IMPROVEMENTS IN AIR COMPRESSING ENGINES
Year: 1881

page_text: LETTERS PATENT to Edward Holt, of Radcliffe, in the County of Lancaster,
Engineer, for an Invention of "IMPROVEMENTS IN AIR COMPRESSING
ENGINES"
PROVISIONAL SPECIFICATION left by the said Edward Holt at the Office of
the Commissioners of Patents on the 21st Juno 1881.
EDWARD HOLT, of Radcliffe, in the County of Lancaster, Engineer.
MENTS IN AIR COMPRESSING ENGINES,"
"IMPROVE-
These improvements have reference to that class of air compressor in which two
or moro single acting compressing cylinders are employed, and have for their object
a means of so connecting the air inlet valves of both cylinders together, that as one
opens the other closes, and vice-versa. These valves are mounted concentrically
with the air compressers pistons at the opposite ends of the cylinders, and aro
enclosed in casings which form the end covers of the air compressor cylinders, the
bottoms of the pistons being recessed to receive the air inlet valves. The air
outlet valves are mounted concentrically with the air inlet valves in the sanie
casings, and are provided with a suitable sleeve packed with rings to make a tight
joint, and which sleeves have on their outside spiral springs to assist the air outlet
valves to close.
In one arrangement the spindles of the air inlet valves are formed hollow so as
to constitute an additional inlet passage for air, and which passage is fitted with
an auxilary air valve and caused to have a tendency to keep closed by means of a
spiral spring surrounding its spindle, and which auxilary valve only opens when
the speed has sufficiently increased to overcome the power of the spring.
This Invention further relates to improved means of finally compressing the air
after it has passed out of the main cylinder and been cooled in the ordinary manner,
and consists in admitting the same through a back pressure valvo and air inlet
valve, which is connected as herein before described to the air inlet valve of tho
main cylinder, into a cylinder by preference of smaller diameter fitted with an
internal cylinder or ram which itself slides to and fro upon a hollow stationary
ram, this ram communicating with a valve box fitted with a suction and. delivery
valve and connected with a water supply, so that as the ram moves to and fro it
serves not only to compress the air, but also at the same time pumps the water
through the easing surrounding itself, and also through the casing surrounding the
main compressing cylinder, and so keeps all parts of the engine properly cooled.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Edward Holt in the Great Scal Patent Office on the 21st
December 1881.
EDWARD HOLT, of Radcliffe, in the County of Lancaster, Engineer. " IMPROVE-
MENTS IN AIR COMPRESSING ENGINES."
These improvements have reference to that class of air compressor in which two
or more single acting compressing cylinders are employed, and have for their object
a means of so connecting the air inlet valves of both cylinders together, that as one
opens the other closes, and vice-versa. These valves are mounted concentrically
with the air compresser pistons at the opposite ends of the cylinders, and their
bottoms are enclosed in casings which form the ond covers of the air compressor
cylinders, the pistons being recessed to receive the air inlet valves. The air outlet
valves are mounted concentrically with the air inlet valves in the same casings, which
are provided with a suitable sleeve packed with rings to make a tight joint, and
which sleeves havo on their outside spiral springs to assist the air outlet valves to
close. In one arrangement the spindles of the air inlet valves are formed hollow
so as to constitute an additional inlet passage for air, and which passage is fitted
with an auxiliary air valve and caused to have a tendency to keep closed by means
of a spiral spring surrounding its spindle, and which auxilary valve only opens
when the speed has sufficiently increased to overcome the power of the spring.
This Invention further relates to improved means of finally compressing the air
after it has passed out of the main cylinder and been cooled in the ordinary
manner, and consists in admitting the same through a back pressure valve and air
inlet valve which is connected, as herein before described, to the air inlet valve of
the main cylinder into a cylinder by preference of smaller diameter, fitted with an
internal cylinder or ram which itself slides to and fro upon a hollow stationary
ram, this ram communicating with a valve box fitted with a suction and delivery
valve and connected with a water supply, so that as the ram moves to and fro it
serves not only to compress the air but also at the same time pumps the water
through the casing surrounding itself, and also through the casing surrounding the
main compressing cylinder, and so keeps all parts of the engine properly cooled.
And in order that this my said Invention may be the more readily seen and
understood, I have hereunto annexed three Sheets of Drawings illustrative of my
improvements in air compressing engines, and will now proceed to describe the
same with the assistance of the various figures and letters of reference marked
thereon.
Fig. 1 is a side view, and Fig. 2 a plan of so much of an air compressing engine
as is necessary to illustrate my Invention, both drawn to a scale of about 14.inches
to the foot; Fig. 3 is a side view half in section of the air compressing cylinders
of the engine, illustrated in Figs. 1 and 2, and drawn upon an enlarged scale.
In all the views A and A are two single acting air compressing cylinders
surrounded with water casings A³, through which water is caused to circulate in
the ordinary manner; these cylinders are fixed concentrically with one another
as illustrated on the same bod plate B, and are each fitted with deep pistons C
(see Fig. 3), the respective rods C and C of which pass out at the opposite open
ends of the cylinders and are there coupled respectively to crossheads CS and C',
these crossheads being again connected together by the side rods C5 passing
through guide brackets C. These brackets C not only act as bearings to take
the weight of the pistons off the bottom of the cylinders, but also prevent the
side rods from buckling. D is the steam engine cylinder, and D' its piston rod,
which is connected to the cross head C by means of an adjustable coupling

page_text: consisting of two flanges D³ bolted together, as illustrated by the bolts D', one
Hango being formed upon the crosshead C and the other being screwed upon the
piston rod D', so that by loosening the lock nut D³ the pistons in the air cylinders
can be adjusted to the greatest nicety instead of lining up the connecting rod
brasses, which would often be the case, seeing that the clearance of the pistons is
very little. The mode of adjustment may be here explained, and is as follows:-
When the piston in the cylinder A¹ slightly comes in contact with its cover from
the shortening of the connecting rod it will be heard but can do no damage. In
this case the bolt D in the flanges of the coupling must be taken out and the
lock nut D loosened; the loose flange should then be turned in the direction of
unscrewing it off the piston rod D' until the bolt holes come opposite to the noxt
corresponding set of holes in the stationary flange upon the crosshead, the bolts
should then be passed through the flanges and screwed up tight, thus putting te
air pistons in their original position.
From the foregoing it will be apparent that the front ends of the air cylinders A
and A¹ are open to the atmosphere, and it now remains to explain the construction
of the rear end covers of the cylinders, which are immediately opposite to and
concentric with each other. These covers marked E are formed of cast iron and
are secured to the cylinders by the flanges E'; they form boxes or casings for both
the air inlet valves F and for the air outlet valves G, whilst openings or passages Fl
are also formed in these covers for the passage of the air entering the cylinders,
and branch pipes G¹ are provided for carrying off the compressed air. The inlet
valves F of both cylinders are coupled together by the adjustible connecting
piece F2, so that as one valve opens the other closes, and vice-versa, so trapping the
air which has entered the one cylinder and opening a passage for the admission of
air into the other cylinder. The outlet or delivery valves G, aro mounted and
capable of sliding to and fro upon a sleeve piece Fs forming part of the cover E,
and are of such a diameter as to close the whole end of the cylinder, a tight joint
being secured by the insertion of packing rings F in the sleeve picce, whilst spiral
springs F are mounted on the outside of these valves to ensure their coming
sharply to their seats the instant that the piston comes to a stand still. G is an
auxilary valve working inside the main inlet valve F, and loaded with a spiral
spring to keep it from opening until the piston has attained such a speed that the
flow of air through the main valve will not keep up the atmospheric pressure when
it opens, according to the speed of the piston, and which auxiliary valve when the
speed of the piston diminishes as it nears the end of its stroke and the slight
vacuim which has been formed in the cylinder decreases, will close by the medium
of the spiral spring, the main valve meanwhile keeping open to the end of the
stroke, and so keeping up the atmospheric pressure. In this manner the inlet
valves regulate themselves according to the speed of the pistons, and allow the
cylinders to receive a full charge of air at atmospheric pressure, no matter what
speed the air compressor may be running at. It will also be seen by refering to
the Drawings that the pistons are recessed to receive the inlet valves, so that the
dead space is reduced to a minumin, one sixteenth of an inch being sufficient; it
is calculated that taking a pressure of 60lbs. per square inch above the atmosphere,
and an average stroke of 30 inches, that the loss from dead space will only be one
per cent. It will also be observed that in this construction of air compressor the
inajor portion of the covers form passages for the cold air to pass through into tho
cylinders, and that there being no passage formed in the outer sides or walls of
the cylinders, and their front ends being open to the atmosphere, that any over-
heating is obviated, and the efficiency of the air compressor is improved
accordingly.
In Fig. 4 I illustrate a side view, and in Fig. 5 a plan of my improved air
compressing engine for compressing air in two or more stages. Fig. 6 represents
a plan of the cooling tank employed in this form of engine (but any other suitable
cooling arrangement might be substituted), all drawn to a scale of about 1 inches
to the foot; Fig. 7 is an enlarged sectional view of the final compression cylinder

page_text: illustrated in Figs. 4 and 5; Fig. 8 is a cross section of Fig. 7 upon the line a-b,
and Fig 9 is a cross section of Fig. 7 upon the line c-d.
In Figs. 4-9 H is the low pressure compressing cylinder which is of similar
construction and fitted with similar air inlet and outlet valves to and upon which
the same letters of reference are used as in Figs. 1 and 2. I is the high pressure
compressing cylinder fitted with a ram J which also acts as a cylinder and slides
to and fro upon a hollow stationary ram K fixed on the clack or valvo box K¹,
which is firmly secured to the bed plate M. This ram serves also as a pump for
causing water to flow round the cylinders H and I through their respective con-
necting pipes I and H', and then to fall through the pipe 12 into the cooling
tank L, Fig. 6, from whence it overflows through the pipe L', this water entering
the ram J through the branch pipe J¹ and inlet valve J, and escaping through tho
delivery valve Js into the pipe H'.
The inlet valve N of this arrangement is coupled to the inlet valvo F of the
low pressure cylinder H by lock nuts for adjusting the lift or opening, and is
kept air tight by passing through the stuffing box and gland O. Instead, however,
of having the larger outlet valve, as in Fig. 1 and 2, this high pressure cylinder
is provided with delivery valves P of the poppet type which are held to their
seats by spiral springs as illustrated. Qis a back pressure valve to provent the
return of the compressed air in case the inlet valve N should not close instantly;
R is a stuffing box joint to prevent any escape of air past the ram J, and S is a
similar stuffing box to prevent the escape of water; T is a cross head shrunk on
to the head of the ram J, and U is another cross head cottered on to the piston
rod V, these two cross-heads being coupled together by the side rods W, as in
Figs. 1 and 2.
The action of this engine is as follows:-The air first enters the cylinder H
through the inlot valve F, and is therein compressed to the desired pressure and
delivered through the delivery valve G into the pipe a', whence it passes through
the pipes M' immersed in the cooling tank L, and then enters the high pressure
cylinder I first through the pipe M and back pressure valve Q, and then through
the inlet valve N. In this cylinder I the compressed air becomes finally compressed
and passes out through the poppet valves P and pipo P¹ to the receiver or other
receptacle.
In Figs. 10 and 11 I represent a side sectional and end view respectively of a
modification of my Invention, in which the covers of two air compressing cylinders
fitted in accordance with my Invention are connected together and form ono
casing X with suitable inlet and outlet branch pipes marked a and b respectively
for the purpose of either exhausting the air or other gas from any desired vessel,
and so forming a vacuim therein, or for compressing air or gases into any confined
vessel. In this case the auxiliary valve is not shewn, but may be applied if it is
required. The action of this modification is sufficiently obvious from the description
hereinbefore given of the other arrangements.
Having thus particularly described and ascertained the nature of this my said
Invention, together with the best methods with which I am acquainted for carrying
the same into practical effect, I wish it to be distinctly understood that I do not
confine myself to the precise details, relative proportions, or dimensions of the
various parts of my improved air compressors, as the same may be considerably
varied without departing from the Invention, but what I claim is,-
1st. Connecting the air inlet valves of air compressing cylinders together, as
and for the purposes herein before described and illustrated on tho accompanying
Drawings.
2nd. The improved construction of end cover for air compressing cylinders fitted
with inlet and outlet valves, substantially as herein before described and illustrated
on the accompanying Drawings.
3rd. The employment of an auxiliary air inlet valve, substantially as and
for the purposo hereinbefore described and illustrated on the accompanying
Drawing

page_text: 4th. In an arrangement for finally compressing air or other gases, the employment
of a cylinder or ram sliding upon a stationary bollow ram fitted with valves, and
acting simultaneously as a pump for water and as a high pressure compressor,
substantially as and for the purposes herein before described and illustrated on the
accompanying Drawings.
5th. Connecting the air inlet valve of the final compression cylinder with the
air inlet valve of the main or low pressure cylinder, substantially as hereinbefore
described and illustrated on the accompanying Drawing.
In witness whereof, I, the said Edward Holt, havo hereunto set my hand
and seal, this 19th day of December, in the year of our Lord 1881.
EDWARD HOLT
(LS)