IMPROVEMENTS IN VALVES OF PERCUSSIVE ROCK DRILLS
Year: 1881

page_text: LETTERS PATENT to John Henry Harrison, of the City of Chester, Engineer,
for an Invention of "IMPROVEMENTS IN VALVES OF PERCUSSIVE ROCK
DRILLS."
PROVISIONAL SPECIFICATION left by the said John Henry Harrison
at the Office of the Commissioners of Patents on the 21st January 1881.
JOHN HENRY HARRISON, of the City of Chester, Engineer. "IMPROVEMENTS
IN VALVES OF PERCUSSIVE ROCK DRILLS."
This Invention relates to the arrangement and construction of the valve gear
employed in controlling the admission and release of the working fluid to machinery
of this class. The cylinder and drill piston are constructed in the ordinary manner.
The valve is made like a hollow beam or lever of the first order, and the same
length as the drill cylinder, and whose longitudinal axis lies parallel with the
corresponding axis of the cylinder. The working fluid is admitted on its upper
side through a hollow fulcrum upon which it vibrates or makes a partial revolution.
This hollow fulcrum does not pass through but stops short of the metal forming the
bottom or opposite side to the inlet of the valve.
On the opposite surface are formed elongated ports corresponding with the ports
in the cylinder, and whose length is in the direction of the axis of the cylinder.
The ports are made extra long in order to reduce the partial rotation of the valve
necessary to place them in communication with the cylinder to the smallest possible
amount. This construction enables the full pressure admitted to the interior of the
valve to be conveyed to the drill cylinder by an extremely short port, and thus
causes it to operate with the greatest possible effect upon the drill piston without
loss from friction in passing through a long port, as in drills of ordinary con-
struction; by the same means the fluid is as suddenly released, thus avoiding back
pressure against the drill piston. A further advantage from the above described
valve arrangement arises from the small capacity of the ports leading into the
cylinder, thus greatly economising the fluid pressure employed in driving the drill.
The partial rotation of the valve which places the drill cylinder in communication
with its interior, or to the atmosphere, is effected by small pistons or rams placed at

page_text: opposite ends of the valve, but at the same side and at right angles to its longi-
tudinal axis. The admission and release of fluid pressure to these valve pistons is
controlled by the movement of the drill piston, which at suitable points in its
stroke uncovers small passages leading from the drill cylinder to the valve
cylinder.
Upon admitting the working fluid to one of these valve pistons it presses against
the extremity of the valve, causing it to move on its fulcrum, thus opening com-
munication between the pressure in the valve and the drill cylinder at one end,
and the exhaust at the other. At the same time the piston at the opposite end of
the valve is driven backwards preparatory to making its forward movement. By
properly proportioning the areas of the inlet, outlet, and cylinder ports, the valve
becomes nearly balanced, requiring much less pressure upon the pistons moving it
than if it were unbalanced, as an ordinary slide. The pressure against the valve
faces, due to the area of the inlet through the fulcrum, is opposed by the pressure
upwards against the area of the ports. In practice the area of the inlet is made
to exceed slightly the area of the ports in order to insure the valve being retained
against the port faces of the drill cylinder.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Henry Harrison in the Great Seal Patent Office on the
20th July 1881.
JOHN HENRY HARRISON, of the City of Chester, Engineer.
IN VALVES OF PERCUSSIVE ROCK DRILLS."
"IMPROVEMENTS
This Invention relates to the construction and arrangement of the valve and
gear employed in controlling the admission and release of the working fluid to
machinery of this class.
Figures 1, 2, 3, on the accompanying Sheet of Drawings illustrate the manner
in which I construct a percussive rock drill, and in which my improvements are
embodied. G is the drill cylinder; H is the drill piston and rod to which the
boring tool is attached by any suitable means.
The valve V, which constitutes the chief feature of the Invention, is made like
a hollow beam or lever of the first order, and is the same length or nearly so as
the drill cylinder. The working fluid is admitted on its upper side through a
hollow fulcrum T, upon which the valve V vibrates or makes a partial revolution.
This hollow fulcrum does not pass through the valve, but stops short of the metal
forming the bottom thereof. On the opposite side to the inlet are formed ports
P, P, and corresponding with ports in the drill cylinder, which are shewn in dotted
lines in Figure 1, and in section in Figure 3 at K. These ports in the valve and
cylinder are made extra long in proportion to their width in order to reduce the
movement in the valve necessary to place them in communication with the cylinder
to the least possible amount. This construction enables the full pressure admitted
to the interior of the valve V to be conveyed to the drill cylinder by an extremely
short port, and thus causes it to operate upon the drill piston without loss from
friction arising from its passage through a long port, as in drills of ordinary
construction. By this arrangement the fluid is as suddenly released (thus avoiding
back pressure against the drill piston) into the chamber J surrounding the valve
which is in communication with the atmosphere through the opening O. The
vibration or partial rotation of the valve which places the drill cylinder in com-
munication with its interior or the atmosphere is effected by small pistons or rams
R, R, placed on opposite ends of the valve V, but at the same side and at right
angles to its longitudinal axis, and moving freely in cylinders S, S. The admission
and release of working fluid to and from these valve pistons or rams is controlled
by the movement of the drill piston, which at suitable points Y, Y, in its stroke
uncovers small passages N, N, leading from the drill cylinder to the valve cylinders.
Upon admitting the working fluid to one of these valve cylinders, the piston or
ram in it presses against the extremity of the valve V causing it to move on its
fulcrum T, thus opening communication between the interior of the valve and the
drill cylinder at the opposite end and the atmosphere at its own end; by the same
movement the piston at the opposite end of the valve is driven backwards in its
cylinder preparatory to making its forward movement, which is performed in a
corresponding manner. The exhaust from the ram cylinders passes through the
port N, into the annular space between the double piston in the drill cylinder,
thence through the opening Q into the atmosphere. By properly proportioning the
areas of the inlet, outlet, and cylinder ports, the valve V becomes nearly balanced,
requiring much less power or pressure upon the valve pistons R, R, than if it were
unbalanced, as an ordinary slide. The pressure upon the valve faces L, L, due to
the area of the inlet T through the fulcrum, is opposed by the pressure upwards
against the area of the ports P, P. In practise the area of the inlet T is made to
exceed slightly the area of the ports in order to insure the valve being always

page_text: retained against the port faces of the drill cylinder. The advantages arising from
this arrangement of valve, and the means adopted for controlling its movement, are
as follows:-The valves being nearly balanced less fluid pressure is required than
if it were not so. The ports in the drill cylinder through which the fluid pressure
is admitted and released are reduced greatly in capacity, requiring a small quantity
of working fluid to fill them compared with other machines. The full live pressure
from the interior of the valve is admitted to the drill cylinder without any
appreciable loss from friction, while the exhaust is as suddenly and fully released
without causing back pressure against the drill piston. Lastly, the construction
of the valve reduces the movement necessary to admit and release the working
fluid to the drill cylinder to an extremely small amount, a point of the greatest
importance in machines of this class, in which the momentum of such parts as the
valve and gear should be reduced as much as possible in order to avoid the
excessive wear and cost of maintenance to which such machines are liable.
Having thus described and ascertained the nature of my said Invention, and
in what manner the same is to be performed, I wish it to be understood that I
claim as my Invention,―
The construction of a valve in the form of a hollow beam or lever, and capable
of partial rotation or vibration upon a hollow fulcrum, through which the working
fluid is admitted, for the purposes above set forth and operating substantially as
above described.
In witness whereof, I, the said John Henry Harrison, have hereto set my
hand and seal, this Eighteenth day of July, in the year of our Lord One
thousand eighteen hundred and eighty one.
JOHN HENRY HARRISON. (L.S.)