IMPROVEMENTS IN APPARATUS FOR COMPRESSING AIR.
Year: 1880

page_text: LETTERS PATENT to David Greig and Max Eyth, both of the Steam Plough
Works, Leeds, in the County of York, Engineers, for an Invention of
LETTERS PATENT to David Greig and Max Eyth, both of the Steam Plough
Works, Leeds, in the County of York, Engineers, for an Invention of
"IMPROVEMENTS IN APPARATUS FOR COMPRESSING AIR.
PROVISIONAL SPECIFICATION left by the said David Greig and Max Eyth
at the Office of the Commissioners of Patents on the 14th October 1880.
DAVID GREIG and MAX EYTH, both of the Steam Plough Works, Leeds, in the
County of York, Engineers. "IMPROVEMENTS IN APPARATUS FOR COMPRESSING
AIR."
The object of this Invention, which refers to air compressors for mining,
tunnelling, and similar purposes, is to reduce or entirely avoid the loss of power
caused by the generation of heat in the air whilst compressing is going on.
The compressing cylinder is at one end provided with the usual set of air
admission valves. The piston carries another set of valves which open towards
the other end (which we will call the right hand end) of the cylinder. This end
is perfectly open towards a receiver of considerable size, containing by means of
At the outlet of this receiver is a
pipes a sufficient amount of cooling surface.
third valve through which the compressed air passes into the working pipes.
The piston has the ordinary alternate motion communicated to it by a steam
engine.
The size of the cooling surface, being practically unlimited, is such that it
maintains the air within the receiver at or near the ordinary temperature of the
outer air.
The different processes going on during compression are now as follows:-
At the end of the backward stroke from left to right the cylinder is completely
filled with fresh air, and the receiver contains air of the working pressure and of a
temperature slightly, if at all, higher than the cooling water.
At the forward stroke all the valves close and the pressure in the receiver pushes
the piston forward, the air expanding adiabatically, whilst the atmospheric air in
the left hand side of the cylinder is being compressed adiabatically also till the
pressures on both sides of the piston are equal

page_text: Up to this time no power of the steam engine has been required to move the
piston. On the contrary, there being all along a considerable, though diminishing,
excess of pressure on the side of the receiver the piston will actually give out
power, which may be stored up in a fly wheel.
The air on the left side of the piston has been heated during compression, that
on the right side (in the receiver) has been cooled by expansion. But as the work
of expansion was much greater than the work of compression the sum of heat thus
gained and lost is necessarily negative, the amount of heat lost by the whole mass
being, in fact, equivalent to the power transmitted to the fly wheel.
The valves in the piston now open and the newly compressed air and the air in
the receiver mix whilst the piston travels to the end of its course.
The average
temperature of the mixture becomes then somewhat less than the original tempera-
ture of the receiver owing to the reason above stated.
Now the backward stroke of the engine begins, the valves in the piston close,
and the air of the receiver is being compressed. But in as much as the air is now
within the actual cooling apparatus the process of compression is going on more or
less isothermally, and no more power is required than that necessary for isothermal
compression.
As soon as the final working pressure is reached the valve on the top of the
receiver opens and a certain amount of perfectly cold compressed air will be
delivered into the working pipes. The power required to move the piston during
its backstroke is obtained partly by the power accumulated in the fly wheel during
the forward stroke of the piston, partly by the actual work of the steam engines,
which drives the compressor. This latter power will be equal to the power necessary
for isothermal compression if the compressed air is delivered at the ordinary
temperature of the outside air, and this will solely depend from the amount of
cooling surface in the receiver, which will be regulated accordingly.
As this arrangement is "single acting," we generally place two cylinders, side by
side or back to back, or connected in any other convenient way, so that one is
taking in air whilst the other is compressing, and vice versa.
It also is evident that the valves in the piston might be placed into the casing
of the cylinder itself, or into the cover, if otherwise properly connected with the
receiver.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said David Greig and Max Eyth in the Great Seal Patent Office on the 13th
April 1881.
DAVID GREIG and MAX EYTH, both of the Steam Plough Works, Leeds, in the
County of York, Engineers. "IMPROVEMENTS IN APPARATUS FOR COMPRESSING
AIR."
The object of this Invention, which refers to air-compressors for mining,
tunnelling, and similar purposes, is to reduce or entirely avoid the loss of power
caused by the generation of heat in the air whilst compressing is going on.
The compressing cylinder is at one end provided with the usual set of air
admission valves. The piston carries another set of valves which open towards
the other end (which we will call the right hand end) of the cylinder. This end
is perfectly open towards a receiver of considerable size, containing by means of
pipes a sufficient amount of cooling surface. At the outlet of this receiver is a
third valve, through which the compressed air passes into the working pipes.
The piston has the ordinary alternate motion communicated to it by a steam
engine.
The size of the cooling surface, being practically unlimited, is such that it
maintains the air within the receiver at or near the ordinary temperature of the
outer air.
The different processes going on during compression are now as follows:-
At the end of the backward stroke from left to right the cylinder is completely
filled with fresh air, and the receiver contains air of the working pressure and of a
temperature slightly, if at all, higher than the cooling water.
At the forward stroke all the valves close, and the pressure in the receiver
pushes the piston forward, the air expanding more or less isothermally owing to
the large surface of the receiver which is in contact with water of a constant
temperature, whilst the atmospheric air in the left hand side of the cylinder is
being compressed adiabatically till the pressures on both sides of the piston are
equal.
Up to this time no power of the steam engine has been required to move the
piston. On the contrary, there being all along a considerable, though diminishing,
excess of pressure on the side of the receiver the piston will actually give out power,
which may be stored up in a fly wheel.
The air on the left side of the piston has been heated during compression, that
on the right side (in the receiver) would have been cooled by expansion if it was
not kept at a constant temperature by the influence of the surrounding water.
The valves in the piston now open, and the newly compressed air and the air in
the receiver mix whilst the piston travels to the end of its course.
The average
temperature of the mixture becomes then somewhat higher than the original
temperature of the receiver owing to the reason above stated. But this increase of
temperature will at once be removed again by the influence of the cooling surface
of the receiver with which the whole amount of air is now in direct contact.
Now the backward stroke of the engine begins, the valves in the piston close,
and the air in the receiver is being compressed. But in as much as the air is now
within the actual cooling apparatus the process of compression is going on more or
less isothermally, and no more power is required than that necessary for isothermal
compression.
As soon as the final working pressure is reached the valve on the top of the
receiver opens, and a certain amount of perfectly cold compressed air will be
delivered into the working pipes. The power required to move the piston during
its back stroke is obtained partly by the power accumulated in the fly wheel
during the forward stroke of the piston, partly by the actual work of the steam

page_text: .
engines, which drives the compressor. This latter power will be equal, or nearly so,
to the power necessary for isothermal compression if the compressed air is delivered
at the ordinary temperature of the outside air, and this will solely depend from the
amount of cooling surface in the receiver, which will be regulated accordingly.
The accompanying Drawings are intended still further to illustrate our Invention.
In Figure 1, A is a steam cylinder working the compressing piston C in cylinder B.
The latter is provided on the left hand side with a cover containing inlet
valves D, D, another set of valves E, E, opening towards the right hand side of the
cylinder; F is the receiver, consisting of a series of pipes surrounded by water, or
of a boss traversed by water tubes, or any other combination giving a great cooling
surface in a comparatively small space; G is the outlet valve through which the air
passes into the working pipes.
Figures 2 to 8 represent the action of the compressor in its different stages during
one up and down stroke of the piston.
Figure 2 is the position at the end of the back stroke. The receiver is filled
with air of the full pressure and cooled to the outside temperature, or nearly so.
The cylinder is full with fresh air, the valves are closed.
In Figure 3 the air in the receiver expands, retaining its temperature by doing
so, whilst the air in the cylinder is being compressed, getting consequently hot.
In Figure 4 the equilibrium between the pressure in the receiver and that in the
cylinder is obtained.
In Figure 5 the valves e in the piston open and the air in the cylinder and that
in the receiver mix freely till the piston has reached the end of its stroke.
In Figure 6 the piston has begun its return journey. The valves e have closed;
valve does not yet open because the pressure in the receiver, although gradually
rising, has not yet reached the working pressure in the pipes.
The valves d open,
admitting fresh air into the cylinder.
In Figure 7 the pressure in the receiver has reached the working pressure, and
from now to the end of the stroke the cooled and compressed air is discharged into
the working pipes, as shown in Figure 8.
As this arrangement is single acting we generally place two cylinders side by side
or back to back, or connected in any other convenient way, so that one is taking in
air whilst the other is compressing, and vice versa.
It also is evident that the valves in the piston might be placed into the casing
of the cylinder itself, or into the cover, if otherwise properly connected with the
receiver.
We do not confine ourselves to the details of the arrangement represented by the
Drawings, but what we claim is, the construction of machinery for compressing air
with a receiver presenting a large area of cooling surface, and in which receiver
the work of compression goes on alternately with temporarily expansion, each
expansion aiding in the compression of the quantity of air next to enter the
receiver.
We also claim our improved apparatus for compressing air, substantially as
described.
In witness whereof, we, the said David Greig and Max Eyth, have hereunto
set our hands and scals, this Eleventh day of April, in the year of our Lord
und and nichte ann
DAVID GREIG. (L.S.)
MAX EYTH.
(L.S.)