HK1019782B - Pump - Google Patents

Description

Pump and method of operating the same

The present invention relates to a centrifugal or semi-axial pump for pumping fluids, mainly sewage.

There are numerous types of pumps and pump impellers described in the literature for this purpose, but all suffer from certain disadvantages. Most importantly, both involve clogging and inefficiency problems.

Sewage contains many types of sewage, the amount and composition of which depend on the type of area where the sewage is discharged and the season of discharge. In urban areas, plastics, hygiene articles, textiles, etc. are most prevalent; whereas in industrial areas wear resistant particles may be discharged. Experience has shown that the worst problem is rags and the like, sticking to the leading edge of the blade and thereby wrapping around the hub of the impeller. Such events result in frequent maintenance and reduced efficiency of use.

In agriculture and the pulp industry, special pumps of various types are used, which should be able to handle straw, grass, leaves and other various organic materials. To this end, the leading edge of the blade is swept back so that dirt is transported outwardly to the outer periphery of the blade without adhering to the leading edge. Various types of shredding methods are used to cut these materials so that they flow more smoothly. Examples are listed in patent documents SE-435952, SE-375831 and US-4347035.

Since the sewage in the sewage contains other types of sewage that are more difficult to treat and since the operating time of sewage pumps is generally much longer, the above-mentioned special pumps do not meet the requirements for pumping sewage, both from a reliability point of view and from an efficiency point of view.

A sewage pump is often operated for 12 hours a day, which means that the energy consumption is very much dependent on the total efficiency of the pump.

Tests prove that the efficiency of the sewage pump is improved by 50 percent compared with the original sewage pump. Since the lifetime cost of an electrically driven pump is generally governed by the total energy consumption cost (C: a 80%), it is clear that the above-noted dramatic efficiency improvement is of paramount importance.

The description of pump impeller design in the literature is extremely generalized, particularly with respect to the problem of blade leading edge sweep. There is no clear definition of the sweep.

Tests have shown that the design of the sweep angle distribution over the leading edge is very important in order to obtain the self-cleaning capability of the pump impeller. The characteristics of the various contaminants also require different sweep angles to ensure good pump performance.

Nothing is given in the literature to tell how to cause dirt to slide and be transported radially outwardly along the leading edge of the blade. It is noted that general statements such as leading edge should be obtuse, swept back, etc. See patent document SE-435952.

When pumping smaller contaminants such as grass and other organic matter, a smaller leading edge sweep angle may be sufficient to cause radial transport of the contaminants and be shredded in the groove between the pump impeller and the pump body. In practice, this shredding is achieved by the shredded waste coming into contact with the impeller and the pump body when the impeller rotates at a peripheral speed of 10 to 25 m/s. This shredding process can be improved by providing cutting means such as slots or the like.

Various notches and cutting devices are described in patent documents SE-435952 and SE-375831. They have in common that the vanes are located behind the shoulder. This means that there is a significant loss of efficiency over pumps having a high efficiency with smooth pump internal profiles used when pumping fresh water.

In one embodiment shown in SE-435952, the shoulder has an axial opening behind it. The theory is as follows: dirt will be carried outwardly by the blades with a sharply swept, leading edge towards the opening. This embodiment is described generally and is not suitable for pumping heavy sewage from sewage.

A solution is described in SE-375831, which uses the opposite principle to send the dirt away from the trough towards the centre. This fact, together with the aforementioned shoulder, makes it impossible to feed dirt into the groove.

As indicated above, this is the case with a sharp sweep of the leading edge of the blade face so that dirt can be carried towards and into the groove of the outer periphery. If this is not done, a serious shutdown immediately occurs. Pump impellers of this type are described in patent documents SE-9704222-0 and SE-9704223-8. There is also a problem of dirt sticking to the outer periphery of the leading edge and blocking the slot as it slides outwardly and reaches the slot between the vane and the inner wall of the pump body.

DE-614426 discloses a device for solving this problem, which does not have the aforementioned shoulder. The pump is a centrifugal pump having a sharp junction between the axial inlet and the radial flow path. The outer periphery of the leading edge is located downstream of the connection in the radial flow path.

It is further pointed out that the device is provided with a three-dimensional opening in front of the front edge, whose height is gradually reduced until it forms a blade, followed by a spiral groove, whose cross-section is triangular and has sharp corners and which widens gradually towards the outer periphery. Furthermore, it is said that the basic principle of such solutions is that the replaceable cutting device will shred the dirt. Should this fail, for example if the cutting device becomes dull, the notch of reduced height will squeeze dirt and jam where space is at a minimum, i.e. in the region of the cutting device.

The above patent thus describes a solution in which, in some cases, a self-cleaning capacity is expected, but this solution entails important drawbacks concerning efficiency, wear resistance and longevity. Furthermore, no detailed description is given of the very important condition of the leading edge of the blade, and therefore of no significance in trying to pump sewage using the device.

The present invention relates to a device for pumping sewage which eliminates the drawbacks of the known solutions described above.

The invention is explained in more detail below with reference to the drawings.

FIG. 1 is a three-dimensional view of a pump body. Fig. 2 is a schematic view of a radial cross-section of the pump of the present invention. Fig. 3 is an axial schematic view of an end face of the pump body. Figure 4 is a partial view of the pump body cut through a groove in an arc.

In the figure, 1 denotes a centrifugal pump body having a cylindrical inlet 2. 3 denotes a pump impeller provided with a cylindrical hub 4 and blades 5. 6 denotes the vane leading edge, 7 denotes the pump body wall, 8 denotes the groove in the wall, 9 denotes the direction of rotation and Z denotes the axis of rotation. 10 and 11 denote the sides of the groove 8, 12 denotes one of the faces in the groove, 13 denotes the groove bottom and h denotes the groove depth.

An important principle of the present invention is: the dirt in the pumped liquid is not shredded by the shredding means. Instead, a more robust structure is used to carry the dirt outwardly to the outer periphery. This means that the machine life can be greatly increased, especially when pumping wear resistant particles. The design is also stable, which means that the wear occurring on the pump body wall is reduced.

The invention relates to a pump having a pump impeller 3 of a particular type, the leading edges 6 of the vanes 5 of which are located upstream of the pump body, i.e. in the cylindrical inlet 2, and which lie in a plane perpendicular to the axis of rotation Z of said impeller.

According to the invention, one or several openings or grooves 8 are provided in the wall of the pump body, which grooves open out on the surface 7 towards the impeller, i.e. from the essentially cylindrical inlet 2 to the inner surface of the centrifugal pump body, and have a shape defined below. One or more grooves 8 are associated with one or more upper vane leading edges 6 so that the dirt is conveyed in the direction of the outlet of the pump.

To ensure that it can be pumped and to determine its other advantages compared to the prior art, a special trajectory and geometry are designed for the tank 8.

In fig. 4, a cylindrical cut-away shape of the groove is shown, characterized in that the groove is connected smoothly at the edge with the pump body surface 7 to 10, where the impeller passes. In said cylindrical section, the other end 11 of the groove, with respect to the pump body wall, is a mainly rectangular surface 12 which transforms continuously into a substantially oval bottom 13, the oval being characterized by a major axis which is at least twice as long as the groove depth. This bottom arc is important since wear resistant particles will be transported away from the surface 7 by the Secondary flow (Secondary Current) and the wear on said surface will be greatly reduced.

Between the smooth junction 10 of the groove with the surface 7 and the groove bottom 13 is a surface 14 with a mainly linear transition. The transition surface is at an angle γ of between 2 and 25 degrees to the surface 7, the angle γ being defined as:

γ＝arctan(ΔZ/(r·Δθ))

wherein Δ Z is the axial distance and r, Δ θ is the tangential elongation

FIG. 3 is the sweep angle β of the groove 8, wherein

Where dr, d θ and dz are infinitesimal displacements along the slot edges.

According to the invention, the sweep angle β is between 10 and 45 degrees along its entire trajectory in order to obtain optimum results.

By means of the invention, several advantages are obtained compared with the solutions known hitherto. The following are given separately as descriptions:

that particular permanent or replaceable shredding device is eliminated because the feeding action removes the dirt and carries it away.

The sweep angle 8 acts as a groove seal which brings about a direct efficiency increase due to the reduction of leakage through the groove.

The wear of the surfaces adjacent to the grooves is reduced, since wear resistant particles are carried away from this area after passing through the grooves. In this way, good efficiency is maintained also when pumping sewage containing wear resistant particles.

A long life is obtained because the wear resistant particles in the pumped medium cause a kind of wear which keeps the parts in their original shape. This means that good performance is maintained also after a certain degree of wear has occurred.

This device is suitable for a pump impeller having an optimal image from a performance point of view, since the trajectory of the groove 8 is transformed from axial to radial.

Claims (4)

1. A centrifugal or semi-axial flow pump for pumping contaminated water, the pump comprising: a pump body (1) having a cylindrical inlet (2) and an impeller (3) comprising a central hub (4) and one or more vanes (5), the vanes (5) having swept-back leading edges (6) which lie in said inlet (2) in a plane which is predominantly perpendicular to the impeller axis (Z), one or more feed channels (8) being provided in the wall of the pump body (1), i.e. on the face (7) opposite said vanes (5), which channels are located upstream of the region of said leading edges and whose trajectory is swept in the direction of rotation of the impeller from the inlet to the outlet of the pump, characterized in that,

as seen from the circular arc cut (B-B) made to the groove (8), the groove edge, through which the impeller (3) passes, is smoothly connected to the pump body surface (7), the angle (γ) between the inclined portion (14) of the groove and the pump body surface (7) being defined as:

γ ═ arctan (Δ Z/(r · Δ θ)), where γ is chosen between 2 and 25 degrees, Δ Z is the axial displacement, and r · Δ θ is the tangential elongation.

2. The pump of claim 1, wherein:

from the circular-arc cut (B-B) made to the groove (8), the opposite side of the groove (8) is described as a side (12) mainly orthogonal, which transforms continuously into an elliptical bottom (13).

3. The pump of claim 2,

said bottom (13) of the groove (8) is shaped as an ellipse, the length of the transverse axis of which is at least twice the groove depth (h).

4. A pump according to claim 1, characterized in that the sweep angle (β) at the edge of the feed groove, i.e. the angle between the edge of the groove (8) and the arc of a circle centered on the axis of the impeller,

the values are chosen between 10 and 45 degrees along the entire trajectory, where dr, d θ and dz are infinitesimal displacements along the groove edges.