Note: Descriptions are shown in the official language in which they were submitted.
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LOAD RESPONSIVE FLUID CONTROL VALVES
This is a continuation in part of application Serial
No . 522,324 filed November 8, 1974 for "Load Responsive Fluid
Control Valves", Serial No. 559,818 filed March 19, 1975 or
"Load Responsive Fluid Control Valves" and Serial No. 655,561
filed February 5, 1976 for "Load Responsive Fluid Control System".
,.
BACKGROUND OF THE INVENTION .:
This invention relates generally to load responsive fluid
control valves and to fluid power systems incorporating such
valves, which systems are supplied by a single fixed or variable
displacement pump. Such control valves can be used in a multiple ~ ;
load system, in which a plurality of loads is individually ~ ~;
controlled under positive and negative load conditions by separate
control valves. '
In more particular aspects this invention relates to ~ ~-
direction and flow control valves capable of controlLing simul- ~`
taneously a number of loads under both positive and negative load
20 conditions. `
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In still more particular aspects this invention relates ~
to direction and flow control valves capable of controlling ` ~'
simultaneously multiple positive and negative loads, which while
controlling a negative load interrupt pump flow to the motor
25 providing the motor inlet with fluid from the pressurized system ~;~
exhaust.
Closed center load responsi~e fluid control valves are
very desirable for a n~ber of reasons. They permit Load control ;~
with reduced power losses and there~ore~ increased system
30 efficlency and when controlling one load at a time provide a -
feature o~ flow control irrespective of the variation in the -~
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magnitude o the load. Normally such valves include a load
responsive control~ which automatically maintains pump discharge
pressure at a level higher, by a constant pressure differential,
than the pressure required to sustain the load. A variable
orifice, introduced between pump and load, varies the flow
supplied to the load, each orifice area corresponding to a
different flow level, which is maintained constant irrespective
of variation in magnitude of the load. The application of such a
system is, however, limited by several basic system disadvantages.
Since in this system the variable control orifice is
located between the pump and the load, the control signal to a
pressure regulating throttlLng device is at a high pressure level, ~;
introducing high forces in the control mechanism~ Another disadvan-
tage of such a control is that it regulates the flow of fluid into
the motor or actuator and therefore does not compensate for fluid
compressibility and leakage across both motor and valve. -~te~d
control valve for such a system is shown in U.S. Patent #3,488,953
.:.
issued to Hausler.
The valve control can maintain a constant pressure
differential and therefore constant flow characteristics when
operating only one load at a time. With two or more loads, simul~
taneously controlled, only the highest of the loads will retain
the flow control characteristics, the speed of actuation of the
lower loads varying with the change in magnitude of the highest `
load. This drawback can be overcome in part by the provision of a ;
proportional valve as disclosed in my U.S. Patent ~3,470,694, dated
October 7, 1969 and also in U.S. Patent ~3,455,210 issued to Allen ~` -
on July 15, 1969. However, while these valves are effective in
controlling multiple positive loads they utilize a controlling
orifice located between the pump and the motor during positive
load mode of operation and therefore control the fluid flow into -~
the fluid motor instead of controlling fluid flow out of the fluid ~
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motor. These valves also while effective when controlling positive
loads, when operating negative loads connect system pump with ~ ?
actuator inlet, unnecessarily using the pump flow and subjecting
actuator to increased loads.
This drawback can be overcome in part by provision of
fluid control valves as disclosed in U.S. Patent #3,807,447
issued to Masuda on April 30, 1974. However, while these valves
utilize actuator exhaust fluid ~or actuator inlet flow require~
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ment when controlling negative loads they regulate actuator inlet
pressure by bypassing fluid to a down stream load circuit. Masuda's
valves and their proportional control system are based on series
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type circuit in which excess fluid flow is successively diverted
from one valve to the other and in which Ioads arranged in series
determine the system pressure. In such a system flow to the last
valve operating a load must be delivered through all of the bypass
..,..: ..:
sections of all of the other system valves, resulting in higher
fluid throttling loss. These valves are not adaptable to simul- ;
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taneous control of multiple loads in parallel circuit operation
since they do not provide system load control pressure signal to
the pump flow control mechanism. Also controls of these valves
respond to the pressure differential due to flow across a variable
orifice therefore varying the area of flow between the actuator
inlet and actuator outlet with variation in the system pressure
: . , , . ,:: .. :
during control of negative load~
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SUMMARY OF THE INVENTION ~
.
It is therefore a principal object of this invention to
provide an improved load responsive direction ancl flow control
; valve which would retain its flow control characteristics when
controlling a positive load by maintaining a constant low pressure
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level at the outlet oE the motor or actuator.
Another object of this invention is to provide an improved
load responsive direction and flow control valve which when
controlling positive load will retain its proportional flow char-
acteristics in a system in which multiple positive loads aresimultaneously controlled.
Still another object of this invention is to provide an
improved load respcnsive direction and flow control valve which
will automatically block system pump from motor or acutator inlet
lO while connecting it with valve exhaust manifold during control of ~ -~
negative load.
Still another object of this invention is to provide an
... .
improved load responsive direction and flow control valve equipped
with a pressurized exhaust manifold, flow from which supplies the
:: ~ .. :
inlet flow requirements of a motor or acutator controlling a
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negative load.
Briefly the foregoing and other additional objects and
advantages of this invention are accomplished by providing a novel
load responsive direction and flow control valve whlch will
provide a proportional flow control of positive load in a system
in which multiple positive loads are simultaneously controlled - -
and which in presence of a negative load will automatically
disconnect the pump from the actuator inlet connecting it with
pressurized valve exhaust manifold.
Additional objects of this invention will become apparent -
when referring to the preferred embodiment of ~he invention as ;~ ,
shown in the accompanying drawing and described in the following ;
detailed description.
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DESCRIPTION OF THE DRAWING
Fig. 1 is a longitudinal sectional view o an embodiment
of a control valve having a throttling and blocking spool ;~
responsive to pressure in the actuator outlet for use in load
responsive fluid control system, with lines, system pump, pump
control, second load responsive valve~ exhaust relief valve and
system reservoir shown diagramatically.
10DESCRIPTION OF THE PREFERRED EMBODIMENT ~ -;
Referring now to the drawing Fig. 1 an embodiment of a
flow control valve, generally designated as 10, is shown interposed `;
between a diagramatically shown fluid motor 11 driving load ~ and -
~a pump 12 of a fixed displacement type driven through a shaft 13
by a prime mover not shown. Similarly, a flow control valve 14,
identical to the flow control valve 10, is interposed between a
diagramatically shown fluid motor 15 driving a load W and the `~
., . ~ .
pump 12. Fluid flow from the pump 12 to flow control valves 10 and
14 is regulated by a differential pressure relief valve 16 which
can be mounted as shown on the pump 12, or be an integral part of
the flow control valve 10. If the differential pressure relief
valve 16 is made part of the valve assembly it is connected to the
fixed displacement pump 12 by a high pressure line capable of
transmitting full flow of the pump~ The differential pressure
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relie valve 16, in a well known manner, by bypassing fluid from
the pump 12 to a reseryoir 17, maintains discharge pressure of the
pump 12 at a level, higher by a constant pressure differential, ~;
than load pressure developed in fluid motor 11 or 15.
The flow control valve 10 although it can be of a three-
way type is shown as a fourway type and has a housing 18 provided
with bore 19, axially guiding a valve spool 20. The valve spool
20 is equipped with lands 21, 22 and 23 which in neutral position
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o the valve spool 20/ as shown in Fig. 1 isolate a fluid supply
chamber 24, load chambers 25 and 26 and outlet chambers 27 and 28.
The outlet chambers 27 and 28 are connected through lines 29, 30,
31 and 32 to an exhaust chamber 33 and throush an exhaust relief
valve, generally designated as 34 and line 35 to the reservoir 17.
The pump 12 through its discharge l.ine 36 and a check : ;
valve 37 is connected to a fluid inlet chamber 38. Similarly the `:
pump 12 is connected through discharge line 39 and a check valve
40 to fluid inlet chamber of flow control valve 1~. Control bore
41 connects the fluid inlet chamber 38 with the fluid supply
chamber 24, the fluid exhaust chamber 33, the fluid outlet chamber
,~
27 and fluid control space 42. A control spool 44, axially slidable
in control bore 41, projects into control space 42 and fluid outlet .
chamber 27 and is provided with stem 45 terminating in throttling
surface 43 and cut off plane 46 and control plane 47. Throttling
surface 43 may be of a conical type as shown in Fig. 1 or in a
well known manner can be substituted by suitable throttling
grooves. The control spool 44, as shown in Fig. 1, isolates the
exhaust chamber 33 from the supply chamber 24 and with cut off
20 plane 46 and throttling surface 43 permits communication between ~;
the fluid inlet chamber 38 and the fluid supply chamber 24. The ``~ .
control spool 44 is biased by spring 46a towards position to ~; ~
provide free passage between the inlet chamber 38 and the supply . .
chamber 24.
Excess pump flow from the differential pressure relief
valve 16 is delivered through line 48 to exhaust line 31, which
communicates with the exhaust chamber 33, a bypass check valve
49, lines 29 and 30 which connect to the outlet chambers 27 and 28,
the exhaust relief valve 34 and through line 50 with all of
exhaust passages of the flow control valve 14. The bypass check
valve 49 is interposed between exhaust line 31 and the fluid
supply chamber 24.
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Positive load sensing ports 51 and 52, located between
load chambers 25 and 26 and the supply chamber 24 and blocked in
neutral position of valve spool 20 by land 22, are connected
through signal passage 54, a chack valve 55 and signal llne 56 .
to the differential pressure relief valve 16. In a similar manner
positive load sensing ports of flow control valve 14 are connected
through line 57, a check valve 58 and signal line 56 to the ,
differential pressure relief valve 16. Negative load sensing ports ;i ~;
59 and 60 located between the load chambers 25 and 26 and the ~ .
outlet chambers 27 and 28 and blocked in neutral position of valve ~.
spool 20 by lands 21 and 23 are connected through signal passage .~
61 with control space 42. ..~ ~ .
The exhaust relief valve, generalIy designated as 34, ,` .
interposed between combined exhaust circuits of flow control valves .~
10 and 14 including bypass circuit of pump 12 and reservoir 17, ~ .:
is provided with a throttling member 62, biased by.. a spring 63 .. ~
towards engagement with seat 64. :
Land 22 is provided with first flow slots 65 located ~ -~
between the load chamber 25 and the supply chamber 24 and second
flow slots 66 located between the load chamber 26 and the supply ...~ ..
chamber 24. Land 22 is also provided with shorter communication
slots 67 and 68 located in the plane of load sensing ports 51 and . ~ :
52. Land 21 is provided with first exhaust metering slots 69 and .. .
first communication slot 70 located between the load chamber 25 ~
and the outlet chamber 27. Land 23 is provided with second exhaust ~ ~:
metering slots 71 and a second communication slot 72 located .
between the load chamber 26 and the outlet chamber 28.
: The sequencing of the control spool 44 is such that when
moved from right to left, when cut off plane 46 closes communi~
cation between the inlet chamber 38 and the supply chamber 24,
control plane 47 is positioned at the point of opening communi~
cation between the supply chamber 24 and the exhaust chamber 33O
Further movement of the control spool 44 rom right to left will .
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establish full flow communication between the exhaust chamber 33
and the supply chambe.r 24.
As previously described with flow control valves 10 and ~.
14 controlling loads ~ and W the diferential pressure relief ;
valve 16, in a well known manner, will regulate fluid flow
delivered f~rom the fixed displacement pump 12 to discharge line
36, by bypassing the fluid flow to line 48 and exhaust line 31,
to maintain the pressure in discharge line 36 higher, by a
constant pressure dif~erential, than the highest load pressure
signal transmitted through the check valve system to the signal
line 56. Therefore with valve spools of flow control valves 10 ` .
and 14 in their neutral position, blocking positive load sensing
ports 51 and 52, signal pressure input to the differential - ~ .
pressure relief valve 16 from the signal line 56 will be at
15 minimum pressure level. `
With fixed displacement pump 12 started up the differ- ~.
ential pressure relief valve 16 will bypass through line A8, .. ..
exhaust line 31, the exhaust relief valve 34 and line 35 all of
pump flow to the system reservoir 17 at minimum pressure.;level,
equivalent to preload in the spring 63, while automatically
maintaining pressure in discharge line 36 at a constant pressure, ` :
higher by a constant pressure differential, than pressure in .:.
signal line 56, which is equal to minimum pressure in exhaust
line 31. Therefore all of pump flow is diverted by the differ- - :
25 ential pressure relief valve 16 to the low pressure exhaust ~;
circuit, as previously described, without entering flow passages
of flow control valves 10 and 14.
Assume that while constant standby pressure condition
is maintained in discharge line 36 the valve spool is initially ~ -:
displaced from let to right to connect the load chamber 25
through communication slot 67 with the positive load sensing port
51 and to connect load chamber 26 through communication slot 72 :;
with the negative load sensing port 60, while lands 21, 22 and 23
' ~t
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still block communication between the supply chamber 24, load .
chambers 25 and 26 and outlet chambers 27 and 28. Assume also that
actuator 11 is subjected to a positive load. I,oad pressure trans~
mitted from actuator 11, the load chamber 25, the positive load
sensing port 51 and signal passage 54, in a well krlawn manner,will ~ ;
open the check valve 55, close the check valve 58 and reacting ~ :
through signal line 56 on the differential pressure relief valve
16 increase pressure in discharge line 36 to maintain a constant . .
pressure differential between the pump pressure in discharge line
lO 36 and load pressure in signal line 56. This pump discharge :: ;
pressure will be transmitted through discharge line 36 to the fluid
inlet chamber 38 and pa~st cut off plane 46 to the ~luid supply
chamber 24. Since control space 42 is connected to the negative
load sensing port 60 which is sub~ected to minimum pressure the
control spool 44 will be maintained by the spring 46a in position ~
as shown in Fig. 1. : :
Assume that from the position in which load chamber 25 .
is connected to the positive load sensing port 51 the valve spool .
20 is further displaced to the right, connecting the load chamber
25 with the supply chamber 24 while the load chamber 26 is still
isolated from the outlet chamber 28 by land 23. The pressure in
the load chamber 25 will begin to rise, this change being trans-
.
mitted through the positive load sensing port 51, in a manner as
previously described, to the differential pressure relief valve 16, .
proportionally increasing the pressure in discharge line 36. This
increase in positive load pressure in the load chamber 25 will .
overcome resistance of load L and start gradually increasing
pressure in load chamber 26. Since the load chamber 26 is connected
through second communication slot 72 and negative sensing port 60 .`~ :~
30 to fluid control space ~2, the rising pressure in the control -
space 42, reacting on the cross-sectional area of ~ontrol spool 44
~ " ,~
will overcome the preload of the control spring 46a and move the
control spool 44 from right to left, closing by cut off plane 46
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communication between the inlet chamber 38 and the supply chamber ',
24. The system will find itself then in a condition of equilibrium ~ ~
with spool 44 assuming a modulating position in which it will , .' ''
maintain the pressure in the load chamber 26 at a relatively ', ''
constant level, as determined by the preload in the spring 46a. ~ .
Further movement of the valve spool 20 from let to right ~ ,
will es~blish communication by second exhaust metering slot 71
between load chamber 26 and the outlet':chamber 28. Since outlet ~ ~;
chamber 28 is maintained at low exhaust pressure level by the ,.,,:'
exhaust relief valve 34, fluid will flow from the load chamber 26
to the outlet chamber 28 resulting in a momentary drop in pressure ' ,
in the load chamber 26. This decrease in pressure will result in
change in the modulating position of control spool 44, which will ' .
automatically assume a new throttling position, to maintain the
load chamber 26 at a constant pressure level. Since both the load ,,: '
chamber 26 and outlet chamber 28 are maintained at constant ' :": '~.
pressure levels, a constant pressure differential is maintained
between these chambers and the flow between these chambers will ~ ~
be proportional to opening of second exhaust metering slots 71, ' ~.
20 which in turn is proportional to the displacement of the valve ~,
spool 20. Therefore each positio~ of the valve spool 20 will
correspond to a certain specific constant flow level from actuator
11, irrespective of the magnitude of the load L. While control '
action of the control spool 44 is taking place the discharge '~ -:
pressure,of the fixed displacement pump 12 in the discharge line ,' i.
36 is automatically maintained by the differential pressure relief
valve 16 at a pressure, higher by a constant pressure differential `-, '
than the pressuxe in the supply chamber 24 and the load chamber
25.
Assume that valve spools of flow control valves lO and 14
were simultaneously actuated to a position, at which fluid flow
is delivered to actuators ll and 15. Assume also that loads L ~ . :
and W are positive and that the load W is higher than load L. ~ "
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Flow control valve 14, in a manner as previously described, will
provide proportional control of load W, fixed displacement pump 12
providing discharge pressure higher by a constant pressure differ- ~ :
ential than the pressure in the supply chamber of the flow control
valve 14. Flow control valve 10 will then be supplied with a
pressure much higher than that necessary to actuate load L. Since,
as previously described, the control spool 44 will assume a -
modulating position, to maintain the load chamber 26 at a constant :~
pressure level, excessive pressure will be throttled at the
throttling surface 43, the flow through the control valve 10 being
proportional to the displacement of the valve spool 20 and indepen~
dent of the discharge pressure of the fixed displacement pump 12. .:.
Assume that while constant minimum standby pressure
condition is maintained in discharge line 36, the valve spool 20 ~' ;
is initially displaced from right to left connecting the load
chamber 26 with positive load sensing port 52 through communication
slot 68 and also connecting the load chamber 25 with the negative
load sensing port 59. Assume also that the fluid motor 11 is
subjected to a negative load, pressurizing the load chamber 25 and
maintaining the load chamber 26 at minimum pressure. Therefore .
pressure signal, transmitted through the positive load sensing port
52, will not change the setting of differential pressure relief
valve 16, the pump 12 maintaining discharge line 36 at minimum
pressure level. The negative load pressure from the load chamber ~
25 will be transmitted through signal:passage 61 to control space ~ :
42 where, reacting on the cross-sectional area of the control
spool 44, it will move the control spool 44 against the biasing
force of spring 46a all the way from right to left, first closing
off with cut off plane 46 communication between inlet chamber 38 ~:
and the supply chamber 24. Control plane 47 of the control spool
44 is so positioned that while cut off plane 46 is cutting off
communication between the inlet chamber 38 and the supply chamber
24, control plane 47 is establishing communication between the
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supply chamber 24 and the exhaust chamber 33. Further movement to
the le~t of control spool ~4 will open wide communicatlon between
the supply chamber 24 and the exhaust chamber 33. Total movement
of control spool 44 to the left is limited by face 73 o the : .
housing 18.
Further movement of the valve spool 20 to the left will
first open communication between the supply chamber 24 and.the , ~.
load chamber 2G and then open communication through first exhaust
.., ., ~ . .
metering slot 69 between the load chamber 25 and the outlet :
10 chamber 27, throttling fluid flow from actuator 11 to the valve :~.
exhaust circuit, maintained at a constant pressure level by
exhaust relief valve 34. High pressure flow out of actuator 11, :. ` ;
during control of negative load, will be replenished on the other
side of actuator from-ffie exhaust chamber 33 through opening
created by displacement of the control plane 47 in respect to the
exhaust chamber 33, connecting exhaust chamber 33 and the supply `, ~ .
chamber 24 and from exhaust line 31 through the bypass check ~
valve 49, at a pressure level of exhaust relief valve~34, while .:
utilizing a combined exhaust flow from the outlet chamber 27 and
the differential.pressure relief valve 16. m e exhaust fluid at ....~
increased pressure is supplied to the actuator inlet during control .~ -:
of negative load, while the fixed displacement pump 12 is completely :..
isolated by cut off plane 46 from the supply chamber 24 and the
actuator 11. Therefore, since none of the potential pump delivery
25 is used as actuator make-up fluid, during control of negative i-:
load, higher pump capacity is made availa~le for simultaneous
control of multiple positive loads. During control of two negative
loads, or example loads L and W, the exhaust circuit is also ;.. ;. .
supplied by line 50 with exhaust fluid rom the flow control valve `~
30 14, the combined exhaust flow o botll control valves and the :~
bypass flow from the diferential pressure relief valve :L6 being ~:. .
available for the make-up flow to the system actuators controlling ` ~
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negative loads, while full pump capacity is being saved for oper~
ation of the other positive loads. ~ -
When valve spool 20 is moved rapidly from left to right ~ :
connecting the fluid supply chamber 24 with the load c~namber 25, ~`
unless the differential pressure relief valve 16 responds fast
enough to raise the discharge pressure in the discharge line 36 ;~ .
and the supply chamber 24 to the level, equal to or higher than . ..
the load pressure existing in the load chambe.r 25, a back flow from
load chamber 25 to the fixed displacemen~ pump 12 can take place,
resulting in momentary drop in load L. To prevent this back flow,
check valves 37 and 40 are provided in the pump discharge line.
Check valves 37 and 40, while preventing back flow, permit the .
differential pressure relief valve 16 to raise the pump p.ressure
to a level at which the check valves 37 and 40 will open permitting . - :
15 free flow between the pump and the actuator. .:
So far the system shown in E'ig. l has been described as
using fixed displacement pump 12, flow of which is controlled by
the differential pressure relief valve 16. Pump 12 can also be of
variable displacement type and can b~ controlled by a differential ~;
pressure compensator which,..in a well known manner, varies the
displacement of the pump to maintain discharge line 36 at a
pressure higher by a constant pressure differential than the load
signal pressure transmitted to differential pressure compensator
from the load sensing circuit by signal line 56. Therefore in an
identical way a fixed displacement pump controlled by a differ~
ential pressure relief valve and a variable displacement pump `~
,. ., ~
controlled by a differential press~re compensator will maintain
a constant pressure differential between discharge line 36 and
signal line 56, in response to the highest system load being
30 operated. Although the load control features of systems using .
fixed and variable displacement pumps are identical, the amount of
flow delivered to exhaust circuit and specifically to exhaust line
31 is different for each pump. When using~fixed displacement pump
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all of the excess pump flow is delivered by the differential
relief valve through line 48 to exhaust line 31. With syskem
valve spools in neutral position all of the pump 10w is directed
by the differential relief valve to exhaust 1ine 31. When using
S a variable displacement pump the pump supplies the exact amounk
of fluid, to satisfy the system demand, none of the pump flow .
normally being diverted to exhaust line 31. Therefore when using
a variable displacement pump less exhaust flow is available to
satisfy inlet flow requirements of system acutators during control
of negative load. N~rmally an acutator, in the form of a cylinder, :
due to the presence of piston rod, displaces different flows from .
each cylinder port per unit length displacement of its piston.
Therefore with use of variable displacement pump, while control~
ling negative load~ the exhaust flow out of the cylinder must be ~ .
greater than its inlet flow re~uirement and therefore piston end
of the cylinder must be subjected to negative load.
Although the preferred embodiments of this invention have ::.
been shown and described in detail it is recognized that the ~.
invention is not limited to the precise form and structure shown ::~
and various modifications and rearrangements as will occur to .
those skilled in the art upon full comprehension of this invention ~`:
may be resorted to without departing from the scope of the ;~.~
invention as defined in the claims. :~ :
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