Improvements in Air Compressors.
Year: 1892

page_text: Date of Application, 1st Jan., 1892
Complete Specification Left, 1st Sept., 1892-Accepted, 22nd Oct., 1892
PROVISIONAL SPECIFICATION.
Improvements in Air Compressors.
We SAMUEL HENRY JOHNSON and CHRISTOPHER CLARKE HUTCHINSON of
the Engineering Works Stratford in the County of Essex Mechanical Engineers
do hereby declare the nature of this invention to be as follows:-
This invention has for its object improvements in the construction of air com-
pressors so as to increase their efficiency and enable them to be worked at high
speed. It is well known that the efficiency of an air compressor, as ordinarily
constructed, is reduced by the amount of clearance necessarily left between the
piston and the cylinder cover, and various devices have from time to time been
employed with the view of minimising this clearance space.
One for instance is to make the outlet valve large enough to cover the whole area
of the cylinder, and thus act the double part of an outlet valve and cylinder cover.
The piston in this case is permitted actually to touch the outlet valve without
danger; but in ordinary cases the piston of an air compressor cannot be constructed
to come so near the cylinder cover, without running grave risk of breaking the
machine through slackness of connecting rods, or other causes.
It is found however that this arrangement cannot be conveniently applied except
in single acting compressors and consequently as the whole power of the engine, or
other source of power driving the air compressing cylinder, is transmitted thereto
during that part of the working cycle of the machine in which the compression is
effected; the whole machine is thereby subject to more excessive shocks and strains
than would be the case if the compression were evenly divided as in a double acting
compressor. Hence in the latter case as the moving parts have to bear much less
stress or strain they can be made lighter and so rendered more suitable for.running
at a higher rate of speed.
This more even distribution of power in an air compressing engine is of great
importance where the air compressing cylinder is driven by means of a strap or belt
which in single acting compressors is liable to slip, and so render the working
uneven and ineffective, besides putting too high and sudden a strain upon
the belt.
Now by this invention we eliminate the clearance space in double acting com-
pressing cylinders by forming the piston in two parts, each free to move on the
piston rod up to a stop at each end which retains the two parts in a normal position;
when working, these parts are by means of a spring or springs separated from each
other and held against stops with a force exceeding the maximum working pressure
for which the machine is intended to he employed. It is obvious that with a piston
so constructed it is practicable to eliminate the clearance space in the bore of the
cylinder altogether, and permit the piston to come almost into contact with the
cylinder covers at each end of the stroke, for in the event of the piston coming into
contact with the cylinder cover, owing to the construction above described, it will
act as if it were a buffer and so eliminate the violence of the shock. By such a
mode of construction a high rate of speed may be employed with a minimum
of risk.
lift.
Our further improvements consist in constructing the inlet and outlet valves of
such a form that they shall afford the largest possible passage for the air passing
through them with the least weight practicable and also with the smallest height of
Under these conditions we secure a valve which works upon its seat with the
least possible amount of knocking and hammering, because by obtaining a valve of
a small weight with a low lift the valve will return more quickly on to its seat, and
having less momentum in falling unnecessary abrasion and wear and tear of parts

page_text: will be avoided and a rapid opening and closing will be effected; hence the loss of
air through the valves, or "slip" as it is sometimes called, is reduced and a higher
efficiency and delivery of a greater volume of air is secured.
To fulfil the foregoing conditions we make the valves of annular gridiron type,
taking care that there is the least possible space between the suction and delivery
valves that will admit of the air passing through with freedom under high speed.
Both inlet and outlet valves we place on the cylinder covers, and external thereto,
in such a way that both valves and seats are immediately accessible for examination
and replaceable with the greatest facility. Further to increase the efficiency. of
the inlet valves we sometimes make them of an alloy of aluminium with silver
containing from 5 to 8 per cent. or thereabout of the latter metal; we do not bind
ourselves to these exact proportions, but we find that such proportions give a very
hard tough alloy combined with lightness, a very important matter when it is
considered that such valves have to be opened and closed two or three hundred
times per minute.
Dated this 31st day of December 1891.
SAML. H. JOHNSON.
C. C. HUTCHINSON.
COMPLETE SPECIFICATION.
Improvements in Air Compressors.
We SAMUEL HENRY JOHNSON and CHRISTOPHER CLARKE HUTCHINSON of
the Engineering Works Stratford in the County of Essex Mechanical Engineers
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 has for its object improvements in the construction of air com-
pressors so as to increase their efficiency and enable them to be worked at high
speed. It is well known that the efficiency of an air compressor, as ordinarily
constructed, is reduced by the amount of clearance necessarily left between the
piston and the cylinder cover, and various devices have from time to time been
employed with the view of minimising this clearance space.
One for instance is to make the outlet valve large enough to cover the whole
area of the cylinder, and thus act the double part of an outlet valve and cylinder
cover. The piston in this case is permitted actually to touch the outlet valve
without danger; but in ordinary cases the piston of an air compressor cannot be
constructed to come so near the cylinder cover, without running grave risk of
breaking the machine through slackness of connecting rods, or other causes.
It is found however that this arrangement cannot be conveniently applied except
in single acting compressors and consequently as the whole power of the engine, or
other source of power driving the air compressing cylinder, is transinitted thereto
during that part of the working cycle of the machine in which the compression is
effected; the whole machine is thereby subject to more excessive shocks and strains
than would be the case if the compression were evenly divided as in a double acting
compressor. Hence in the latter case as the moving parts have to bear much less
stress or strain they can be made lighter and so rendered more suitable for running
at a higher rate of speed.
This more even distribution of power in an air compressing engine is of great
importance where the air compressing cylinder is driven by means of a strap or belt
which in single acting compressors is liable to slip, and so render the working
uneven and ineffective, besides putting too high and sudden a strain upon
the belt.
Now by this invention we eliminate the clearance space in double acting com-
pressing cylinders by forming the piston in two parts, each free to move on the
piston rod up to a stop at each end which retains the two parts in a normal position ;
8.
19

page_text: other and held against stops with a force exceeding the maximum working pressure
g, these parts are by means of a spring or springs separated from each
for which the machine is intended to be employed. It is obvious that with a piston
so constructed it is practicable to eliminate the clearance space in the bore of the
5 cylinder altogether, and permit the piston to come almost into contact with the
cylinder covers at each end of the stroke, for in the event of the piston coming into
contact with the cylinder cover, owing to the construction above described, it will
act as if it were a buffer and so eliminate the violence of the shock. By such a
mode of construction a high rate of speed may be employed with a minimum
0 of risk.
Our further improvements consist in constructing the inlet and outlet valves of
such a form that they shall afford the largest possible passage for the air passing
through them with the least weight practicable and also with the smallest height of
lift.
Under these conditions we secure a valve which works upon its seat with the
least possible amount of knocking and hammering, because by obtaining
a small weight with a low lift the valve will return more quickly on to its seat, and
a valve of
having less momentum in falling unnecessary abrasion and wear and tear of parts
will be avoided and a rapid opening and closing will be effected; hence the loss of
air through the valves or "slip" as it is sometimes called, is reduced, and a higher
efficiency and delivery of a greater volume of air is secured.
To fulfil the foregoing conditions we make the valves of annular gridiron type,
taking care that there is the least possible space between the suction and delivery
valves that will admit of the air passing through with freedom under high speed.
Both inlet and outlet valves we place on the cylinder covers, and external thereto,
in such a way that both valves and seats are immediately accessible for examination
and replaceable with the greatest facility. Further to increase the efficiency of the
inlet valves we sometimes make them of an alloy of aluminium with silver containing
from 5 to 8 per cent. or thereabout of the latter metal; we do not bind ourselves to
these exact proportions, but we find that such proportions give a very hard tough
alloy combined with lightness, a very important matter when it is considered
that such valves have to be opened and closed two or three hundred times per
minute.
In order however that the nature of this our said invention may be more fully
ascertained and the means whereby we carry the same into effect may be more
clearly shown we shall now proceed to describe same, due reference being made to
he drawings hereto annexed :-
DESCRIPTION OF DRAWINGS
Figure 1 is a sectional elevation of a double acting air compressor, constructed in
ccordance with this invention.
Figure 2 is a sectional elevation of a pair of outlet and inlet valves and
eats.
Ficure alt.
igure is a sectional elevation of a double acting air compressor, constructed in
accordance with this invention.
Figure 2 is a sectional elevation of a pair of outlet and inlet valves and
seats.
Figure
pian view of same.
P & P show two piston blocks held apart by the spiral springs s and s¹, which
are compressed between the piston blocks with a force sufficient to prevent them
from being further compressed when the piston is working at the maximum air
pressure for which the machine is intended. A is a sleeve with flange screwed on
to the piston rod secured against the collar c retaining the two piston blocks with
the springs between them. N is a lock-nut to secure all the parts in their place.
Figure 1 shows an alternative mode of constructing the piston in which a single
volute spring is made to take the place of the spiral springs. V & V₁' are the valve
boxes at opposite ends of the cylinder carrying the inlet and outlet valves as shown.
In the enlarged view of these valves (Figure 2) D is the stud which secures the
valves in place in the valve box, the head of which forms the stop for the delivery
valve. E is the inlet valve, El being the gridiron seat for same; F & F are the
corresponding parts of the delivery valve. At h h h h are shown recesses round the

page_text: projecting flanges of the valve seats in which a strand of asbestos fibre is put to
secure a tight joint. The stem of the inlet valve seat .E' projects at j, the
projecting part is screwed and provided with an adjustable nut which controls
the lifting piece P shown in plan below, by which the inlet valve is lifted off its
seat when it is desired to make the machine single acting and working at a high
pressure.
„Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
-claim is:
1. In an air compressor the device for eliminating the clearance space at one or
both ends of the stroke in the cylinder by means of the pistons movable on the
piston rod between stops and fitted with springs to keep them apart substantially as
described and shown.
2. In an air compressor the arrangement of replaceable annular gridiron valves
and seats with suction and delivery valves in pairs placed external to the cylinder
-substantially as described and shown.
Dated this 31ot do of Anoush 1000
SAML. H. JOHNSON.
C. C. HUTCHINSON.