IMPROVEMENTS IN VENTILATING APPARATUS
Year: 1881

page_text: "
LETTERS PATENT to William Cunningham, of Dundee, in the County of
Forfar, North Britain, Engineer, for an Invention of IMPROVEMENTS IN
VENTILATING APPARATUS."
PROVISIONAL SPECIFICATION left by the said William Cunningham at the
Oflice of the Commissioners of Patents o the 11th November 1881.
WILLIAM CUNNINGHAM, of Dundee, in the County of Forfar, North Britain,
Engineer. "IMPROVEMENTS IN VENTILATING APPARATUS."
This Invention has for its object to provide improved apparatus for ventilating,
such apparatus operating in a positive manner upon large volumes of air, at slow
speeds, with low pressures, with a comparatively small expenditure of power, and
with little or no noise.
In carrying out the Invention two rotating propellers are arranged and operate
in a casing on a principle employed in apparatus described more than a century ago,
and adopted in recent years in what are known as Roots blowers. The propellers
are on parallel horizontal shafts which in one modification of the apparatus are
placed one above the other, and each propeller is made with two diametrically
opposite wings having segmental cylindrical outer surfaces of large radius, whilst
between the wings there are segmental cylindrical surfaces of small radius. The
two propellers are so placed and so driven in concert, as that when a wing of either
is passing through the middle space between the shafts, its cylindrical surface
almost touches a cylindrical surface of small radius of the other propeller at the
middle plane of the casing. The wings pass through the outer halves of their
courses in such a manner as to be in approximately airtight contact with the
interior of the casing, and their action is such as in a well understood way to draw
in air at one side of the plane in which the shafts are placed, and force it out at
the other side, suitable ducts or passages being provided to lead the air to and from
the casing as may be required.
Instead of gearing together the shafts of the two propellers by toothed wheels
which are noisy and otherwise objectionable, they are made to rotate properly in

page_text: concert by means of a belt and pulleys. The belt is by preference made of the best
leather well stretched, so as to be capable of working for a considerable time
without stretching further to an injurious extent. The belt may be made of any
suitable flexible material that is not liable to become too rapidly elongated in use.
In one modification studs are riveted to the belt at regular distances to gear with
holes in the pulleys on the two propeller shafts; and in another modification the
belt has formed in it holes which may be protected with metal eyelets, and which
will gear with studs or projections on the pulleys. The belt which is an endless
one is led round two guides pulleys besides the pulleys on the propeller shafts; and
these guide pulleys run on studs which can be adjusted in position. The guide
pulleys whilst distending the belt and leading it in the proper direction from one
pulley to the other, also serve for making the two propellers work properly
together, since by shifting the two guide pulleys in opposite directions one propeller
can be turned relatively to the other if required.
For large sizes of the improved ventilating apparatus the casing is by preference
made of wood strengthened by iron frame work; and the wings and segmental
cylindrical surfaces are also by preference made of wood. For small sizes tinned
or galvanised or otherwise-coated sheet iron may be conveniently used to a large
extent in the construction of the casing, or propeller, or both. For maintaining
sufficient closeness between the outer surfaces of the wings and the parts of the
casing nearly in contact with which they move, strips of a suitable flexible
material, such, for example, as double-ply waterproof cloth, may be fixed to the
casing at each end of the curved part of the casing, but not quite so far apart as
the length of the cylindrical surface of the wing.
The improved mode of driving hereinbefore described is applicable to blowers,
-constructed-as-regards-the-casing and propellers as in any existing modifications of
blowers operating on the same principle as Roots' blowers.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Cunningham in the Great Seal Patent Office on the
10th May 1882.
WILLIAM CUNNINGHAM, of Dundee, in the County of Forfar, North Britain,
Engineer. "IMPROVEMENTS IN VENTILATING APPARATUS."
My said Invention has for its object to provide improved apparatus for
ventilating or changing the air in enclosures or spaces, such apparatus operating in
a positive manner upon large volumes of air at slow speeds, with low pressures,
with a comparatively small expenditure of power, and with little or no noise.
In carrying out my Invention two rotating propellers are arranged and operate
in a casing on a principle employed in apparatus described more than a century
ago, and adopted in recent years in what are known as Roots' blowers. Instead of
gearing together the shafts of the two propellers by toothed. wheels, which are
noisy and otherwise objectionable, they are made to rotate properly in concert by
means of a belt and pulleys. The belt is by preference made of best leather well
stretched, so as to be capable of working for a considerable time without stretching
further to an injurious extent. The belt may however be made of any suitable
flexible material that is not liable to become too rapidly elongated in use.
In one
modification studs are fixed to the belt at regular distances to gear with holes in
the pulleys on the two propeller shafts, and in another modification the belt has
formed in it holes, which may be protected with metal eyelets, and which will gear
with studs or projections on the pulleys. In a third modification a twin belt is
employed, being formed of two narrow belts connected by metal pieces, which are
placed at regular intervals and engage in notches in a projecting ridge formed on
each pulley. The belt which is an endless one is led round two or more guide
pulleys besides the pulleys on the propeller shafts, and these guide pulleys, one or
more of which can be adjusted in position, distend the belt and lead it in the
proper directions to and from the other pulleys.
For large sizes of my improved ventilating apparatus the casing is by preference
made of wood strengthened by iron framework, and the wings and segmental
cylindrical surfaces of the propellers are also by preference made of wood. For
small sizes tinned or galvanized or otherwise coated sheet iron may be con-
veniently used to a large extent in the construction of the casing or propeller, or
both. My improved mode of driving is applicable to blowers constructed as
regards the casing and, propellers, as in any existing modifications of blowers
operating on the same principle as Roots' blowers.
And in order that iny said Invention and the manner of performing the same
may be properly understood, I hereunto append four Sheets of explanatory
Drawings to be hereinafter referred to, and representing my improved ventilating
apparatus.
Figure 1, on Sheet 1, of the accompanying Drawings, is an end elevation of the
ventilator casing with the pulleys and endless belt, by means of which the two
propellers are made to work properly in concert; Figure 2 on Sheet 2 is a side
elevation with one half in vertical section, and showing the casing and the pro-
pellers inside of it; Figure 3 on Sheet 3 represents the two propellers, one of
them being in end elevation, and the other in vertical section; and Figures 4 to 9
on Sheet 4 are views of details, and are hereinafter more particularly described.
In the Drawings the same reference numerals are used to mark the same or like
parts wherever they are repeated.
The two propellers 11, 12, are on parallel horizontal shafts 13, 14, which in the
modification shown in the Drawings are placed one above the other, and each

page_text: propeller is made with two diametrically opposite wings 15 having segmental
cylindrical outer surfaces 16 of large radius, whilst between the wings 15 there
are cylindrical surfaces 17 of small radius. The two propellers 11, 12, are so
proportioned and placed relatively to each other, and so driven in concert as that
when a wing 15 of either is passing through the middle space between the shafts
its cylindrical surface 16 almost touches a cylindrical surface 17 of small radius of the
other propeller, and the middle plane that passes through the shafts. The wings 15
pass through the outer halves of their courses in such a nanner as to be in
approximately airtight contact with the top 18-18 and bottom 19-19 of the
casing. The casing consists of the said top 18-18 and bottom 19-19 and of
vertical ends 20, which latter are at right angles to the shafts 13, 14, whilst there
are openings at each side of the casing between the top 18 and bottom 19, these
openings being in practice in communication with the passages or ducts for leading
the air to and from the casing (which passages or ducts are not shown in the
Drawings). The two propellers 11, 12, rotate in opposite directions, and their
action is such as in a well understood way to draw in air at one side of the plane
in which the shafts, 13, 14, are placed and force it out at the other side.
The propellers 11, 12, are constructed of wood and fixed upon castiron centres,
which are keyed upon the shafts 13, 14. The smaller parts 17 are conveniently
made in the form of complete cylinders, and the wings 15 extend from the
cylinders 17 to the outer cylindrical wing segments 16, the said wings 15 of course
forming partitions or paddles which extend from end to end of the propellers (that
is in the direction of the shafts), as well as from the cylinders 17 to the outer.
segments 16. The parts of the propellers are strengthened by various framing
pieces fixed at right angles to the wings 15 and to their cylindrical segments 10, and
-by-diagonal-braces 21, the arrangement of which strengthening details will be
easily understood from the Drawings.
The casing consists of castiron end frames 22, having horizontal frames 23 bolted
to and connecting their upper and lower ends, there being fixed by screws to the
inner sides of the end frames 22 a number of horizontal wooden frame bars 24,
which are by preference strengthened by iron plates screwed to them and which
have the boards forming the casing ends 20 fixed to their inner edges. The
frames 22 at opposite ends of the casing are also connected by diagonal tie rods 25,
which are fixed by screw nuts to projecting brackets 26 cast on the frames. The
shafts 13, 14, are carried in bearing blocks 27 fixed to horizontal bars 28 formed
on the ends frames 22, and one shaft 13 has fixed on one end of it a pulley 29 for a
driving belt.
Motion is transmitted from one propeller shaft 13 to the other 14 by means of
pulleys 30, 31, fixed on one end of each shaft, and by means of an endless belt 32
and guide pulleys 33, 34, 35, these guide pulleys being on studs fixed to the end
frame 22, and one of them being adjustable. One modification of the pulley and
belt details is shown enlarged in Figures 4, 5, and 6 on Sheet 4 of the Drawings,
Figure 4 being a partially sectioned elevation of one of the propeller pulleys 31
and a guide pulley 35, Figure 5 being a face view of a part of the belt 32, and
Figure 6 being a section of the guide pulley 35. In this modification rounded
studs 36, one of which is shown separately in Figure 5, are riveted at regular
intervals along the middle of the belt 32, and holes to receive the studs are formed
in the rims of the propeller pulleys. A simple groove is formed in the rim of the
guide pulley 35 to admit the studs.
A preferable modification of the pulley and belt details is shown enlarged in
Figures 7, 8, and 9 on Sheet 4 of the Drawings, and is the same as that shown in
Figures 1 and 2. In this modification a twin belt 32 is employed a portion of
which is shown in face view and in section in Figure 8, whilst one of the pro-
peller pulleys 31 is shown in elevation in Figure 7 and in section in Figure 9.
The twin belt 32 consists of two narrow leather belts placed a little apart, and
connected by metal pieces 37 riveted to the belts at regular distances. The middle
parts of the metal pieces 37 between the belts are rounded, and as the twin belt 32

page_text: passes round either propeller pulley 30, 31, the rounded parts of the metal pieces 37
engage in notches in a feather or flange 38, formed so as to project from the middle
of the rim of the pulley. The twin parts of the belt 32 pass on each side of the
feather or flange 38, and this feather or flange has its notches formed with inclined
or flared sides, so that if at any time a belt piece 37 does not fall exactly in the
centre of a notch it will come in contact with the inclined side of the notch in a
gentle manner, and the parts will become readjusted to each other without con-
cussion or noise. The twin belt 32 is shown as having the metal pieces 37 fixed
on one side of it, and in consequence of this the rims of the two propeller pulleys
30, 31, have to be a little different, the cylindrical part of the rim having to be
slightly recessed at the notches in one case but not in the other.
In order that the two propellers 11, 12, may be adjusted accurately in position
relatively to each other, one of the pulleys 31 is made adjustable on its boss or
hub 39, as shown in Figures 7 and 9, the centre of the pulley being fixed to the
boss or hub by bolts which pass through elongated slots. A similar adjustment
could also be obtained by varying the positions of the guide pulleys 33, 34, their
studs being for that purpose made adjustable.
For maintaining sufficient closeness between the outer surfaces of the wing
Begments 16, and the parts 18-18 and 19-19 of the casing nearly in contact
with which they move, strips of a suitable flexible material, such, for example, as
double-ply waterproof cloth or woollen cloth, may be fixed to the casing at each
end of the curved parts 18-18 and 19-19; but these strips should not be quite
so far apart as the circular length of the cylindrical surface 16 of each wing.
Instead of the kinds of belt (32), herein before described, there might be employed
in carrying out my Invention a flat band or pair of bands of steel wire, or a
round steel wire cord or pair of cords, or a hoop or pair of hoops of thin steel, or
a pitch chain may be used, the pulleys being in this last case covered with firm
leather or other material not liable to cause noise.
My improved apparatus may be advantageously used for all purposes of
ventilation where moderate currents and low pressures are desired, and it may be
combined with any suitable apparatus for heating or cooling the air acted on by
it. An important application of the apparatus consists in using it for changing
the air in connection with apparatus for cooling water, in the manner described
in the Specification of Letters Patent granted to me, and dated 22 December 1875,
No. 4441.
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 and in terms of the herein-
before in part recited Letters Patent is,-
1. The arranging or combining together of the parts of ventilating apparatus,
substantially in the improved manner herein before described.
2. The connecting of the two propellers and driving them in concert by means
of an endless belt or belts combined with pulleys on the shafts of the propellers,
the belt or belts being fitted or formed with projections, or equivalents, or with
holes to engage with holes or notches or projections on the pulleys, substantially as
hereinbefore described.
In witness whereof, I, the said William Cunningham, have hereunto set my
hand and seal, this Ninth day of May, in the year of our Lord One
thousand eight hundred and eighty two.
WILLIAM CUNNINGHAM. (LS)