U.S. patent number 3,552,274 [Application Number 04/732,441] was granted by the patent office on 1971-01-05 for pneumatic piston return system for impact tools.
This patent grant is currently assigned to Signode Corporation. Invention is credited to Paul W. Bojan, Robert L. Wolfberg.
United States Patent |
3,552,274 |
Bojan , et al. |
January 5, 1971 |
PNEUMATIC PISTON RETURN SYSTEM FOR IMPACT TOOLS
Abstract
A piston return system for air cylinders wherein live air, when
introduced into the cylinder on the pressure side of the piston
initiates the power stroke. During the power stroke and for a short
time thereafter, a special deformable ring which operates in the
manner of a check valve introduces live air into an annulus which
surrounds the cylinder and communicates with the other side of the
piston, such air serving to return the piston when air pressure is
relieved on the pressure side thereof.
Inventors: |
Bojan; Paul W. (Chicago,
IL), Wolfberg; Robert L. (Chicago, IL) |
Assignee: |
Signode Corporation (Chicago,
IL)
|
Family
ID: |
24943517 |
Appl.
No.: |
04/732,441 |
Filed: |
May 27, 1968 |
Current U.S.
Class: |
91/416; 91/399;
91/422; 91/461 |
Current CPC
Class: |
B25C
1/041 (20130101) |
Current International
Class: |
B25C
1/04 (20060101); F15b 015/17 (); F15b
013/042 () |
Field of
Search: |
;91/416,399(Cursory),461(Cursory),422(Cursory) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Maslousky; Paul E.
Claims
We claim:
1. In a pneumatically operable device for repeatedly exerting a
work force in one direction, a casing having a tubular body
portion, a sleevelike cylinder in said body portion and, in
combination with the wall thereof, defining a narrow fixed volume
annulus, a piston slidable in said cylinder between retracted and
advanced positions, a wall closing the forward end of the cylinder
and annulus and defining a variable volume expansion chamber
forwardly of the piston, a closure head for the rear end of the
cylinder and defining a pressure chamber rearwardly of the piston,
the upper end of said annulus opening into and being in
communication with said pressure chamber, said cylinder having a
port in the wall thereof establishing communication between said
expansion chamber and annulus in all positions of the piston, valve
means selectively operable to admit live air at working pressure to
said pressure chamber to drive the piston forwardly to its advanced
position and to relieve such pressure to allow the piston to return
to its retracted position under the influence of expansion of air
in said expansion chamber and annulus, an annular elastomeric
sealing ring interposed between the extreme upper end region of the
cylinder and said wall of the body portion of said casing, said
sealing ring being automatically effective during forward movement
of the piston as well as after the piston has assumed its full
forward position to bypass live air therearound and thus admit such
live air at working pressure directly into said annulus from said
pressure chamber for flow through said port and into said expansion
chamber for storage thereof, said annular sealing ring being
effective when air pressure in the pressure chamber is relieved to
seal said annulus against the escape of the stored air therein
whereby the stored air is effective through said port and in the
expansion chamber to initiate and complete the return stroke of the
piston.
2. In a pneumatically operable device, a tubular casing defining a
relatively deep socket having a cylindrical rim region, a
sleevelike cylinder disposed in said socket and, in combination
with the wall of the latter, defining a narrow fixed volume annulus
having an upper rim, a piston slidable in said cylinder between a
retracted and an advanced position, a wall closing the forward end
of the cylinder and defining a variable volume expansion chamber
below the piston, a closure head for the rear end of the cylinder
and defining a pressure chamber rearwardly of the piston and in
open communication with the upper rim of said annulus, said
cylinder having a port in the wall thereof establishing
communication between said expansion chamber and annulus in all
positions of the piston, valve means selectively operable to admit
live air at working pressure to said pressure chamber to drive the
piston forwardly to its advanced position and to relieve such
pressure to allow the piston to return to its retracted position
under the influence of expansion of air in said expansion chamber
and annulus, and unidirectional valve means automatically effective
when live air is admitted to said pressure chamber and the pressure
therein exceeds that in the annulus to allow such air to enter the
upper rim of the annulus, said latter valve means being effective
when pressure is relieved in said pressure chamber to seal the
annulus against escape of the entrapped air.
3. In a pneumatically operable device, the combination set forth in
claim 2, wherein said unidirectional valve means comprises a
resilient sealing ring surrounding the upper rim region of the
cylinder and interposed between the cylinder wall and the wall of
said socket, one of said walls being provided with a groove
floatingly receiving the sealing ring therein, the forward side of
said sealing ring being formed with a series of recesses therein
which bypass air around the sealing ring when the latter is in
engagement with the forward side surface of the groove.
4. In a pneumatically operable device, the combination set forth in
claim 2, wherein said groove is an external groove which is formed
exteriorly in the upper rim region of the cylinder wall.
Description
The present invention relates to impact tools of the type employing
a pneumatically operable piston and cylinder assembly for powering
the driver ordinarily associated with such tools. The invention has
particular reference to a novel means for returning the piston of
such an assembly to its retracted position after the piston has
delivered its power stroke.
Insofar as piston return means are concerned, pneumatically
operable piston and cylinder assemblies may, broadly, be divided
into two groups. In one group the piston is returned by spring
pressure and in the other group the piston is returned by air
pressure. It is to this latter class of piston and cylinder
assemblies that the present invention pertains.
Numerous air return systems are currently employed for returning a
piston to its retracted position within a cylinder. Certain of
these systems rely upon the use of live air for driving the piston
in both directions. Such systems possess the obvious disadvantage
that a large volume of air must be expended during each operating
cycle. To obviate this limitation, certain other air return systems
have been devised in which all, or at least a limited portion of
the air which is expelled from the cylinder during the power stroke
of the piston is collected in a fixed pressure chamber and
compressed therein by the compressive action of the piston during
the power stroke. After the piston has completed its power stroke,
this stored and compressed air is returned to the cylinder and
caused, by expansion thereof, to return the piston to its retracted
position. While such systems conserve an appreciable amount of
compressed air, the placement of the pressure chamber entails
difficulty in cylinder design. Placement of the pressure chamber at
the end of the cylinder on the driver side of the piston requires a
cylinder of undue length, while placement of the pressure chamber
at one side of the cylinder increases the overall bulk of the
system. In either event, the use of offset pressure chambers,
regardless of their location with respect to the cylinder, consumes
a space which must be sufficiently large as to enclose a volume of
air under pressure which, when released into the cylinder on the
driver side of the piston, will maintain an effective expansion
force sufficient to completely return the piston and hold it in its
retracted position until the next succeeding power stroke thereof.
Small porting areas for large air displacements, as well as
unreliable valve mechanism also present difficulties that have not
been overcome by such air expansion piston return systems.
The present invention is designed to overcome the above-noted
limitations that are attendant upon the construction and operation
of conventional piston return systems of the air return type and,
accordingly, the invention, in its broadest aspect, contemplates
the provision of a novel air return system wherein that portion of
the cylinder chamber which is disposed on the driver side of the
piston at the time the latter is at the end of its power stroke is
utilized as an expansion chamber into which live air is injected
momentarily for piston return purposes. The live air is obtained by
the simple expedient of bypassing air from the pressure side of the
cylinder around the edge of the piston and past the piston sealing
ring which is of special construction and functions as a check
valve for the unidirectional passage of live air into the expansion
chamber at such time as the piston completes its power stroke.
Thus, when the application of live air is terminated and the
pressure side of the cylinder is bled to atmosphere, the entrapped
air within the expansion chamber, which is unable to bypass the
piston in the opposite direction, expands and returns the piston to
its initial position due to the pressure differential on opposite
sides of the piston. In one illustrated commercial embodiment of
the invention, the volume of the expansion chamber on the driver
side of the piston is effectively increased by surrounding the
cylinder with a narrow cylindrical annulus which communicates with
the expansion chamber on the driver side of the piston. This
annulus appreciably increases the amount of air which may be stored
for expansion purposes without adding to the overall length of the
cylinder while at the same time it does not appreciably increase
the overall width of the cylinder wall.
In a modified form of the invention, the same piston and cylinder
construction is preserved but a conventional piston sealing ring is
employed while a special check valve type of sealing ring is
employed for sealing the annulus, the ring allowing live air to
enter the annulus when the piston has completed its power stroke
and preventing escape of such air during expansion thereof for
piston return purposes.
In another modified form of the invention, substantially the same
piston and cylinder construction is preserved but conventional
sealing rings are employed both for sealing the piston to the
cylinder wall and for sealing the annulus, live air being admitted
to the annulus when the piston has completed its power stroke by
way of a passage leading to the annulus and which is caused to
communicate with the source of live air under the control of the
main actuating valve which supplies air to the cylinder for
performance of the power stroke of the piston.
In all of the forms of the invention briefly outlined above, tool
size is kept to a minimum and tool operation under the control of a
single valve lever such as a conventional valve operating trigger
element is made possible so that, insofar as tool operation is
concerned, conventional operating procedure is employed.
The improved piston return system of the present invention as
briefly outlined above has been designed for use primarily in
connection with portable impact tools such as magazine fed stapling
and nailing machines, and other devices which rely for their action
upon the pressure stroke of a driver. It is to be distinctly
understood however that the invention is not necessarily limited to
such use and piston and cylinder assemblies constructed in
accordance with the principles of the invention may, with or
without suitable modification, as required, be employed for other
purposes too numerous to mention. Irrespective however of the
particular use to which the invention may be put, the essential
features thereof are at all times preserved.
The provision of an impact tool which is extremely simple in its
construction and which therefore may be manufactured at a low cost;
one which is comprised of a minimum number of parts, especially
moving parts, and which therefore is unlikely to get out of order;
one which is rugged and durable and which therefore will withstand
rough usage; one which is capable of ease of assembly and
disassembly for purposes of inspection of parts, replacement or
repair thereof; and one which, otherwise, is well adapted to
perform the services required of it, are further desirable features
which have been borne in mind in the production and development of
the present invention.
In the accompanying three sheets of drawings forming a part of this
specification, three illustrative embodiments of the invention have
been shown as being operatively applied to a commercial stapling
tool or machine.
In these drawings:
FIG. 1 is a sectional view taken substantially centrally and
longitudinally through a portable stapling tool constructed
according to the present invention and embodying the novel piston
return system thereof;
FIG. 2 is a sectional view taken on the line 2-2 of FIG. 1;
FIG. 3 is an enlarged fragmentary detail view taken radially
through the cylinder wall of the tool and in the vicinity of the
piston when the latter is at the bottom of its power stroke;
FIG. 4 is a fragmentary sectional view similar to FIG. 3 but taken
in the vicinity of the piston when the latter is near the end of
its return stroke;
FIG. 5 is a top plan view of a check valve element employed in
connection with the invention, the element being in the form of an
annular elastomeric sealing ring;
FIG. 6 is a bottom plan view of the sealing ring shown in FIG.
4;
FIG. 7 is an enlarged sectional view taken radially through the
sealing ring of FIG. 6 and along the line 7-7 thereof;
FIG. 8 is a sectional view taken diametrically through a modified
form of sealing ring capable of use in connection with the
invention;
FIG. 9 is an enlarged fragmentary sectional view taken
substantially centrally and longitudinally through the upper
cylinder and valve regions of a modified form of stapling tool, the
undisclosed portions of the tool being substantially identical to
the corresponding parts of the tool shown in FIG. 1;
FIG. 10 is a fragmentary sectional view similar to FIG. 4 but
embodying the modified form of tool shown in FIG. 9 and showing the
position of the sealing ring at the time the piston has completed
its power stroke;
FIG. 11 is a fragmentary sectional view similar to FIG. 10, showing
the position of the sealing ring during the return stroke of the
piston; and
FIG. 12 is an enlarged fragmentary sectional view similar to FIG.
9, illustrating a further modified form of the invention.
Referring now to the drawings in detail and in particular to FIG.
1, the piston return system of the present invention has, for
exemplary purposes, been illustrated as being operatively embodied
in a portable gun-type percussion or impact tool in the form of an
air-operated, magazine-fed stapling tool which has been designated
in its entirety at 20. The impact tool involves in its general
organization a composite tool casing which is comprised of four
principal parts, namely a cylinder enclosing body portion 22 from
which there projects rearwardly an integral lateral extension or
handle portion 24, a closure head 26, a nosepiece 28, and a staple
magazine 30.
The body portion 22 is of tubular construction, the upper end
thereof being open while the lower end is closed by means of a
relatively thick bottom wall 32. The tubular body portion 22
surrounds and encloses a thin-walled sleevelike cylinder 34 within
which there is mounted for vertical reciprocation a piston 36 which
carries a driver 38 for staples S disposed in the staple magazine
30. The upper end of the driver is secured by means of a taper pin
39 in a slot 40 formed in the piston and the lower end thereof is
guided in a slot 42 formed in the bottom wall 32. The bottom wall
32 is provided with a stepped recess 44 within which the lower rim
portion of the cylinder 34 is pressed with a tight fit and also
within which there is piloted an annular elastomeric bumper pad 46
designed for engagement with the piston 36 when the latter
completes its downward power stroke. An elastomeric seal 48 for the
driver 38 is centered within the annular bumper pad to prevent
egress of air from the lower regions of the cylinder in a manner
and for a purpose that will be made clear presently.
The magazine 30 may be of any conventional type and no claim is
made herein to any novelty associated with the same. In the
illustrated from of magazine, the staples S are supported in
straddling relation on a guide bar 50 disposed within a magazine
chamber 52 and are urged forwardly in the magazine toward a driver
slot 54 which is formed in the nosepiece in alignment with the
driver 38 by means of the usual spring-pressed follower (not
shown). The forward upper edge of the guide bar 50 constitutes a
shearing edge by means of which the leading staple S in the staple
cartridge may be sheared from the cartridge each time it is engaged
by the driver 38.
As best seen in FIGS. 1 and 4, the upper circular rim of the
cylinder 34 terminates flush with the upper rim of the tubular body
portion 22 and is provided with a thickened flange 56 which is
formed with a continuous annular groove 58 therein for reception of
an O-ring 60 by means of which the cylinder 34 is sealed to the
inner wall surface of the body portion 22. The wall of the cylinder
34 is spaced a slight distance from the wall of the body portion
22, the two walls being coaxial so that they define therebetween an
annulus 62 which is of full cylinder height. A series of ports 63,
preferably four in number are formed in the cylinder wall and
establish communication between the interior of the cylinder 34 and
the annulus 62. These ports 63 are disposed near the bottom wall 32
and, as clearly shown in FIG. 3, are equally and circumferentially
spaced around the cylinder wall below the lowermost effective level
of the piston 36. The portion of the cylinder chamber below the
piston constitutes a variable volume expansion chamber 64 while the
annulus 62 constitutes an auxiliary fixed volume expansion chamber
the function of which is to increase the capacity of the chamber 64
so that a greater amount of compressed air will be available for
expansion purposes in order to effect the return stroke of the
piston 36, all in a manner that will be described in greater detail
presently.
As best seen in FIGS. 3 and 4, the piston 36 is generally of
cylindrical design and the side wall thereof is provided with an
annular groove 66 in the upper region of the piston and within
which there is disposed a sealing ring 70 (see also FIGS. 5, 6 and
7) which functions in the manner of a check valve during
reciprocation of the piston to allow live air to flow around the
piston from the pressure side thereof to the expansion chamber
during the pressure stroke of the piston and especially at such
time as the piston remains bottomed against the elastomeric bumper
pad 46 and to prevent reverse flow of air around the piston during
the return stroke of the latter under the influence of expanding
air within the expansion chambers 62 and 64. The sealing ring 70 is
formed of a suitable elastomeric material such as rubber, either
natural or synthetic, or a rubber substitute and it is in the form
of a modified O-ring in which the underneath side thereof is
relieved by the provision of a series of circumferentially spaced
transverse grooves 72 which constitute air passages for the
downward flow of air around the piston 36 in the manner shown by
the arrows in FIG. 3 at such time as the piston is bottomed against
the bumper pad 46. The specific operation of the sealing ring 70
will be described in greater detail subsequently and at such time
as the operation of the stapling tool 20 is set forth.
Referring again to FIG. 1, the closure head 26 is secured in any
suitable manner as for example by fastening bolts (not shown) to
the upper open end of the body portion 22. A gasket 74 is
interposed between the closure head and the upper rim of the body
portion in sealing relationship. The outer end of the integral
hollow handle portion 24 is adapted to be connected by a suitable
nipple fitting 76 to a flexible conduit 78 leading to a source of
air under pressure.
The closure head 26 overhangs the upper rim of the body portion 22
and a reentrant or inturned flange 80 divided the interior of the
composite casing into an upper chamber 82 and a lower chamber 84,
the former chamber constituting a pressure chamber for the cylinder
34 and communicating with the upper end of the latter through a
port 86. The two chambers 82 and 84 communicate with each other
through a port 88.
An elongated valve spool 90 projects through the port 88 and has an
enlarged lower end 92 guided in a socket 94 provided internally in
the handle portion 24 and sealed to the wall of the socket by an
O-ring 96. The upper end of the valve spool 90 is provided with an
enlargement 98 which is guided in a socket 100 formed internally of
the closure head 26. The medial region of the valve spool 90 is
formed with a third enlargement 102 which constitutes a closure
valve for the port 88 which establishes communication between the
chambers 82 and 84.
The socket 94 normally communicates through an air passage 106 with
the chamber 84 and a ball check valve assembly 108 is adapted upon
actuation of a pivoted trigger element 110 to become closed and
prevent such communication between the socket 94 and 84. The socket
100 communicates through a passage 112 with the atmosphere and
through a port 114 with the chamber 82. An O-ring 116 encompasses
the port 114 and is designed for sealing engagement with the
enlargement 98 when the valve spool 90 is in its lower position.
When the valve spool is in its uppermost position, the chamber 82
is bled to the atmosphere through the port 114 and passage 112.
The check valve assembly 108 includes a ball valve element 120
disposed in a valve chamber 122 and normally closes a passage 124
leading to the atmosphere and opposes the passage 106. A hollow
thrust pin 126 is slidable in the passage 124 and operates to
displace the valve element 120 when the trigger element 110 is
depressed.
In the operation of the above-described impact tool 20, the spool
valve 90 will normally be maintained in its uppermost position
since air pressure within the chamber 84 will be effective through
the passage 106 to maintain full working pressure upon the
underneath side of the enlargement 92, as well as to maintain
pressure upon the closure valve 102. Such closure valve will
therefore close the port 88 and pressure within the upper end of
the cylinder 34 will be bled to the atmosphere through the port 114
and passage 112.
Upon depression of the trigger element 110, the ball valve element
120 will become dislodged from the passage 124, thus bleeding the
valve chamber 122 to the atmosphere. The valve element 120 will
close the passage 106 so that air at working pressure within the
chamber 84 will act upon the enlargement 92 and cause the spool
valve 90 to move downwardly, thus opening the port 88 and at the
same time causing the enlargement 98 to make sealing engagement
with the O-ring 116, thus closing the port 114. At this time,
working pressure within the chamber 84 will be transmitted through
the port 88 to the chamber 82 where it will be applied through the
port 86 to the upper end of the cylinder 34, thus forcing the
piston 36 downwardly. The amount of air which bypasses the sealing
ring 70 during the downward stroke of the piston is very slight and
has little, if any effect upon the power which is applied to the
piston 36 and its driver 38. However, when the piston reaches the
end of its power stroke as shown in dotted lines in FIGS. 1 and in
full lines in FIG. 3, full line pressure remains effective upon the
upper end face of the piston and the sealing ring 70 is forced
downwardly against the lower side wall of the groove 66 and live
air then passes around this sealing ring as indicated by the arrows
in FIG. 3 so as to enter the expansion chamber 64 beneath the
piston and fill the latter. As soon as the air pressure in the
expansion chamber 64 exceeds the air pressure in the annulus 62,
this live air flows radially outwardly through the ports 63 and
fills such annulus. This flow of live air continues until the
pressure of air in the chambers 62 and 64 substantially balances
the pressure of air above the piston (i.e. equals line pressure)
and then, as soon as the trigger element 110 is released, the ball
valve element 120 will again close the passage 124 so that the
spool valve 90 will return to its uppermost position and bleed the
upper end of the cylinder 34 to the atmosphere through the port 114
and passage 112, whereupon the piston 36 will perform its return
stroke under the influence of the expansion of air in the expansion
chamber 64 and annulus 62. The full expansion pressure of such air
is applicable to the piston inasmuch as the sealing ring 70 now
becomes wedged between the upper side wall of the groove 66 and the
side wall of the cylinder 34 as shown in FIG. 4 so that air may not
bypass the sealing ring or piston.
In order that after the return stroke of the piston has been
completed no entrapped air will remain in the expansion chamber to
thus dampen the next succeeding power stroke of the piston, a
series of small splinelike grooves 130 (FIG. 4) are formed in the
wall of the cylinder 34 at the extreme upper end thereof, four such
grooves being adequate to afford the desired bleeding effect. These
grooves communicate at their upper ends with relief areas or
passages 132 which are provided in the underneath side of the
closure head 26 so that the residual air may be bled to the chamber
82 for discharge through the port 114 and passage 112. The gasket
74, also is relieved to accommodate such bleeding of residual air.
Obviously, a very small amount of air will pass through the grooves
130 at the commencement of the power stroke, but as the piston
moves out of the range of the grooves 130, no further bypassing of
air around the piston will take place during the power stroke and
no appreciable decrease in the effectiveness of such power stroke
will be encountered.
From the above description, it will be apparent that upon release
of the trigger element 110 and subsequent return of the piston to
its uppermost position, the various pneumatic tool
instrumentalities will be restored to their normal or initial
positions preparatory to a subsequent staple driving operation.
In the modified form of stapling tool 220 disclosed in FIGS. 9, 10
and 11, the composite tool casing including the body portion 222
with its handle extension 224, the cylinder 234, closure head 226
and nosepiece 228 remain substantially the same as the
corresponding parts of the tool 20 previously described. However,
in the tool 220 the disposition of the two sealing rings 60 and 70
(FIGS. 1, 3 and 4) have been reversed while minor porting
arrangements have been effected to accommodate such reversal. Due
to the similarity of construction between the two forms of the
invention, similar reference numerals but of a higher order have
been applied to the corresponding parts as between the disclosures
of FIGS. 1, 3 and 4 and of FIGS. 9, 10 and 11 thus avoiding
needless repetition of description.
In the form of the invention disclosed in FIGS. 9, 10 and 11, the
piston 236 is sealed to the wall of the surrounding cylinder 234 by
a conventional O-ring 260 so that no leakage or bypassing of air
around the piston takes place except when the piston 236 is near
the top of its stroke, either during the power or the return stroke
thereof. However, in order to provide live air for expansion in the
expansion chamber 264 and annulus 262, a sealing ring 270 of the
unidirectional check valve type, and which may be identical with
the sealing ring 70 of FIG. 1, is installed in the annular groove
258 provided in the thickened flange 256 at the upper end of the
cylinder 234, while the relief areas 332 provided in the underneath
side of the closure head 226 are of greater radial extent than are
the relief areas 132 and communicate with the small annulus 333
which surrounds the upper side wall flange of the groove 258.
Otherwise, the porting arrangement of the tool 220 remains
precisely the same as that of the tool 20.
The operation of the tool 220 is similar to that of the tool 20
and, upon depression of the trigger element 310 and consequent
downward movement of the spool valve 290, air under line pressure
will be admitted to the chamber 282 above the piston 236, thus
causing the latter to deliver its downward power stroke. As soon as
the piston 236 has cleared the grooves 330, air will be bypassed
around the piston and, at such time as it reaches the bottom of its
power stroke, live air within the chamber 282 will pass through the
relief areas 332 and vertical passages 333 and enter the annular
groove 258 where it will bypass the O-ring 270 and enter the
annulus 262, such air also passing radially inwardly through the
ports 263 and entering the expansion chamber 264. Upon release of
the trigger element 310, the air which has filled both the annulus
262 and expansion chamber 264 will utilize its expansive force in
returning the piston 236 to its initial position while the O-ring
270 will prevent escape of air from the annulus upwardly through
the passage 333. As is the case in connection with the previously
described form of the invention, the splinelike grooves 330 which
are similar in function to the grooves 130 in the form of the
invention shown in FIG. 1 will insure complete collapse of air
pressure in the cylinder 234 after the piston 236 has been fully
returned. These grooves 330, being small and few in number, do not
diminish the effect of the power stroke of the piston. They merely
evacuate the cylinder after the piston has been returned.
In a further modified form of the invention which has been
illustrated fragmentarily in FIG. 12, the same principle of piston
return under the influence of expanding air in the expansion
chamber 464 beneath the piston 436 and in the annulus 462 has been
preserved. Again, in order to avoid repetition of description,
similar reference numerals but of a still higher order have been
applied to the corresponding parts as between the disclosures of
FIGS. 9 and 12. In this latter form of the invention, the relief
areas 332 and vertical passages 333 have been eliminated so that no
live air may enter the expansion chamber 464 or annulus 462 by
either bypassing it around the piston 436 as in the first form of
the invention, or by utilizing a check valve type of sealing ring
as in the second form of the invention. However, relief areas 532
communicate with the splinelike grooves 530. Conventional O-ring
seals 460 and 470 are employed both in the groove 466 of the piston
and the groove 458 of the cylinder 434. In order to admit live air
into the annulus 462 and expansion chamber 464 at the time the
piston 436 completes its power stroke, a passage 533 is provided in
the wall of the body portion 432, this passage establishing
communication between the annulus 462 and the socket 494 within
which the enlargement 492 of the valve spool 490 is disposed. Thus,
at such time as the trigger element 510 is depressed so as to shift
the valve spool 490 downwardly, the passage 533 is uncovered by the
enlargement 492 and the annulus 462 and expansion chamber 464
receive a supply of live air directly from the chamber 484 for
subsequent expansion and consequent piston return purposes in the
manner previously described in connection with both the tool 20 and
the tool 220.
In FIG. 8 a modified form of check valve type sealing ring 670
which is capable of substitution for either of the sealing rings 70
or 270 has been shown. The ring 670, which is formed of elastomeric
material is generally circular in cross section and, in order to
prevent seating of the ring against one side of the groove in which
it may be positioned, a multiplicity of spacer lugs 671 are formed
on one side of the ring. These lugs establish intervening voids or
passageways 672 for unidirectional air flow therethrough.
The invention is not to be limited to the exact arrangement of
parts shown in the accompanying drawings or described in this
specification as various changes in the details of construction may
be resorted to without departing from the spirit of the
invention.
* * * * *