Year: 1889

page_text: Date of Application, 25th Sept., 1889.
Complete Specification Left, 17th July, 1890-Accepted, 23rd Aug., 1890.
I, THOMAS THORP of Whitefield near Manchester in the County of Lancaster
Architect and Engineer, do hereby declare the nature of this invention to be as
follows-
This invention relates to apparatus of that kind in which a tool for chiselling,
caulking, hammering or such like operations, is caused to reciprocate rapidly by
compressed air or other elastic fluid acting alternately at the opposite ends of a
piston as determined by a slide valve moved by the working fluid as the piston
attains each end of its stroke. The piston which works to and fro in a cylindrical
casing is of considerable length having a broad groove in the middle and a narrower
groove near each end. In the middle of the cylindrical casing there is a groove
recess and in this is fitted an annular slide valve the length of which is less than
the width of the groove: so that the valve has space to slide to and fro in the
groove. The outer periphery of the annular slide valve has grooves, which, as
the slide valve. moves to and fro make communications. between ports and pas-
sages formed in the casing for inlet and outlet of the working fluid. There are
holes through the middle of the slide valve which, always make communication
from the supply passage of fluid under pressure. to the middle groove of the
piston, and there are holes in the casing, by which, the two end grooves of the
piston are put in communication with the discharge passage.
When the piston attains one end of its stroke,, the, one end of the annular slide
valve is subjected to the pressure in the middle groove of the piston, whilst the
opposite end, of the slide valve is relieved. from. pressure by. the groove in which
it works being in communication with one of the end grooves: of the cylinder.
Owing to the difference of pressure on the two ends of the slide valve, it is
caused to make a rapid stroke, altering the communication with the supply and
discharge passages, so that the piston is caused to make its return stroke, where-
upon a like, shifting of the slide valve takes place. Thus as long as there is a
supply of working fluid under pressure, and a free discharge, the piston is caused
to reciprocate rapidly. As the piston makes its forward stroke a stem projecting
from the piston strikes the stem of the percussion tool and forces it forwards in
opposition to a. spring which draws back the tool as the piston makes its back
stroke.. A buffer spring is arranged at the back end of the cylinder to take the
blow of the piston when it makes its back stroke. The casing terminates in a
handle by which the operator holds the tool and guides it to its work, and
within, convenient reach of his hand there is a hole or a valve that can be closed.
so as to shut off the supply or the discharge of the working fluid when it is
desired to stop the action.
2000

page_text: what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement :-
This invention relates to apparatus of that kind in which a tool for chiselling,
caulking, hammering or such like operations, is caused to reciprocate rapidly by
compressed air or other elastic fluid acting alternately on opposite ends of a piston
as determined by a slide valve moved by the working fluid as the piston attains
each end of its stroke. The accompanying drawing is a longitudinal section of the
pneumatic apparatus for working a tool according to this invention. A is the stem
of the tool which, being struck forward by the piston and returned by the spring a
against a buffer spring a travels rapidly to and fro its collar a² working in a guide
tube a³ forming part of the front part of A' of the pneumatic apparatus. B is
the handle, preferably of wood screwed into a sleeve b which is free to slide a
certain distance along the back parts C C¹ of the apparatus, and is pressed back
by a spring b. To the bandle B is attached a piston valve b2 which, when the
handle is back as far as permitted by the end of slot 63 in the sleeve b
coming against the supply pipe C2 closes the mouth of the supply pipe, so that
the apparatus becomes inactive. But when the operator presses forwards the
handle B so as to force the tool A against the material on which it operates, then
the piston valve 6' uncovers the supply orifice and the working fluid supplied
by C then acts as I shall presently describe. One side of the piston b is
flattened or has a groove cut along it, and a screw 6 bearing against this pre-
vents b² from turning. The back part C of the apparatus is connected to the
front part A¹ by means of a sleeve D which has a shoulder at d engaging against
a collar on C and which screws at d¹ on to A¹. Inside the sleeve D between
the shoulder of A¹ and the shoulder of C is fixed an annular lining E which has
ports and passages formed in it as shewn. An annular port e in the middle is
in communication by passages el with passages be from the supply chamber in C;
two sets of ports es lead through E into a space surrounding E from which
there is an outlet opening da through the sleeve D, and two sets of narrow ports et
and lead from this space through ports in cand in a. Within the lining E is
the annular slide valve F which is free to move a short distance between the
shoulder at the end of C and the shoulder at the end of A. This slide valve has
a port through its middle and has two recesses formed on its outside. The
piston P has a wide groove p in its middle and two narrower grooves p1 and p2.
on each side of its middle. It has a stem p³ to strike the stein of the tool A
and at the end of its instroke it strikes a buffer spring p'. The action is as follows..
The working fluid supplied by C flows by the passages and e' into the annular
port e, and thence while the slide valve is in the position shewn by passages p
into the space behind the piston P. At the same time fluid can flow from the
space in front of the piston P by passages 2 and e to the ports e and thence
away by d². When the piston is thus caused to make its forward stroke, the front
edge of the groove p passes the back edge of and the front edge of the groove 2)²
passes the front edge of cas the groove p is always charged through the middle
port of the slide valve with fluid under pressure, and as the groove p² presents
a passage from the space behind the slide valve to the escape ports e, the slide
valve is rapidly forced back, altering the communications by the ports so that
the working fluid under pressure is supplied to the space in front of the piston P,
and the fluid can escape from behind the piston, which is thus caused to make
its back stroke. As it completes its back stroke the back edge of the groove pr
passes the front edge of c and the back edge of the groove p¹ passes the back
edge of a; and thereupon the slide valve F is rapidly forced forward to the posi-
tion shewn, causing the piston to be again propelled forwards. Thus, by the
rapid alternations of pressure on the ends of the slide valve F causing it to move
to and fro, and the consequent alternations of pressure on the piston P, this
piston is caused to reciprocate rapidly, its front stem pa striking the stem of the
tool A and causing it to operate percussively on the material against which it.
is pressed. The passages p do not quite reach the end of the cylindrical. space

page_text: in which the piston P works, so that there is a cushion of fluid in front of the
piston as it is completing its forward stroke.
Having thus particularly described and ascertained the nature of this invention
and in what manner the same is to be performed I would have it understood
that I do not claim the construction of the piston P with a front stem p* of smaller
diameter, nor do I claim the use of a sliding handle B operating a valve, these
improvements having been described in a previous Specification No. 11723 of 1889,
but what I claim in respect of pneumatic percussive tools is:
The combination of the grooved piston P with the annular slide valve F and the
annular lining E and their ports and passages arranged and operating substantially
as described.
ABEL & IMRAY,
Agents for the Applicant.