IMPROVEMENTS IN ENGINES FOR COMPRESSING AIR OR GAS
Year: 1878

page_text: LETTERS PATENT to John Alexander, of Gartsherrie Iron Works, in the
County of Lanark, North Britain, for the Invention of "IMPROVEMENTS IN
ENGINES FOR COMPRESSING AIR OR GAS."
Sealed the 29th March 1878, and dated the 14th January 1878
PROVISIONAL SPECIFICATION left by the said John Alexander at the Office
of the Commissioners of Patents on the 14th January 1878.
JOHN ALEXANDER, of Gartsherrie Iron Works, in the County of Lanark, North
Britain. " IMPROVEMENTS IN ENGINES FOR COMPRESSING AIR OR GAS."
This Invention has for its object to improve the construction and action of
engines for compressing air or gas, and to simplify and render more durable certain
parts thereof.
In engines of the kind to which the present improvements are applicable, one or
more steam cylinders and pistons or other suitable motive-power details are through
a rotating crank shaft made to work the piston or pistons of one or more compressing
cylinders, the valves of which are arranged to draw in air or the gas to be compressed
and to compress it and deliver it into a receiver.
The first part of the Invention relates to the valves of the compressing cylinder
or cylinders, and consists in employing a peculiar modification of slide valve worked
from an eccentric or crank on the rotating shaft. There may be a single
valve slide for the two ports of each cylinder, but it is preferred to have a separate
slide to each port, the two slides being worked by one rod. Each valve slide is
made with a cavity for putting the cylinder port in communication with an inlet
port when moved towards one end, but the slide does not uncover the cylinder port
when moved toward the other end. The valve slide is made with a port through it
for the passage of the compressed air, and this port in the slide is fitted with a lifting
or clack valve, which may be of leather or rubber, or other suitable material, by
preference strengthened with metal plates. The lift valve in the valve slide prevents
the compressed air or gas in the casing from expanding into the cylinder at the
beginning of each compressing stroke, and the air or gas is compressed in the

page_text: cylinder until its pressure equals that in the casing and it then lifts the valve
in the slide and passes into the casing, and thence into the receiver.
The second part of the Invention relates to certain self-acting apparatus for
preventing the expenditure of power when the air or gas in the receiver has at any
time reached what is considered a proper maximum pressure. This apparatus com-
prises a loaded piston arranged to be acted on by the pressure in the receiver, and
connected to equilibrium or other suitable valves in passages communicating with the
ends of the compressing cylinder or with the valve casing or casings and the inlet or
atmosphere. On the maximum pressure being attained in the receiver the loaded
piston opens the valves to which it is connected, and the compressing piston or
pistons can then merely make the air or gas circulate through the passages. As a
result of this the speed of the steam or other motive-power engine will tend to
increase; but a speed governor with which the engine is fitted, and which may be
of any suitable known kind will immediately act on the throttle or other regulating
valve, and check the speed. Or, instead of employing a separate speed governor, the
throttle or regulating valve of the motive-power engine may be connected to the
loaded piston herein-before referred to so as to be acted on by it.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Alexander in the Great Seal Patent Office on the 4th July
1878.
JOHN ALEXANDER, of Gartsherrie Iron Works, in the County of Lanark, North
Britain. "IMPROVEMENTS IN ENGINES FOR COMPRESSING AIR OR GAS."
My said Invention has for its object to improve the construction and action of
engines for compressing air or gas, and to simplify and render more durable certain
parts thereof.
In engines of the kind to which my present improvements are applicable, one or
more steam cylinders and pistons or other suitable motive-power details are, through
a rotating crank shaft, made to work the piston or pistons of one or more com-
pressing cylinders, the valves of which are arranged to draw in air or the gas to be
compressed, and to compress it and deliver it into a receiver.
The first part of my Invention relates to the valves of the compressing cylinder
or cylinders, and consists in employing a peculiar modification of slide valve worked
from an eccentric or crank on the rotating shaft. There may be a single valve slide
for the two ports of each cylinder; but I prefer to have a separate slide to each port,
the two slides being worked by one rod. The valve slide is arranged to put the
cylinder port in communication with the inlet port in the manner in which an
ordinary steam engine slide valve forms a communication between the cylinder
port and the exhaust port; but the compressed air passes out by a lift or clack
valve fitted to a part of the valve slide which is over the cylinder port during
the compressing stroke, and this lift valve is not opened until the air in tho

page_text: cylinder has become compressed to a pressure slightly greater than that in the
valve chest and passage leading to the reservoir.
The second part of my Invention relates to certain self-acting apparatus for
preventing the expenditure of power when the air or gas in the receiver has at
any time reached what is considered a proper maximum pressure. This apparatus
comprises a loaded piston arranged to be acted on by the pressure in the receiver,
and connected to equilibrium or other suitable valves in passages communicating
with the ends of the cylinder, or with the valve casing or casings and the inlet or
atmosphere.
And in order that my said Invention and the manner of performing the same may
be properly understood, I hereunto append a Sheet of explanatory Drawings, to be
herein-after referred to, and representing an air-compressing cylinder as fitted with
my improved valve apparatus. In these Drawings the same reference numerals aro
used to mark the same or like parts wherever they are repeated.
Figure 1 on the accompanying Sheet of Drawings is a longitudinal vertical section
of the compressing cylinder and its valve casings, and Figure 2 is a corresponding
transverse vertical section.
Figure 3 is a plan as with one of the valve casing covers removed, and Figures 4
and 5 are an enlarged plan and section of one of the valve slides; whilst Figure 6
is an enlarged vertical section of apparatus to be used in carrying out the second part
of my Invention.
The cylinder is provided with two valve casings 1, 2, in connection respectively
with the end passages 3, 4, for each of which there is a separate valve slide 5,
worked by a rod 6, passing through a stuffing box at the inner end of each valve
casing. The two valve rods 6 are attached to a single central block 7, which is
moved by a lever 8 on a rocking shaft 9, having on it another lever 10, which is
connected by a rod 11 to the eccentric on the crank shaft, not shown. Each valve
slide 5 is made with a cavity 12, and always covers the inlet port 13, which is in
each case formed with external openings on both sides of the valve casing. The
valve slide 5 also always covers the cylinder port 3, 4, but is formed with a grated
port 14, on the outer side of which there is applied a lift valve 15. This lift valve
15 consists of a sheet of vulcanised rubber or other suitable flexible material fixed
between two metal plates, and the valve is guided on pins 16, so that it can rise
parallel ways, and thus open on all the sides. The lift valves 15 in the valve slides
5 prevent the compressed air (or gas) in the valve casings 1, 2, from expanding into
the cylinder at the beginning of each compressing stroke, and the air (or gas) is
compressed in the cylinder until its pressure equals, or slightly exceeds that in the
valve casings 1, 2, and it then lifts the valve 15 in the slide 5, and passes into the
casing 1 or 2, and thence by pipes 17 into the receiver. The valve slides 5 are
connected by links 18 to pistons 19, which work in cylinders 20 formed on the
covers of the valve casings 1, 2. The pistons 19 are open to the atmosphere on their
outer sides, and the pressure on their inner side balances a considerable part of the
pressure on the valve slides 5, so that the latter require less power to work them, as
is well understood.
The apparatus provided according to the second part of my Invention for pre-
venting the expenditure of the driving power when the desired maximum pressure
of air or gas in the receiver is attained, is in the example delineated shown as
applied to the pipe piece 17, by which the valve casings 1, 2, communicate with tho
receiver. In this apparatus a cylinder 21, which communicates with the receiver
by a small pipe 22, has in it a piston 23, with a short slotted rod which is acted on
by a weighted lever 24, and which is attached to the spindle 25, of a pair of equili-
brium valves 26. These valves 26 are fitted to seats in a casing 27, which, by one
branch 28, communicates with the pipe piece 17, and by another 29 with the
atmosphere (or in the case of a gas-compressing engine with the inlet pipes). The
lever 24 is weighted to correspond with the maximum pressure which it is intended
to have in the receiver, and when that pressure is exceeded, the piston 23 overcoming
the action of the weight moves down and opens the valves 26, and allows any

page_text: air under pressure in the pipe piece 17 and valve casings 1, 2, to pass freely out.
In this modification a check valve must be fitted between the pipe piece 17
and the receiver to prevent the return of air from the receiver when the valves 26
are opened.
•
In another modification separate pairs of the valves 26 are applied in connection
with each end of the cylinder, and not in connection with the valve casings.
As a result of the action of the piston 23 and valves 26, the speed of the steam
or other motive-power engine will tend to increase, in consequence of the reduction
of resistance through the opening of the valves 26; but a speed governor with
which the engine is fitted, and which may be of any suitable known kind will imme-
diately act on the throttle or other regulating valve and check the speed. Or,
instead of employing a separate speed governor, the throttle or regulating valve of
the motive-power engine may be connected to the loaded lever 24 of the piston 23,
so as to be acted on by it in a manner to diminish the supply of steam to the engine
at the same that the valves 26 are opened.
Having thus particularly described my said Invention, and the manner of
performing the same, I have to state that I do not restrict myself to the
precise details herein described or delineated, but that what I believe to be
novel and original, and claim as the Invention secured to me by the herein-before
in part recited Letters Patent is,―
1. The fitting of the cylinders of engines for compressing air or gas with valve
slides having lift valves applied to them, substantially as and for the purposes-herein-
before described.
2. The fitting of engines for compressing air or gas with valves to be acted on
through a piston by the pressure in the receiver, so as to prevent the further com-
pression of air and expenditure of power after the desired maximum pressure is
attained, substantially in the manner herein-before described.
In witness whereof, I, the said John Alexander, have hereunto set my hand
and seal, this Twenty-sixth day of June, in the year of our Lord One
thousand eight hundred and seventy-eight.
JOHN ALEXANDER, (L.S.)