Improvements in Centrifugal Pumps and Fans.
Year: 1892

page_text: Date of Application, 19th Dec., 1892-Accepted, 28th Jan., 1893
OMILLE DE DUIFICATION.
Improvements in Centrifugal Pumps and Fans.
I, HEINRICH LUDEWIG of 119 Schillerstrasse, Charlottenburg, near Berlin in
the Empire of Germany Professor do hereby declare the nature of the said inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement:-
As is well known centrifugal, rotary or turbine pumps are generally only suitable
for large volumes and short lifts. The wheel of these pumps is provided with
internal webs by means of which the water is forced from the centre to the periphery
in order to utilize the centrifugal force. The radial webs provided in the pump
wheel form the passages through which the water is forced up, which passages in
consequence of the constantly increasing distance from the centre of the wheel
assume a steadily increased cross section.
As the quantity of water passing through these passages for a given speed of the
wheel is always the same, it is obvious that the relative speed of the water in such
passages is gradually lessened as it passes from the centre to the periphery of the
wheel.
This loss of speed of the flowing water forced through these passages will be all the
greater in proportion as the areas of the cross sections of the passages for the water
increase from the centre to the periphery. This increase in area of the cross
sections will be all the more, in proportion as the difference between the radii at
the inlet and outlet of the wheel is greater, and in proportion as the angles formed
by the webs at the inlet and outlet of the wheel are smaller.
The angles here mentioned are those formed by the curvature of the webs in
reference to the periphery of the wheel.
It is necessary to have a great difference in the radii of the wheel between the
inlet and outlet so as to get the greatest possible effect from the centrifugal force
particularly for great lifts or high forcing.
The small angle for the curvature of the webs is essential, when, for practical
reasons the inner radius of the wheel cannot be made very small and the capacity
of the pump is rather low. Moreover the small angles are suitable to render the
pump more effective relatively to the driving power required.
If therefore it is desired to use a centrifugal pump under unusual conditions for
small delivery and great lifts or high forcing it is all the more necessary to take
into account the above mentioned facts, that is to say, that in pumps of small
capacity and for high lift or forcing the relative speed of the water in the passages
of the wheel will decrease rapidly from the centre to the outlet.
Such a rapid decrease in the relative speed of the water passing through the
passages is a great disadvantage in regard to the centrifugal effect which latter in
consequence of the loss of speed in the water due to the increase in the area of the
cross section, loses the effect obtained through the great difference in the radii at
the centre and at the periphery and therefore the water has to be brought up
again to its initial speed.
In order to obviate this disadvantage it has been the practice to decrease the
width of the wheel from the centre to the periphery as a means for compensating to
some extent for the increase of area in cross section of the passages. This means is
very narrowly confined in its general application, a considerable narrowing of the
width of the wheel from the centre towards the periphery causes a long narrow, and
correspondingly low figure for the area of the cross section of the passages and
results in a disadvantageous form of cross section of such passages as it offers
a greater frictional surface to the water and at the same time causes the water films

page_text: passing through these passages of long narrow rectangular cross section to flow at
unequal speeds.
The present invention provides a thoroughly effective means for overcoming the
disadvantage accruing from the increase of area in cross section of the passages and
the relative decrease of speed in the flow of the water resulting therefrom.
Instead of the usual webs forming the water passages in the wheel it is provided
according to this invention with a number of passages SS see Figure 1. starting
from the periphery of the inner circle, which passages not only may be made
parallel but can be made narrower at the periphery of the wheel so as to obtain a
gradually decreasing area and thereby cause the speed of the water jets to be
greater at the outlet than at the inlet. The passages formed on a common
disc may be regarded as curved tubes and therefore it is intended to call them
"jet tubes."
These "jet tubes" are arranged so as to form at the periphery of the inlet
a knife edge in order to allow free access thereto of the water.
From the inner periphery the passages become distinctly separated from each other
at a steadily increasing distance which is greatest at the outer periphery of the
wheel. Each of these "jet tubes" S S, delivers its water jet into the pressure
chamber D at the periphery of the wheel from which it flows into the delivery pipe
fixed to the pump in the usual manner.
In order to cut the delivered water in the chamber D off from the space in which
the wheel turns and consequently also from the suction space S₁ it is necessary to
provide the wheel with a closed rim such as that shown at K.
This rim K by means of facings d d provided thereon bears tightly against
corresponding facings on the casing so that the space D has no communication with
the space L. Similar facings d cut the suction chamber S₁ of the pump off
from the space L L between the wheel and casing. Other facings d³ ³
desired be arranged as shown so as to ensure the severance of all injurious
may
communication.
if
In the present arrangement the separate water jet tubes are caused to communi-
cate with the space D at the outer rim of the wheel through the rim K which
latter is cut through by the tubes S so as to form passages a a.
as shown in the drawing be cast to a common disc; at the part where the tubes
The jet tubes can
come close together, that is, towards the centre of the wheel, the tubes may be of
U form, or in other words, they may be open on one side and be provided with a
special cover F F for that part to permit of cleaning and of ready access generally
to the jet tubes.
A common covering disc could also be used in connection with tubes open entirely
along one side. In the latter case it would be comparatively easy to smooth the
tubes internally so as to secure the least possible friction of the water passing
through the tubes. As a modification instead of forming the tubes of a rectangular
section, they could be made of a circular section. If the tubes in this latter case
were required to be of the same diameter from end to end they could be
advantageously formed from gas piping which at the inlet end would be cut and
pressed together whilst at the outlet end they could be easily fitted into the 4
rim K.
The number of tubes required varies according to the quantity to be delivered by
the pump.
The greater the number of tubes the more regular will be the delivery into the
space D.
In the drawing four tubes are shown. In order to ensure a reasonable 5
section for the tubes in a pump of low capacity it is advantageous to adopt a less
number of tubes and even a single tube only might be used running in a spiral form
from the centre to the rim. In this case the wheel, having to run at great speed,
must be well balanced by adapting a corresponding false tube or other suitable
counterbalance.
In order to ensure the passage of the water without shock from the suction
chamber S¹ into the tubes a small introducing wheel or chamber as shown in
5

page_text: Figure 2, and used sometimes in turbines, can be applied in front of the wheel, this
has not been hitherto used in centrifugal pumps but as it does not affect the real
object of this invention in respect to its efficiency the said introducing wheel can be
omitted. As shown in the drawing at Figure 2. the introducing wheel or chamber
for the purpose of facilitating the flow of the water is of a conical form and dies
away in the plane of the pump wheel.
Figure 3. shows how the jet tubes run into the conical body of the pump wheel
and for this purpose, only the lower portion of the pump wheel is illustrated,
showing the upper part cut away to allow the construction of the water passages to
be clearly seen. When as is often the case the water inlet into the wheel is
arranged, in a similar manner to radial turbines, radially from the inner side and
without a leading in or introducing wheel or chamber, the form of the pump wheel
and also that of the jet tubes become much more simple which latter, in this case, are
only bent in a single direction and not in a double direction with respect to the
plane of the wheel.
The same arrangement of pump can be used not only for water but can also be
adapted for air as a fan or serve as an air compressor and in this case the
advantage of having overcome the difficulty in regard to the increasing area of
cross section in the ordinary centrifugal pump, will be of much greater
consequence.
The area of the jet tubes can be gradually lessened from the inlet to the
outlet which will ensure a high degree of compression for the air passing through
the pump.
Just as the jet tube pump is especially suited for high forcing pumps it is
clear that great advantage will be obtained by its adoption for fans and air
compressors.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is-
A jet tube centrifugal pump or fan for lifting and forcing liquids and compressing
air or gases consisting of the arrangement of pump wheel provided with one or
several jet tubes and having a rim which cuts off communication between the
discharging or compressing chamber of the pump and the internal spaces and which
rim is cut through by the jet tubes in such a manner that the fluid from the latter
is forced or discharged into the compression or delivery chamber substantially as
herein shown and described.
Dated this 19th day of December 1892
H. LUDEWIG,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.