LOCKING DEVICE FOR LOCKING THE STATOR PACK OF MOTOR-DRIVEN PUMPS

Abstract: A locking device for locking the stator pack of a pump (1) comprises shell means (2) suitable for containing pumping stages suitable for pumping a fluid, crown means (3) provided with connecting and fixing means (9) arranged for connecting flange means (8) of said pump (1) to said crown means (3), said flange means (8) being suitable for hermetically closing said shell means (2), elastic ring means (4) arranged between said shell means (2) and said crown means (3), suitable for preventing said crown means (3) from sliding in an axial direction inside said shell means (2), said elastic ring means (4) comprising wedge means provided with a friction surface (7) suitable for being coupled with a respective conjugate surface (7a) of said crown means (3).

Description: Locking device for locking the stator pack of motor-driven pumps The present invention relates to a locking device for locking the stator pack of submersible centrifugal pumps. Said device is suitable for locking the pack of the diffusers preventing the pack from moving inside the cylindrical shell of the pump, particularly along an axial direction. Italian patent IT 1005473, filed in the name of the same applicant, discloses a locking device comprising a pair of end crowns each of which is fixed inside the cylindrical shell, respectively upstream and downstream the stator pack, by means of an elastic ring having circular section and toroidal shape inserted into a corresponding groove obtained inside said shell. Each crown is provided with threaded holes suitable for receiving respective screws passing through closing flanges arranged at opposite ends of the shell and centred thereon. The crown arranged downstream the stator pack acts as an axial stop for the pack, while the crown arranged upstream the pack acts as a fastening element for the upper flange. The upper flange abuts on a collar provided with a step centring and abutting the collar on a peripheral region of the first diffuser of the pack. In this manner, when the upper flange is fixed to the respective crown by means of the screws, the stator pack is tightened between the collar and the crown arranged at the opposite end. In a variation, said device comprises a crown which is welded at an end of the pump shell and is not fixed to the shell by means of elastic ring. A drawback of the devices of this type is that, when the flanges are fixed to the shell by means of the screws, the tightening torque has to be limited to a pre-established value for preventing the elastic ring from being extruded into the space existing between the crown and the shell so as to deform the groove and bend the shell, or even exiting from the groove. While the pump is working, then, the elastic ring is stressed not only by the stresses caused by the tightening of the screws, but also by the pressure of the liquid, so that such locking device is may be applied only to pumps having limited head and small number of stages. Since the internal diameter of the shell, the external diameter of the crown and the groove arranged for receiving the elastic ring are subjected to size variations due to manufacturing tolerances, the tightening torque of the screws must have a limited value for preventing dangerous ejection of the ring from the seat thereof in condition of maximum clearance . Furthermore, a locking device is known comprising two rows of slots punched in the outer cylindrical shell of the pump on two planes parallel to each other and orthogonal to the axis of the pump, arranged respectively upstream and downstream the stator pack. Through said slots, nibs may be introduced into the shell, said nibs being provided on nuts which are capable of engaging the threaded ends of tie rods arranged parallelly to the axis of the pump and passing through holes obtained in the closing flanges of the pump. The above-mentioned nibs act as stops for the end diffusers of the stator pack so allowing said diffusers to be locked. In a further version the pump may comprise a flange welded at one end thereof and a device analogous to the above-described device at the other end. A drawback of such devices consists in that punching or shearing the slots on the external shell produces out-of-round deformations of the shell which makes it difficult to introduce the pack into the shell and requires onerous operations of adjustment. Furthermore, shearing the above-mentioned slots hardens the steel which the shell is made of so promoting starting of corrosion. The tightening stress, furthermore, is not uniformly distributed on the circumferential edge of the shell, but is concentrated in regions from which cracks and corrosion under fatigue start. Eventually, the assembly of a locking device of such type, i.e. provided with a special reference nut, is rather complex and such to require a high loss of time. Furthermore, a locking device is known comprising a pair of flanges, each arranged at one of the ends of the shell, which protrude from said shell and are provided with holes arranged externally with respect to the diameter of the shell and suitable for allowing tie rods to be housed. On the threaded ends of such tie rods nuts are engaged which tighten the shell, and consequently the stator pack, between the flanges of the pump. A variation consists in the absence of an external metallic shell and the use of diffusers each provided with its own shell. Devices of this type are very bulky and considerably increase the radial overall dimensions due to the presence of the tie rods, which are sized according to the maximum pressure exerted by the pump during working. Furthermore, devices of this type are uneconomic since, when a single external metallic shell is used, the shell carries out only a function of containment of the diffusers and it is necessary to further provide a plurality of axial tie rods arranged for bearing axial compression of said diffusers. Finally, a locking device is known comprising a pair of flanges threaded on their external diameter and each arranged at one of the ends of the shell. The threads of said flanges engage a respective threaded section obtained on the internal surface of the shell. The- stator pack of the diffusers is locked by screwing to the shell the two treaded flanges. In a version of the above-mentioned device, the shell comprises a first flange welded at one end thereof and suitable for acting as a stop for the first diffuser of the pack and a second threaded flange screwed at the other end. In devices of this type, however, it is rather difficult to obtain high tightening torques; consequently it is not always possible to give to the pack of the diffusers the desired pressure. In addition, high tightening torques are difficult to be obtained because the shell and the flange are made of similar material, which involves high risks of seizing during screwing. Furthermore, pumps provided with such devices are difficult to be disassembled due to the presence of encrusting material, such as sludge or slime, which may accumulate at the threaded coupling. An object of the present invention is to improve the known locking devices. Another object of the present invention is to provide a device for locking the stator pack of a pump comprising an elastic ring which is easy to be inserted into and extracted from a respective seat. A further object of the invention is to provide a locking device comprising an elastic ring which is substantially free from deformations during working, so that the risk of an ejection of the ring from the groove in which it is housed is reduced. According to the invention, a locking device for locking the stator pack of a pump is provided, comprising shell means suitable for containing pumping stages suitable for pumping a fluid, crown means provided with connecting and fixing means arranged for connecting flange means of said pump to said crown means, said flange means being suitable for hermetically closing said shell means, elastic ring means arranged between said shell means and said crown means, suitable for preventing said crown means from sliding in an axial direction inside said shell means, characterised in that said elastic ring means comprises wedge means provided with a friction surface suitable for being coupled with a respective conjugate surface of said crown means . Advantageously, said elastic ring means comprises tooth means suitable for engaging respective groove means obtained in said shell means. In such manner, a pre-established axial position in said shell for said elastic ring means is provided. Preferably, said friction surface is a conical surface. Advantageously, moreover, the ring means is broken in a section of the peripheral edge thereof, which allows a limited circumferential deformation, however sufficient to allow the tooth means to firmly engage the groove means obtained in the shell. Further advantageously, said flange means is associated with support means provided with a support step which engages the first of the diffusers of the pack of the pump. Therefore, when the screws are tightened, the flange means presses the support means which locks the stator pack of the pump so preventing any movement thereof. Owning to the present invention it is possible to obtain a device in which the locking action is obtained by coupling friction surfaces arranged for mutually locking. The wedge means, therefore, act as axially rigid elements so preventing the risk of ejection. Furthermore, since the tooth means, in a working condition, are mainly stressed on the surfaces arranged perpendicularly to the axis of the shell, no force component acts on said tooth means promoting said tooth means to exit from the respective groove means. Owing to the present invention, eventually, it is possible to produce a locking device for locking a stator pack which may be used also in pumps of high head, or in any case also in pumps for which at this moment the solution disclosed in IT 1005473 is not suitable due to the high hydraulic internal pressure. The invention can be better understood and carried out with reference to the enclosed drawings which show some exemplifying and not restrictive embodiments thereof, in which: Figure 1 is a longitudinal broken section of a pump provided with a locking device according to the invention; Figure 2 is an enlarged detail of Figure 1; Figure 3 is a further enlarged detail of Figure 1 which shows an elastic ring inserted into a respective seat; Figure 4 is a section taken along the plane IV-IV of Figure 2 which shows the elastic ring in the region in which it is broken. With reference to Figures 1 to 3, a pump 1 is shown comprising an external shell 2 consisting of a steel tubular element into which a crown 3 is housed. Between the crown 3 and the shell 2 an elastic ring 4 is arranged comprising a protruding portion 5 arranged for being housed into a groove 6 obtained in the shell 2. The elastic ring 4 comprises a conical surface section 7 suitable for being coupled with a respective conjugate surface 7a of the crown 3. The pump 1 further comprises a closing flange 8 suitable for closing the shell 2 which is fixed to the crown 3 by means of screws 9 engaging threaded holes obtained in the above- mentioned crown 3. While the screws 9 are tightened, the ring means 4 are kept firmly connected to the shell 2 because the protruding portion 5 couples with the groove 6, while the crown 3 moves towards the flange 8 bringing the conjugate surfaces 7 and 7a to keep in contact with each other. With reference to Figure 4, an inclined cut 15 breaking the circumference of the ring 4 is shown; the above-mentioned cut 15 allows the ring 4 to be the quickly removed using a standard flat-end screwdriver when the pump 1 is disassembled. The cut 15 allows the ring 4 to deform so as to allow the protruding portion 5 to be housed into the groove 6. Since during working the ring 4 does not lock the crown 3 owing to an elastic deformation, but rather locks the crown 3 by substantially acting as a body rigidly fixed to the shell 2, advantageously the ring 4 is made of steel for a better stress strength. With reference again to Figures 1 to 3, impellers 10, keyed onto the shaft 11 and fixed thereto through a further screw 16, and the diffusers 12 are further arranged internally to the shell 2. The flange 8 comprising the valve body of the pump 1 abuts on a support 13 provided with a step 14 which engages the first diffuser 12 so locking said diffuser 12 and the whole stator pack of the pump 1 and, therefore, preventing the stator pack from sliding in an axial direction. The pump 1 is provided, in the not-shown portion arranged downstream the stator pack, with a further crown, provided with a further ring similar to the above-described ring, said crown acting as a supporting and stopping element for the stator pack. In another not-shown version, the crown arranged downstream the stator pack, is not fixed to the shell by means of an elastic ring, but is directly welded to said shell. The pump is assembled in the way described hereinafter. The impellers 10 and the diffusers 12, alternated in a suitable sequence, are inserted on the shaft 11 abutting, at the bottom, on the driving joint of the shaft 11, not shown, and being tightened, at the top, with the screw 16 which engages a threaded hole obtained in the upper end of the shaft 11. The pack so assembled is then inserted into the shell 2 until it abuts on the lower crown, not shown, fixed to the shell by elastic ring 4, or by welding. Subsequently, the sub-group of the support 13 is inserted into the shell 2 and then the crown 3 is introduced and pushed until it contacts the shoulder of the support 13 for allowing the groove 6 obtained in the shell 2 to become accessible. Then the elastic ring 4 is inserted into the shell 2 until the protruding portion 5 thereof engages the groove 6 obtained in the shell 2. The flange 8, comprising the stop valve, is placed on the upper end of the shell 2, so that the holes present on the flange 8 are properly aligned with the threaded holes present on the crown 3 previously inserted into the shell 2. At this point the screws 9 are inserted into the respective holes and are screwed into the threaded holes of the crown 3 until the value of the pre-established tightening torque is reached; during this operation the crown 3 rises so engaging the elastic ring 4. In a first phase, the surface 7a of the crown 3 slides on the conjugated surface 7 of the ring 4, expanding the ring 4 until the protruding portion 5 perfectly adheres to the internal surface of the groove 6; in the second phase, once the ring 4 has reached the lower stop at the end of the inclined surface 7a of the crown 3, the very stage of pre-loading the hydraulic pack begins until the closing flange 8 reaches the shoulder at the upper edge of the shell 2. In a variation of the described tightening device the flange 8 does not reach the shoulder on the upper edge of the shell 2: in this case the axial load on the pack is obtained tightening the screws 9 until the pre-established tightening torque is reached.

Claims: CLAIMS 1. Locking device for locking the stator pack of a pump (1), comprising shell means (2) suitable for containing pumping stages for pumping a fluid, crown means (3) provided with connecting and fixing means (9) arranged for connecting flange means (8) of said pump (1) to said crown means (3), said flange means (8) being suitable for hermetically closing said shell means (2), elastic ring means (4) arranged between said shell means (2) and said crown means (3), suitable for preventing said crown means (3) from sliding in an axial direction inside said shell means (2), characterized in that, said elastic ring means (4) comprises wedge means provided with a friction surface (7) suitable for being coupled with a respective conjugate surface (7a) of said crown means (3) . 2. Device according to claim 1, wherein said friction surface is a conical surface (7) . 3. Device according to claim 1, or 2, wherein said elastic ring means (4) comprises tooth means (5) suitable for engaging respective groove means (6) obtained in said shell means (2) . 4. Device according to claim 3, wherein said elastic ring means (4) comprises a cut (15) in a section of a peripheral edge thereof suitable for allowing said elastic ring means (4) to deform in a circumferential direction for allowing said tooth means (5) to engage said groove means (6). 5. Device according to one of the preceding claims wherein said elastic ring means (4) are made of steel. 6. Device according to one of the preceding claims wherein said flange means (8) is associated with support means (13) suitable for engaging an end diffuser (12) of said stator pack for preventing said stator pack from moving in an axial direction inside said shell (2) .

Inventors: CARRERI REMO, CARRERI, REMO
Applicants: CAPRARI S P A, CARRERI REMO, CAPRARI S.P.A., CARRERI, REMO
Application year: 2001
Main classification: F04D29
IPC codes: F04D1, F04D29