|Title of Invention||
|Abstract||There is disclosed a pump impeller for a pump meant for pumping sewage water, wherein said impeller has one or more vanes (2) with leading edges (3) swept backwards towards the periphery, such that the sweep angle ( ) of the leading edge varies between 40 and 55 degrees at the hub connection (4) and between 60 and 75 degrees at the periphery (5).|
|Full Text||The invention concerns a pump impeller and more precisely a pump impeller for
centrifugal-or half axial pumps for pumping of fluids, mainly sewage water.
In literature there are lot of types of pumps and pump impellers for this purpose
described, all however having certain disadvantages. Above all this concerns
problems with clogging and low efficiency.
Sewage water contains a lot of different types of pollutants, the amount and structure
of which depend on the season and type of area from which the water emanates. In
cities plastic material, hygiene articles, textile etc are common, while industrial areas
may produce wearing particles. Experience shows that the worst problems are rags
and the like which stick to the leading edges of the vanes and become wound
around the impeller hub. Such incidents cause frequent service intervals and a
In agriculture and pulp industry different kinds of special pumps are used, which
should manage straw, grass, leaves and other types of organic material. For this
purpose the leading edges of the vanes are swept backwards in order to cause the
pollutants to be fed outwards to the periphery instead of getting stuck to the edges.
Different types of disintegration means are often used for cutting the material and
making the flow more easy. Examples are shown in SE-435 952, SE-375 831 and
US-4 347 035.
As pollutants in sewage water are of other types more difficult to master and as the
operation times for sewage water pumps normally are much longer, the above
mentioned special pumps do not fullfil the requirements when pumping sewage
water, neither from a reliability nor from an efficiency point of view.
A sewage water pump quite often operates up to 12 hours a day which means
that the energy consumption depends a lot on the total efficiency of the pump.
Tests have proven that it is possible to improve efficiency by up to 50% for a
sewage pump according to the invention as compared with known sewage
pumps. As the life cycle cost for an electrically driven pump normally is totally
dominated by the energy cost (c:a 80%), it is evident that such a dramatic
increase will be extremely important.
In literature the designs of the pump impellers are described very generally,
especially as regards the sweep of the leading edges. An unambiguous
definition of said sweep does not exist.
Tests have shown that the design of the sweep angle distribution on the leading
edges is very important in order to obtain the necessary self cleaning ability of
the pump impeller. The nature of the pollutants also calls for different sweep
angles in order to provide a good function.
Literature does not give any information about what is needed in order to obtain
a gliding transport of pollutants outwards in a radial direction along the leading
edges of the vanes. What is mentioned is in general that the edges shall be
obtuse-angles, swept backwards, etc. See SE-435 952.
When smaller pollutants such as grass and other organic material are pumped,
relatively small angles may be sufficient in order to obtain the radial transport
and also to disintegrate the pollutants in the slot between pump impeller nd the
surrounding housing. In practice, disintegration is obtained by the particles being
cut through contact with the impeller and the housing when the former rotates
having a periphery velocity of 10 to 25 m/s. This cutting process is improved by
the surfaces being provided with cutting devices, slots or the like. Compare SE-
435 952. Such pumps are used for transport of pulp, manure, etc.
When designing a pump impeller having vane leading edges swept
backwards in order to obtain a self cleaning, a conflict arises
between the distribution of the sweep angle, performance and
other design parameters. In general it is true than an increased
sweep angle means a less risk for clogging, but at the same time
the efficiency decreases.
The invention brings about a possibility to design the leading edge
of the vane in an optimum way as regards obtaining of the
different functions and qualities for reliable and economic pumping
of sewage water containing pollutants such as rags, fibres, etc.
Accordingly, the present invention provides a pump impeller of a
centrifugal- or half axial type to be used in a pump for pumping
sewage water, characterized in that the impeller is provided with
one or several vanes, the leading edges of which being swept
backwards towards the periphery, the exact sweep angle, defined
in every point on the leading edge as the angle between the
normal to the leading edge and the relative velocity of the pumped
medium at that point, has a value within an area limited by the
interval 40-55 degrees at the connection of the leading edge to the
hub and 60-75 degrees at the periphery and having a mainly even
Preferably, the angle between the normal to the leading edge and
the relative velocity of the pumped medium at each point on the
leading edge, has a value within an area limited by the interval 45-
55 degrees at the connection of the leading edge to the hub and
62-72 degrees at the periphery and having a mainly even variation
In another embodiment of the invention, the leading edge of the vane is located
essentially in a plane perpendicular to the impeller shaft where the absolute
velocity of the pumped medium is mainly axial. The connection of the leading
edge to the hub may be located adjacent the end of said hub.
The first component, shown in Fig 5, quantifies a band of the sweep angle
distribution which admits a good function and efficiency. The range is connected
to size, periphery velocity and material friction. The independent variable that is
used to describe this, here called normalized radius, is defined as follows :
Normalized radius = (r — r1) / (r2 — r1) Equation 1
where r1 is the radius of the hub connection, r2 out to the periphery of the
leading edge and where the radius according to a cylinder coordinate system
having origo in the center of the impeller shaft, defines the shortest distance
between the actual point and a point on the extension of the impeller shaft.
The basics in this part of the invention being that the sweep angle of the leading
edge is increased considerably outwards, from a minimum of 40 degrees at the
hub connection to a minimum of 55 degrees at the periphery. The upper limit,
60-75 degrees, defines a border line above which the frequency as well as the
reliability are influenced in a negative way.
The second part of the invention concerns a special embodiment which has the
very advantageous ability that the sweep angle will be almost independent of the
operation point, i.e. different flows and heads, which also corresponds with
different velocity triangles (C,U, W).
The definition of the sweep angle will be described below with reference to the
Fig 1 shows a three dimensional view of a pump impeller according to the
invention, Fig 2 a radial cut through a schematically drawn pump according to
the invention, while Fig 3 shows a schematic axial view of the inlet of the
impeller. Fig 4 shows an enlargement of an area on the leading edge of an
impeller vane, while Fig 5 is a diagram showing the relation between the back
sweep of the leading edge and a standard radius according to the invention.
In the drawings, 1 stands for an impeller hub, 2 a vane having a leading edge 3.
4 stands for the connection of the leading edge to the hub and 5 the periphery of
the edge. 6 stands for the normal to the edge in a certain point. 7 stands for the
wall of the pump housing, 8 the end of the hub, 9 the direction of rotation, a
sweep angle, WR the projected relative velocity, the velocity of the fluid in a corotating
coordinate system, and z the impeller shaft direction.
In order to design a desired pump impeller geometry in an optimum way, a
correct definition of said sweep angle is a provision. The exact sweep angle a is
in general a function of the geometry of the leading edge in a meridional view (r -
z) as well as in an axial view (r - ?), see Figs 2 and 3.
The exact definition will be a function of the curve that describes the form of the
leading edge 3 and the local relative velocity W at that curve. This can be
mathematically stated in the following way :
With traditional designations of the velocity triangle (C, U, W) the relative velocity W
(r)is a function of the position vector r in a co-rotating cylindric coordinate system.
In the normal way the relative velocity W (r,?,z ) can also be explained in its
components (Wr, W?, Wz ).
The three dimensional curve along the leading edge 3 can in a corresponding corotating
coordinate system be described as a function R which depends on the
position vector r, i. e. R = R (r, ?, z ).
An infinitesimal vector which is in parallel with the leading edge in every point can be
defined as dR. From the definition of scalar product an expression is obtained for the
sweep angle a, defined as the angle between the normal to dR and Wr, where Wr is
defined as the orthogonal projection of WR onto the direction of W at zero
incidence. This means that WR and W are equal at or close to the nominal
operating point, sometimes referred to the best efficiency point.
a = p/2- arccos[(dR.WR)/(|dR | -|Wr|)] Equation 2
At the nominal operation point of the pump impeller the following is generally valid:
W= Wr. i. e. the current angle bn and the vane angle are equal, where:
bN = arccos (W?/ I W |) Equation 3
if it is assumed that the absolute inlet velocity does not have any circumferencial
component, i. e. We equals with the periphery velocity of the impeller.
By using these definitions and assumptions it will be shown below that µ is
independent of the flow. The conditions are that the leading edge lies in a
plane that is essentially perpendicular to the direction z of the impeller shaft and that
the leading edge is located where the absolute inlet velocity is essentially axial,
which means that the radial component of Wr is near zero. For the same reasons
the circumferencial component of Wr, i. e in ? direction, equals with the peripheral
velocity of the impeller and is independent of the flow. The axial component of Wr
gives a neglectable contribution to a as dRz is zero according to the above . This
follows from the definition of scalar product. Accordingly the flow dependant variable
I Wr I does not influence a in Equation 2, since the numerator as well as the
denominator change proportionally.
According to a preferred embodiment of the invention the leading edge of the vane is
located in a plane essentially perpendicular to the impeller shaft. With the knowledge
that a pump very often operates within a broad field as concerns volume flow and
head, the preferred embodiment admits that the self cleaning ability can be kept
independant of different operation conditions.
The third part of the invention concerns a preferred embodiment where the
connection of the leading edge to the hub is located adjacent the end 8 of the hub 1,
i. e. the latter has no central protruding tip. This diminishes the risk for pollutants
being wound around the central part of the impeller.
WE CLAIM :
1. A pump impeller of a centrifugal- or half axial type to be used in a pump
for pumping sewage water, characterized in that the impeller is provided with
one or several vanes (2), the leading edges (3) of which being swept backwards
towards the periphery, the exact sweep angle (a), defined in every point on the
leading edge as the angle between the normal (6) to the leading edge and the
projected relative velocity (WR) of the pumped medium at that point, has a value
within an area limited by the interval 40-55 degrees at the connection (4) of the
leading edge to the hub (1) and 60-75 degrees at the periphery (5) and having a
mainly even variation therebetween.
2. The pump impeller as claimed in claim 1, wherein the angle (a) between
the normal (6) to the leading edge (3) and the projected relative velocity (WR) of
the pumped medium at each point on the leading edge, has a value within an
area limited by the interval 45-55 degrees at the connection (4) of the leading
edge to the hub (1) and 62-72 degrees at the periphery (5) and having a mainly
even variation therebetween.
3. The pump impeller as claimed in claim 1, wherein the leading edge (3) of
the vane (2) is located essentially in a plane perpendicular to the impeller shaft
(z) where the absolute velocity of the pumped medium is mainly axial.
4. The pump impeller as claimed in claim 1, wherein the connection (4) of
the leading edge (3) to the hub (1) is located adjacent the end (8) of said hub.
5. A pump impeller of a centrifugal- or half axial type, substantially as
herein described, particularly with reference to and as illustrated in the
6. A pump for pumping sewage water incorporating a pump impeller of a
centrifugal- or half axial type as claimed in claims 1 to 5.
There is disclosed a pump impeller for a pump meant for pumping
sewage water, wherein said impeller has one or more vanes (2) with leading
edges (3) swept backwards towards the periphery, such that the sweep angle
(a) of the leading edge varies between 40 and 55 degrees at the hub
connection (4) and between 60 and 75 degrees at the periphery (5).
|Indian Patent Application Number||1667/CAL/1998|
|PG Journal Number||43/2007|
|Date of Filing||17-Sep-1998|
|Name of Patentee||ITT MANUFACTURING ENTERPRISES INC.|
|Applicant Address||1105, NORTH MARKET STREET, WILMINGTON, DELAWARE 19801|
|PCT International Classification Number||F 04 D 29/38, 29/24|
|PCT International Application Number||N/A|
|PCT International Filing date|