Improvements in Centrifugal Fans and Pumps.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in Centrifugal Fans and Pumps.
I, SAMUEL CLELAND DAVIDSON, of Sirocco Engineering Works, Belfast, Ireland,
Merchant, do hereby declare the nature of this invention to be as follows:-
My invention relates to that class of centrifugal fans and pumps in which the
fluid operated on is taken in axially and discharged circumferentially.
In the Specification of Letters Patent No. 4609 of 1898 I have shown and
described a fan or pump the rotary member of which is constructed with numerous
elongated blades extended in approximately axial direction and arranged in
substantially drum form so as to enclose within them a relatively large and
practically unobstructed intake chamber, and having an inlet opening to said
chamber of diameter substantially equal to that of said chamber, said blades
being shaped to whirl the fluid centrifugally, and the fan or pump constructed
to permit the whirling fluid discharged from the blades to escape tangentially
outward therefrom. The blades which are preferably made of thin sheet metal
are so numerous as to follow each other in close succession, being spaced apart
preferably a distance approximating two thirds of their radial depth, or it may
be as much as twice such depth. The blades may be flat and arranged in radial
planes, or they may be made in two or more planes at an angle to each other,
or they may be formed as curved plates, their concaves being on the forward
or advancing side.
In the construction shown in my said specification the blades are extended in
a direction parallel to the axis of rotation. According to my present invention
the blades are extended obliquely to the axis of rotation so as to be materially
out of parallel therewith.
"
In this specification the word 'fan" is understood as including a pump.
The word axially" means in a direction coincident with or parallel with the
axis of rotation. The word "blades" is used to indicate the vanes or wings
which impart motion to the fluid. The expression "intake chamber" is em-
ployed to indicate a chamber or space enclosed within the series of blades. The
word "
is used to designate the inlet opening in the casing or stationary
member of the fan, through which opening the fluid enters the intake chamber.
By the
intake end" of the blades is understood that end which is nearest the
eye; the "length" of the blades is their longest measurement; the " depth
of the blades is their width measured radially from the inner to the outer edge;
and the ports are the intervening spaces between the blades.
eye
"
دو
"
One purpose of my present invention is to provide means by which the
efficiency of any portion of the blade may be increased or diminished. When
the blades are arranged parallel to the axis of rotation, as in my said specification
I have found in practice that those portions of the blades which are nearest the
intake end of the fan show the least efficiency, and that the efficiency rises
rapidly toward the opposite ends of the blades. The efficiency of the blades
also increases or diminishes with their speed. According to my present inven-

page_text: tion I provide for varying the efficiency of different portions of the blades by
so arranging the blades obliquely to the axis of rotation as to impart varying
speeds to their different portions. My invention also provides for varying the
efficiency of different portions of the blades by making them of varying width or
depth and also by varying the widths of the ports between the blades. My
present invention provides a fan the intake chamber of which is in the form
of a truncated cone. More than one intake chamber may be provided. An
entire or partial casing or fixed member of the fan may be used or not.
Any suitable means for supporting the blades may be employed. In the
preferred arrangement of my improved fan or pump the blades are supported at
their inner ends by a disc formed integrally with the hub of the fan, and at their
outer ends by an annular support which is connected to the hub by adjustable
stays. The blades are formed at each end with suitable flanges by means of
which they are riveted or otherwise fixed to the disc and the annular support.
The blades extend obliquely to the axis of rotation and enclose within them
an intake chamber of the form of a truncated cone. This arrangement has
the effect of increasing the speed of the blades at the larger end of the fan, the
speed gradually decreasing toward the smaller end thereof. This increase of
speed is accompanied by a proportionate rise in efficiency of the larger end of
the fan, and when this end is open the loss of efficiency experienced at this end
of a cylindrical fan is reduced. Thus in a fan of suitable proportions the dis-
charge may be equalized to such an extent than an approximately uniform
efficiency will be maintained at all points between the ends of the fan.
Another effect of this arrangement is that the ports between the blades are
wider at the end of the fan having the greater diameter, and diminish gradually
toward the smaller end of the fan, and the intake ends of the ports are corre-
spondingly widened. This effect is advantageous within certain limits, and to
an extent also increases the efficiency of the intake end of the fan.
Another feature of my invention consists in making the blades of varying
depth, the blades being widest in radial direction at the larger end of the fan,
and tapering toward the smaller end.
In a modification the ports between the blades are closed at their intake ends
by an annular support, the stays being in this case connected to a supplemental
hub fixed to the driving shaft. The blades may be parallel sided, with square
ends, which are formed with flanges that are rivetted to the annular support.
These ends also of the blades are thus rigidly supported, this construction being
suitable for use at high speeds or with heavy fluids.
My invention is also applicable to a fan which is open at both ends, so that
the fluid operated on is taken in axially through both ends thereof. With a
fan of this construction I preferably arrange the blades in such manner that
practically two intake chambers are formed, each of approximately the shape of
a truncated cone. In one arrangement the intake chambers are formed so
that their smaller ends meet, the blades being formed in two parts, and at
their junction these parts may be supported by a middle support. In this form
of fan two annular end supports are used in addition to the middle support, and
each support is connected by stay rods to the hub, which is fixed to the operating
shaft preferably about midway between the ends of the fan. The effect of the
construction is to increase the efficiency at the ends of the fan, and thus sub-
stantially equalize the discharge from all points of the circumference.
In the forms thus far described the circumferential discharge is modified by
increasing the efficiency of the intake end or ends of the fan, thereby tending
to equalize the discharge. This is an important advantage, for the reason that
the volumetric discharge of the fan as a whole is increased.
It is, however, within my invention to increase the efficiency of the inner end
of the fan, by increasing the diameter of that end, thereby forming the intake
chamber as a truncated cone open at its smaller end. A part of the space of the
intake chamber may be filled if desired by a conical member. In this form of

page_text: fan the disc support at the inner end is enlarged, and the annular support at the
intake end is reduced in diameter.
Practically the same effect may be obtained in a fan which is open at both
ends and in which the intake chambers are each in the form of a truncated cone,
the two chambers connecting with their larger ends adjacent. The effect of
this construction is that the efficiency is greatest at the middle portion of the
fan, and falls rapidly toward the ends.
It will be observed that in all of the arrangements herein described the intake
chamber is of conical shape, or more properly speaking it is in the form of a
truncated cone. The exact degree of obliquity of the blades to the axis of
rotation is not essential; in practice I prefer it should be such, if the medial
lines of two diametrically opposite blades were prolonged to a meeting point,
that the angle thus formed should be considerably less than a right angle. In
other words it is essential that the space enclosed within the series of blades
should be practically a chamber, and not a mere depression; in the preferred
form the length of the chamber is greater than its diameter.
The rotary member may be supported from its driving shaft in any suitable
manner compatible with strength and lightness of construction, and which will
allow of a practically unobstructed intake chamber, which is a very important
feature in the construction of the centrifugal fans herein described.
It is essential to my invention that the fan blades shall be shaped to whirl
the fluid centrifugally, in contradistinction to merely exerting a wedge-like
action upon it tending to thrust it outwardly in radial direction unaccompanied
by rotation or whirling of the fluid around the exterior of the blades. The
operation of my fan when propelling air, appears to be accompanied by the
existence of a thin shell or film of rapidly whirling air immediately surrounding
the drum-like series of blades, which air is apparently compressed, and outside
of this shell the air passing through the fan discharges tangentially.
To realize the advantages of my invention, it is practically essential that the
inflow of fluid to the intake chamber be unobstructed within the intake chamber.
and that the inlet opening be of the full diameter of said chamber, as any
throttling of this opening results into a proportionate diminution of volumetric
efficiency. It is also practically essential that the whirling fluid discharged
from the fan blades shall be permitted to escape tangentially outward therefrom,
as any attempt to divert the revolving fluid inwardly within the radius of the
circle described by the outer edges of the blades results in a rapid diminution
of efficiency. But the whirling fluid can be collected in a casing, and if the
outlet from this casing be arranged beyond the radius of the circle described by
the outer edges of the blades, the fluid will freely escape through said outlet,
its whirling motion being thereby resolved into a direct motion, after which
it can be led through a suitable conduit in any desired direction.
1
D
1.
1000
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.
I, SAMUEL CLELAND DAVIDSON, of Sirocco Engineering Works, Belfast, Ireland!.
Merchant, do hereby declare the nature of this invention and in what manner

page_text: the same is to be performed to be particularly described and ascertained in and
by the following statement:-
My invention relates to that class of centrifugal fans and pumps in which the
fluid operated on is taken in axially and discharged circumferentially.
In the Specification of Letters Patent No. 4609 of 1898 I have shown and
described a fan or pump the rotary member of which is constructed with numerous
elongated blades extended in approximately axial direction and arranged in
substantially drum form so as to enclose within them a relatively large and
practically unobstructed intake chamber, and having an inlet opening to said
chamber of diameter substantially equal to that of said chamber, said blades
being shaped to whirl the fluid centrifugally, and the fan or pump constructed
to permit the whirling fluid discharged from the blades to escape tangentially
outward therefrom. The blades which are preferably made of thin sheet metal
are so numerous as to follow each other in close succession, being spaced apart
preferably a distance approximating two thirds of their radial depth, or it may
be as much as twice such depth. The blades may be flat and arranged in radial
planes, or they may be made in two or more planes at an angle to each other,
or they may be formed as .curved plates, their concave being on the forward
or advancing side.
In the construction shown in my said specification the blades are extended in
a direction parallel to the axis of rotation. According to my present invention
the blades are extended obliquely to the axis of rotation so as to be materially
out of parallel therewith.
"
In this specification the word "fan" is understood as including a pump.
The word axially" means in a direction coincident with or parallel with the
axis of rotation. The word "blades" is used to indicate the vanes or wings
which impart motion to the fluid. The expression "intake chamber'
is em-
ployed to indicate a chamber or space enclosed within the series of blades. The
word "eye is used to designate the inlet opening in the casing or stationary
member of the fan, through which opening the fluid enters the intake chamber.
By the intake end" of the blades is understood that end which is nearest the
eye the "length "of the blades is their longest measurement; the "depth
of the blades is their width measured radially from the inner to the outer edge;
and the "ports" are the intervening spaces between the blades. The blades
which I preferably employ are elongated,' that is to say, of greater axial length
than radial depth, said length being not less than three times and preferably
nine or more times the radial depth of each individual blade.
33
One purpose of my present invention is to provide means by which the
efficiency of any portion of the blade may be increased or diminished. When the
blades are arranged parallel to the axis of rotation as in my said previous specifica-
tion I have found in practice that those portions of the blades which are nearest the
intake end of the fan show the least efficiency, and that the efficiency rises
rapidly toward the opposite ends of the blades. The efficiency of the blades
also increases or diminishes with their speed. According to my present inven-
tion I provide for varying the efficiency of different portions of the blades by
so arranging the blades obliquely to the axis of rotation as to impart varying
speeds to their different portions. My invention also provides for varying the
efficiency of different portions of the blades by making them of varying width or
depth and also by varying the widths of the ports between the blades. My
present invention provides a fan the intake chamber of which is in the form
of a truncated cone. More than one intake chamber may be provided. An
entire or partial casing or fixed member of the fan may be used or not.
Any suitable means for supporting the blades may be employed.
I will now proceed to describe by way of example certain forms of my inven-
tion with reference to the accompanying drawings. in which:-
Figure 1 is a diametrical section of the preferred form of my improved fan:

page_text: Figure 2 is an end view looking into the intake chamber (only a few of the
blades being shown); and
Figures 3 to 6 are diametrical sections showing modified forms.
Referring first to Figures 1 and 2, A indicates the rotary member of the fan
as a whole, B the blades, C the hub, and D the operating shaft.
A casing may be used or not with this form of fan; a partial casing or fixed
member of the fan is indicated in dotted lines at I in Figure 1, the eye or
opening through it being lettered J. The blades are shown as supported at their
inner ends by a disc e formed integrally with the hub of the fan, and at their
outer ends by an annular support E which is shown as connected to the hub C
by adjustable stays F. The blades B are formed at each end with suitable
flanges by means of which they are rivetted or otherwise fixed to the disc c
and the annular support E.
As shown the blades B extend obliquely to the axis of rotation and enclose
within them an intake chamber G of the form of a truncated cone.
This arrange-
ment has the effect of increasing the speed of the blades at the larger end of the
fan, the speed gradually decreasing toward the smaller end thereof. This in-
crease of speed is accompanied by a proportionate rise in efficiency of the
larger end of the fan, and when this end is open as in Figures 1 and 2 the
loss of efficiency experienced at this end of a cylindrical fan is reduced. Thus
in a fan of substantially the proportions shown in Figures 1 and 2 the discharge
is or may be equalised to such an extent that an approximately uniform
efficiency will be maintained at all points between the ends of the fan.
Another effect of this arrangement is that the ports H between the blades are
wider at the end of the fan. having the greater diameter, and diminish gradually
toward the smaller end of the fan, and in the construction shown in Figures 1
and 2 the intake ends of the ports are correspondingly widened. This effect is
advantageous within certain limits, and to an extent also increases the efficiency
of the intake end of the fan.
Another feature of my invention consists in making the blades of varying
depth as shown in Figures 1 and 2, the blades being widest in radial direction
at the larger end of the fan, and tapering toward the smaller end.
In the modification shown in Figure 3 the ports between the blades are closed
at their intake ends by an annular support E, the stays F being in this case
connected to a supplemental hub C' fixed to the operating shaft D. The blades B
may be parallel sided, with square ends, which are formed with flanges 61 that
are rivetted to the annular support E¹. These ends also of the blades are thus
rigidly supported and this construction is suitable for use at high speeds or with
heavy fluids.
My invention is also applicable to a fan which is open at both ends, so that
the fluid operated on is taken in axially through both ends thereof. With a
fan of this construction I preferably arrange the blades in such manner that
practically two intake chambers are formed, each of approximately the shape of
a truncated conc. In the arrangements shown in Figure 4 the intake cham-
ber G G are formed so that their smaller ends meet, the blades B being
formed in two parts B B₁ and at their junction these parts may be supported
by a middle support E2. In this form of fan two annular end supports E E are
used in addition to the middle support, and each support is connected by stay
rods F F to the hub, which is fixed to the operating shaft, preferably about mid-
way between the end of the fan as shown. The effect of the construction shown
in this figure is to increase the efficiency at the ends of the fan, and thus sub-
stantially equalise the discharge from all points of the circumference.
In the forms thus far described the circumferential discharge is modified by
ncreasing the efficiency of the intake end or ends of the fan, thereby tending to
equalise the discharge. This is an important advantage, for the reason that
the volumetric discharge of the fan as a whole is increased.
It is, however, within my invention to increase the efficiency of the inner end

page_text: of the fan, by increasing the diameter of that end, thereby forming the intake
chamber as a truncated cone open at its smaller end. This form is shown in
Figure 5 the intake end being shown as facing a casing I. A part of the space
of the intake chamber may be filled if desired by a conical member K. In
this form of fan the disc support c at the inner end is enlarged, and the annular
support E at the intake end is reduced in diameter.
Practically the same effect may be obtained 'in a fan which is open at both
ends, and in which the intake chambers are each in the form of a truncated cone,
the two chambers connecting with their larger ends adjacent. The effect of
this construction is that the efficiency is greatest at the middle portion of the
fan, and falls rapidly towards the ends. A fan of this type is shown in Figure 6
in which G G are the two intake chambers.
It will be observed that in all of the arrangements herein described and shown
the intake chamber is of conical shape, or more properly speaking it is in the
form of a truncated cone. The exact degree of obliquity of the blades to the
axis of rotation is not essential; in practice I prefer it should be such, if the
medial lines of two diametrically opposite blades were prolonged to a meeting
point, that the angle thus formed should be considerably less than a right angle:
In other words it is essential that the space enclosed within the series of blades
should be practically a chamber, and not a mere depression. In the preferred
form the length of the chamber is greater than its diameter.
The rotary member may be supported from its operating shaft in any suitable
manner compatible with strength and lightness of construction (that shown
being preferred) which will allow of a practically unobstructed intake chamber,
which is a very important feature in the construction of the centrifugal fans
herein described.
It is essential to my invention that the fan blades shall be shaped to whirl
the fluid centrifugally. in contra-distinction to merely exerting a wedgelike
action upon it tending to thrust it outwardly in radial direction unaccompanied
by rotation or whirling of the fluid around the exterior of the blades. The
operation of my fan when propelling air, appears to be accompanied by the
existence of a thin shell or film of rapidly whirling air immediately surrounding
the drum-like series of blades, which air is apparently compressed, and outside
of this shell, the air passing through the fan discharges tangentially.
To realise the advantages of my invention, it is practically essential that the
inflow of fluid to the intake chamber be unobstructed within the intake chamber
and that the inlet opening be of the full diameter of said chamber, as any
throttling of this opening results in a proportionate diminution of volumetric
efficiency. It is also practically essential that the whirling fluid discharged from
the fan blades shall be permitted to escape tangentially outward therefrom, as
any attempt to divert the revolving fluid inwardly within the radius of the circle
described by the outer edges of the blades results in a rapid diminution of
efficiency. But the whirling fluid can be collected in a casing, and if the outlet
from this casing be arranged beyond the radius of the circle described by the
outer edges of the blades, the fluid will freely escape through said outlet, its
whirling motion being thereby resolved into a direct motion, after which it
can be led through a suitable conduit in any desired direction.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. In a centrifugal fan or pump, wherein the fluid operated on is drawn in
axially and discharged circumferentially, the employment of a series of numerous
blades of greater axial length than radial depth extended obliquely to the
axis of rotation so as to enclose within them a conical intake chamber of rela-
tively large diameter at or near its base substantially as set forth.
2. In a centrifugal fan or pump wherein the fluid operated on is drawn in
i

page_text: axially and discharged circumferentially, the employment of a series of numerous
blades of greater axial length than radial depth, arranged as referred to in
Claim 1, and extended so as to enclose within them a truncated conical intake
chamber of relatively large diameter open a one end, substantially as set forth.
3. In a centrifugal fan or pump wherein the fluid operated on is drawn in
axially and discharged circumferentially, the employment of two series of
numerous blades of greater axial length than radial depth arranged as referred
to in Claim 1, the two series of blades being extended in opposite directions so
as to enclose within them two co-axial abutting truncated conical intake cham-
bers of relatively large diameter and open at their outer ends, substantially as
set forth.
4. The improved centrifugal fans or pumps substantially as hereinbefore de-
scribed and shown respectively in Figures 1 and 2; and in Figures 3, 4, 5 and 6
of the accompanying drawings.
Dated this 14th day of Santambor 1900
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.