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Патент USA US2118779

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May 24, 1938.
2,118,779
C. H. RIPPL
DUAL PRESSURE CONTROL FOR PNEUMATICALLY OPERATEDAPPARATUS
Filed Jan. 15, 1937
2 Sheets-Sheet l
39
FLUID PRESSURE
SOURCE
48-»;
L44
46~
--53
,
,45
PRESSURE
REDUCING
MEANS
55
' '53
FIG.I.
1NVENTOR.
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BY
CW RM
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L.
May 24, 1938.
c, H_ RlPPL _
I
2,118,779
DUAL PRESSURE CONTROL FOR PNEUMATICALLY OPERATED APPARATUS
Filed Jan. 15, 1937
2 Sheets-Sheet 2
f(90
O 89
,1‘
1
1
F
g
0
88
L
l-l
B
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A\78
/3
COMPRESSED
FLUID SOURCE
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INVENTOR,
CHARLES H. RIPPL. *
BY
252274 My (QM/4y
ATTORNEY.
Patented May 24, 1938
2.118.779
UNITED STATES PATENT OFFICE
2,118,779
DUAL PRESSURE CONTROL FOR- PNEU~
MATICALLY OPERATED APPARATUS
Charles H. Rippl, Cleveland, Ohio, assignor to
The Clark Controller Company, Cleveland,
Ohio, a corporation of Ohio
Application January 15, 1937, Serial No. 120,806
12 Claims.
This invention relates to fluid pressure oper
ated apparatus and to controls therefor by which
different parts of the apparatus may be operated
by different ?uid pressures.
The invention is particularly applicable to
6
pneumatically operated welding machines and to
the
pneumatically
operated
electric
timing
switches for timing the welding current utilize-d
thereby and to the controls therefor whereby
10 the switch may be operated at a high pressure
(such for example as the full pressure of the
source) and the welding machine may be oper
ated at a reduced pressure; and while the in
vention has other uses it will be illustrated and
described herein as applied to that use.
embodiment of my invention in connection with a
well known gun type of Welding device;
Fig. 3 is a view illustrating in modi?ed form
a valve arrangement illustrated diagrammatically
in Figs. 1 and 2.
Referring to the drawings I have shown gen
orally at l a welding machine comprising an
upper head 2 supporting a pneumatic cylinder 3
in which is reciprocated a piston 4 normally held
in an upper position by a spring 5 and arranged
to be forced downwardly upon the admission of
compressed air to the cylinder above the piston
and to move downwardly an upper electrode 5
paratus;
connected to the piston.
A lower head ‘I has associated therewith a lower
electrode 8. Work pieces 9 may be supported
on the lower head ‘I and when the upper electrode
is moved downwardly the work is engaged be
tween the two electrodes and electric current sup
plied by mains l0 and I! to the electrodes pro 20
duces the weld on the work pieces 9.
The 'parts of the machine just described are
illustrated diagrammatically and their exact con
struction and arrangement constitute no essential
part of the present invention and inasmuch as 25
such Welding machines are well known further
To provide a control for pneumatically operated
welding apparatus by which a relatively low oper
ating pressure may be applied to a welding gun
illustration or description thereof is deemed un
necessary herein.
Illustrated generally at I2 is an electric cur—
or other welding machines and a relatively high
operating pressure may be applied to a welding
current timing switch apparatus in controlled
illustrated diagrammatically. The switch I2 com
It is among the objects of the invention:
To provide generally an improved control for
?uid pressure operated apparatus;
To provide a control for ?uid pressure operated
in) apparatus by which different operative pressures
may be applied to the apparatus in an improved
manner;
To provide an improved control for ?uid pres
sure operated apparatus whereby high and low
pressures may be successively applied to the ap
[ll
(Cl. 303-—6)
rent timing switch, pneumatically operated and 30
To provide a control for a plurality of ?uid
pressure operated devices by which one device
may be operated responsive to operation of an
prises a valve housing l3 controlling the appli
cation of pneumatic pressure to the switch 12
and the exhausting of the same therefrom in the
operation of the switch. The exact construc 35
tion and arrangement of the parts of the switch
l2 constitutes no essential part of the present in~
vention. Such a switch constitutes the subject
matter of the co-pending application of Edward
G. Beiderman, Serial No. 84,981 ?led June 13, 1936
for “Improvements in time controlled electric
switches”, and reference may be had thereto for
a fuller showing and description. Likewise the
exact construction of the parts within the valve
housing I3 constitutes no essential part of this 45
other in an improved manner.
invention, one construction of the same con
sequence.
To provide an improved valve construction for
controlling application of pneumatic pressure to
a welding current timing apparatus responsive
to pressure conditions at a welding gun or other
welding machine.
To provide a control for ?uid pressure operated
apparatus by which a plurality of devices may
be operated successively in an improved manner
from a common fluid pressure source.
Other objects will be apparent to those skilled
in the art to which my invention appertains.
My invention is fully disclosed in the following
$.30 description taken in connection with the accom
panying drawings in which:
Fig. 1 is a diagrammatic view illustrating an
embodiment of my invention when used in con
nection with a welding machine of one type;
55
Fig. 2 is a diagrammatic view illustrating the
stituting a part of the subject matter of the co
pending application of Charles H. Rippl, Serial
Number 120,362 ?led January 13, 1937 for "Im
prcvements in pressure control for pneumatically 50
operated switches” and reference may likewise be
had thereto.
The diagrammatically illustrated timing switch
valve comprises a plunger l4 vertically recipro
cably supported in a frame [5 supported normally 56
2
2,118,779
at its lower end Iii upon the frame and having
below its lower end a piston rod l1 carrying a
piston i3 reciprocable in a cylinder ii! in the valve
housing i3. A spring 26 normally holds the
plunger down. When the plunger l4 moves up
4.9 is retained in the upper end of its bore by a
spring 5! inside of the valve, the tension of the
spring being adjustable by a screw 52 which ex
tends outwardly through the housing and is ex
ternally adjustable.
wardiy, a cam 92! thereon engages a cam fol
lower roller
on an oscillatable arm 23 and
The further description of the valve device 40
will be given in connection with a description of
the roller
riding over the cam face rocks the
arm 23 clockwise against the tension of a spring
The cam 25 passes upwardly beyond the roller
22 and then the spring
returns the arm coun
ter-clockwise, the arm having a normal position
determined by a stop
engaging the lower end
its operation which follows.
of the arm and mounted on a panel or other
ducted by a conduit 55 through a pressure reduc~
ing device 56 to a conduit 5'! and thence to a duct
58 where the pressure is cut off by the valve 42.
The parts are now ready to operate and with
support
When the cam 2i returns down—
wardly it rocks the roller 22 out of its path with
out moving the arm
the roller for this purpose
being mounted on a pivoted arm 2?, the rear end
of which is normally engaged with a stop 28 by a
20 spring 29.
The tension of the spring 26 may be adjusted
by a screw 3b engaging the upper end of the
spring and supported on the frame I5.
The arm
is secured to a shaft 3| mounted at
25 one end portion to oscillate in a bearing 32 on
the frame [5 and at another end portion in a
bearing
Rigidly secured to the shaft 3| is
a pair of switch arms 34-34 having contacts
on their upper ends, and a mating pair
30 of contacts 36-36 are mounted on pivoted arms
the arms being yieldable against springs
til-38.
When in the upward movement of the plunger
M above described, the arm 23 is rocked clock
wise, the switch arms 3é-—34 are moved to effect
engagement of the pairs of contacts 35-—-36 and
when the arm 23 again rocks counterclockwise
the switch arms 34%—34 are moved to break the
circuit at the contacts. Thus the contacts are
maintained closed for a time interval and while
closed electric current flows from a pair of supply
mains 534 and H35 by wires $86 and I8‘! through
the switch arms 3l'—3'l, contacts 36-38 and
and switch arms 34-~34 through the mains
H3 and H to supply welding current as above de
scribed.
As fully set forth in the above mentioned co
pending patent applications, the stroke of the
plunger is may be timed to cause the said cur
50 rent impulse to have any desired duration for
performing the weld on the work 9, by adjust
ment of the spring 28, the spring 24, the shape
of the operating face of the earn 2!, the rate of
admission of air by the valve structure in the
housing 53 to the cylinder i9 and in some cases
by
kinetic energy of an inertia weight 38 on
the arm 23.
At 3Q is a source of fluid pressure from which
the ?uid pressure to operate the switch i2 and
the machine l is supplied, under the control of, a
valve device 453, comprising a main stationary
housing Iii, and a valve element 52 of cylinder
form reciprocable in a cylindrical bore 43 to con
trol various'?uid passages to be described. The
valve element 52 is normally held in a downward
position by a spring
that position of the valve
element 62 being determined by a stop ?ange 45,
and the up-stroke of the valve element 42 being
determined by engagement of the stop flange 45
with a shoulder lit.
The valve element is ar
ranged to be moved upwardly by an electric wind
ing til acting on a solenoid plunger 48.
Within the stationary housing 4! is a piston
vaive (l9 of tubular form closed at its upper end
and reciprocable in a bore 5d. The piston valve
Fluid under pressure at the source 39 is con
ducted by a conduit 53 to a duct 54 at the valve 10
device but with the parts of the valve device 4!!
in their normal position the pressure is cut off
thereat by the valve 49. The fluid is also con
work 9 placed in the machine I, the operator of
the apparatus closes a switch 59 and current flows
from the ‘supply mains l84--l85 by wires 60-60
to energize the winding 41 and raise the plunger
58 and valve 42.
When the valve 42 moves to its upper position,
a duct 6| therein establishes communication from
the duct 58 through a duct 62 to a conduit 63
which admits the ?uid pressure to the cylinder 3
of the machine l which moves the electrode 6
downwardly to engage the work for welding.
The pressure within the cylinder 3 is communi
cated by a conduit 64 back to the valve device .
where it communicates with a duct 65 which
opens inwardly into the valve cylinder 50. This
duct is normally sealed by the upper end of the
valve 49. The pressure in the conduit 64 at the
start of the machine piston 4 downwardly is less
than the pressure applied to the cylinder 3 by
the conduit 63 as is common with piston and
cylinder devices such as that of the machine I
which are designed to develop a high ?nal pres
sure within the cylinder, but after the piston 4
has moved to engage the electrodes and the full
pressure from the conduit 63 builds up in the
cylinder 3, the pressure in the conduit 64 corre
spondingly builds up and therefore after the elec
trodes 6 and 8 are fully engaged with the work 9,
this built up back pressure communicated to the
valve 49 through the duct 65 moves the valve
downwardly against the spring 5| to a bottom
position at which the lower end 56 of the valve
engages a stop 67!. In this position an annular 50
chamber 68 in the outer wall of the valve 49
establishes communication between the duct 54
above referred to and a duct 69 to which is con
nected a conduit 10 leading to the valve housing
E3 of the switch l2 and the pressure from the
source is now applied through this conduit to
operate the switch I2 to send a welding current
impulse through the work 9, as above described.
The weld is thus completed and then the oper
ator may open the switch 59 and the spring 44 60
will restore the valve 42 to its original position.
In this position of the Valve, the cylinder 3
may exhaust its pressure backwards through the
conduit 53 to the duct 62 and thence, as shown,
through the duct GI and out to atmosphere by a
duct ‘H. Similarly, the conduit 64 may dis
charge backward through the duct 65 and by way
of ducts l2, ‘l3 and 74 to atmosphere. The ducts
l2, ‘l3 and 74 likewise provide a discharge for the 70
pressure in the cylinder 50 above the valve 49 so
that the valve may be restored by its spring 5|;
and ?nally, the pressure at the switch l2 may be
discharged backward through the conduit 10 to
the duct 69 which is now out off by the valve 49
3
2,118,779
and thence by way of ducts ‘I4, ‘I5 and 16 may dis
charge to atmosphere.
In the above described operation, it will be
apparent that the machine I is supplied by pres
sure from the source 3I at less than the source
pressure due to the pressure reducing device 56.
There are numerous reasons why machines such
as that indicated at I are preferably operated at
relatively low pressure. Particularly is this true
10 when the machine I is of. the hand operated type.
In some instances, the machines I built by a
welding machine manufacturer are designed to be
operated at a relatively low pressure whereas
operation of the switch I2 may better be effected
15 to better control and time a welding current
impulse by higher pressure. On the other hand,
it is always desirable to be able to supply all of
the operating pressure from a single source such
39 and with the arrangement above described
20 both pressures are available, one for the machine
I and the other for the switch I2.
The pressure reducing device 56 may be of
any suitable or known construction, its structure
not constituting an essential part of the pres
25 ent invention, it being only essential that when
?uid is supplied thereto as by the conduit 53 at
one pressure, it will flow out therefrom as by
the conduit 51 at a reduced pressure. Such de
vices are well known in this art and a further
30 description is deemed unnecessary.
As will be clear from the foregoing description,
the valve device 40 is automatic, a single oper
ating movement given thereto as for example, by
the plunger 48, supplying the reduced pressure
35 to the machine I and automatic means within
the valve 40 (the valve 49) supplying the full
pressure of the source to the switch I2 but only
after the electrodes 8 and 9 are fully engaged
with the work whereby it is not possible for the
40 switch I2 to operate until the electrodes are en
gaged with the work.
In order to prevent the accumulation of pres—
sure (or vacuum) under the valve 42, a bleeder
duct I42 is provided communicating with the
atmosphere and with the under side of the valve,
and a similar duct I45 under the valve 49 is pro—
vided for a like purpose.
referably the upper end of the valve 49 is pro
vided with an annular bead I43 at which the
upper end of the valve seals the duct 05. The
pressure applied to the valve is therefore com
municated to less than its full diameter but
after the valve starts to move and the seal is
broken at the bead I43, the full end area of the
valve is exposed to the pressure so that its oper
ation will be positive and it will move the full
stroke promptly.
If, however, the seal at the
bead I43 should leak, then the full end area of
the valve would be exposed to the pressure pre
60 maturely and to avoid this, a bleeder duct I44
is provided communicating with the atmosphere
and with the upper end of the valve 49 outside of
the annular bead I43.
In Fig. 2 is illustrated the application of my
invention to the type of welding machine or~
operation of the timing switch ‘I8 as a whole, es
tablish a welding circuit by wires 89-—89 to the '
supply mains 90-90. The timing switch device
18 may be identical with that shown in Fig. 1
at l2, and comprising the valve housing I3 of
that ?gure.
The welding gun '51 has, in the frame there
of , a duct 9| communicating at one end with the
cylinder 80 and at the other end closed off by an
operable piston valve 92; and the duct 9I has a
branch duct 93 normally communicating with
an exhaust duct 94 around a reduced diameter
neck portion or the piston valve 92.
The duct 9i also communicates with a branch
duct 90 connected to a back pressure conduit 91.
Pressure is supplied to the gun 11 through a
conduit I98 communicating with a duct 99 nor
mally shut o? by the piston valve 92. The piston
valve 92 is normally held in its inoperative po
sition by a spring I00 and is provided with a
button “1!. When the operator presses the but
ton IOI, the valve 92 is moved downwardly as il
lustrated in the drawings which causes a large
diameter portion I02 of the valve to shut off
the exhaust 03-94 and to open a pressure sup- ;.
ply through the ducts
gun 11, as described;
button IN, the spring
to out off the pressure
haust.
99 and 9I to operate the
and upon releasing the
I00 returns the valve 92
supply and open the ex
Guns of this construction are well known in
the art and it is believed that the brief descrip
tion and, in some respects, diagrammatic illus
tration thereof herein is su?icient.
The valve device ‘I9 comprises a stationary -;
housing 503 having cylindrical bore I04 there~
in in which reciprocatcs a piston valve I05 of
tubular form closed at its lower end. A spring
I06 within the valve holds it downwardly, the
pressure being adjustable by a screw IIl‘I extend- .;
ing through the wall of the housing for external
adjustment. In the upward movement of the
valve to be described, it is stopped on a stop I08
on the housing,
The source of pressure is shown diagrammati- ,
cally at I09 and ?uid is conducted therefrom by
the conduit H9. A branch conduit III conducts
the ?uid to a pressure reducing device II2
whence it flows to the conduit I98.
The conduit II? also communicates with a 50
duct H3 which
the normal downward posi
tion of the valve is cut off by the valve.
When the gun ‘I1 is operated as above de
scribed to admit pressure to its cylinder 80, the
back pressure in the conduit 91 as explained in 5"
connection with the form of Fig. l is at a reduced
pressure but as the electrodes 83 and 84 are
moved toward and upon the work 85, the pres
sure in the conduit 91 builds up. This pressure
is communicated from the conduit 91 through ‘I
a duct M4 to the valve cylinder I04 and when
it reaches the value for which the spring I 06
is adjusted, the valve is raised and by means of
an annular chamber I I5 in the outer wall of the
valve, establishes communication from the duct
dinarily referred to as a welding gun shown gen
I I3 to a duct I I5 communicating with the switch
erally at ‘IT.
operating conduit 98.
Full force pressure is thus applied to the
The current timing switch being
shown at ‘I8 and a valve device at ‘I9.
The welding gun 11 comprises a cylinder 80
having a piston 8I therein returnable by a spring
82, the piston 8I arranged to move the electrode
03 toward a stationary electrode 84 to clamp the
work 85 therebetween preparatory to welding it.
The electrodes 03 and 84 are connected by wires
86 and 81 to switch arms 88-B8 which upon
switch and operates it to provide the timed cur
HI
rent impulse.
After the weld is made and the button IOI is
released, as above described, the pressure in the
conduit 91 is exhausted out through the ex
haust 94 by way of the duct 93 and the valve
I05 is returned downwardly by the spring I06.
2,118,779
Thereupon the conduit 98 communicates by
means of the duct H6, and a duct ill with an
annular chamber H8 in the outer‘ wall of the
valve I05 and thence communicates with the
atmosphere by a duct H9 whereby pressure
from the valve housing I3 is exhausted.
As in the ?rst described form, the gun Tl may
be operated at a reduced pressure from the
source I09 and the timing switch ‘(8 may be
operated at full pressure and the automatic valve
arrangement ‘l9 insures that the electrodes of the
welding gun will be fully engaged with the work
before the switch 18 can operate. This form is
simpler than that shown in Fig. 1 because of
the fact that the pressure exhausts for the gun
cylinder 88 and for the conduit 91 are on the
gun structure itself.
The valve I05 preferably seals the duct H4 on
an annular bead M6 which functions like the
bead I43 above described and a bleeder duct
I4‘! is provided for the purposes described in con
nection with the bleeder duct I44 of Fig. 1. A
bleeder duct I48 is provided to function like the
bleeder ducts M5 and M2 of the form of Fig. 1.
3
illustrated one form. of structure
ch may be
in practice for the diagrann
atically illustrated valve of Figs. 1 and 2.
The
back pressure conduit We communicates with a
cylinder llii formed in a housing member l22
the same pressure; or ii the second-to-operate
device is the one to operate at the reduced pres
sure; or, in fact, if the two devices are operated
from entirely separate sources or fluid pressure.
Although I have illustrated the welding cur
rent to the welding electrodes 83—8f-'a of lie-8 as 10
supplied directly from current supply mains, it
is to be understood that it may be supplied from
the secondary of the transformer as is, in some
applications, the customary practice.
Changes and modi?cations may be madev with“
in the scope and spirit of my invention without
sacri?cing its advantages and within the scope
of the appended claims.
I claim:
,
1. In a ?uid pressure system for operating two 20
devices one at high velocity and the other at low
velocity, each device having an expansible ?uid
pressure chamber, a source of relatively high
?uid pressure and a source of relatively low ?uid
pressure, conduit means between the lower pres 25
sure source and the chamber of the low velocity
device, an operable valve controlling the conduit
which is threadedly jointed to another housing
to admit ?uid pressure to the chamber of the
lower velocity device to operate it, and to cause
pressure in the chamber to rise toward the pres 30
member I23 at see.
A piston I25 reciprocates
sure of the source, a fluid pressure operable valve
in the cylinder 52E, being held downwardly by
a spring 526, and being supported by a piston
rod 22? extending upwardly through the housing
having conduit communication with the said
chamber of the low velocity device and operable
pier her i272 into the open lower end of the hous~
.ing member i235 and having a pin E23 projected
through the rod above the housing £22.
The housing member £23 has a cylinder l29
therein in which is reciprocable a guide Kill. A
.11) valve stem i3! is projected downwardlyrthrough
the guide Hill and a pin N32 is projected through
the rod below the guide £30.
The red, at its upper end, extends through a
small bore E33 into a cylindrical passageway I34
and the bore H3 is sealed by a packing I35 which
is compressed. around the valve stem by a washer
53$ held tightly thereupon by a spring !3? sur
rounding the stem 53! and reacting at one end
upon the washer 536 and at the other end upon
the guide l-‘iil.
Upon the upper end of the valve stem i3! is
mounted a disc form valve iilB which is held
downwardly upon an annular valve seat I39 by
the spring 1351. Above the valve 638, the housing
I23 is connected to the source pressure conduit
Mn. A switch pressure supplying conduit Id!
communicates through the side of the housing
with the passageway i534.
Fluid under pressure in the conduit Mil is cut
60 off from the conduit Mi normally by the valve
(33. When the back pressure in the conduit 529
has reached a value determined by the spring
M5, the piston £25 is moved upwardly and the
upper end of the piston rod it? engages the lower
end of the valve stem i135
lifts the valve i555?
whereupon the full pressure from the conduit
M9 is communicated to the conduit Ml for the
purposes hereinbefore described in connection
with Figs. 1. and 2.
70
Although I have illustrated and described my
invention in connection with a pressure reducing
means by which one pressure operated device
such as a welding apparatus may be operated at
one pressure and another device such as an elec
75
my invention may be practiced and the advan~
tages of the pressure operated valve operating
after initiation of operation of one of the devices,
may be enjoyed, if both devices are operated at
ric switch may be operated at another pressure,
upon rise of pressure in the chamber to a pre
determined value, conduit means between the 35
source of high fluid pressure and the high velocity
device and controlled by the fluid pressure oper
able valve to admit high source pressure to the
chamber of the high velocity device upon opera
tion of the fluid pressure operable valve.
40
2. The system described in claim 1 and in which
the operable valve is electro-magnetically 0per~
able and means is provided to restore it, and con~
duit means is provided by which when it is re~
stored it effects exhausting of the pressure com
municated to the ?uid pressure operable valve.
3. The system described in claim 1 and in which
the operable valve is provided with means to re
store it and conduit means is provided by which
when it is restored it exhausts the pressure com
municated to the ?uid pressure operable valve. 50
4. In a fluid pressure system for operating two
devices one operable by relatively high ?uid pres
sure and the other operable by relatively low fluid
pressure, each device having an expansible ?uid
chamber, a source of relatively high fluid pressure
and a source of relatively low fluid pressure, con
duit means between the lower pressure source and
the chamber of the low pressure operable device,
an operable valve controlling the conduit to admit ll)
?uid pressure to the chamber of the low pressure
sure
operable
in the
device
chamber
to operate
to riseit,toward
and tothe
cause
pressure
of the source, a fluid pressure operable valve hav
ing conduit communication with the said cham
ber of the low pressure operable device and oper
able upon rise of pressure in the chamber to a
65
predetermined value, conduit means between the
source of high ?uid pressure and the high pres
sure operable device and controlled by the ?uid 70
pressure operable valve to admit high source pres~
sure to the chamber of the high pressure oper
able device upon operation of the fluid pressure
operable valve.
5. The system described in claim It and in 75
2,118,779
5
which means is provided to restore the operable
which means is provided to discontinue the ap
valve, and, upon restoring, it discontinues the
plication of ?uid pressure to the pressure op
erable valve and means is provided to then restore application of ?uid pressure to the pressure op
it, and, upon restoring, it exhausts ?uid pressure erable valve, and means is provided to then re
store the pressure operable valve, and, upon re
from the chamber to one of the devices.
6. The system described in claim 4 and in which storing, it exhausts pressure from the chamber
means is provided to discontinue the application of the high pressure operable device.
10. The system described in claim 4, and in
of ?uid pressure to the pressure operable valve
and means is provided to then restore it, and, which means is provided to restore the operable 10
valve, and, upon restoring, it exhausts pressure
10 upon restoring, it exhausts ?uid pressure from from the chambers of both of the devices.
the chamber of the high pressure operable device.
11. The system described in claim 4 and in
'7. The system described in claim 4 and in which
means is provided to restore the operable valve, which means is provided to restore the operable
valve, and, upon restoring, it discontinues the ap
and, upon restoring, it discontinues the applica
tion of ?uid pressure to the pressure operable plication of ?uid pressure to the pressure operable
valve and means is provided to then restore the valve, and means is provided to then restore the
pressure operable valve.
pressure operable valve.
12. The system described in claim 4 and in
8. The system described in claim 4 and in which
means is provided to restore the operable valve, which means is provided to restore the operable
valve, and, upon restoring, it exhausts pressure
and upon restoring, it discontinues the applica
tion of ?uid pressure to the pressure operable valve from the chambers of both devices, and discon
and means is provided to then restore the pressure tinues the application of pressure to the pres
operable valve, and, upon restoring, it exhausts sure operable valve, and means is provided to
pressure from the chamber of one of the devices. then restore the pressure operable valve.
CHARLES H. RIPPL.
9. The system described in claim 4 and in
25
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