EP1325232B1 - Centrifugal wheel pump - Google Patents

Abstract

The invention relates to a centrifugal wheel pump comprising a bearing tube (18) which contains an axial bore hole (12) for receiving a pump shaft, and blades (36, 36n) for guiding a liquid flow between a suction area and a pressure area. Said blades (36, 36n), formed in an even number, are provided on the bearing tube (18), emanate therefrom and are arranged at an equal distance from each other. Among said blades (36) which are disposed in a spiral or spindle shaped manner around the bearing tube (18), every second blade is guided along the outside edge (38n) of two shorter neighbouring blades (36n), in the direction of the longitudinal axis (A) of the bearing tube (18). Furthermore, the outside edges (38) next to the input side of the long blades (36) extend at an inlet angle with the straight diameter of the bearing tube (18), said angle being adapted to each respective working point.

Description

The invention relates to an impeller for a centrifugal pump according to the preamble of claim 1.

Such an impeller can be found in EP-A-0 359 445. Around the one end of the tapered shaft are arranged six strip-like blades for guiding a liquid flow. Three of these blades are connected with their almost radially to the axis of rotation extending end portions of the tapered shaft end and limit entry areas. Outside this, the other three blades start lesser in length and carry a funnel-shaped cover connected to an impeller ring. This race is provided with a circumferential slot opening which is divided from the outlet side end edges of the six blades into six through holes as end portions of channels extending between the blades.

The blade edges extend in a part of the impeller in a cylinder contour and then determine an inclined to the impeller ring surface, which is covered by a conical vortex wall.

A centrifugal pump with on the front stepped end of an inner shaft provided with an axial bore impeller DE 41 08 257 C2 of the Applicant can be seen. This impeller rotates in a - with a bearing support housing with the interposition of housing cover and seals screwed - volute. The housing cover contains a slide bearing.

To improve the absorbency of radial centrifugal pumps helical axial Vorschaltläufer with its own delivery height - so-called. Inducer - are used, which increase the static pressure in the suction of the subsequent radial wheel. With the current Inducers you can achieve a substantial reduction - up to 50% - of the so-called NPSH value ("Net Positive Suction Head") from the efficiency peak to the minimum delivery rate. To evaluate the suction behavior, the so-called NPSH3% value has prevailed, which can be measured relatively easily for different volume flows. In general, this NPSH3% value in pump construction describes the net energy level in the inlet cross-section of the pump, at which the delivery head of the pump drops by 3%. The net energy level is the absolute energy level minus the evaporation pressure level. In this case, the evaporation pressure level H _D = p _D / is to be calculated with the vapor pressure p _D , which belongs to the temperature prevailing in the inlet cross-section of the pump. As with the specific holding energy, the NPSH value also distinguishes between a NPSHA value (existing NPSH) and a pump-specific value NPSHR (required NPSH).

In attempts to improve the absorbency, one quickly came to limits from which there was no further reduction in NPSH values or other characteristics of the pump were significantly deteriorated. Good NPSH values can currently only be achieved by using an Inducers. However, its use leads to higher manufacturing costs, a deterioration in efficiency, increased noise emissions and also requires a special intake manifold, also often a modified drive shaft.

In consideration of this prior art, the inventor has set itself the task of developing an impeller for radial centrifugal pumps with significantly better NPSH values, without worsening the other performance data of the centrifugal pump. In addition, the rigidity and strength of the construction are to be increased and lower power loss due to the gap flow at the impeller blades arise. This impeller should be with the lowest possible manufacturing costs - can be realized technically well.

It has been shown that the NPSH3% value of the pump is significantly influenced by the impeller shape and conventional impellers for radial centrifugal pumps with usually five or seven geometrically identical blades lead to no favorable result. The new impeller shape is characterized in particular by the fact that it has an even number of blades - usually four, six or eight blades -, with every second blade is extended spiraling far in the axial direction forward.

According to a further feature of the invention, the inlet-side outer edges of the long blades at an angle - to a diameter straight line of the bearing tube - arranged, which is adapted to the respective operating point. The course of these entry edges is pulled obliquely backwards. It has proven to be favorable to let the inlet-side outer edges of the short blades extend at an entry angle to a straight line of the bearing tube and to adapt the entry angle of the short blades to the local flow conditions.

According to the invention, the entry angles of the long blades are greater than the angles between the direction of rotation of the blades of the inflow in the relative system.

On the other hand, the exit angles should be the same for all blades; the outlet-side end edges of the blades close with an axis parallel an acute angle between 10 ° and 20 ° - preferably about 15 ° - a.

It is within the scope of the invention that those outlet-side end edges of the blades are to connect at one end to a radial wall of the bearing tube and at the other end to an impeller ring approximately parallel to the radial wall. In addition, the impeller ring or a cover disc according to the invention extends from the end edges of the blades to the outer edges of the short blades on the inlet side.

It is also important that the impeller ring should project slightly beyond the outer edges of the short blades. According to another feature, the impeller ring has a part-circular curvature in a longitudinal direction, which merges into an approximately axially parallel region ending at a front edge; the adjoining the front edge region of the impeller ring should contain a gradation.

It is also advantageous that the outer surface of the impeller ring with the inner surface of a spaced housing wall bounds a sealing gap; the cover disk or the impeller ring extends from the impeller outlet to just above the leading edge of the short blades, where that suction-side sealing gap is located.

• deutlich bessere NPSH-Werte gegenüber herkömmlichen Radiallaufrädern;
• geringere Leistungsverluste infolge der Spaltströmung an den Laufradschaufeln;
• keine wesentliche Verschlechterung der sonstigen Leistungsdaten;
• keine wesentliche Erhöhung der Herstellungskosten gegenüber einem normalen Laufrad;
• niedrigere Herstellungskosten als die eines normalen Laufrades mit Inducer;
• verminderte Geräuschemission gegenüber Laufrädern mit Inducer;
• kürzere axiale Abmessungen als ein normales Laufrad mit Inducer.

In particular, by the impeller ring or the cover plate, the rigidity and strength of the construction is increased. In addition, the shape of the impeller according to the invention still has the following advantages:

• significantly better NPSH values compared to conventional radial impellers;
• lower power losses due to the gap flow on the impeller blades;
• no significant deterioration of other performance data;
• no significant increase in manufacturing costs compared to a normal impeller;
• lower manufacturing costs than a normal impeller with Inducer;
• reduced noise emission compared to impellers with inducer;
• shorter axial dimensions than a normal impeller with inducer.

Fig. 1:

eine Schrägsicht auf ein Laufrad mit Laufradring für eine Kreiselpumpe;

Fig. 2, 4:

jeweils einen Längsschnitt durch das Laufrad in dessen Längsachse nach Linie II - II der Fig. 1 bzw. Linie IV-IV der Fig. 3;

Fig. 3:

die Frontsicht auf das Laufrad;

Fig. 5:

eine Schrägsicht auf das Laufrad ohne Laufradring;

Fig. 6:

den vergrößerten Längsschnitt des Laufradringes mit einem zugeordneten Gehäuseabschnitt;

Fig. 7:

eine Skizze zur Darstellung eines Eintrittswinkels.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing; this shows in

Fig. 1:

an oblique view of an impeller with impeller ring for a centrifugal pump;

2, 4:

in each case a longitudinal section through the impeller in the longitudinal axis along line II - II of Figure 1 and line IV-IV of Fig. 3;

3:

the front view on the wheel;

Fig. 5:

an oblique view of the impeller without impeller ring;

Fig. 6:

the enlarged longitudinal section of the impeller ring with an associated housing portion;

Fig. 7:

a sketch to illustrate an entrance angle.

In an impeller 10 for a centrifugal pump otherwise not shown for clarity is on a - equipped in the longitudinal axis A with a through hole 12 - bearing tube 18 of length a of about 315 mm and the outer diameter d of for example 90 mm rearward a radial wall 20 molded. The through hole 12 has, between two end portions 14, 14 _{e of} the diameter d ₁ of about 50 mm, a central portion 15 of larger diameter d ₂ of about 60 mm, which is located at the inlet side for the liquid - left in Fig. 2 - Shortened shorter end portion 14 by means of a conical shoulder region 16. This end section 14 connects to an annular end face 17 of the bearing tube 18.

The impeller 10 is rotatably mounted in a housing of the centrifugal pump, not shown, between a suction and a pressure chamber for conveying a liquid.

The inner contour K of the radial wall 20 is determined in the longitudinal section of Fig. 2 between the outer tube surface 19 of the bearing tube 18 and an annular outer edge 22 of the radial wall 20 of a partial arc. On the other hand, an iw radial longitudinal section contour Q forms a back surface 24 of the radial wall 20, from which a coaxial annular wall 26 of small height h of 20 mm is formed. The distance z of the back surface 24 of the adjacent end wall 17 _{e of} the bearing tube 18 - and thus the free rear Kraglänge - here measures about 50 mm.

At an axial distance i (here 85 mm) from the outer edge 22 of the radial wall 20 extends an annular edge 28 of an impeller ring or cover 30 of width b of about 50 mm and a diameter e of 375 mm, which corresponds to that of the outer edge 22 and something is greater than four times the outer diameter d of the bearing tube 18 and that distance i between the radial wall 20 and impeller ring 30th

The longitudinal section of the impeller ring 30 is formed by the annular edge 28 from a partial circular arc section K ₁ , which passes achswärts in a parallel to the longitudinal axis A wall portion; this ends at a longitudinally stepped by a rotation of the impeller ring 30 at 31 stepped - turn annular - front edge 32. The diameter e ₁ of here 290 mm corresponds to about three quarters of the mentioned diameter e.

In an area bounded by the radial wall 20 and the impeller ring 30 intermediate space 34 is an even number of - in its longitudinal extent helically shaped - blades 36, 36 arranged _n ; Each second blade 36 is brought with its outer edge 38 - spirally - close to the inlet-side end face 17 of the bearing tube 18. Between each two of these long blades 36 extends a short blade 36 _n whose outer edge 38 _{n is} located within the impeller ring 30. Extending side end edges 40, 40 _{n of} the blades 36, 36 _n extend between the annular outer edge 22 of the radial wall 20 and the parallel annular edge 28 of the impeller ring 30. They run at an acute angle w of about 15 ° to an axis-parallel A ₁ . This outlet-side inclination angle w for all blades 36, 36 _n or end edges 40, 40 _n of the same size, whereas the so-called entry angle p and p ₁ at the inlet-side outer edges 38 and 38 _n to diameter straight lines D are different. the entry angles y of the long blades 36 are adapted to the respective operating point (FIG. 5).

The blades 36, 36 _n are formed on both the bearing tube 18 and its radial wall 20 and the impeller ring 30, and the long blades 36 protrude - as described - in the axial direction of the front edge 32 of the impeller ring 30. There is their Side edge 38 curved according to that helix, as Fig. 5 illustrates especially.

6, the impeller ring 30 is associated with a portion of a housing wall 42, which is provided on its inner surface 44 along a longitudinal - with a gradation 31 of the impeller ring 30 opposite - inner step 46. The latter ends at an outer step 48 which extends at a distance n parallel to the front edge 32 of the impeller ring 30. So arises between this and the housing wall 42 a Sealing gap 50 a gap length c of about 15 to 20 mm and a gap width q of 0.3 to 0.5 mm here.

In the section of a long blade 36 according to FIG. 7, its leading edge is denoted by 37 and the impeller rotation direction by x, the inflow direction in the absolute system by y. The entry angles s of the long blades 36 are adapted to the operating point such that they are 4 ° to 10 ° greater than the entry angles t of the inflow direction y ₁ in the relative system.

The inlet angles s _{1 of} the short blades 36 _n are selected so that they correspond to the local inflow angles of the flow in the region of the operating point of the pump and are adapted to the local flow conditions.

Claims (12)

1. Impeller for a centrifugal pump with a central shank, provided with an even number of blades (36, 36_n) for conducting a stream of liquid between a suction area and a pressure area, wherein blades (36, 36_n) of at least two different lengths are provided and the outlet side end edges (40, 40_n) of the blades (36, 36_n) at one end adjoin a radial wall (20) of the impeller (10) and at the other end an impeller ring (30) approximately parallel to the radial wall (20),
   characterised in that every other of the blades (36, 36_n) moulded on to the shank constructed as a bearing tube (18) with an axial bore (12) to accommodate a pump shaft is conducted beyond the outer edge (38_n) of two adjacent shorter blades (36_n) in the direction of the longitudinal axis (A) of the bearing tube (18) and the impeller ring (30) has a partially circular curve (K₁) in longitudinal section, which passes into an approximately axially parallel area ending at a front edge (32).
2. Impeller according to claim 1, characterised in that the impeller ring (30) extends from the end edges (40, 40_n) of the blades (36, 36_n) as far as the entry-side outer edges (38_n) of the short blades (36_n).
3. Impeller according to claim 1 or 2, characterised in that the impeller ring (30) projects minimally above the outer edges (38_n) of the short blades (36_n).
4. Impeller according to claim 1, characterised in that the area of the impeller ring (30) adjoining the front edge (32) contains a gradation (31).
5. Impeller according to one of claims 1 to 4, characterised in that the outer face of the impeller ring (30) limits a sealed gap (50) with the inner face (44) of a housing wall (42) opposite at a distance (g).
6. Impeller according to one of claims 1 to 3, characterised in that the blades (36, 36_n) are conducted round the bearing tube (18) spirally or like a spindle.
7. Impeller according to one of claims 1 to 3, characterised in that the inlet-side outer edges (38) of the long blades (36) run at an entry angle (s) to a straight line diameter (D) of the bearing tube (18).
8. Impeller according to claim 1 to 7, characterised in that the inlet-side outer edges (38_n) of the short blades (36_n) run at an entry angle (p₁) to a straight line diameter (D) of the bearing tube (18).
9. Impeller according to claim 7 or 8, characterised in that the entry angles (s) of the long blades, limited in each case by the direction of rotation (x) of the impeller (10) and the section of the long blades (36), are larger than the angles (t) between the direction of rotation (x) of the blades of* the inflow in the relative system and the angle is matched to the respective operating point (Fig. 7).
10. Impeller according to one of claims 1 to 8, characterised in that the entry angle (p₁), limited in each case by the direction of rotation (x) of the impeller (10) and the section of the short blades (36_n), is adapted to the local flow circumstances.
11. Impeller according to one of claims 1 to 10, characterised in that the outlet-side end edges (40, 40_n) of the blades (36, 36_n) enclose an acute angle (w) with a line parallel to the axis (A₁).
12. Impeller according to claim 11, characterised by an angle (w) of between 10° and 20°, preferably approximately 15°.

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