IMPELLER FOR WASTEWATER PUMP

Description

[0001] The invention relates to an impeller for centrifugal pumps with at least one blade for conveying media containing solids.

[0002] Various impellers can be used in centrifugal pumps for conveying media containing solids, such as channel impellers, free-flow impellers, or single-blade impellers. Channel impellers are open or closed impellers with a reduced number of blades. One, two, or three blades in radial or semi-axial impellers have proven effective.

[0003] Free-flow pumps are also used to pump media containing solids. These pumps are also known as vortex pumps, and their pumping capacity is transferred to the fluid by a rotating, bladed disc, the so-called free-flow impeller.

[0004] Semi-open impellers are also used in wastewater systems.

[0005] The blade shape plays a crucial role in impeller design. The design of the leading edge is particularly important. In wastewater pumps, the leading edge frequently becomes coated with fibers present in the pumped medium. These fibers are often not carried away from the impeller leading edge because the flow resistance on the suction and discharge sides creates a balance between the respective resistance forces. If fibers accumulate at the leading edge, more fibers can accumulate, leading to the formation of larger deposits. This behavior is particularly pronounced when high particle clearance is required. Particle clearance is an important parameter for characterizing the operational capability of wastewater pumps.The ball passage is also referred to as the free, unconstricted impeller passage and describes the largest permissible diameter of the solids to ensure a blockage-free passage.

[0006] The large flow cross-sections necessary for sufficient ball passage promote the formation of blockages. Particularly at partial load, for example with low flow rates, large flow cross-sections lead to dead zones. These dead zones cause blockages. Such blockages frequently occur on the blades, especially at the leading edges, particularly when a large ball passage is required.

[0007] In single-blade pumps, such blockages necessitate higher power output to operate the centrifugal pump. In multi-blade pumps, blockages can also lead to asymmetrical flow in the channels. Such asymmetrical flows affect not only the required power output but also the delivered volume flow rate and the delivery head.

[0008] DE 40 15 331 A1 describes an impeller with only one blade. The single-blade impeller, manufactured by a casting process, forms a channel between a front cover plate and a rear support plate. The cross-section of this channel decreases from the inlet to the outlet. For the first 180° of rotation, the suction side forms a semicircle concentric to the axis of rotation. The single-blade impeller is designed to prevent cavitation erosion.

[0009] Unlike single-blade impellers, multi-blade impellers are characterized by higher efficiency. However, such impellers also have special requirements regarding the prevention of deposits from solid particles. With multi-blade impellers, special measures must be taken to avoid blockages.

[0010] WO 2015 / 000677 A1 discloses, among other things, a pump suitable for wastewater with blades that have a backward curved path starting from a hub.

[0011] DE 28 55 385 B1 and EP 0 114 932 A1 each describe a single-blade impeller for conveying long-fibered, suspended solids or viscous media, wherein the blade outlet, with clearance, sweeps a housing wall lying in a radial plane.

[0012] From EP 0 874 161 A1 a centrifugal pump with an impeller is known which has a single helically shaped blade.

[0013] DE 10 2011 007 907 B3 discloses an impeller for centrifugal pumps with at least two blades for conveying media containing solids.

[0014] The object of the invention is to provide an impeller for a wastewater pump in which deposits are effectively prevented. In particular, the impeller is intended to prevent the build-up of fibers on the leading edges. Furthermore, the impeller is intended to ensure the highest possible efficiency of the centrifugal pump used. Finally, the impeller is intended to prevent cavitation erosion.

[0015] This problem is solved according to the invention by an impeller having the features of claim 1. Preferred variants can be found in the dependent claims, the description and the drawings.

[0016] According to the invention, α is an angle between a leading edge of the blade and a circumferential direction and β is an angle between a leading edge of the blade and a meridional direction, wherein, depending on the dominant velocity, the associated angle α and / or β is less than or equal to 45°.

[0017] To solve the problem of fiber buildup on the blade, the drag of the fibers during their transport along the leading edge of the blade is considered. The velocity impacting the leading edge is decomposed into a normal component and a tangential component. The normal component acts as a pressure, while the tangential component is responsible for fiber transport. Both rotating and non-rotating systems can be considered in the fluid dynamic analysis. Since the relative velocity can be decomposed into circumferential and meridional components, these directions can also be assigned to specific force components.

[0018] If, according to the invention, the respective dominant areas are separated by the magnitude of the respective velocity, for the condition cm = u, a limiting radius is obtained for axial impeller inlet using the flow coefficient. φ = c m u to R g = R a ·φ.

[0019] The velocity u is the circumferential velocity. The symbol Ra denotes the outer radius of the blade.

[0020] The angle β is less than or equal to 45°. Alternatively or additionally, the angle α is also less than or equal to 45°.

[0021] The inventive approach leads to the fact that in the inner areas, i.e. in the area smaller than the limit radius R g, the angle β is to be less than or equal to 45° and in the outer areas, i.e. in the area larger than the limit radius R g, the angle α is to be less than or equal to 45°.

[0022] In the recirculation region, the meridional velocities in the inner region increase significantly, so the angle β in this direction becomes more important.

[0023] The impeller according to the invention makes it possible to operate the centrifugal pump even in an operating range with low specific rotational speeds and low peripheral speeds. Due to its unsteady nature, the flow characteristics generated by the impeller according to the invention have a positive effect on the pumping performance.

[0024] The inventive approach, which shifts the fiber transport along the leading edge of the blades through the action of the tangential components of the respective dominant velocity, ensures improved pump performance characteristics and better, blockage-free transport in both single-blade and multi-blade pumps. For single-blade pumps, this approach, in conjunction with a diagonal meridian section, is a known solution.

[0025] After being transported along the leading edge, the fibers slide over the asymmetrical and smoothed hub directly into the blade channel.

[0026] In semi-open multi-blade excavators, transport takes place towards the blade tip, where guide or transport grooves can take over the further processing of the fibers.

[0027] In order to take advantage of the effect of the larger velocity component, small angles β, preferably less than 45° in the region smaller than the limiting radius Rg, and small angles α, preferably less than 45°, should dominate in the region larger than the limiting radius Rg.

[0028] In a particularly advantageous embodiment of the invention, the impeller is semi-open. It is preferably advantageous if the impeller is designed as a radial impeller. The impeller can have one or more blades. In a particularly advantageous embodiment of the invention, the impeller has two blades.

[0029] Further features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to drawings and from the drawings themselves.

[0030] This shows: Figure 1 shows an axial section through a wastewater pump, Figure 2 shows a view of the suction nozzle of the pump. Figure 1 Figure 3 shows a perspective partial section of the suction inlet area of ​​the wastewater pump, Figure 4 shows a section through the suction inlet area, Figure 5 shows a top view of the impeller, Figure 6 shows half of a perspective view of the impeller, Figure 7 shows the definition of angle β in a schematic side view of the inlet area of ​​the blade, Figure 8 shows a definition of angle α in a top view of an impeller.

[0031] Figure 1 shows a cross-sectional view through a wastewater pump. In the Figure 1The centrifugal pump shown is a submersible motor pump. The wastewater, containing impurities, enters the pump through the suction inlet 1. The impeller 2 is non-rotatably connected to a shaft 3, which sets the impeller 2 in rotation. The impeller 2 is arranged in a pump housing 4, which in this embodiment is designed as a volute casing.

[0032] An insert 5, designed as a wear wall or wear ring in the exemplary embodiment, projects into the suction inlet 1 of the pump. The shaft 3 is set in rotation by a drive 6, which in the exemplary embodiment is designed as an electric motor. The drive 6 comprises a rotor 7 and a stator 8.

[0033] The pump housing 4 is sealed by a housing cover 9. The housing cover 9 is sealed against the shaft 3 by a mechanical seal 10. The shaft 3 is supported by bearing elements 11.

[0034] Figure 2shows a view of the centrifugal pump looking towards the suction inlet 1. The impeller 2 comprises, as shown in the illustration in Figure 2 two blades 12. The impeller 2 has a hub 13 in its center and is connected to the shaft 3 via a fastening means over this hub 13.

[0035] The fluid leaves the centrifugal pump via a pressure port 14.

[0036] Figure 3 Figure 1 shows a perspective partial sectional view of the components that form the suction inlet 1. The insert 5 is attached to the pump housing 4. For this purpose, several bores 15 are provided in the insert 5. The insert 5 can be attached to the pump housing 4 via the bores 15 using fasteners.

[0037] Wheel 2 rotates as shown in the illustration. Figure 3counterclockwise. The impeller 2 is equipped with two blades 12, which are mounted on a support disc 16. In the exemplary embodiments, the two blades 12 and the support disc 16 are formed in one piece. The blades 12 have a curved profile.

[0038] The medium containing solid additives flows axially through the suction port 1 towards the impeller 2 and radially outwards from the impeller 2, so that the medium leaves the centrifugal pump through the pressure port 14.

[0039] The blades 12 have a backward-curved profile. All blades 12 of the impeller 2 are congruent to each other and have the same shape. Each blade 12 extends radially outwards from the hub 13 with a curvature. In the illustration according to Figure 3 The two blades 12 are arranged offset from each other by 180°.

[0040] Figure 4shows a cross-sectional view of the sucking mouth area according to the illustration in Figure 3 The insert 5 is a stationary part. The impeller 2 is a rotating component. The blades 12 extend radially outwards from the hub 13 in a backward-curving direction.

[0041] This is also shown again in the representation according to Figure 5 .

[0042] Figure 6 Figure 1 shows one half of the wheel 2 in a perspective view from the side. The area of ​​the hub 13 is shown here purely to illustrate the constructive design of the wheel by means of two cylindrical bodies. This cylindrical shape can be omitted in the design of the wheel 2.

[0043] A leading edge 17 is attached to the hub 13 at each blade 12. The leading edge 17 of each blade 12 extends between the two points A and B.

[0044] Figure 7 Figure 1 shows the area of ​​the leading edge 17, depicted in black. The angle β is formed between the two auxiliary lines 18 and 19. According to the invention, the angle β is less than or equal to 45°. β represents an angle between a leading edge 17 of a blade 12 and a meridional direction. α describes an angle between a leading edge 17 of a blade 12 and a circumferential direction. Both angles α and β are, according to the invention, less than or equal to 45°.

[0045] Figure 8 Figure 1 shows a top view of an impeller and a definition of the angle α. The angle α is measured between the circumferential direction (i.e., a circular direction) and a tangent at a point on the leading edge of the blade at the considered radius.

[0046] α i is the angle at the inner radius R i , α g the angle α at the limiting radius R g and α a the angle at the outer radius R a .

Claims

1. Impeller for centrifugal pumps with at least one vane (12) for conveying solids-containing media, with an angle α between a leading edge (17) of the vane (12) and a circumferential direction and with an angle β between a leading edge (17) of the vane (12) and a meridional direction, wherein a dominant speed significantly influences the transport of the fibres along the leading edge (17) of the vane (12), and either a meridional component cm or a circumferential component u of the flow velocity is dominant according to the radius of the leading edge (17), characterized in that the associated angle (α, β) is less than or equal to 45° according to the dominant speed, wherein two ranges are obtained based on the magnitudes of the respective speeds, wherein, for an axial impeller entry, a limit radius Rg is obtained using a flow coefficient φ = c m u at Rg = Ra * φ, where Ra is the outer radius of the vane, wherein the angle β is less than or equal to 45° in a range below the limit radius Rg and the angle α is less than or equal to 45° in a range above the limit radius Rg.

2. Impeller according to Claim 1, characterized in that the impeller (2) has exactly one vane (12).

3. Impeller according to Claim 1, characterized in that the impeller (2) has more than one vane (12), preferably has exactly two vanes (12).

4. Impeller according to one of Claims 1 to 3, characterized in that the impeller (2) is of semi-open design.

5. Impeller according to one of Claims 1 to 4, characterized in that the impeller (2) is designed as a radial impeller.