EP3467319B1 - Centrifugal pump with improved suction neck seal - Google Patents

Description

The invention relates to the technical field of centrifugal pumps, in particular so-called split-case pumps with a two-part housing. The invention specifically relates to a centrifugal pump with a pump housing and at least one impeller arranged therein for conveying a liquid from the suction side to the pressure side of the pump unit, the impeller having a suction neck which is sealed off radially from the pump housing by a wear ring. Furthermore, the invention relates to a centrifugal pump unit with a centrifugal pump according to the invention.

In centrifugal pumps, the impeller separates the interior of the pump housing into a suction side and a pressure side, with the impeller sucking in the liquid to be pumped through the suction mouth ring-shaped surrounded by the suction neck on the suction side, accelerating it tangentially and ejecting it almost radially to the pressure side. This type of pump is therefore also called a centrifugal pump and the impeller is called a radial impeller. In order to avoid a hydraulic bypass between the suction and pressure sides, ie a flow of liquid from the pressure side back to the suction side, which considerably reduces the efficiency of the centrifugal pump, the impeller is sealed off from the pump housing. In principle, this can be done axially or radially. With axial sealing, a seal rests against the axial outer edge of the suction neck. Due to the axial forces acting on the pump shaft towards the suction side during operation, due to hydraulic pressure shocks in the pipe system connected to the pump and/or due to the mechanical drive of the centrifugal pump, the axial seal usually also acts as an axial bearing and is therefore subject to high wear . Therefore usually a radial Sealing of the suction neck is preferred, in which a suction ring bears sealingly radially on the outside on the outer circumference of the suction neck.

The quality of the seal between the pressure side and the suction side of the centrifugal pump also has a major influence on the hydraulic efficiency here. In order to keep the losses low, it is necessary to keep the gap between the impeller and the pump housing as small as possible. Since the hydraulic forces can cause the shaft to bend and thus reduce the gap, appropriate reserves must be taken into account when dimensioning. So-called wear rings are often used as suction rings, in which the gap is smaller and contact between the impeller and the wear ring is deliberately accepted if the shaft bends. Ideally, the operating gap levels itself out after a certain period of time. In order to avoid blocking, a production-related minimum gap is also required here. However, this places high demands on the accuracy of the components during manufacture and assembly.

This applies all the more, the larger the centrifugal pump and its components are. For example, wear rings with a nominal diameter of 500mm or larger are used in so-called split case pumps. The axially divided housing weighs up to a ton and must therefore be lifted with a crane during assembly. It must also be taken into account that the wear ring wears out during operation, which means that the radial gap between the wear ring and the suction neck increases over time. The efficiency of the centrifugal pump deteriorates accordingly and the pump characteristic shifts in the direction of lower speeds. To avoid this, the wear ring must be serviced regularly and replaced if necessary. At the same time, extremely high wear can also make early replacement necessary.

The maintenance or replacement of the wear ring is associated with a considerable amount of work and time and usually leads to a longer standstill of the centrifugal pump, usually at least one or two days. It is first necessary to decouple the electric drive from the pump. For dismantling, the pumped liquid must also be removed from the pump housing be drained. The pump housing must then be dismantled and the upper housing section lifted off using a crane. The pump shaft and impeller must then be removed so that the wear ring is accessible.

From the Korean publication script KR 2016006533 A a radially sealing suction neck seal for a centrifugal pump impeller is known, which consists of a first inner ring lying against the suction neck of the impeller and a second outer ring fastened to the pump housing, the rings being wedge-shaped when viewed in axial cross section and the wedge surfaces lying against one another. The axial position of the outer ring can be defined by means of an adjustment screw, with the outer ring being held resiliently on the screw. By unscrewing the screw, the head of which lies on the pressure side of the impeller in the pump chamber, clearance is created so that a spring presses the outer ring against the screw head and against the wedge surface of the inner ring. This allows the gap width to be adjusted when the gap between the impeller and the inner ring increases due to wear of the inner ring.

From the patent US 8,690,534 B1 discloses an auxiliary seal for the shaft of a centrifugal pump intended for use in a nuclear power plant, the auxiliary seal transitioning from a non-sealing condition to a shaft-sealing condition when the pump is at a standstill if the main shaft seal fails.

It is the object of the present invention to provide a centrifugal pump with an improved radial suction neck seal in which the sealing gap can be set very precisely to a minimum size and in which the maintenance effort is significantly reduced.

This object is achieved by a centrifugal pump having the features of claim 1. Advantageous developments are specified in the dependent claims and are explained below.

According to the invention, a centrifugal pump unit is proposed, comprising a pump housing and at least one impeller arranged therein for promoting a Liquid which has a suction neck which is sealed off radially from the pump housing by a slotted wear ring, the pump housing having an adjustment unit by means of which the diameter of the wear ring can be adjusted. The essence of the invention is therefore to provide an adjustable suction neck seal. Due to the adjustability or readjustability, the radial seal of the suction neck can be adjusted to a minimal gap after assembly of the pump on the one hand, and readjusted to a minimal gap again in the event of maintenance or servicing on the other hand. As a result, significantly lower gap losses and, in turn, higher efficiency are achieved. It is no longer necessary to replace the wear ring thanks to the adjustability.

In the following, the term "adjust" is used both for the initial adjustment after assembling the pump and for "readjustment" after a corresponding number of operating hours. The seal can be adjusted while the pump is running. It is not necessary to dismantle or remove the centrifugal pump from the connected hydraulic system for the setting. Thus, the maintenance effort is significantly reduced and downtimes are largely avoided, or at least minimized.

A slit wear ring is a ring which is interrupted at least at one point on its circumference by a slit, so that two circumferential ends of the wear ring lie opposite one another at a distance. This distance makes it possible to change the inner diameter of the wear ring, which is effected according to the invention by the adjustment unit. As the diameter decreases, the circumferential ends move toward each other, making the slot smaller.

The wear ring suitably has only one slit, i.e. it is designed in one piece, which makes handling easier when assembling the suction neck seal and simplifies the structural design overall, since a measure to prevent flow through the slit is only required at one point on the wear ring, as will be explained later is deepened. Essentially, the wear ring has approximately a C-shape in this one-piece design variant. However, the slot is significantly smaller compared to the perimeter than a typical C-shape. For example, the slot may have a circumferential width of between 0.5% and 3% of the circumference.

In principle, however, the wear ring can also be slotted several times. This means that it consists of two or more ring segments, between the circumferential ends of which a slot-forming distance is formed. In this embodiment variant, the sum of the slots can have a width in the circumferential direction of between 0.5% and 3% of the circumference. It makes sense for the slits to be of the same size, so that with a number n of slits, each slit has a width in the circumferential direction of between 0.5/n% and 3/n% of the circumference.

The adjustment unit is preferably set up to exert a force directed radially inwards on the outer circumference of the wear ring. This causes a radial compression of the wear ring with a corresponding adjustment of the inside diameter of the wear ring to the outside diameter of the suction neck of the impeller. The sealing gap between wear ring and suction neck can thus be reduced to a minimum, theoretically even down to 0mm.

The wear ring can, for example, be made of metal such as gunmetal, gray cast iron or stainless steel, but alternatively can also be made of plastic such as PTFE.

According to an advantageous embodiment variant, the adjustment unit has an outer ring and an inner ring between which there is a circular wedge connection, the outer ring being angularly adjustable relative to the inner ring in the circumferential direction, the diameter of the inner ring being reducible and the wear ring on the radial inside of the inner ring. Thus, the outer ring forms an outer part of the circular spline joint and the inner ring forms an inner part of the circular spline joint. The inner circumference of the outer ring has a circular wedge profile, and the outer circumference of the inner ring has a complementary circular wedge profile.

A property inherent in a circular wedge connection is that the two rings are pressed against one another by their twisting relative to one another. The forces in the circular wedge connection act radially on the connection partners. The outer ring exerts a radially inward force on the inner ring. This causes a reduction in the inside diameter of the inner ring, which in turn passes this on to the wear ring, so that its inside diameter also becomes smaller and the sealing gap is reduced. This has the advantage that the gap can be set much more precisely over the entire circumference and readjustment of the sealing gap is particularly easy.

The outer ring is preferably designed in one piece. This ensures that a torque acting on a point on the circumference acts on the entire ring in order to rotate it. Compared to a multi-part design of the outer ring, this has the advantage that the force effect and rotary movement do not first have to be transmitted to the parts of the outer ring via appropriate means. As a result, the structural design of the adjustment unit is particularly simple. The one-piece outer ring then has the above-mentioned circular spline profile in the form of at least one circular spline along its inner circumference. The inner circumference can thus carry a single, two or more circular wedges.

So that the diameter of the inner ring can be reduced, the inner ring can consist of a compressible material, for example an elastomer. It is therefore elastic and yields as a result of a radially inwardly directed force. It should be noted, however, that the elasticity must last for a long time, and in particular should last for several years, so that corresponding requirements must be made of the material.

In order to avoid this problem, the inner ring can be made of a dimensionally stable material, in particular metal or plastic. However, in order to allow the diameter to be reduced, provision must be made here to slit the inner ring so that there is a gap along the circumference between two corresponding circumferential ends. By reducing the diameter, these circumferential ends then move towards each other and reduce the gap. It should be noted that the terms slot and gap are technically synonymous, but within the meaning of the invention the term "gap" is used in relation to the inner ring and the term "slot" is used in relation to the wear ring.

In one embodiment variant, the inner ring can be formed from just one segment of a circle. It is therefore in one piece and therefore only has a gap along its circumference. Its shape is essentially C-shaped. Correspondingly, at least one circular wedge complementary to the outer ring is formed along the outer circumference of the circular segment in order to cooperate with the at least one circular wedge of the outer ring. Thus, in a sub-variant, a single complementary circular wedge can be formed along the outer circumference of the one circular segment forming the inner ring. Alternatively, in another sub-variant, two or more circular wedges can be present along the outer circumference of the one circular segment forming the inner ring.

According to another embodiment variant, the inner ring can be formed from an annular arrangement of two or more circle segments. It is therefore in several parts and suitably has a gap between two adjacent circular segments along its circumference. At least one circular wedge, which is complementary to the outer ring, is correspondingly formed along the outer circumference of the circular segments in order to be able to connect with the at least one circular wedge of the outer ring to cooperate. Thus, in a sub-variant, a single complementary circular wedge can be formed along the outer circumference of all circle segments forming the inner ring. The circle segments are thus at the same time also segments of the one complementary circular wedge and together form this one complementary circular wedge. In another sub-variant, there are two or more complementary circular wedges along the outer circumference of all circular segments forming the inner ring.

Ideally, the number of circular segments of the inner ring is equal to the number of circular wedges of the outer ring or equal to the number of complementary circular wedges. The distribution of the complementary circular wedges can preferably take place in such a way that each circle segment carries exactly one complete complementary circular wedge of the circular wedge connection on its back, i.e. on its radial outside. This simplifies the production of the circle segments, since the jump in height from one circle wedge to the next does not occur within a circle segment.

It is of particular advantage if the circular wedge connection between the outer ring and the inner ring consists of three circular wedges and three complementary circular wedges. This achieves a self-centering effect of the circular spline connection.

In a preferred embodiment variant, it can therefore be provided that three circular wedges are formed along the inner circumference of the outer ring and the inner ring is formed from an annular arrangement of three circular wedge segments, the respective outer circumference of which forms a complete circular wedge that is complementary to the circular wedges of the outer ring.

It should be noted that the inner ring can be dimensionally stable, in particular made of metal or plastic, in both a one-piece and in the segmented, multi-part embodiment variant, but alternatively also be elastic, in particular made of an elastomer.

The circular segments of the inner ring are preferably held in a radially displaceable manner. This simplifies assembly and ensures a defined movement. In addition, the holder prevents the inner ring from turning away in the circumferential direction and thus tightening or loosening the circular spline connection. This could happen if the impeller touches the wear ring at certain points and pulls it along due to the forces acting, which in turn would pull the inner ring along.

In the circumferential direction, the circle segments are in particular stationary in relation to the pump housing, so that the inner ring does not rotate when the outer ring is pivoted. Thus, in order to pivot the outer ring relative to the inner ring, a minimum adjustment angle is required for the outer ring.

In one embodiment, the outer ring can be pivoted in an L-shaped support ring attached to the pump housing. This support ring thus surrounds the outer ring on the outer circumference and on an axial end face and holds it in position. The outer ring can thus also be pivoted relative to the support ring and slides in it.

In order to fix the circular segments in place in the circumferential direction and at the same time to keep them radially movable, the support ring can have axially protruding guide pins which engage in corresponding recesses in the circular segments. The recesses can be grooves or slots, for example. The grooves or slots may extend substantially radially or along a secant to allow the entire segment to move radially. Suitably, the guide pins are distributed equidistantly along the circumference. The guide pins can be formed by cylinder pins, for example. The guide pins are preferably screwed to the support ring. Alternatively, they can be welded, soldered, pressed or glued to it.

In principle, the slot in the wear ring can have any shape. It is particularly easy to produce if the front edges of the peripheral ends are formed at right angles to the peripheral direction in such a way that the slot extends purely axially between the peripheral ends. It thus has an I-shape and a minimal longitudinal extension. Alternatively, the longitudinal extension of the slot are at an angle other than 90 degrees to the circumferential direction. Further, the peripheral ends can also be formed to obtain other slit shapes such as a V-shaped, U-shaped, Z-shaped, labyrinth-shaped or meander-shaped slit. It should be noted that the more complex the slot is designed, the better it seals.

Since the slit forms a sort of bypass between the suction side and the pressure side of the impeller, part of the pumped liquid can flow through the slit from the pressure side past the impeller to the suction side. In order to prevent such a flow, it is advantageous if a blocking means lies in the slot, i.e. between the peripheral ends of the wear ring, in particular in a sealing manner. For example, the blocking means can be an elastic sealing element. This would then be compressed due to the reduction in diameter of the wear ring, so that the slit is always tight.

According to an alternative embodiment variant, the blocking means is a wing nut, the diametrically opposite wings of which extend into elongated recesses in the peripheral ends in the installed state as intended. At the same time, the recesses form guides during the circumferential movement of the circumferential ends and hold them in position via the form fit with the wing screw.

The blocking means, in particular the wing screw, is preferably located, in particular screwed, in a bore of one of the circle segments. As a result, there is a fixed connection between the wear ring and the inner ring, which prevents relative movement between the wear ring and the inner ring, in particular when the impeller rubs against the wear ring. In combination with the guide pins fastened to the support ring, the entire arrangement of adjustment unit and wear ring is thus secured against twisting in the circumferential direction.

It is advantageous if the circle segments are of identical design. In this case, when assembling the adjustment unit, it is not necessary to distinguish between different types of circular segments, in particular between those that have a hole for the blocking means and those that do not have such a hole to have. Thus, all circle segments have a corresponding hole for the blocking means, but only one of these holes is used in a wear ring with a single slot, the other holes are unused. In the case of a wear ring with two or three slots, however, the additional bores can be used for a second and third blocking means, which then lies in the corresponding second or third slot.

Suitably the centrifugal pump comprises an actuator for pivoting the outer ring relative to the inner ring. Ideally, this is accessible from outside the pump housing, if necessary with an appropriate tool, so that no time-consuming dismantling of pump components is required.

According to one embodiment variant, the actuating device can comprise a pin protruding radially from the outer ring and a screw lying in a threaded bore in the pump housing, preferably arranged tangentially thereto, which is operatively connected to the pin in such a way that the screwing-in depth of the screw determines the angular position of the pin. Here, the screw can be rotatably accessible from outside the pump housing. The mode of operation of this actuating device is such that the screw, which can be a grub screw, for example, increasingly pushes the pin backwards (as seen from the screw) as the screwing depth increases, changing its angular position and pivoting the outer ring. This means that the outer ring or pin is in an initial pivoting position from which it will move away as the screw is driven deeper into the threaded hole.

According to an alternative embodiment variant, the actuating device can comprise a gear or worm wheel portion, which is preferably arranged on the outer periphery of the outer ring or forms part of its outer periphery, and a helical worm engaging in the gear or worm wheel portion. In this case, the screw can be rotatably accessible from outside the pump housing. The mode of operation of this actuating device is similar to that of the former. However, instead of the screw, the snail is rotated here, the rotation of which, as in a Common to worm gears, a displacement of the toothed wheel or worm wheel portion causes longitudinal extension of the worm, which changes the angular position of the outer ring. Again, the outer ring or pin is initially in an initial pivoted position from which it moves away as the worm is rotated.

The wear ring, together with the adjustment unit or at least parts thereof, in particular together with the inner ring, the outer ring, the support ring and the pin or gear or worm wheel section, can form a preassembled, in particular replaceable assembly, referred to below as the suction neck seal assembly, so that the assembly of the centrifugal pump and the wear ring can be replaced quickly and easily if service is required.

A reduction in the efficiency of the centrifugal pump can be caused not only by a worn wear ring, but also by an impeller damaged as a result of cavitation. In the latter case, of course, adjusting the sealing gap between the impeller and the wear ring does not help, so that the impeller has to be replaced. In order to determine the cause of the impairment of efficiency and to avoid the wrong maintenance measures being taken, it can be provided that the pump housing has a closable inspection opening leading into the suction chamber in front of the impeller for the passage of a flexible endoscope for the purpose of inspecting the gap between the wear ring and the pump has impeller. If this gap size is correct, the assumption of a damaged impeller is obvious. Furthermore, the endoscope can help to achieve a precise adjustment of the sealing gap.

In one embodiment variant, the centrifugal pump can have a second impeller which has a further suction neck. In another embodiment variant, the impeller can be double-flow and have a further suction neck opposite the suction neck. In both variants, the further suction neck can also be sealed radially to the pump housing by a corresponding second slotted wear ring, and the pump housing can have a corresponding second adjustment unit, by means of which the diameter of the second wear ring can be set or adjusted. The second wear ring and/or the second adjustment unit can/ can have the same features, properties and advantages as previously described in relation to the first wear ring or in relation to the first adjustment unit.

The invention is preferably used in so-called split case pumps. The pump housing can be divided axially, in particular consisting of an upper housing part and a lower housing part, preferably in such a way that the axis of rotation of the pump shaft lies within the parting plane between the two housing parts.

The invention also relates to a centrifugal pump assembly comprising a centrifugal pump according to the invention and an electromotive drive unit for driving the centrifugal pump unit. For this purpose, the drive shaft of the drive unit is mechanically coupled to the pump shaft and drives the impeller mounted on the shaft.

• Fig. 1: eine erfindungsgemäße Kreiselpumpe im vertikalen Axialschnitt
• Fig. 2: eine Radialschnittdarstellung der Kreiselpumpe nach Fig. 1 durch den Saughals des Laufrads
• Fig. 3: eine Radialschnittdarstellung der Saughalsdichtungsbaueinheit der Kreiselpumpe nach Fig. 1 ohne Pumpengehäuse
• Fig. 4: Ansicht der Innenseite des Schleißrings gemäß Richtung X in Fig. 3
• Fig. 5: eine axiale Schnittansicht der Saughalsdichtungsbaueinheit gemäß Schnittlinie E-E in Fig. 3

Further features, properties and advantages of the invention are explained below using exemplary embodiments. Show it:

• 1 : a centrifugal pump according to the invention in vertical axial section
• 2 : a radial section view of the centrifugal pump 1 through the suction neck of the impeller
• 3 : a radial sectional view of the suction neck seal assembly of the centrifugal pump 1 without pump housing
• 4 : View of the inside of the wear ring in direction X in 3
• figure 5 : an axial sectional view of the suction neck seal assembly according to section line EE in 3

1 shows a centrifugal pump 50 for conveying a liquid in the design of a so-called split case pump with a pump housing 1 of spiral design divided horizontally along the axis of rotation 18 into an upper housing part 1a and a lower housing part 1b. The housing parts 1a, 1b border in the parting plane 9 (see 2 ) to each other. An impeller 2 is arranged in the pump housing 1, which is non-rotatably mounted on a pump shaft 4 by means of a shaft protective sleeve 46 with an annular groove 47 (see Fig figure 2 ) is mounted. The pump shaft 4 is driven by an electric motor drive unit, not shown, with a clutch or gear between the pump shaft 4 and the drive shaft, to enable separate installation and assembly of the two devices. Centrifugal pump 50 and drive unit together form a centrifugal pump unit. The housing parts 1a, 1b have an enormous weight, sometimes up to a ton in total, so that the centrifugal pump 50 has to be assembled and disassembled with a crane.

The impeller 2 separates the interior of the pump housing 1 into a suction side 5, from which the impeller 2 draws in the liquid to be pumped, and a pressure side 7, which connects to a spiral chamber 3 located radially outside of the pump impeller 1. In the area of the spiral chamber, the pump housing 1 forms a spiral housing 3a. The impeller 2 accelerates the liquid and ejects it tangentially, while the spiral chamber 3 directs the liquid to the discharge side 7.

The impeller 2 is double-flow in this embodiment. This means that it is essentially mirror-symmetrical and has two opposite suction mouths 5 through which the impeller 2 sucks in the liquid. Due to the symmetry of the impeller 2, the pump housing 1 is also constructed essentially symmetrically in relation to the plane of symmetry of the impeller 2. In contrast to conventional impellers of a radial design, the impeller blades 12 here extend in the axial direction on both sides toward the respective suction mouth 5 . The double-flow impeller 2 of the embodiment variant described here lacks a support disk on which the blades are usually arranged in single-flow impellers.

Instead, the blades 12 are each covered on both sides by a cover disk 10, which, starting from its essentially radial extent at the outer edge in the form of a radial disk, becomes arcuate, viewed in cross-section, as it gets closer to the pump shaft 4, into an axial extent in the form of a cylindrical Ring transitions, which is concentric to the axis of rotation 18 and the suction mouth 5 of the impeller 2 is limited. This cylindrical ring of the cover disk 10 forms the suction neck 10a of the impeller 2 and can have a diameter of up to 500mm. The suction neck 10a must at its radial Outside to be sealed towards the pump housing 1 to prevent a backflow (bypass) of liquid from the pressure side 3, 7 to the suction side 5 of the impeller. Because this worsens the efficiency of the centrifugal pump 50 and affects the pump characteristic.

For this purpose, a wear ring 14 is present, which rests with its inner circumference 14a on the outside of the suction neck 10a, with a sealing gap between the suction neck 10a and the wear ring 14 being provided. The wear ring 14 is made of metal such as gunmetal, cast iron or stainless steel, or of plastic, such as PTFE.

Due to component and assembly tolerances, the sealing gap cannot be set precisely and is usually not constant over the circumference, which is caused, for example, by a deflection of the shaft 4. In practice, it can therefore happen that the wear ring 14 is partially in contact with the suction mouth 10a and loops in after commissioning. In addition, the sealing gap increases during operation due to wear and the efficiency drops, so that maintenance of the centrifugal pump 50 becomes necessary.

According to the invention, the centrifugal pump 50 according to the invention comprises an adjustment unit 20, 21, 29, which enables the sealing gap to be set precisely after the centrifugal pump 50 has been installed, but also allows the sealing gap to be readjusted after numerous operating hours, for example as part of routine maintenance or in the event of extraordinary service.

The setting or readjustment of the sealing gap, collectively referred to below as “setting”, is achieved according to the invention in that the inner diameter of the wear ring 14 can be changed. For this purpose, the wear ring 14 is slotted and the adjusting unit 15, 21, 29 is set up to adjust the diameter of the wear ring 14. A suction neck seal that can be adjusted and readjusted is thus formed.

The wear ring 14 used here is simply slotted, it is therefore in one piece and essentially has a C shape. This means that the slot is interrupted at only one point on its circumference by a slot 24, so that there are two Circumferential ends 27a, 27b of the wear ring 24 spaced opposite each other, see 4 . This distance makes it possible to change the inner diameter of the wear ring 14 to a certain extent, which is brought about by the adjusting unit 20, 21, 29 according to the invention. For example, in the initial state, the slot can have a width in the circumferential direction of between 0.5% and 3% of the circumference, for example 12.5 mm. Due to the reduction in diameter, the peripheral ends 27a, 27b move toward one another, so that the slot 24 becomes correspondingly smaller.

The adjustment unit 15, 21, 29 is set up here to exert a radially inwardly directed force on the outer circumference of the wear ring 14, which causes a radial compression of the wear ring 14 evenly over the circumference and leads to a corresponding reduction in the inside diameter of the wear ring, for example depending on the size of the wear rings up to 4mm. The adjusting unit 15, 21, 29 is in the figures 2 and 3 clearly visible, which represent a radial section through the suction neck 10a in the area of the suction neck seal.

The adjusting unit 15, 21, 29 essentially comprises an outer ring 21, an inner ring 15 and an actuating device 29. There is a circular wedge connection between the outer ring 21 and the inner ring 15, and the outer ring 21 is relative to the inner ring 15 angularly adjustable in the circumferential direction, which can be effected by the actuating device 29. The outer and the inner ring 21, 15 are, independently of one another, made of metal, in particular high-grade steel, or of plastic, e.g. PTFE, and are in any case dimensionally stable. The mutually facing surfaces of the outer and inner rings 21, 15 are at least finished or have an even lower surface roughness in order to minimize the friction between the circular wedges when the outer ring 21 pivots.

The inner periphery 21a of the outer ring 21 carries a circular spline in the shape of three circular splines. The individual circular wedges are clearly recognizable by their step-like transitions, since the radial thickness of the outer ring 21 increases in the circumferential direction along a circular wedge up to a maximum and steps back to a minimum radial thickness at the start of the next circular wedge. The outer ring 21 is in one piece and thus forms a kind of circular wedge ring.

The outer circumference 15a of the inner ring 15, on the other hand, carries a complementary circular spline profile in the form of three complementary circular splines. The inner ring 15 is here in several parts, i.e. segmented, more precisely formed by three mutually independent circular segments 15 which are arranged in a ring. The three complementary circular wedges are distributed over the circular segments 15 in such a way that each circular segment 15 has a complete complementary circular wedge on its outer circumference 15a. The radial thickness of the circle segments 15 increases in relation to the outer ring 21 in the opposite circumferential direction.

The inner circumference 15b of the inner ring 15 is cylindrical. The wear ring 14 rests on it. Both the circular wedges of the outer ring 21 and the circular wedges of the inner ring 15 have the shape of a logarithmic spiral, so that a centering effect on the wear ring 14 is achieved. The circular segments 15 are arranged at a distance from one another, forming a gap 19, in order to enable radial movement and thus a reduction in the inner diameter.

By pivoting the outer ring 21 counterclockwise relative to the inner ring 15, the inner periphery 21a of the inner ring 21 slides along the outer periphery 15a of the circumferentially stationary inner ring 15 with the thinner end of the splines first. In relation to a stationary circumferential point, the radial thickness of the outer ring 21 thus also increases in both rings 15 , 21 , as a result of which the outer ring 21 exerts a radial force on the inner ring 15 . As a result, the circular segments 15 deviate with a radial movement, which results in a reduction in the inner diameter of the inner ring 15, which in turn passes this on to the wear ring 14, so that its inner diameter also becomes smaller. This enables the sealing gap to be adjusted.

Due to the radial movement of the circle segments 15, the gaps 19 become narrower. In order to prevent the inner ring 15 from rotating in the event that the impeller 2 starts up against the wear ring 14 and the wear ring 14 rotates as well, the Circular segments 15 stationary in the circumferential direction, but nevertheless kept radially movable. For this purpose, essentially radially extending elongated holes 17 are provided in the circle segments 15, in which cylindrical guide pins 18 lie. Grooves can also be provided instead of the elongated holes. Each circle segment 15 has a single slot 17 of this type, with the slots being distributed equidistantly. The elongated holes 17 are suitably formed in that section of the circle segments 15 which has the greatest radial thickness. The elongated holes 17 have a length such that a radial movement of the circle segments 15 is possible up to 2 mm.

The guide pins 18 are attached to a support ring 20, in particular screwed, welded, soldered, pressed or glued to it. They extend essentially axially away from the support ring 20 . The support ring 20 is formed here in an L-shape from sheet metal and thus comprises an axial, perforated disk-shaped section 20a and a cylindrical section 20b, as is shown in figure 5 can be seen, which is an axial sectional view of the suction neck seal assembly 45 along section line EE in 3 Looking at the inner circumference 14a of the wear ring 14 forms. The support ring 20 surrounds the outer circumference of the outer ring 21 which lies correspondingly sliding in the support ring 20 . The outer ring 21 can thus also be pivoted relative to the support ring 20, but is fixed in its movement in the axial direction. The perforated disk-shaped section 20a, which covers the outer ring 21 on an axial end face and carries the guide pins 18 on its axial inner side directed toward the outer ring 21, serves this purpose. On the other axial end face, the outer ring 21 is covered by a press ring 48 which is pressed into a radial recess in the cylindrical section 20b. This radial recess is characterized by a smaller radial thickness of the cylindrical section 20b of the support ring 20 at an axial end at which the support ring 20 thus encompasses the press ring 48 on the outside.

The support ring 20 is held on the pump housing via a form fit with locking bolts 23, which are part of a fastening bracket 22 and are formed in particular on the circumferential ends thereof. The bracket 22 is semicircular and rests on the outside of the support ring 20, see 2 . It is firmly connected to the pump housing 1 or to the lower housing part 1b.

In the exemplary embodiment shown here, the slot 24 in the wear ring 14 has an I-shape, as shown in FIG 4 can be seen, which is a view from direction X according to 3 points to the inner circumference of the wear ring 14. The slot 24 extends at right angles to the circumferential direction, axially parallel to the axis of rotation 18. The front edges of the circumferential ends 27a, 27b are thus located parallel and perpendicular to the circumferential direction. As in figure 4 can also be seen, the outer ring 21 behind the wear ring 14 protrudes slightly. It thus has a greater axial length. In contrast, the inner ring 15 has an identical axial length to the wear ring 14 and is visible through the slot 24 .

A blocking means 25 is arranged in the slot 24 in order to prevent the slit 24 from forming a bypass for liquid flowing back, ie from being flown through. The blocking means 25 is formed here by a wing nut with two wings extending diametrically from a shaft 28 . In each of the two circumferential ends 27a, 27b there is an elongated recess 26a, 26b which extends in the circumferential direction and is open towards the respective end edge, into which a wing of the wing nut 25 extends in a form-fitting manner. The recesses 26a, 26b serve as a guide and prevent axial displacement of the peripheral ends 27a, 27b. The length of the recesses 26a, 26b is equal to or greater than the length of a wing.

The wing screw 25 is screwed with its shank 28, which has a corresponding external thread, into a bore 16 with a corresponding internal thread in one of the circle segments. The wear ring 14 is thus firmly connected to the inner ring 15 via the wing screw 25 . In combination with the guide pins 18 fastened to the support ring 20, the overall arrangement of adjustment unit 15, 21, 29 and wear ring 14 is thus secured against twisting in the circumferential direction.

In order to simplify assembly and not having to differentiate between different circle segments 15, all circle segments 15 are of identical design. Thus, all circle segments 15 have said bore 16 for a Blocking means, however, only one of these holes 16 is used in the embodiment shown here.

Part of the adjusting unit 15, 21, 29 is also an actuating device 29 for pivoting the outer ring 21 relative to the inner ring 15. For this purpose, a pin 31 in the form of an eyebolt protrudes radially from the outer ring 21 and extends through a recess 33 specially provided for this purpose in the support ring 20 extends into a chamber 30 formed in the pump housing 1, 1a. A ball joint 32 is arranged in the eye of the eyebolt 31 and is connected to the axial end 35a of a bolt 35, for example with a positive fit, latched or by means of a thread. The ball joint 32 allows the angle between the pin 31 and the screw 25 to be balanced when the outer ring 21 is pivoted.

It should be mentioned that the ball and socket joint 32 can be replaced by a simple swivel joint, since here only an angle compensation in one spatial direction has to take place.

The screw 35 is designed as a grub screw and is also part of the actuating device 29. It lies in a threaded bore 36, which is offset tangentially or somewhat radially but extends parallel to a tangent to the fastening location of the pin 31. The screw-in depth of the screw 35 thus determines the angular position of the pin 31, since it presses against the pin 31 with its axial end 35a.

It should be mentioned at this point that the connection between the joint 32 and the screw 35 does not have to be tight, as movement of the pin 31 in only one direction is required. This movement is effected when the screw 35 is screwed into the threaded bore 36 far enough to strike the pin 31 and then screwed past it. If screw 35 were subsequently turned back, it would only move away from pin 31 and outer ring 21 would remain in the pivoted position. A fixed connection, for example in the form of a form fit (locked or by means of a thread) has the advantage over the loose connection that a reversible adjustment can be effected, ie in two directions, turning the screw 35 back, i.e. pivoting back again of the outer ring 21 can reach. This enables the setting to be corrected, for example if the screw 35 has been tightened too much and the wear ring 14 consequently grips the suction mouth 10a firmly.

The threaded hole 36 opens out so that the screw 35 is accessible from outside the pump housing. It can be rotated with an appropriate tool without opening the pump housing 1, 1a. The bore 36 is closed by a sealing plug 37 which is spaced apart from the grub screw 35 to form a free space 38 . The plug 37 is removed to operate the actuator 29.

The mode of operation of this actuating device 29 is such that the screw 35 increasingly pushes the pin 31 backwards with increasing screwing depth, ie in the direction of the arrow α in 3 presses, changing its angular position and pivoting the outer ring 21. This means that the outer ring 21 or the pin 31 is in the initial state in an initial pivoting position which is in the figures 2 and 3 shown, from which it moves away as the screw 35 is driven deeper into the threaded bore 36. The angular adjustment can be limited by a stop of the pin 31, for example by means of the recess 33 in the support ring 20 or by a wall of the chamber 30, which the pin reaches when the screw 35 is screwed to its maximum depth. The possible angle adjustment range of the outer ring 21 is in 3 represented by dashed border lines. It can be between 0° and 15° or even between 0° and 20°.

The wear ring 14, together with the inner ring 15, the outer ring 21, the support ring 20 and at least the pin 31 of the actuating device 29, forms a preassembled and, if necessary, replaceable subassembly 45, thus a suction neck seal subassembly, so that the centrifugal pump can be assembled and the wear ring replaced in the service can be carried out quickly and easily.

Since the centrifugal pump 50 has an impeller 2 with two suction necks 10a, such a suction neck seal assembly 45 is correspondingly duplicated, as are the actuating devices 29, which are actuated independently of one another be able. The wear ring 14 assigned to the second suction neck 10a and/or the adjustment unit 15, 21, 29 assigned to the second suction neck 10a therefore have the same features, properties and advantages as they previously had in relation to the wear ring 14 assigned to the first suction neck 10a or in relation to of the adjustment unit 15, 21, 29 assigned to the first suction neck 10a.

As explained in the introduction to the description, a reduction in the efficiency of the centrifugal pump 50 can be caused not only by a worn wear ring 14, but also by an impeller 2 damaged as a result of cavitation, so that adjusting the sealing gap would bring no improvement. In accordance with a double-flow impeller 2 1 It should also be noted that there are two suction necks 10a, and therefore two sealing gaps, whose wear rings 14 can wear out differently, so that the sealing gap only needs to be adjusted for one of the two wear rings 14.

It is therefore advantageous if the cause of the reduction in efficiency can be determined without great effort. coming back on 1 this shows a simple measure for finding the cause of the impairment in efficiency. It is provided here that a closable inspection opening 43, which opens into the suction chamber 5 in front of the impeller 2, is provided in the pump housing 1, 1b, and that the sealing gap is inspected with an endoscope 39. Such an endoscope 39, which in the usual way has a flexible hose 40 with a Bowden cable for navigation and a camera 42 at the end, and a monitor unit 41 for displaying the image recorded by the camera 42, can be easily guided through the inspection opening 43 and to the impeller 2 be navigated to take a picture of the impeller 2 or the sealing gap. Such an inspection opening 43 can be used in the centrifugal pump 50 according to FIG 1 be present on both sides of the pump housing 1, 1b so that both sides of the impeller are equally accessible. The inspection opening 43 is tightly closed by a closure element 44, which is preferably self-sealing.

If the gap dimension of the sealing gap is correct, the assumption of a damaged impeller 2 is obvious, the blades 12 of which are also inspected with the endoscope 39 be able. Furthermore, the endoscope 39 can help to achieve a precise setting of the sealing gap, since the camera image on the monitor unit 41 shows whether and by how much the sealing gap needs to be reduced.

The above exemplary embodiments only serve to illustrate the invention and are not to be understood as limiting it. In particular, the use of the adjustable suction neck seal according to the invention is not limited to split case pumps, as described in 1 is shown. Rather, it can be used in any centrifugal pump, in particular in any glanded pump.

Reference List

1

pump housing

1a

upper pump housing

1b

lower pump housing

2

Wheel

3

spiral chamber,

3a

volute casing

4

pump shaft

5

suction side, suction chamber

6

suction mouth

7

pressure side

8th

shaft axis

9

parting line

10

cover disk

10a

suction neck

11

hub

12

shovel

14

wear ring

14a

inner circumference of the wear ring

15

circle segment

15a

Outer circumference of the circle segment

15b

Inner circumference of the circle segment

16

threaded hole

17

Long hole

18

guide pin

19

gap

20

L-shaped support ring

20a

perforated disc-shaped section of the support ring

20b

cylindrical section of the support ring

21

outer ring

21a

inner circumference of the outer ring

22

mounting bracket

23

locking bolt

24

slot

25

locking means, wing screw

26a, 26b

elongated recess

27a, 27b

Circumferential end of the wear ring

28

shaft

29

actuating device

30

chamber

31

pen

32

ball joint

33

recess

35

grub screw

35a

Axial end of the grub screw

36

drilling

37

sealing plug

38

free space

39

endoscope

40

tube

41

monitor unit

42

camera

43

inspection opening

44

closure element

45

suction neck seal assembly

46

shaft sleeve

47

Ring groove of the shaft sleeve

48

press ring

50

centrifugal pump

Claims (18)

1. Centrifugal pump (50) with a pump casing (1, 1a, 1b) and at least one impeller (2) arranged within it to transport a liquid, which has a suction neck (10a) that is sealed radially to the pump casing (1, 1a, 1b) by a wear ring (14), characterised by the wear ring (14) being split and the pump casing (1, 1a, 1b) having an adjustment unit (15, 21) by means of which the diameter of the wear ring (14) can be adjusted.
2. Centrifugal pump (50) according to claim 1, characterised by the adjustment unit (15, 21) being constructed to exert a force directed radially inwards on the outer circumference of the wear ring (14).
3. Centrifugal pump (50) according to claim 1 or 2, characterised by the adjustment unit (15, 21) having an outer ring (21) and an inner ring (15), with a cotter ring connection between them, in which the angle of the outer ring (21) is adjustable in the circumferential direction relative to the inner ring (15), the diameter of the inner ring (15) can be reduced and the wear ring (14) contacts the radial inner side of the inner ring (15).
4. Centrifugal pump (50) according to claim 3, characterised by the outer ring (21) being a one-piece ring with at least one cotter ring formed along its inner circumference (21a).
5. Centrifugal pump (50) according to claim 3 or 4, characterised by the inner ring (15) being formed by only one circle segment or by a ringshaped arrangement of two or more circle segments (15), in which at least one cotter ring complementary to the outer ring (21) is formed along the outer circumference (15a) of the one circle segment or all circle segments (15).
6. Centrifugal pump (50) according to claim 5, characterised by the circle segments (15) being held so they can be shifted radially.
7. Centrifugal pump (50) according to at least one of the claims 3 through 6, characterised by the outer ring (21) lying in an L-shaped supporting ring (20) attached to the pump casing (1, 1a, 1b) so the outer ring (21) can swivel.
8. Centrifugal pump (50) according to claim 7, characterised by the supporting ring (20) having axially projecting guide pins (18) that engage in corresponding recesses (17) in the circle segments (15), notably in the form of slotted holes (17) or grooves.
9. Centrifugal pump (50) according to one of the preceding claims, characterised by a sealing device (25) engaging in a slit (24) between the perimeter ends (27a, 27b) of the wear ring (14) to prevent the flow of liquid through the slit (24).
10. Centrifugal pump (50) according to claim 9, characterised by the sealing device (25) being a wing nut (25), the diametrically opposite wings of which extend into oblong recesses (26a, 26b) in the perimeter ends (27a, 27b) in the intended installed state.
11. Centrifugal pump (50) according to at least one of the claims 5 or 6 and one of the claims 9 or 10, characterised by the sealing device (25) engaging in a bore (16) in one of the circle segments (15), notably being screwed in.
12. Centrifugal pump (50) according to at least one of the claims 5 or 6, characterised by the shape of the circle segments (15) being identical.
13. Centrifugal pump (50) according to one of the claims 3 through 12, characterised by an operating device (29) to swivel the outer ring (21) relative to the inner ring (15).
14. Centrifugal pump (50) according to claim 13, characterised by the operating device (29) comprising a pin (31) projecting radially from the outer ring (21) and a screw (35) engaging in a tapped bore (36) in the pump casing (1, 1a), effectively connected to the pin (34) so that the screw-in depth of the screw (35) determines the angular position of the pin (34), in which the screw (35) is in particular accessible and turnable from outside the pump casing (1, 1a).
15. Centrifugal pump (50) according to one of the preceding claims, characterised by the wear ring (21) with the adjustment unit (15, 21) forming a pre-assembled, exchangeable assembly.
16. Centrifugal pump (50) according to one of the preceding claims, characterised by the pump casing (1, 1a, 1b) having an inspection opening (43) that can be closed, leading into the suction chamber (5) before the impeller (2) for the insertion of a flexible endoscope (39) to inspect the gap width between the wear ring (14) and impeller (2).
17. Centrifugal pump (50) according to one of the preceding claims, characterised by the pump casing (1a, 1b) comprising an upper casing section (1a) and a lower casing section (1b), notably so that the rotation axis (8) of the pump shaft (4) lies within the parting plane (9) between the two casing sections (1a, 1b).
18. Centrifugal pump unit comprising a centrifugal pump (50) according to one of the preceding claims and an electric motor drive unit to drive the centrifugal pump (50).

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