IMPROVEMENTS IN AIR-COMPRESSING ENGINES
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by John Alexander at the Office of the
Commissioners of Patents on the 23rd December 1876.
JOHN ALEXANDER, of Gartsherrie Iron Works, in the County of Lanark, North
Britain. "IMPROVEMENTS IN AIR-COMPRESSING ENGINES."
•
This Invention has for its object to make air-compressing engines more effective
and satisfactory than as hitherto made by arrangements rendering the action of the
valves in connection with the compressing cylinder rapid and certain.
The valves may be of the kind and to a certain extent of the arrangement
described in the Specification of Letters Patent granted to the present applicant,
and dated 24 February 1875 (No. 674), but the present improvements are also
applicable to valves sliding on flat port faces or on port faces which are more or less
curved.
In one modification either a single valve is used for both ends of the cylinder, or
there are separate valves for each end but attached to one rod; and the rod which
passes out through a stuffing box in the usual way is acted on by a projection or lug
on the slide block of the piston rod or in any equivalent manner.
The slide block
does not act directly on the valve rod, but on approaching each end of its stroke it
compresses a spring which bears on a collar on the valve rod; the valve rod is held
by a catch whilst the spring is being compressed and until the slide block almost
reaches the end of its stroke, but then the slide block acts on a trigger which
releases the catch, and the spring acts on the rod and effects the complete shift of .
the valve or valves in a sudden manner. The parts are repeated so that similar
actions take place at both ends of the stroke. In this modification self-acting or
clack valves are required in the passages by which the compressed air is led away
from the cylinder.
In a second modification the valves for the two ends of the cylinder are separate.
A spring and trigger arrangement like that of the first modification is used for
shifting the valves at the end of the stroke, but an additional spring is applied
between collars or discs on the rods of the separate valves, together with an
additional catch and trigger, which prevents one of the valves from making its
complete shift at once. On the compressing piston reaching one end of the cylinder

page_text: the valve at that end which has been open for the discharge is suddenly moved
through its entire traverse, so as to put that end of the cylinder in communication
with the inlet, but the valve at the other end is moved only so far as to close that
end from the inlet without opening it to the discharge. In consequence of this the
compressed air in the discharge passage cannot re-expand into the cylinder and 5
thereby occasion loss of power. Then, when the piston has moved so far as to have
compressed the air in the cylinder to about the pressure of the air in the discharge
passage, a projection suitably adjusted on the slide block acts on the additional
trigger and causes the additional spring to complete the traverse of the valve and
open the port to the discharge. In this modification a self-acting or clack valve 1
may not be required in the discharge passage.