Improvements in Pneumatic Impact Tools.
Year: 1894

page_text: Date of Application, 3rd July, 1894-Accepted, 11th Aug., 1894
COMPLETE SPECIFICATION.
Improvements in Pneumatic Impact Tools.
I, JOHN FRANKLIN CLEMENT, of 22nd and Bainbridge Streets in the City and
County of Philadelphia, State of Pennsylvania, one of the United States of
America, Doctor of Dental Surgery, 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 impact tools of the kind in which a reciprocating piston
or hammer acts upon a tool-carrying stem, the reciprocation being effected by air
under pressure passing through certain ports and passages as determined by an
air-actuated reciprocating valve, the space in the cylinder on the one side of the
piston being open to the exhaust when the space on the other side receives the air
under pressure.
One object of my invention is to prevent the kicking or jerking of the tool in the
hands of the operator or in its mechanical support. This I attain by so restricting
the area of the exhaust passage behind the hammer as to cushion the piston in its
back stroke without obstructing its free forward movement, or lessening the force
of the blow in the forward stroke, provision being also made for regulating the
area of the exhaust from behind the piston so as to vary the speed of the tool without
detracting from the force of the blow.
A further object of the invention is to provide a valve for accurately governing
the admission of air to the cylinder and thus regulate, as desired, the force of the
blow delivered, and a still further object is to prevent heating of the tool-carrying
stem due to vibration and to ensure the prompt return of the stem to its retracted
position by the back stroke. These objects I attain as I shall describe referring to
the accompanying drawings.
Figs. 1, 2, 3 and 4, are sections of an impact tool according to my invention, the
several views showing the piston in different positions and illustrating also the
movement of the controlling valve;
Fig. 5 is a part transverse section on the line a a, Fig. 1 ;
Fig. 6 is a sectional plan on the line bb Fig. 1, with the valve in elevation ;
Fig. 7 is a sectional plan on the line d d Fig. 1;
Figs. 8 and 9 are sectional views illustrating, in two extreme positions, a special
device for directing air to and exhausting it from the valve chamber for the purpose
of effecting a shifting of the valve;
Fig. 10 is a sectional plan on the line ff Fig. 8, with the valve in elevation ;
Fig. 11 is a sectional plan on the line 9 g Fig. 9, with the valve in elevation ;
Fig. 12 is a view illustrating a modified form of device for operating the air inlet
valve;
Fig. 13 is a side view, on an enlarged scale, of the valve employed for governing
the flow of air to the cylinder;
Fig. 14 is an enlarged sectional view of the valve for governing the exhaust of
air from behind the piston.
1. is the cylinder closed at one end by a head 2, in which is guided the stem 3
which carries the tool either a dental mallet, a rock drill, a caulking tool, a
chipping chisel, or any other tool to which it is desired to impart blows in rapid
succession.
The bore of 2 is closed at the end by a screw cap 4 and encloses a collar 5.
formed upon the stem 3, and between this collar 5 and the screw cap 4 is interposed
sleeve 6 of india rubber or other suitable elastic material, the thickness of this
leeve being such that it does not quite fill the space around the stem 3 when

page_text: the stem is moved quite inward, by the resiliency of the sleeve but when the
stem is thrust outward by the blow of the piston hammer, the longitudinal
compression of the sleeve 6 causes it to expand laterally so as to fill the space
around it as shewn in Fig. 2 and thus to prevent any lateral vibration of the stem.
The sleeve 6 thus not only performs the function of a spring for returning the
stem 3 to its retracted position but also, by preventing lateral vibration of the stem,
it prevents the heating which has been found to result when a coiled metal spring
is employed.
Within the cylinder 7 is free to slide the piston hammer 8, the end portions of
which so fit the cylinder as to prevent any material leakage of air past them, the
central portion being somewhat reduced in diameter so as to present around it an
annular chamber which when the piston is in its extreme positions communicates
with the atinosphere through openings 10 and 11.
Into. the end of the cylinder opposite to the head.2 is fitted a plug 12 which is
bored transversely to form a valve chamber 13 in which a valve 14 is free to slide
transversely. This valve as shown in Fig. 13, has on a central stem opposite end
discs 15, and at a little distance within them intermediate discs 16. The opposite
ends of the valve chamber. are closed by caps 17.
The central portion of the valve chamber 13 communicates by ports 18 with a
chamber formed in the outer portion of the plug 12 to receive the inlet valve 19
which is, in the form of an inverted cone seating on the end of the chamber which
is likewise of conical form. The valve. 19, has a central passage 20 for receiving
air under pressure from a flexible pipe secured to the outer end of the valve stem
and it has lateral ports 21 which are closed when the valve is seated; but when
the valve is retracted, air can pass from the central passage 20 through the
ports 21 and through the ports 18 into the central portion of the valve chamber 13,
as shewn in Fig.,5.
The valve 19 is urged by a spring 22 interposed between a shoulder on the valve
and a screw cap 23.
The outer face of this cap 23 has on it a series of inclines upon which are seated
corresponding inclines on the inner face of a collar 24, fixed to the valve stem.
When the collar 24 is turned in the one direction the valve 19 is also turned and
the valve is withdrawn from its seat, allowing ingress of air; when it is turned in
the opposite direction the valve 19 is permitted to close so as to close the ingress
of air.
The valve
The valve chamber 13 communicates, through one port 25, with the end of the
cylinder behind the piston hammer 8, and also through a port 26 and passages 27
and 28 with the end of the cylinder in front of the piston hammer.
chamber 13 also communicates with two exhaust passages 29 and 30. The
passage 29 contains a hollow valve 31 with a conical inner end having ports 32
communicating with the central bore 33 of the valve, as shown in Fig. 14. By
screwing this valve more or less in, the exhaust through the port 29 can be more
or less throttled.
The ends of the valve chamber 13 communicate by passages 34 and 35 with the
cylinder at different parts of its length as shown in Figs. 1 to 4.
The operation of the tool is as follows:
-
When the valve 14 in the chamber 13 is in the position shown in Fig. 1, air
passes from the valve chamber through the port 25 and into the cylinder. 7 in rear
of the piston hammer and forces it forwards, the air escaping from the front of the
piston by the passages 28 and 27 and port 26, thence through. the space between
the left hand discs 15 and 16 and the exhaust port 30 to the atmosphere.
As the piston 8. approaches the end of its forward stroke it uncovers the front
end of the passage 34 and air under pressure flows from the cylinder and pressing
on the valve 14 moves it to the position shown in Fig. 2, air escaping from the
opposite end of the valve chamber 13 through the passage 35, thence through the
annular space 9 and the exhaust port 10.
.Air under pressure is now directed through the port 26 and passages 27 and 28

page_text: to the end of the cylinder in front of the piston which is therefore forced back-
wards, the air behind it escaping through the port 25, thence through between the
right hand discs 15 and 16 and through the exhaust port.29 and its regulating-
valve 31, as shown in Fig. 3.
By adjusting the valve 31 the escape of air can be so throttled that the air
behind the piston will act as a cushion thus preventing the kicking or jerking of
the tool in the hands of the operator, or in any mechanical support in which it may
be mounted.
As the piston approaches the end of its back stroke its annular space 9 makes.
communication between the passage 34 and the exhaust port II and at the same
time the piston uncovers the front end of the passage 35 and permits air under
pressure to pass to the left end of the valve chamber 13 and press the valve 14
back as shown in Fig. 4, the air from the right end of the chamber 13 escaping
by 34, 9 and 11. The cycle is then repeated.
In the modified construction shown in Figs. 8, 9, 10 and 11, the piston hammer 8.
is formed without the annular space 9 but has projecting back from it two pins 36.
and 37 each having outer and inner ports 38 and 39 cut diagonally across them in
opposite directions and the ports of 36 being inclined in a direction opposite to
those of 37.
The ends of the valve chamber 13 communicate with passages 40 and 41 and
with passages 42 and 43 respectively, 40 and 42 leading to the pin 36 and 41 and 43.
leading to the pin 37.
The chamber of the pin 36 communicates by a port 44 with the central portion
of the valve chamber 13 and the chamber of the pin 37 communicates by a port 45
with the atmosphere.
When the hammer is fully retracted the inner port 39 of the pin 36 directs air
from the central portion of the valve chamber 13 through 40 to one end of the
valve chamber 13 so as to move the valve 14 so as to admit air to the cylinder
behind the piston, the air escaping from the opposite end of the chamber 13 through
the passage 43, through the port 39 of the pin 37, and thence through the exhaust
port 45, as shown in Fig. 10.
When the piston approaches the end of its forward stroke the outer ports 38 of
the pins 36 and 37 come into play, as shown in Fig. 11, and air from the central
portion of the valve chamber 13, is directed by the port 44, outer port 38 of 36,
and passage 42 to the end of the valve chamber 13 so as to move the valve to the
position shown in Figure 11, so that air passes to the front of the piston hammer 8.
As the valve 14 is moved to the position shown in Fig. 11, the air escapes from
the front of it by the passage 41, the outer port 38 of the pin 37, and thence
through the exhaust port 45.
The pins 36 and 37 thus constitute sliding valves which direct air to and let air
escape from the opposite ends of the valve chamber 13 alternately, thus moving
the valve 14 so as to determine the flow of air into and from the ends of the
cylinder.
In Fig. 12 I have shown a modified form of inlet valve 19 the valve stem having
an external screw thread working in a sleeve 46 which is free to turn on the
plug 12 and by turning which the valve 19, not turning, can be raised and
lowered.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. An impact tool having a cylinder fitted with a reciprocating piston hammer
and a projecting tool stem, a transverse valve and chamber and air inlet and
exhaust ports, substantially as specified.
2. For regulating the exhaust during the back stroke of the piston in order to
effect cushioning, a hollow valve provided with ports and adjustable in an exhaust
port, forming a seat for it, substantially as specified.

page_text: 3. For regulating the inlet of air to the valve chamber a hollow valve provided
with lateral ports and adjustable in the inlet chamber, which forms a seat for the
valve and has ports communicating with the governing valve chamber, substantially
as specified.
4. For retracting the tool stem and preventing vibration, a sleeve of rubber or
other elastic material, substantially as specified.
5. The modified arrangement shown in Figs. 8 to 11 for moving the governing
valve, by sliding pins fitted in the piston and having upper and lower diagonal
ports governing passages substantially as specified.
Dated this 3rd day of July 1894.
ABEL & IMRAY,
Agents for the Applicant.