U.S. patent number 3,905,276 [Application Number 05/293,469] was granted by the patent office on 1975-09-16 for multiple spool power pack unit.
This patent grant is currently assigned to United States Surgical Corporation. Invention is credited to Graham W. Bryan, Douglas G. Noiles.
United States Patent |
3,905,276 |
Noiles , et al. |
September 16, 1975 |
Multiple spool power pack unit
Abstract
A power pack for converting gas pressure into rectilinear
movement of a drive shaft. The power pack is actuated by unseating
the primary spool of a spool mechanism having a primary spool and a
secondary spool releasing a volume of pressurized gas and thereby
driving a shaft adapted to be associated with a mechanism requiring
an input of rectilinear movement. Differential pressures cause the
spool mechanism to be reseated, thus allowing the drive shaft,
biased toward the spool, to return to its rest position. The
operation of the power unit depends upon the formation of
pressure-tight chambers by the spool mechanism and associated
O-rings and the sealing ability of the primary spool to slidably
seal the flow of pressurized gas.
Inventors: |
Noiles; Douglas G. (New Canaan,
CT), Bryan; Graham W. (Ridgefield, CT) |
Assignee: |
United States Surgical
Corporation (Baltimore, MD)
|
Family
ID: |
23129206 |
Appl.
No.: |
05/293,469 |
Filed: |
September 29, 1972 |
Current U.S.
Class: |
91/398; 91/410;
91/403; 91/433 |
Current CPC
Class: |
A61B
17/0684 (20130101); A61B 2017/00544 (20130101) |
Current International
Class: |
A61B
17/068 (20060101); A61B 17/00 (20060101); F15b
013/04 () |
Field of
Search: |
;91/433,418,398,403,410
;137/625.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,257,410 |
|
Feb 1961 |
|
FR |
|
1,002,091 |
|
Aug 1965 |
|
GB |
|
Primary Examiner: Cohen; Irwin C.
Attorney, Agent or Firm: Fleit & Jacobson
Claims
What is claimed is:
1. A gas powered driving unit for converting gas pressure into
rectilinear motion in a drive shaft, the unit comprising a main
casing, a piston chamber having an abutment surface at one end
thereof, piston means including a drive shaft mounted for
reciprocation in said piston chamber, an inlet valve body mounted
in said main casing adjacent said piston means, said inlet valve
body defining a spool chamber and a valve chamber interconnected by
a port, spool means slidably mounted in said spool chamber, said
spool means comprising a primary spool body and a secondary spool
body, each said body being capable of independent movement within
said spool chamber, valve means mounted in said valve chamber, gas
feed means leading to said valve means for the introduction of
pressurized gas, said valve means being constructed to convey gas
from said gas feed means into said spool chamber, said primary
spool body being slidably mounted in said spool chamber and in one
position sealing against said valve means to effect the sealing of
said valve means stopping gas conveyance of said valve means, means
biasing said primary spool body into said one position trigger
means for unseating said primary spool body from said valve means
and for enabling said pressurized gas to initially thrust said
primary spool body and then said secondary spool body in the
direction of said piston means until in contact with said abutment
surface, and for introducing said pressurized gas to said piston
chamber to thrust said piston means away from said spool means,
said primary and secondary spool bodies being together returned by
gas pressure into positions wherein said primary spool body seats
against said valve means to intercept the passage of pressurized
gas therethrough, and exhaust means disenabled when said piston
means is thrust away from said spool means by said pressurized gas,
and enabled to exhaust the gas from said piston chamber, whereby
said piston means moves towards said spool means.
2. A gas powered driving unit for converting gas pressure into
rectilinear motion in a drive shaft, the unit comprising a main
casing, piston means including a drive shaft reciprocally mounted
in said casing, an inlet valve body mounted in said main casing,
said inlet valve body defining a spool chamber and a valve chamber
interconnected by a port, spool means slidably mounted in said
spool chamber, said spool means comprising a moveable primary spool
body and an independently moveable secondary spool body, means
biasing said piston means against said primary spool body said
primary spool body abutting said secondary spool body to form a
substantially ring shaped seat, a first O-ring housed within said
seat, said O-ring providing a gas-tight seal between the inlet
valve body and said spool means and adapted to urge said primary
spool away from said secondary spool when pressure from said piston
means acting on said primary spool body is lessened, valve means
mounted in said valve chamber, gas feed means connected to said
valve means for the introduction of pressurized gas, said valve
means being adapted to convey pressurized gas from said feed means
into said spool chamber to move said spool means, said primary
spool body being slidably mounted in said spool chamber to assume a
position in repose seating against said valve means to effect the
sealing of said valve means and stop the conveyance of gas by said
valve means, trigger means for unseating said primary spool body
from said valve means, and for enabling said pressurized gas to be
conveyed into said spool chamber, and exhaust means disenabled when
said piston means is thrust away from said spool means by said
pressurized gas, and enabled for exhausting gas from said main
casing, whereby said piston means moves towards said spool
means.
3. A driving unit as claimed in claim 2 wherein the depth of the
substantially ring shaped seat section formed by the primary spool
body is less that the depth of the seat section formed by the
secondary spool body.
4. A driving unit as claimed in claim 2, wherein said valve means
has a throughgoing passage allowing gas to pass therethrough into
said spool chamber.
5. A driving unit as claimed in claim 2, wherein said inlet valve
body defines a stepped spool chamber and the outer surface of the
valve body defines a plurality of annular rings carved into the
inlet valve body with feed means being provided in said inlet valve
body to connect said valve chamber with a source of gas.
6. An inlet valve body as claimed in claim 5, wherein said inlet
valve body includes a filter chamber therein, said filter chamber
being connected to said valve chamber by a passageway.
7. An inlet valve body as claimed in claim 5, wherein each of said
spool chamber steps has a different diameter, the larger step
chamber section being of sufficient diameter to hold the primary
spool and the other stepped section being of sufficient diameter to
hold at least a portion of the secondary spool body.
8. A driving unit as claimed in claim 2, wherein said primary spool
body has a forward head, said forward head being adapted to engage
said piston means, with the other end terminating in a projecting
tip, said projecting tip being adapted to engage said valve means
to effect the sealing of gas passing through said valve means.
9. A primary spool body as claimed in claim 8, wherein said forward
head's outer edge forms a rib with a shoulder cut therein, said
shouldered rib forming a substantially ring shaped seat in
cooperation with the second spool to hold an O-ring, said shoulder
cooperating with said secondary spool body to place said O-ring
under compression so that the O-ring will expand toward the piston
means forcing the primary spool body away from the secondary spool
body when the compressive forces of the piston means are removed
from the forward head of the primary spool body.
10. The primary spool body as claimed in claim 9, wherein a port is
cut through the outer rib of said forward head.
11. A gas powered drive unit as claimed in claim 2, wherein said
secondary spool body has a substantially annular body configuration
with a bore cut therethrough and a primary spool engaging rib
projecting from said annular body.
12. A secondary spool body as claimed in claim 11, wherein said
secondary body rib has a shoulder cut therein, said shoulder being
adapted to engage against the primary spool body to form a seat for
an O-ring.
13. A secondary spool body as claimed in claim 11, wherein one end
of said secondary spool body has a plurality of radial slots formed
therein.
14. A gas-powered driving unit for converting gas pressure into
rectilinear motion in a drive shaft, the unit comprising a main
casing, an inner casing mounted in said main casing, said inner
casing defining a piston chamber, piston means slidably mounted in
said piston chamber, said piston means comprising a drive shaft, a
piston head connected to said drive shaft, said piston head having
a ring cut therein, an O-ring mounted in said ring, and spring
means surrounding said drive shaft and biasing said piston head, an
inlet valve body mounted in said main casing adjacent said inner
casing, said inlet valve body defining an interconnected stepped
spool chamber and a valve chamber, a plurality of channels cut in
the outer surface of said inlet valve body and gas feed means
provided in said inlet valve body to connect said valve chamber
with a source of gas for the introduction of pressurized gas, spool
means slidably mounted in said spool chamber, said spool means
comprising a moveable primary spool body and an independently
moveable secondary spool body mounted on said primary spool body,
said primary spool body comprising a forward head at one end
adjacent said piston means, with the other end terminating in a
projecting tip and an annular rib projecting from said body, said
secondary spool body having a substantially annular configuration
with a throughgoing bore, a rib projecting from said annular body
to engage said primary spool, said engaging rib abutting said
primary spool forward head to form a substantially ring-shaped
seat, a first O-ring mounted in said seat to provide a gas tight
seal between the inlet valve body and said spool means, a second
O-ring mounted around said primary spool body to provide a gas
tight seal between said primary spool body and said secondary spool
body, a third O-ring mounted around said secondary spool body to
provide a gas tight seal between said secondary spool body and said
inlet valve body, valve means mounted in said valve chamber for
enabling the passage of pressurized gas, said valve means being
adapted to engage the projecting tip of said primary spool body to
seal gas conveyed by said valve means, trigger means to unseat the
projecting tip of said primary spool body from said valve means,
and gas exhaust means defined by said spool means and said inlet
valve body.
Description
BACKGROUND OF THE INVENTION
The general concept of a gas powered driving unit as disclosed by
the present application is not new. See for example, U.S. Pat. Nos.
3,613,507, issued Oct. 19, 1971; 3,618,842, issued Nov. 9, 1971 and
3,643,851, issued Feb. 22, 1972, all of which are assigned to the
present Assignee. Additional prior art of interest can be found in
the art cited by the Patent Office during the prosecution of the
above-identified patents.
The power unit described in each of the above-noted patents
functions capably. However, each of the above-mentioned power units
suffers from certain disadvantages. For example, the power unit
described in U.S. Pat. No. 3,613,507 has a small seal area which
with repeated seatings may become damaged thus preventing good
contact between mating surfaces. Consequently, the sealing area
increases because of plastic deformation and can ultimately create
an area large enough for pressure forces to exceed spring forces in
the other direction and hence the power unit could fail due to
leakage.
In the power unit described in U.S. Pat. No. 3,618,842, the
pressure chambers are defined by a series of O-rings which after
long periods of wear may result in leakage between one chamber and
the next.
In the third U.S. Pat., No. 3,643,851, the gas chamber is defined
by a plurality of sliding diaphragms. These diaphragms were found
to be somewhat weak and, in time, often developed leaks.
It is towards the elimination of the above-noted disadvantages and
the simplification of known power pack units that the present
invention is directed.
SUMMARY OF THE INVENTION
The present invention relates to a power pack capable of converting
gas pressure into rectilinear movement, using a minimum amount of
pressurized gas and with a minimum of moving parts. Pressurized gas
is fed into the inventive power pack and when the power pack is
idle the spool mechanism of the power pack is sealed off from the
gas pressure. The two-part movable spool mechanism is maintained in
constant contact with the gas pressure through the action of a
pilot valve which has a gas port through its center. The contact
between the rear of the spool mechanism and the pilot valve seals
off the pressurized gas with the flat surface of the outer end of
the valve abutting the flat surface of the inlet valve body
allowing the pilot valve to have random orientation contact without
damaging the seal.
The power pack of the present invention is fired when the driving
piston and integral drive shaft are moved against the force of the
piston return biasing spring. This movement allows the spool
mechanism to become unseated from the pilot valve and held in its
unseated position through the action of pressurized gas acting upon
the surfaces of the spool mechanism. When the spool is unseated the
source of pressurized gas acts upon the piston integral with the
drive shaft. The drive shaft is then driven by the pressurized gas
through a firing cycle.
During the return movement of the piston, the force on the face of
the spool mechanism remote from the gas port becomes greater than
the force on the face of the spool mechanism adjacent the gas port,
so that the spool mechanism is driven toward the gas port seating
it against the pilot valve to seal the source of gas pressure. When
the drive shaft is returned by its biasing spring, the gas in the
piston chamber is exhausted, and the piston is brought into contact
with the spool mechanism. At this time the power unit is ready for
another drive cycle.
The operation of the inventive power pack is dependent upon the
self energizing seal of the pilot valve, and the two-part spool
mechanism with its sealing O-rings. Furthermore, the total area of
the pilot valve sealing surface is such that it cannot become
enlarged enough to misfire as there is always a sealing contact
between the flat surfaces of the valve lip and the flat end surface
primary spool projecting tip allowing a random orientation contact
of the pilot valve body without damaging the seal. In addition, the
unit provides for a cushioning effect on its various component
parts. The rearward thrust of the spool mechanism causing contact
with the pilot valve body is cushioned by two independent forces.
The first force, and the lesser of the two, originates in the pilot
valve biasing spring which at all times urges the pilot valve
toward the spool mechanism and thus absorbs the contact force when
the spool mechanism strikes the pilot valve body. The second force
originates in the pressure of the inlet acting on the net
cross-sectional area of the pilot valve body.
Also, the forward unit of the drive shaft is against the biasing
spring which at all times urges the drive shaft and integral piston
toward the spool mechanism.
As constructed, the power pack forming the present invention has
two major moving elements comprising a spool mechanism having two
movable parts and a movable pilot valve body. The life of the power
pack is substantial because of the minimal amount of wear on the
apparatus so that it has great reliability for long periods of use.
Furthermore, the apparatus also provides a means of transforming
pressure forces into rectilinear motion in an efficient and
reliable manner.
By utilizing the present invention, whose parts have tolerances
that are relatively loose, the need for high precision machinery is
eliminated as the manufacturing tolerances do not have to be so
precise. Even without close tolerance of the parts as compared with
similar units of the prior art, substantial thrust is able to be
developed in the drive shaft with the effect that the moving parts
are returned to their prefiring positions by combining the effects
of the gas pressure and a single biasing spring.
Other features and advantages of the invention will be apparent
from the following description of the embodiments of the invention
as shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross section through a power pack constructed
in accordance with the teachings of the present invention.
FIG. 2 is a cross section view of the inlet valve body shown in
FIG. 1 in relation to the piston.
FIG. 3 is the right end elevation view of the inlet valve body of
FIG. 2.
FIG. 4 is a cross section view of the secondary spool body shown in
FIG. 1.
FIG. 5 is the left end elevation view of the secondary spool body
of FIG. 4.
FIG. 6 is a cross section view of the primary spool body shown in
FIG. 1.
FIG. 7 is the left end elevation view of the primary spool body
shown in FIG. 6.
FIG. 8 is a cross section view of the pilot plug housing shown in
FIG. 1.
FIG. 9 is plan view of the pilot plug housing shown in FIG. 8.
FIG. 10 is the right end elevation view of the pilot plug housing
of FIG. 8.
FIG. 11 is an enlarged cross section view of the pilot valve body
shown in FIG. 1.
FIG. 12 is the left end elevation view of the pilot valve body of
FIG. 11.
FIG. 13 is a side view of the filter shown in FIG. 1.
FIG. 14 is a plan view of the filter illustrated in FIG. 13.
DETAILED DESCRIPTION OF THE DRAWINGS:
As shown in FIGS. 1-14 the inventive power pack generally discloses
an outer casing 22 in which is mounted an inlet valve body 30
containing a primary spool body 62, a secondary spool body 79, a
pilot housing 46 and a pilot valve body 54. A drive shaft 24 is
slidably mounted in the outer casing with the foremost end of the
drive shaft (not shown) being the output side of the power pack and
serving to operate any device depending upon a rectilinear motion
input for its performance.
The rearwardmost end of the drive shaft takes the form of a piston
26 slidably mounted in a piston chamber 28 defined by an inner
casing member 29. The piston 26 is held in position by a piston
return spring 25 which exerts a force on the piston 26 of
approximately 11 to 12 pounds. The inner casing member 29 is
mounted in a fixed position within the outer casing 22.
Mounted in the outer casing 22 adjacent the inner casing member 29
is an inlet valve body 30. The inlet valve body 30 as shown in
FIGS. 2 and 3 defines two centrally located interconnected
chambers; a stepped spool chamber 58 and a pilot housing chamber 45
which are interconnected by port 56 and vents 47. The stepped spool
chamber 58 preferably comprises two sections or steps each of which
has a different diameter, the larger section 57 being of sufficient
diameter to hold the primary spool body 62, the other 59 being of
sufficient diameter to hold the second spool body 79. The outer
surface of the inlet valve body 30 defines a plurality of annular
channels 36, 94, 124 and 126. An exhaust port 92 is cut through the
inlet valve body 30 to connect chamber section 57 with an annular
exhaust channel or ring 94. The inlet valve body also defines a
filter chamber 37 which is connected to the pilot housing chamber
45 by inlet passageway 42.
A stainless steel capillary tubing 32 leads from the gas pressure
source (not shown) through the outer casing 22 into the gas feed
channel 36 of the inlet valve body so that the source of
pressurized gas can operate the working mechanism of the power pack
20. The pressurized gas enters channel 36 from the capillary tubing
32 at 34 and travels into the inlet valve body filter chamber 37.
The gas is filtered by filter 38 on its way into passageway 42
which communicates with annulus 48 in housing chamber 45. The
annulus 48 is defined by the inlet valve body 30, the outer surface
of the pilot housing 46 and O-ring 50 seated inside the housing
chamber 45 and abutting the housing body shoulders 43. The pilot
housing 46 as shown in FIGS. 1, 8 and 9, is preferably threaded so
that it can be screwed into the inlet valve body 30 by means of a
driving slot 110. A blind hole is drilled in the pilot housing to
form the pilot valve chamber 44. The blind end of chamber 44 is
used as a spring seat for the pilot valve biasing spring 108. The
chamber 44 is preferably stepped to allow clearance for shoulder
103 on pilot valve body 54. A filter chamber 53 holds filter 55.
The filter chamber 53 communicates with the pilot chamber 44 by
means of a port 57 cut through the pilot housing 46. Filter chamber
53 also communicates with feed chamber 48 by passageway 51. A pilot
valve body 54 is slidably fitted into pilot housing chamber 44 in a
gas tight relationship by means of O-ring 100.
The pilot valve body 54 as shown in FIGS. 11 and 12 is constructed
with a bore 96 which allows gas entering port 56 to flow through
it. An annular channel 98 is cut into the valve body to hold O-ring
100 so that the O-ring 100 will form a gas-tight seal between the
wall of chamber 44 and the outer surface of the valve body 54. The
biasing spring 108 has one end seated in the blind end of chamber
44 and the other end surrounding the pilot valve body at the spring
rest 99 where it abuts against the pilot valve body to urge the
pilot valve body away from the blind end of chamber 44 toward the
spool mechanism. The other end of the pilot valve body which
performs the sealing functions comprises a shoulder portion 103,
the front surface of which has a flat surface to contact the flat
surface of the inlet valve body contact area 60. Counterbore 41 in
the pilot housing provides clearance for shoulder 103. The forward
edge of the pilot valve body slopes upward from the flat surface of
shoulder 103 to form an annular ring 102 which has a flat sealing
surface surrounding the bore 97. Thus there is formed on the
forward edge of the pilot valve body a geometric surface which does
not have to hit the same point repeatedly and therefore never
spreads the seal area. When the valve is closed, ring 102 abuts
flat surface 68 on primary spool 62. Inlet gas pressure works on an
area created by diameter of body 54 less diameter of bore 96 to
hold the valve closed. The same pressure also works on the much
smaller area of ring 102 less that of bore 96. The net effect is
that the inlet gas pressure holds the valve closed providing that
the bias of spring 25 is strong enough to prevent the gas pressure
on body 54 from moving primary spool 62.
Adjacent the pilot valve chamber 44 is spool port 56 cut through
the inlet valve body contact area 60. The spool port 56 allows the
pressurzed gas passing though the pilot valve bore 96 to pass into
the stepped spool chamber 58. A plurality of vents 47 are also cut
through the inlet valve body contact area 60 substantially parallel
to the spool port 56 and located approximately adjacent the flat
forward surface of the pilot valve body shoulder 103. As the pilot
valve body 54 moves forward its shoulder 103 hits the contact area
60 thus stopping the pilot body and keeping it in position until
its return.
Mounted in the inlet valve spool chamber 58 is a primary spool body
62 as shown in FIGS. 6 and 7 having a centrally positioned bore 64
connected to the spool chamber by a feed port 66. The feed port 66
serves to admit gas to the working surface of piston 26 from the
pilot valve bore 96 against the piston head 26. The rearward end of
primary spool body 62 forms a projecting tip 68 which is adapted to
seat against the pilot valve body 54 forming a gas-tight seal and
preventing gas from entering into spool chamber 58, except when the
unit is actuated. The end of projecting tip 68 has a flat surface
and a greater total area than the area of the pilot valve lip 102.
In addition, sealing contact is always between flat surfaces, so
that there can be random orientation contact without damaging the
seal. The primary spool body 62 also defines an annular rib 70
having a shoulder 72 upon which is seated a free floating O-ring
74. The annular rib 70 preferably fits within bore 80 of the
secondary spool body 79 to guide the primary spool body along the
inner surface 81 of the secondary spool body. The other end of the
primary spool body 62 defines a forward head 63 which is adapted to
engage piston head 26. The outer circumference of the forward head
terminates in an outer rib 76 having a shoulder 77 cut therein. An
escape port 75 is cut through the outer rib 76 so that gases
exhausted by the returning piston 26 escape through port 75 in the
forward head 63 into chamber 83 formed by the primary spool body
and secondary spool body in the spool chamber 58. The shoulder 77
is adapted to form a channel or seat in cooperation with the
secondary spool to hold O-ring 78. The shoulder 77 in cooperation
with the secondary spool body places the O-ring 78 under
compression so that the O-ring will expand toward the piston 26
thus forcing the primary spool body 62 forward when the compressive
forces of the piston 26 on the forward head 63 of the primary spool
body are lessened.
As shown in FIGS. 1, 4 and 5, a secondary spool body 79 having a
bore 80 therethrough surrounds the annular rib 70 of the primary
spool body 62 to form the O-ring seat for O-ring 74. The rear of
the secondary spool body 79 has a plurality of radial slots 82 cut
from the outer surface of the spool body 79 to the bore 80 so that
when the rear end wall of the secondary spool body 79 engages the
rear wall of body chamber section 59, the annulus 87 is in
communication with bore 80. The outer surface of the spool body 79
is stepped outward from the end wall to define a shoulder 84 and a
seat 85 which are adapted to seat and hold a free floating O-ring
86. The forward portion of the secondary spool body 79 takes the
form of an annular ring 88. The ring 88 has an annular notch 89 cut
into it to form the other part of the seat for O-ring 78, in
cooperation with the abutting shoulder 77 of the primary spool
body. It should be noted that the abutting shoulder 77 of the
primary spool body does not form a level seat for O-ring 78 when it
abuts notch 89. Exhaust channels 90 are provided through the ring
88 so that the exhaust gas moved by the return of the piston 26 can
pass from exhaust area 87 through primary spool exhaust port 75
into chamber 83. From chamber 83 the gas passes through channels 90
into exit port 92 and the exhaust ring 94 of the inlet valve body.
The gas is carried by the exhaust ring 94 to exhaust conduit 95 in
the outer body 22 where the gases are vented to the atmosphere.
In the unit, a washer 116 is preferably placed under the head of
the plug housing in contact the inlet valve body surrounding O-ring
118 to provide a suitable gas seal. In addition, inlet valve body
O-rings 120 and 122 are placed in respective channels 124 and 126
of the inlet valve body so that the inlet gas is sealed between
these O-rings.
The unit is maintained in its readiness condition by means of a
coil spring 25 acting on the piston 26, which spring exerts a force
greater than that developed by the spring 108, plus the gas
pressure acting on the area of the diameter of the body 54. A
trigger notch (not shown) is located in an output shaft 24 integral
with the piston 26. Upon activation of a trigger 27 the output
shaft 24 and its integral piston 26 move in the direction of arrow
A. Then, under the force of spring 108 and that developed by the
pressurized gas, the pilot valve body 54, the spool bodies 62, 79
and the piston 26 move in unison until the front face of the pilot
valve body 54 abuts surface 60 of the inlet valve body 30.
The piston is pulled further forward by the trigger to allow the
force of the gas pressure passing through bore 97 of the pilot
valve body to act against the rearward surface of the primary spool
62 in combination with the resilient action of O-ring 78 against
shoulder 77 to move the primary spool body 62 until the driving
head 63 of the primary spool body abuts against the piston chamber
walls 29 creating a seal therewith. The pilot valve body 54 cannot
follow the primary spool body 62 because port 56 is smaller than
the shoulder 103 of the pilot valve body. Thus, after projecting
tip 102 of the pilot valve body 54 projects into port 56 the pilot
valve body shoulders 103 strike the flat surface of the contact
area 60 stopping movement of the pilot valve body. Pressurized gas
pours through the bore 96 of the pilot valve body into the spool
chamber 58 to seat O-ring 74 against shoulder 72, guide ring 70 and
the inner surface 81 of the secondary spool body to form a
gas-tight seal. As the primary spool body 62 is moved forward, gas
continues to pass through orifice 66 in the primary spool body 62
into the lesser pressure of chamber 64 of the primary spool to
drive piston 26 forward. At the same time that pressurized gas
begins to enter the spool chamber 58 the gas travels through radial
slots 82 of the secondary spool body causing the O-ring 86 to seat
against the shoulder 84, end wall 85 and the inner surface of the
spool chamber 58 to form a gas-tight seal. When the primary spool
body 62 has traveled forward, the gas pressure pushes the secondary
spool body forward until its forward edge contacts shoulder 77 of
the primary spool body. The contact between the primary spool
shoulder 77 and the secondary spool seats O-ring 78 in a state of
compression so that it can act on the primary spool body when the
piston 26 is removed from contact with the primary spool body.
When the piston chamber 59 is filled with gas, the pressure ratios
become such that the spool mechanism is returned rearward to its
initial position. As a greater area of pressure is formed on the
face of the primary spool body on the piston side as opposed to the
lesser area of pressure formed on the rear surfaces of the primary
spool body and secondary spool body, the greater force pushes the
primary spool body rearward by carrying both spool bodies back
until the flat end surface of the tip projection 68 is seated
against the pilot spool body lip 102 to seal the pilot valve body
bore 96 and close the valve. As the spool mechanism is returned,
gas pressure acting on the diameter of the pilot valve body 54
serves along with spring 108 to absorb the effect of the tip
projection 68 striking the lip 102. This cushioned action
eliminates impact on lip 102 so that the surfaces will continue to
form a gas-tight seal after repeated use.
Functionally, the pilot valve works fully well without spring 108.
The purpose of spring 108 is to insure that the valve is in the
closed position when initially pressurized. The force due to
pressure acting on pilot valve body is several times greater than
that of spring 108. For example, in the preferred embodiment the
pressure force on the spring 108 is less than one pound with the
pressure force acting on the pilot valve body being equal to 5 to 6
pounds.
A gas exhaust is provided in the apparatus as the pressurized gas
returned by the returning piston head 26 acted on by spring 25, is
forced into the annular channel 87 formed by the forward face of
the primary spool and the inner casing 29, the inlet valve body 30
and O-ring 78. The O-ring 78 forms a gas-tight seal so that the gas
passes from annular channel 87 through the primary spool body at
port 75 into an annular chamber 83 formed by the primary spool body
62 and the secondary spool body 79. The gas exits from chamber 83
through passage 90 and port 92 into an annular exhaust ring or
channel 94 which is connected to the atmosphere by exhaust channel
95. At this time, the apparatus is ready to begin a repeat cycle of
operation.
While the preferred embodiment of the invention has been disclosed,
it is understood that the invention is not limited to such an
embodiment since it may be otherwise embodied in the scope of the
appended claims.
* * * * *