the vehicle acting on the lift arm
mechanism 20 to be transmitted through the plunger 31 to the
hydraulic chamber 150 whereat the hydraulic fluid in chamber 150 a
is forced out through port 123 seating ball check valve 124 tightly
against its valve seat and passing out through suitable passageways
in the valve housing 110 to be returned to the hydraulic fluid
reservoir 116. In this manner, whether the hydraulic power unit is
actuated by the air motor 60 or manually through operation of the
pump cylinder 160, release of the load is effected by unseating
ball check valve 156 from its valve seat within the valve housing
110. The unseating of this ball check valve allows the hydraulic
fluid to return through passages (not shown) to the hydraulic fluid
reservoir 116. When the load has been returned to its initial
stable position, the action of the tension spring 13 provides a
sufficient load to fully retract the lift mechanism 20 and move the
plunger-piston assembly 130 to the right as shown in FIG. 4.
While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that this invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *