Improvements in Centrifugal Ventilators and Centrifugal Pumps.
Year: 1895

page_text: Date of Application, 25th M r., 1895-Accepted, 1st June, 1895
COMPLETE SPECIFICATION.
Improvements in Centrifugal Ventilators and Centrifugal Pumps.
I, FRIEDRICH PELZER, of 18 Holländische Strasse Dortmund in the Empire of
Germany, Engineer, do hereby declare the nature of my said invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
It is a well-known fact that in order to render centrifugal ventilators and pumps
effective, a rapid rotary movement must be imparted to the air or other fluid.
In most cases such rotary velocity is equal to a multiple of those velocities
which would be imparted to the fluids when driven by ordinary piston pumps
through a conducting channel and not by centrifugal force. It will therefore be
evident that the fluid moving at the normal velocity in the entrance channel must
attain its maximum velocity in the propelling apparatus, centrifugal pump or
centrifugal ventilator respectively, and on leaving the latter be reduced again to
its normal velocity.
To prevent any considerable loss in effect, the arrangement must be such that
said alterations in the movements of the fluid, both as regards direction and
velocity, take place as gradually as possible. The centrifugal ventilators and
pumps at present in use improperly and insufficiently fulfil such conditions i.e. as
far as concerns the entrance of the fluid into the propelling wheels and the
transition of same from the axial to the rotary direction.
Rittinger's, Seer's and other similarly-constructed ventilators, for instance, are
so arranged that the ends of the blades or wings turned towards the axle are bent.
reversely to the direction of movement, in order to prevent the rotary movement
being momentarily imparted to the current of air moving in axial direction.
Even if with such constructions the impact on the air on entering the blades is
thus somewhat moderated (which is never the case with most ventilators of other
descriptions) as compared with blades whose ends are radially arranged, the impact
on the air, when the ventilator is rotating very rapidly, is nevertheless strong
enough to cause a strong whirl in the wheel.
This will be best understood, for example, by striking an indiarubber ball with
a stick of suitable strength. It will be seen that the rapidity imparted to the ball
by the stroke of the stick is greater than the rapidity of the movement of the stick
in striking.
In order to remove these defects to some extent, the free edges of the
ventilator wings of Pelzer's scoop-ventilators were provided with so-called
Dutch-scoops.
For two reasons, however, such scoops were still very imperfect, firstly, because
they could not be lengthened in axial direction to any considerable extent without
rendering the wheels less durable and strong and, secondly, because the intersecting
lines produced on the scoop surfaces by cylinders concentric to the ventilator axle
were such that their projections on planes parallel to the axle and perpendicular to
the respective ventilator-blades formed almost straight lines; in order however to
effect a gradual transition of the movements of the fluids from the axial to the
rotary direction, such construction must be avoided.
The object of this invention, therefore is to fully overcome all such defects in
connection with centrifugal ventilators and centrifugal pumps and I will now
describe same with reference to the accompanying drawings in which:
Fig. 1 is a vertical section of a centrifugal ventilator.
Fio 2 is an end elevation seen from the left of Fio 1

page_text: Fig. 3 is a sectional view on line ―y of Fig. 1.
Figs. 4, 5, 6 and 7 are illustrative diagrams.
The main blades F F are considerably lengthened in the direction of or towards
the suction space S by extension blades F1, F. In thus extending, the blades F', F',
however, it is necessary that same are, at the same time, durable and strong, as
also easy and cheap of construction; the scoop arrangement previously mentioned,
therefore, will not meet the purpose in question. I overcome these difficulties by
providing a special wheel R, R for the extension blades, such wheel having hub n, n,
spokes p,
and casing u, u and being keyed in front and independently of the main
wheel onto the axle of the ventilator.
The edges e, e opposite the main wheel are radially arranged, whereas the axial
extensions of the blades F¹, F' towards the suction space S are so bent or twisted
that a gradually increasing rotary velocity is imparted to the axial current of air
passing through all the zones (indicated by the dotted circles 1 to 7 Fig. 2); it is
essential that the rotary velocity of such current of air on entering the corre-
sponding parts of the main-wheel is increased to such an extent as to be equal to
the rotary velocity of the air in the corresponding zones of such main wheel.
The longer the blades F', F' are extended in axial direction, the better is the
rotary motion gradually imparted to the axial current of air. It is taken for
granted that the intersecting lines produced by the zone cylinders on the extension
blades F, F¹ are of such form that their projections on the above mentioned planes
rise as uniformly as possible from the plane of the respective main blade towards
the cross-sectional plane of the suction canal.
The intersecting lines of the zones however, must not rise to such an extent as to
cause the air entering the wheel R in axial direction to impinge against the back
of the blades F1, Fi and thus seriously impede and reduce the axial velocity of
same. This would take place if the angle a forming such intersecting lines with
the cross sectional plane were smaller than an angle, the tangent of which is equal
being the axial velocity of the air entering and u the cir-
cumferential velocity of the respective zones.
V
to
и
(tang a=
ย
a
;
This will be understood from Fig. 7. Let line ei represent a straight part of an
intersecting line inclined at the angle a towards the cross-sectional plane e, €1
supposing now a point at i moving with the velocity v=ie in the direction ie and
the line ei moving simultaneously with the velocity u ee in the direction e e' the
point e,
In this
after the point i has reached e¹ will also have advanced to e¹.
case = = tang a. If the angle a is smaller than here taken, so that the
26 b
velocity is greater than the value i e' while the value e et =u remains constant,
on taking eas intersecting line of a plane vertical to the plane of the drawing,
which latter plane moves with velocity u in the direction e e¹, the air near e i
but outside the angle a, would move in the direction and impinge with the velocity v
against the plane ei and be retarded thereby.
If, on the contrary, the angle a were greater than here taken, the plane e i
moved in the direction and with the velocity u would drive before it the air moving
with the velocity and direction v and increase its velocity. In the latter case,
however, the air entering in axial direction is at the same time deflected in the
direction u viz. on the movement of the extension blades of a centrifugal ventilator
or a centrifugal pump, in such manner that a rotary movement is imparted
to same.
The abovementioned zone intersecting lines of cylinders concentric to the
ventilator-axle and on or connected with the blades F, F1 must, therefore, be so
formed that the angles which they produce at the parts deviating most from the
vertical towards the cross-sectional plane, that is, at the end facing the suction
space, form a somewhat larger angle than the one whose tangent is equal to →

page_text: being as before the axial velocity and u the circumferential velocity of the
respective zones.
The action hereby aimed at of the gradual transmission of the rotary motion to
the fluids in reducing to a minimum the injurious effects of the strong impingements
of the fluid against the blades and of the counter pressure by the action against the
surfaces of the blades, is attained when the extension blades are formed so that
the projection lines resulting from the zone intersecting-points of the extension
blades on the above-named projection planes, are formed as shown in Figs. 4 and 5.
In Fig. 6 the plane of the drawing represents one of the projection planes
placed perpendicular to a main blade of the ventilator and parallel to the ventilator
axis. At the point e is a line perpendicular to the projection plane i.e. also per-
pendicular to the plane of the drawing, which line represents the point of contact
of the edges of a main blade and the extension blade adjacent thereto.
The edges of the extension blade facing the suction space is intersected by
the zone-cylinders at the points b1 62 63 etc. to b' above the plane of projection.
Fig. 4 more fully illustrates the construction of the intersecting line projection e b
and Fig. 5 that of the intersecting line projection .e b' shown in Fig. 6.
As illustrated by Figs. 4 & 5 these constructions are arrived at, by dividing the
line e m (ie. the axial length of the path, on which the air passing through
the ventilator is within reach of the extension blades) into x equal parts
(x 8 here) by parallel line drawn at right angles to same.
The complement of the angle a is then divided into (a + 1) equal parts and
the lines e A to e drawn, thus coinciding with the hypothenuse c, of the
triangle a b c. The line e I is now drawn from e to the first parallel, said line e I
coinciding with the line e', then the line I, II parallel to the line e² etc. to VII, VIII
parallel to the line e8.
If the complement of the angle (90 - a) were not divided into a + 1 viz. 9 equal
parts, but into 8 parts only, the last division VII, VIII would have to be parallel
to the side c of the triangle.
ย
น
The inclination of the intersecting lines VII, VIII would then be such
that would be equal to tangent a viz. the effect would be totally lost, whereas
with the present arrangement, these parts of the extension blades between the
last two parallel lines, like any preceding one, cause a rotary movement of the air.
In this manner a part of a polygon having unlike sides is obtained.
If now
an arc is described from the point with radius o and so as to intersect point VIII
the tangent of such are at e being perpendicular to line b, it is found that the
are shown in Fig. 4 deviates very little from the arc drawn through the polygon,
whereas in Fig. 5 this deviation is totally insignificant. In practice, however, it is
not necessary that these surfaces have a mathematical exactness, nor is it easy to
attain such exactness; it is therefore sufficient to construct these intersecting line-
projections of the extension blades as arcs whose centre points are on the line b or
its extension and which extend from the point e to VIII (Figs. 4 and 5).
In Fig. 6 the projections of the intersecting lines of the extension blades are
shown on a plane perpendicular to the plane of the respective main blade and
parallel to the ventilator axis, such projections consisting of arcs, produced as
intersection lines by cylinders concentric to the ventilator axis and at equal
distances apart and the surfaces of the extension blades curved as nearly as possible
to the proper extent.
Such extension blades may be constructed by means of flat or sheet iron patterns
whose upper edges are shaped in their order according to the arcs e b', e b², e b³ etc.
to e 7 (Fig. 6). The patterns are placed at their proper distance apart on a flat
plate and secured thereto.
The extension blade to be bent, after being sufficiently heated, is now placed and
secured on the pattern in suitable manner and hammered until its surface comes in
contact with all the upper edges of the pattern.

page_text: Centrifugal ventilators or centrifugal pumps provided with such separate wheels
for the main and extension blades are thus considerably lengthened or extended in
axial direction. If it were desired to simultaneously draw in the air at both sides,
it would only be necessary to erect the same construction in the wall at O (Fig. 1)
as shown on the left sides. In so doing, however, the apparatus would not only be
rendered very clumsy and expensive in construction, as compared with the single
side ventilator, but would also require considerably more space.
With the present known apparatus, however, which draw the air from one side
only, there is a far higher pressure in the space O than in the suction space S,
even if same has been most carefully packed. The result is that the blade wheel
is drawn in the direction of or towards the suction room S with a force corre-
sponding to the difference in tension of the two spaces and an area corresponding
to the diameter of the blade wheel.
This force causes friction at those parts where resistance must be offered, such
friction, in cases where high differences of tension are to be produced, becoming
correspondingly high and causing the bearings to get hot. In order to avoid these
defects, as shown in Figs. 1, 2 & 3 the centrifugal ventilator is provided with
deflecting plates bb and perforations ii in the outer flange of the hub. The
deflecting plates bb do not extend as far as the outer wail ww of the ventilator,
but between their outer and almost radially-inclined edges and the wall w w there
is a slot s s interrupted only by the main blades F F and the securing bolts, said
slot communicating with the perforations ii between the space O and the inner
blade cells of the ventilator; the action of the rotating blade wheel in the space O
therefore is capable of producing the same depression as in the suction space S.
The plates also deflect the air in the slightest possible curve from the axial
to the radial direction.
Having now particularly described the nature of my invention and in what
manner the same is to be performed, I declare that what I claim is :-
1. In centrifugal ventilators and centrifugal pumps drawing in air from one side
only, the arrangement of deflecting plates (b) above the hub and between every
two blades or wings of the main wheel, said plates deflecting the current of air or
other fluid from the axial to the radial direction and equalizing the difference in
tension otherwise present between space (0) and suction space (S) by means of
slot-like opening (ss) between the outer edges of said deflecting plates and the
back-wall (ww) of the wheel in combination with the perforations (ii) in the
hub (nn) substantially as described and shown in the drawings.
2. In a centrifugal ventilator or pump of the kind described in Claim 1.
the arrangement of a second wheel (R, R) in front of the suction end of the
main wheel and provided with extension blades (FF) forming a continuation
of the main blades (F F) of the main wheel and whose surfaces are
on the
same plane at the contact edges (ee) as the blades of the main wheel, but in
the further axial extension are so bent or twisted that the projections of the
intersecting lines formed on the surfaces of the extension blades by cylinders
concentric to the ventilator-axle on planes parallel to the axis and perpendicular
to the main wings or blades of the ventilator and centrifugal pump respectively
produce arcs or curves whose centre points are on the lines e s or its extensions,
(Figs. 4, 5 & 6) substantially as described and shown in the drawings.
F. PELZER,
Per W. H. Beck,
115, Cannon Street, London, E.C., Agent.