Improvements in and relating to Valves and Pistons for Compressed Air and the like Engines.
Year: 1893

page_text: Date of Application, 8th Dec., 1893
Complete Specification Left, 21st July, 1894-Accepted, 15th Sept., 1894
PROVISIONAL SPECIFICATION.
[Communicated from abroad by EDWARD PRINCE and WILLIAM DUNCAN,
Charters Towers, Queensland, Australia, Engineer.]
Improvements in and relating to Valves and Pistons for Compressed
Air and the like Engines.
I, JOHN MCDONALD, 43 Threadneedle Street London E.C., Australian Agent,
do hereby declare the nature of this invention to be as follows:-
This invention relates to pistons & valves for use with compressed air and the
like engines and is carried out as follows. I provide a piston rod upon which are
two piston heads said piston rod & heads working in a cylinder.
Between the
piston heads & sliding upon the piston rods is a circular valve, channelled or
grooves so as to convey the compressed air or the like to the piston heads. The
action is as follows, when the piston rod has moved the desired distance in one
direction the compression of the air between the piston head & the valve when it
approaches same causes the valve to move a distance sufficient to close one port
& open another so that the compressed air now acts upon the other piston head &
so on.
The piston rod has a groove cut in same for conveying off the air from the space
between the piston head & valve until the desired distance between same is reached
when this outlet is closed by the movement of the piston rod through the valve
aforesaid. Suitable outlet ports are provided.
The compressed air or the like acts upon the outer surfaces of the piston heads
alternately, being conveyed to the ends of the cylinder through suitable ports in
same, through the medium of the valve aforesaid.
This form of piston is most convenient for operating what are known as rock
drills for boring purposes.
Dated this 8th day of December 1893
Improvements in and relating to Valves and Pistons for Compressed
Air and the like Engines.
I, JOHN MCDONALD 43 Threadneedle Street London E.C. Australian Agent,
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:—
This invention relates to pistons & valves for use with compressed air and the
like engines and is carried out as follows, reference being made to the annexed
drawing in which ;
Figure 1. is a sectional side elevation of my invention.
Figure 2. longitudinal section through cylinder.
I prefer a piston rod a upon which are two piston heads b & b said piston rod a
and heads band 'working in a cylinder c. Between the piston heads b and b
& sliding upon the piston rod a is a circular valve d, channelled or grooved at e so
as to convey the compressed air or the like from the inlet port to the ends of the

page_text: piston heads b and b₁ through the channels g and g¹. h and h¹ are the outlet ports.
The action is as follows. When the piston rod a has moved the required
distance in one direction, the compression of the air between the piston head b¹ and
the valve d causes the valve to move a distance sufficient to close one port or
channel and open the other channel or port g so that the compressed air now
acts upon the piston head & so on. i is a groove cut in the piston rod a, so that
as the heads and approach the valve d the air between, as it is compressed
escapes to the other side of the valve g & so the valve g does not move until the
end of the groove is covered by the valve d & compression takes place & the valve
.is moved, a certain amount of pressure being required to move valve d. The
compressed air or the like acts upon the outer surfaces of the piston heads
alternately, being conveyed through the channels or ports and g through the
medium of the valve aforesaid, This forn of piston is very convenient for
operating what are known as rock drills for boring purposes.
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 :-
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1. The combined construction and arrangement of the various parts substantially
as described and illustrated herein.
2. In valves and pistons for compressed air and the like engines, a sliding valve
having a groove or channel opening and closing the ports, a piston rod upon which
said valve slides, having a relief escape groove or slot in same and carrying the
piston heads, the whole working in a cylinder; the movement of said piston rod &
heads operating the valve aforesaid when the escape of air between the valve and
piston head is prevented or cut off, owing to the passage of the relief or escape
groove aforesaid through the sliding valve, substantially as described and
illustrated herein.
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