Improvements in Pneumatic Hammers.
Year: 1899

page_text: Date of Application, 5th Sept., 1899-Accepted, 27th Jan., 1900
Improvements in Pneumatic Hammers.
I, ELIAS GUNNELL, of 9,830 Avenue H., Chicago, Illinois, U.S.A., Mechanical
Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
My invention relates to that class of devices, commonly known as pneumatic
hammers, in which a reciprocating piston operated by compressed air or other
motive fluid hammers upon a tool or tool-holder inserted in or carried by the
front end of the cylinder, and has for its object the provision of means whereb
the construction of the tool may be simplified and the force of the blow
of the piston materially increased as compared with that of pneumatic ham-
mers now generally used. These results are accomplished in the manner
and by the means to be now described by reference to the accompanying drawings,
in which Figure 1 represents a middle longitudinal section of my improved
hammer with the piston shown at the rear end of its stroke; Figure 2 a similar
view with the piston approaching the end of its forward stroke; and Figure 3
a similar view with the piston at the end of its forward stroke and the valve
shifted for the return stroke.
The same letters of reference are used to indicate identical parts in the several
views.
In the present instance, my improved hammer is illustrated as equipped for
the operation of riveting, and adapted for use in connection with a riveting
apparatus, such, for instance, as that illustrated and described in British Letters
Patent 19910 of 1898, which will account for the particular form of it illustrated
in the drawings, as hereafter explained; but such apparatus and such employ-
ment of my new hammer have nothing to do with the essential features of my
invention.
A is the main cylinder of the tool, which has formed in it a differential piston-
chamber B whose forward half or portion has the larger diameter and its rear
portion the smaller. The rear end of the cylinder and piston-chamber are in
the present instance partially closed by a tail-piece C which is screwed into the
rear end of the cylinder A and is provided with a flange abutting against its
rear end. This tail-piece has nothing to do with my present invention, being
employed in the present instance simply to adapt the fool for use in the rivet-
ing apparatus heretofore referred to, and its place may be taken by any suitable
cap or cylinder-head, which, where the hammer is to be used as a hand-tool,
will be provided with the usual handle and throttle-valve for controlling the .
admission of the motive fluid to the tool. The only essential thing in respect
to this end of the tool is the large inlet passage 1) for the motive fluid, opening
into the rear end of the cylinder, through which the full and unrestricted supply
of motive fluid is constantly admitted to the rear end of the piston-chamber
when the main throttle-valve is open and the tool is in operation.
Screwed into the opposite or front end of the cylinder A is a cylindrical block

page_text: or head E provided wih a central bore to receive the shank F of the riveting
die G. The inner end of this block or head E, within the cylinder A, is bored
out in a suitable manner to receive a cylindrical valve H provided upon its
periphery with a forwardly facing annular shoulder a to which the pressure of
the motive fluid is constantly admitted through a passage I extending rearward
through the cylinder A and communicating at its rear end with the rear end of
the piston-chamber. The constant pressure of the motive fluid against this
shoulder a tends to hold the valve in its rearward or right-hand position,
Figures 1 and 2, and in such position the front end of the piston-chamber is
in free communication with the atmosphere through the interior of the valve H
and exhaust-openings J formed in the wall of the cylinder-structure. When,
however, the valve is forced forward to the position shown in Figure 3 its front
end enters and snugly fits. a circular recess K.formed in the block E and thereby
cuts off the front end of the piston-chamber B from the exhaust ports J. A
cushioning ring K' is in the present instance shown seated in a groove in the
bottom of the recess K to receive the end-thrust of the valve.
Leading forward from the rear half or portion of the main piston-chamber
is a passage L which opens at its forward end into the large portion of the piston-
chamber at the extreme front end of the latter. Also leading forward through
the wall of the cylinder A is a second passage M, shown in dotted lines, which
communicates with the smaller half of the piston-chamber near the rear end of
the latter, and at its forward end opens into the enlarged portion of the cylinder
at the front end of the main piston-chamber, in which the valve H moves, the
front end of such passage being closed by the valve H when the latter is in
its rear position as in Figures 1 and 2.
The niston N has a main body portion fitting the rear half of the piston-chamber
and an enlarged portion or head N¹ fitting the large half of the piston-chamber.
In front of the part N¹ the piston is reduced to even less diameter than its rear
portion, forming a stem or striking portion N1, upon which, just forward of
the enlargement N¹, is formed a circumferential shoulder or collar b.
Opening through the wall of the cylinder A, immediately in front of the
enlargement or head N¹ of the piston when the latter is in its extreme rearward
position, Figure 1, are exhaust-ports O.
Under the above described construction and arrangement of parts, the opera-
tion is as follows:
With the piston and valve in rearward position, as in Figure 1, and the front
end of the piston-chamber consequently open to the exhaust, when motive fluid
is turned on to the tool, the piston will be driven forward by the pressure behind
it. As it approaches the forward end of its stroke, its stem Nu will enter and pass
through the valve H, and, as it nearly completes its stroke, the enlarged portion
or shoulder b on said stem will enter the rear end of the valve H, Figure 2. This
shoulder bis of such diameter as to snugly fit the internal bore of the valve,
and consequently when it thus enters the rear end of the valve communication
between the front end of the piston-chamber and the exhaust-ports J (through
the interior of the valve) will be cut off. At the instant the shoulder 7 of the
piston-stem thus enters the rear end of the valve, the extréme rear end of the
piston will uncover the rear end of the passage L, Figure 2, thereby admitting
the motive fluid from the rear end of the piston-chamber, through said passage,
to the extreme front end of the piston-chamber, between the rear end of the
valve H and the annular forward face of the head N of the piston, and this
pressure so admitted to the rear end of the valve H will overcome the pressure
acting constantly upon the smaller annular shoulder a of the valve, as hereto-
fore explained, and drive the valve forward to the position shown in Figure 3.1
Such forward movement of the valve will uncover the front end of the passage M,
so that the motive fluid will then be admitted to the front end of the piston-
chamber through both of the passages L and M. As the piston delivers its blow
upon the shank. Fof the riveting-die G and rebounds therefrom it will, at the

page_text: very beginning of its backward movement, cover and close the rear end of the
passage L, but the motive fluid will continue to be admitted to the front end
of the piston-chamber through the passages M, since the pressure of the motive
fluid in the front end of the piston-chamber, acting upon the rear end of the
valve, will maintain the valve in the forward position to which it has been moved,
with the exhaust outlet from the front end of the piston-chamber closed as before
explained. The motive fluid admitted to the front end of the piston chamber
through the passage M and acting upon the entire forward area of the piston
(both the front end of the stem N and the annular face of the head N¹) will
overcome the constant pressure upon the rear end of the piston, which has driven
the piston forward, and will drive the piston backward. As the piston approaches
the rear end of its stroke, it will uncover the exhaust ports 0 (at the same time
closing the rear end of the passage M) whereupon the pressure in front of the
piston will immediately escape, and the valve being thus relieved from the pres-
sure which has been holding it in forward position will be immediately shifted
to rearward position by the constant pressure acting against its annular shoulder a,
thereby opening the front end of the piston-chamber to the exhaust through
the interior of the valve and exhaust-ports J as well as through the exhaust-
ports uncovered by the piston; whereupon the piston will be immediately
driven forward again by the constant pressure behind it, and the above described
operation be repeated. At its forward movement, the piston will at once close
the exhaust-ports 0, but the front end of the piston-chamber will remain in
free communication with the atmosphere through the exhaust ports J, so that
there will be no compression of air in front of the piston to resist its forward
movement and to lessen the force of its blow. The exhaust-ports thus serve
the two-fold purpose of providing an exhaust outlet controlled by the piston for
relieving the pressure upon the large area of the valve at the end of the rear-
ward stroke of the piston, and, second, of providing a large and free exhaust
from the front end of the piston at the end of its rearward stroke and permit-
ting the instant escape of the pressure in front of the piston without waiting for
the valve to shift.
From the foregoing description, it will be understood that the piston is driven
forward by a constantly acting pressure behind it, and that at the end of its
forward movement a preponderating pressure is admitted to its forward end,
to drive it rearward again, against the resistance of the constant pressure behind
it.
It is a desideratum in tools of this character that the motive fluid shall be
admitted behind the piston in the fullest and freest possible manner at the
beginning of the forward stroke of the piston, in order that the latter may be
driven forward at the maximum velocity and thereby strike a blow of maximum
force upon the shank of the working tool. Where a valve is employed to inter-
mittently admit and exhaust the motive fluid at the rear end of the piston-
chamber, there is necessarily more or less restriction to the inflow of the motive
fluid through the port or ports controlled by the valve, and it is consequently
impossible to utilize in such case the full power of the motive fluid supplied to
the tool. By the provision of my invention the motive fluid is constantly ad-
mitted to the rear end of the piston-chamber through a port or passage which is
or may be of full size of the conduit through which the motive fluid is conveyed
to the tool, and as it is acting upon the rear end of the piston all the time its
maximum power is utilized to drive the piston forward at the instant the exhaust
ports in front of the piston are opened and the latter reverses its stroke and
starts forward again. I-am therefore enabled, under any given conditions, to
obtain a more powerful blow from a piston of given size and length of stroke
than where the inflow of motive fluid to the rear end of the piston-chamber is
more or less throttled by the employment of a valve controlling the inlet and
exhaust at that end of the niston-chamber.
Inasmuch as it is not only a desideratum that the piston shall be driven for-

page_text: ward at maximum velocity, but also that it shall be returned gently or slowly,
in order that its blows upon the working tool may not succeed each other too
rapidly, and in order that it may not produce objectionable shock or jar at the
end of its rearward stroke, a very small preponderating pressure area upon the
front end of the piston will serve to return the piston to rearward position in
the desired manner, and by properly proportioning the front and rear pressure
areas of the piston, the rearward movement of the piston may be regulated as
desired.
· It will further be noted that, accompanying the advantages above set forth,
my tool presents a simplicity of construction and economy of manufacture of an
important character as compared with many other tools of this character now
in use.
As heretofore explained, the particular tool illustrated in the drawing has been
designed for use in my riveting apparatus, in which, when the motive fluid is
turned on to the tool, the riveting set or die G is constantly pressed against the
point of the rivet, and therefore no means for holding the die in place in the
tool (against the pressure of the motive fluid in the front end of the piston-
chamber) need be employed; but when employed as a hand-tool, suitable means
for such purpose will be provided.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what
I claim is:-
1. A pneumatic hammer comprising a cylinder, a differential piston therein
having its forward pressure area superior to its rear pressure-area, to which
latter the motive fluid is constantly admitted, and a valve located at the front
end of the piston-chamber and co-operating with the piston to intermittently
admit the motive fluid to the front end of the piston-chamber to drive the piston
rearward.
2. A pneumatic hammer comprising a cylinder, a differential piston therein
having its forward pressure-area superior to its rear pressure-area, to which
latter the motive fluid is constantly admitted, and a differential valve located at
the front end of the piston-chamber, to whose smaller pressure-area the motive
fluid is constantly admitted and to whose larger pressure-area the motive fluid is
intermittently admitted through a passage controlled by the piston.
3. A pneumatic. hammer comprising a cylinder, a differential piston therein
having its forward pressure-area superior to its rear pressure-area, to which latter
the motive fluid is constantly admitted, and a differential valve located at the
front end of the piston-chamber, to whose smaller pressure-area the motive fluid
is constantly admitted, and to and from whose larger pressure-area the motive
fluid is intermittently admitted and exhausted through ports and passages con-
trolled by the piston.
4. A pneumatic hammer comprising a cylinder, a differential piston therein
having its forward pressure-area superior to its rear pressure-area, to which
latter the motive fluid is constantly admitted, and a differential valve located at
the front end of the piston chamber, to whose smaller pressure-area the motive
fluid is constantly admitted and whose larger pressure-area is exposed to the
front end of the piston-chamber and acted upon by the motive fluid intermit-
tently admitted to and exhausted from the front end of said chamber through
ports and passages controlled by the piston.
15. A pneumatic hammer comprising a cylinder, a differential piston therein
to whose smaller rear end the motive fluid is constantly admitted to drive the
piston forward, and a cylindrical valve located in the front end of the cylinder
and through which the front end of the piston passes to deliver its blow, said
valve co-operating with the piston to intermittently admit the motive fluid to
the front end of the piston-chamber and to drive the piston rearward.
6. A pneumatic hammer comprising a cylinder, a differential piston therein
to whose smaller rear end the motive fluid is constantly admitted, and a differ-

page_text: ential cylindrical valve located in the front end of the cylinder, and through
which the front end of the piston passes to deliver its blow, the motive fluid
being constantly admitted to the smaller pressure area of said valve and inter-
mittently admitted to and exhausted from its larger pressure area through ports
and passages controlled by the piston.
7. A pneumatic hammer comprising the cylinder A having a differential
piston-chamber B into whose rear end opens the main motive fluid inlet 1, the
differential piston located in said chamber and composed of the rear body-por-
tion N. enlargement or head N', and forward portion or stem N", the latter
provided with a shoulder b, and the cylindrical differential valve H located in
the front end of the cylinder and having the annular shoulder a to which the
motive fluid is constantly admitted, the said valve and piston co-operating with
each other and controlling the exhaust ports J and O and the live-air passage M
in the cylinder.
8. A pneumatic hammer comprising the cylinder A having a differential
piston-clamber B into whose rear end opens the main motive fluid inlet D, the
differential piston located in said chamber and composed of the rear body por-
tion N, enlargement or head N¹, and forward portion or stem N", the latter
provided with a shoulder b, the cylindrical differential valve H located in the
front end of the cylinder and having the annular shoulder a to which the motive
fluid is constantly admitted, said valve and piston co-operating with each other
and controlling the exhaust ports J and O and the two live-air passages L and M
in the cylinder.
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.