Year: 1886

page_text: Date of Application, 13th Dec., 1886
Complete Left, 23rd Aug., 1887
Complete Accepted, 18th Oct., 1887
invention to be as follows :-
This invention has reference to that description of Rock Drilling Machinery acting
by percussion, in which the motion of the Rock Drill is effected by steam, compressed
air or other fluid under pressure, admitted to and exhausted from the Drill cylinder
by means of a piston valve (or slide valve worked by a piston at either end) which is
worked by the motion of the Drill piston.
Two passages or ports are so arranged in conjunction with a recess in the Drill
piston (which is always open to the exhaust) that by the motion of the Drill piston,
Huid under pressure is admitted to and exhausted from the valve casing, so that the
motion of the valve is effected without gearing.
Such an arrangement was described in the Specification of Crease's Patent, dated
24th Octr. 1863, No. 2624.
'
According to the present improvement, the valve casing is a smaller cylinder than
the Rock Drill cylinder and in it works a piston valve (or slide valve worked by a
piston at either end) the movement of which to and fro, controls the admission &
exhaust of the fluid pressure alternately to each end of the Rock Drill piston and
consequently its movement.
The piston valve in its turn is moved by the Drill piston uncovering alternately a
small port or passage at each end of the valve cylinder, which allows of the piston
valve being moved by the fluid pressure and the recess in the Drill piston alternately
receiving the exhaust from these ports.
The improvement consists in making the top part of the piston valve smaller in
Diar. and to work in a smaller cylinder than the bottom part of this valve.
The effect of this is as follows:
The drill piston making an up stroke uncovers the small part to the underside of
the piston valve cylinder, the fluid pressure forces the valve up and as the bottom of
the piston valve is larger in area than the top, there will be proportionately more

page_text: pressure to force it up and less resistance due to the smaller quantity of exhaust to be
forced out through the small port at the top of the piston valve cylinder and through
the recess in the Drill piston to the atmosphere.
The result of this is that the valve is moved over very sharply, admitting fluid
pressure to the top of the Drill piston and arresting its upward movement so smartly
that it is not necessary to use India-rubber or other buffers for protecting the top
cover of the Drill cylinder.
The down stroke of the Drill piston is now delivered and when the small port to
the top of the piston valve cylinder is uncovered, fluid pressure forces the valve down.
But as the top area of the piston valve is less than the area of the bottom, there is
proportionately less pressure to force the valve down and more resistance due to the
larger quantity of exhaust to be forced out through the small port at the bottom
of the piston valve cylinder and through the recess in the Drill piston to the
atmosphere.
The result of this is that the valve moves over comparatavely slow and the benefit
of this is that the Drill piston delivers a blow equal to its full momentum on the
stone or material being operated upon, before the fluid pressure acts on the underside
of the Drill piston to raise it into position for another stroke.
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page_text: Prave motions OI KOOK Dr1118.
DAVID DONALD Engineer Penryn Cornwall do hereby declare the nature of my
invention for IMPROVEMENTS IN VALVE MOTIONS OF ROCK DRILLS and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
This invention has reference to that description of Rock Drilling machinery acting
by percussion, in which the motion of the Rock drill is effected by steam, compressed
air or other fluid under pressure, admitted to and exhausted from the drill cylinder
by means of a piston valve (or slide valve worked by a piston at either end) which is
worked by the motion of the drill piston.
Two passages or ports are so arranged in conjunction with a recess in the Drill
piston (which is always open to the exhaust) that by the motion of the drill piston,
fluid under pressure is admitted to and exhausted from the valve casing, so that the
motion of the valve is effected without gearing.
Such an arrangement was described in the Specification of Crease's Patent, dated
24th Octr. 1863, No. 2624..
According to the present improvement, the valve casing is a smaller cylinder than
the Rock Drill Cylinder and in it works a piston valve (or slide valve worked by a
piston at either end), the movement of which to and fro, controls the admission &
exhaust of the fluid pressure alternately to each end of the Rock Drill piston and
consequently its movement.
The piston valve in its turn is moved by the Drill piston uncovering alternately a
small port or passage at each end of the valve cylinder, which allows of the piston
valve being moved by the fluid pressure and the recess in the Drill piston alternately
receiving the exhaust from these ports.
The improvement consists in making the top part of the piston valve smaller in
diameter and to work in a smaller cylinder than the bottom part of this valve.
The effect of this is as follows: The drill piston making an up stroke uncovers
the small port to the underside of the piston valve cylinder; the fluid pressure forces
the valve up and as the bottom of the piston valve is larger in area than the top, there
will be proportionately more pressure to force it up and less resistance due to the
smaller quantity of exhaust to be forced out through the small port at the top of the
piston valve cylinder and through the recess in the drill piston to the atmosphere.
The result of this is that the valve is moved over very sharply, admitting fluid
pressure to the top of the drill piston and arresting its upward movement so smartly
that it is not necessary to use India-rubber or other buffers for protecting the top
cover of the drill cylinder.
The down stroke of the drill piston is now delivered and when the small port to
the top of the piston valve cylinder is uncovered, fluid pressure forces the valve down.
But as the top area of the piston valve is less than the area of the bottom, there is
proportionately less pressure to force the valve down and more resistance due to the

page_text: of the arm piston, to 14150 1 1110 p
DESCRIPTION. OF THE DRAWING.
A. A. is a section of a Rock Drill Cylinder, with valve casing B and valve C with
its smaller end C. D. D. is the Drill piston which moves to and fro in the cylinder A,
the Drill bit being secured to the end, which is not shewn. S is the steam or air
inlet. E E, the exhaust ports. F the recess in the Drill piston, which is always in
communication with the exhaust through the holes G. G. H. I. the top & bottom
steam or air ports. J. K. the small ports at each end of the valve cylinder.
When the piston valve is in the position shewn, fluid pressure is admitted through
the port H to the top of the Drill piston & the down stroke of the piston is delivered.
When the small port J to the top of the piston valve is uncovered by the Drill
piston, fluid pressure forces the valve down. But as the top area of the piston
valve C is less than the area of the bottom C, there is proportionately less pressure
to force the valve down and more resistance due to the larger quantity of exhaust to
be forced out through the small port K and recess in drill piston F to the atmosphere.
The result is that the valve moves over comparatively slow and the benefit is that the
drill piston delivers a blow equal to its full momentum, as there is no cushioning.
The valve has now been forced down, admitting fluid pressure through the port I
to the bottom of the drill piston and exhaust from the top through the port H &
exhaust E, and the Drill piston makes an up stroke. When the small port K is
uncovered, fluid pressure forces the valve up and as the bottom C of the piston valve
is larger in area than the top C¹ there is proportionately more pressure to force it up
& less resistance due to the smaller quantity of exhaust to be forced out through the
port J & recess in drill piston F to the atmosphere.
The result is that the valve is moved over very sharply, admitting fluid pressure
to the top of the drill piston and arresting its upward movement so smartly that it is
not necessary to use India-rubber or other buffers for protecting the top cover of
the drill cylinders.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that what
I claim is :
Making the top piston which moves the valve, which regulates the action of the
steam to the main piston of percussive Rock drills; so that it is smaller in diameter
and to work in a smaller cylinder than the bottom piston, substantially as heretofore
described.
To of A 1887