EP1649171B1

EP1649171B1 - Locking device of the stator pack of pumps

Info

Publication number: EP1649171B1
Application number: EP04763665A
Authority: EP
Inventors: Antonio Gambigliani Zoccoli
Original assignee: Caprari SpA
Current assignee: Caprari SpA
Priority date: 2003-07-31
Filing date: 2004-07-30
Publication date: 2008-11-26
Anticipated expiration: 2024-07-30
Also published as: ES2318316T3; ATE415562T1; CN1826472A; DK1649171T3; WO2005015027A1; ITMO20030225A1; CN100451350C; EP1649171A1; DE602004017996D1; ITMO20030225A0

Abstract

A locking device of the stator pack of a pump comprises casing means (4) arranged to contain pumping stages of a fluid to be pumped, flange means (2) suitable for closing said casing means (4), screw means (3, 8) cooperating with nut screw means (5, 14) for fixing together said flange means (2) and said casing means (4), said screw means (3, 8) having a contour that is, at least at a non-active thread side (16), substantially non-complementary to a further contour of said further nut screw means (5, 14); a locking device of the stator pack of a pump comprises casing means (4) suitable for containing the pumping stages of a fluid to be pumped, flange means (2) suitable for closing said casing means (4), connecting means (3, 5) arranged for reciprocally fixing said flange means (2) and said casing means (4) and seal means (24) arranged to insulate said connecting means (3, 5) from said fluid.

Description

The present invention relates to a locking device of the stator pack of pump diffusers, in particular centrifugal submersible pumps.
Such a device is suitable for locking the pack of the diffusers thus preventing any movement thereof, in particular in an axial direction, inside the cylindrical casing of the pump.
Locking devices are known comprising a pair of flanges provided on their external diameter with threading and each one of which is arranged at an end of the casing. Such threading engages in a corresponding threaded area obtained on the internal surface of the casing. The stator pack is locked by screwing the two threaded flanges and tightening the pack of diffusers between these flanges.
Alternatively, a flange is provided that is welded to an end of the casing and another flange screwed to the casing using similar methods to those disclosed above.
One drawback of the known devices is that it is not possible to exert the desired pressure on the pack of diffusers.
In fact, with such devices it is rather difficult to rotate the flange by applying a desired tightening moment.
Furthermore, in order to be able to effectively tighten the pack of diffusers, the flange must be screwed to the casing by using high tightening moments. In fact, the thread comes into contact with the threaded area on a significant portion of the respective threads, which generates resistant torques, which, owing to the friction, can reach considerably high values.
Another drawback of such devices is that they are difficult to dismantle.
This drawback is further accentuated by the presence of encrusting matter such as for example solid residue, oxides or slime, that are present in the fluid and infiltrate between the threading and the threaded area, thus acting as an adhesive.
To unscrew the flange it is therefore necessary to apply a high twisting torque thereto having a value that is hardly obtainable using common dismantling tools.
Another drawback of the known devices is that they can be used only for pumps having a casing with a relatively high thickness.
In fact, the threaded area obtained on the casing constitutes a zone of weakness of the casing and, if the casing has a limited thickness, the threaded area undergoes plastic deformation during operation, namely when the pump is crossed by fluid having high pressure.
This deformation tends to axially extrude the flange from the casing, making locking ineffective and irreversibly damaging the casing, which has to be replaced.
WO 01/83996 discloses a locking device for locking the stator pack of a pump (1), comprising 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 the pump (1) to the crown means (3) - which flange means (8) is suitable for hermetically closing the shell means (2) - elastic ring means (4) arranged between the shell means (2) and the crown means suitable for preventing the crown means (3) from sliding in an axial direction inside the shell means (2). The elastic ring means (4) comprises wedge means provided with a friction surface (7) suitable for being coupled with a respective conjugate surface (7a) of the crown means (3).
DE 9208801U discloses a pump unit consisting of a wet operation engine propelling a centrifugal pump. The pump unit is provided with a casing (1) made of plastics and consisting of two parts, a suction-side pump casing portion (2) with intake connection and a pressure-side casing portion (3) with pressure connection. The suction-side pump casing portion (2) and the pressure-side casing portion (3) can be mutually connected by means of a bayonet coupling (4, 5).
FR 2056783 discloses a centrifugal pump for liquid-containing containers. The pump (1) comprises a motor (2) and a watertight joint (3), through which the motor (2) is supported on a wall (13) of the container and which is integral with a threaded neck (4) of the pump (1). On the threaded neck (4) a fixing element (5) can be screwed, which in turn is connected with a cap (8) by means of a bayonet coupling. It is possible to tighten the fixing element (5) on the threaded neck (4) by rotating the cap (8), once the latter is bayonet coupled with the fixing element (5).
One object of the present invention is to improve the locking devices of the stator pack of pumps.
Another object is to obtain a locking device of the stator pack of pumps that can easily be fitted to and dismantled from a body of the pump.
A further object is to obtain a locking device of the pack of the pump diffusers that is sufficiently resistant not to be damaged when subjected to the pressure exerted by the pumped fluid, even when the device is applied to pumps operating at high pressure.
A further object is to limit the depositing of encrusting matter on a locking device of the stator pack of pumps.
According to the invention, a locking device of the stator pack of a pump is provided, comprising casing means arranged to contain pumping stages of a fluid to be pumped, flange means suitable for closing said casing means, screw means provided with thread means and cooperating with nut screw means provided with further thread means for fixing together said flange means and said casing means, characterised in that said thread means has contour that is substantially non-complementary to a further contour of said further thread means.
Owing to this aspect of the invention, it is possible to obtain a locking device of the stator pack of a pump in which between the thread means of the screw means and corresponding further thread means of nut screw means preset axial and diametral mechanical clearance are present.
This enables flange means to be easily fitted to and dismantled from the casing means, inasmuch as the thread means and the further thread means are in contact along a surface of limited extent that does not generate great friction during screwing the flange means to and unscrewing the flange means from the casing means.
Furthermore, the mechanical clearance enables, during a phase of dismantling of the device, axial shifting of the flange means in relation to the casing means, such as to remove any encrusting matter that may be present between the screw means and the nut screw means.
The invention may be better understood and implemented with reference to the attached drawings, which illustrate an embodiment thereof by way of nonlimiting example, in which:

Figure 1 is a fragmentary section taken along a longitudinal plane of a locking device according to the invention;
Figure 2 is an enlarged detail of Figure 1;
Figure 3 is a detail like the one in Figure 2 in which flange means of the device are shifted axially in relation to casing means.

Figure 1 shows a locking device 1 of the stator pack of a pump.
The locking device 1 comprises a flange 2 of circular shape, in metal material, provided with threading on one of its external surfaces. The threading defines a screw element 3 arranged to engage in a corresponding nut screw element 5 defined by a threaded area obtained inside a casing 4 arranged to contain the stator pack of the diffusers - not shown - of the pump.
The casing 4 comprises a tubular element in steel, at an end 6 of which the nut screw element 5 is obtained.
At a further end of the casing 4, opposite the end 6, is directly welded a closing cover against which the flange 2 presses the pack of the diffusers.
Alternatively, at the further end a further nut screw element can be provided arranged to engage with a further screw element of a further flange similar to the flange 2 disclosed above.
In this case, the stator pack is tightened against the flange 2 and the further flange.
The screw element 3 has a contour that is different from a further contour of the nut screw element 5.
More in detail, in Figures 2 and 3, the screw element 3 comprises a thread 8 that has an axial height C.
Similarly, the nut screw element 5 comprises a further thread 14 that defines a helicoidal groove 7 that has a further axial height S.
The nut screw element 5 can be obtained through plastic deformation of the end 6 of the casing 4.
In this case, the further thread 14 is obtained in a portion of metal material having a constant thickness..
The further axial height S of the further thread 14, and consequently of the groove 7, is greater than the axial height C of the thread 8 that is received inside it.
In this way, between the groove 7 and the thread 8 - when they are coupled - there is defined a mechanical clearance G1 of a preset amount.
The thread 8 comprises an active side 15 and a non-active side 16.
The active side 15 is configured in such a way as to be more tilted, at least at a crest 27 of the thread 8, than the non-active side 16, in relation to a longitudinal axis Z of the device 1.
The further thread 14 comprises a further active side 18 and a further non-active side 19.
The further active side 18 is configured in such a way as to be more tilted, at least at a further crest 28 of the further thread 14 that the further non-active side 19, in relation to the Z axis.
In particular, the active side 15 and the further active side 18 are arranged substantially perpendicularly to the axis (Z).
The contour of the thread 8 and the further contour of the further thread 14 are substantially complementary in correspondence of the active side 15 and of the further active side 18 and substantially non-complementary in correspondence of the non-active side 16 and of the further non-active side 19.
The screw element 3 and the nut screw element 5 are movable between an active configuration, indicated by X in Figure 2, in which the operative side 15 interacts with the further active side 18, and a non-operative configuration, indicated by Y in Figure 3, in which the active side 15 is distant from the further active side 18.
In the non-operative configuration Y, between the active side 15 and the further active side 18 there is defined a gap 29 having a width A and such dimensions as to allow the passage of particles of solid matter dispersed in the fluid between the screw element 3 and the nut screw element 5.
In the operative configuration X, the active side 15 interacts with the further active side 18 along a contact zone 17 of limited surface extent.
The thread 8 and the further thread 14 are such that the reaction that occurs in the contact zone 17 has a line of action directed substantially parallel to the Z axis.
In other words, the screw element 3 and the nut screw element 5 are subjected during use to a substantially axial load.
It is thus significantly increased the resistance of the coupling to the axial loads due to pressurised fluid.
In addition, the limited surface extent of the contact zone 17 enables the phase of fitting the locking device 1 to be facilitated inasmuch as the contact reaction has a limited friction component.
Consequently, the torque value required for screwing the flange 2 is rather limited.
Furthermore, the external diameter of the nut screw element 5 is greater than the external diameter of the screw element 3.
Consequently, also diametrically there exists mechanical clearance G of a preset quantity between the thread 8 and the groove 7.
The thread 8 has a depth h greater than the depth of the further thread 14 and, therefore, than the depth H of the groove 7.
The pump is assembled in the manner disclosed below.
The diffusers, which form the stator pack, and the impellers, are arranged in the correct sequence to form a preassembled pack, which is inserted inside the casing 4 till making it to rest against said closing cover arranged at the further end of the casing 4.
Subsequently, tightening is achieved by screwing the flange 2 to the casing 4.
The flange 2 presses the stator pack as the screw element 3 is screwed onto the corresponding nut screw element 5, until a preset preload value is reached.
Alternatively, fitting of the flange 2 can be achieved by using a pusher tool that is not shown, comprising an anchoring element that engages in projections 22 of the nut screw element 5 and a push rod arranged in contact with internal zones of the stator pack.
The projections 22 are obtained in an external surface 23 of the casing 4, at the groove 7 defined by the further thread 14 in the nut screw element 5.
This pusher tool is pressed on the stator pack in such a way as to compress it and facilitate screwing of the flange 2, which occurs without further pressure on the pack of the diffusers.
With reference to Figure 3, during dismantling of the locking device 1, the flange 2 can be subjected to axial shifts towards the inside of the casing 4, in a direction indicated by the arrow F.
Such axial shifts are obtained by mechanical impacts given in an axial direction to a top of the flange 2 and are made possible by the fact that between the thread 8 and the groove 7 there is the axial mechanical clearance G1.
The axial shifts enable any encrustation of matter to be broken up that has formed through depositing of residues or slime present in the fluid that has infiltrated between the screw element 3 and the nut screw element 5, causing sticking of the coupling.
In the non-operative configuration Y, portions of the encrustation may be removed from the contact zone 17 through the gap 29 defined between the screw element 3 and the nut screw element 5.
Subsequently, the flange 2 can easily be unscrewed without having to apply high torsional moments.
The locking device 1 enables the dismantling phase to be significantly facilitated, considerably limiting seizure or sticking of the coupling, even in the presence of polluted fluids.
The locking device 1 furthermore comprises seal means 24 arranged to insulate the screw element 3 and the nut screw element 5 from the fluid.
The seal means 24 comprises a first gasket 9 and a second gasket 10, arranged respectively above and below the threaded coupling.
The first gasket 9 is received in a cavity 12 obtained on the flange 2 upstream of the thread 8 and the second washer 10 is received in a housing 13 obtained on the flange 2 downstream of the thread 8.
The first gasket 9 and the second gasket 10 are such as to cooperate with internal surfaces 11a, 11b of the casing 4 to ensure a seal against fluid and substantially insulate the coupling zone between the flange 2 and the casing 4 from encrusting material, such as for examples residues or slime conveyed by the fluid.
The first gasket 9 comprises an appendage 25 arranged to partially envelop an edge zone 26 of the casing 4.
The second gasket 10 is placed in direct contact with the pumped fluid.
The pumped fluid thus presses the second gasket 10 against the flange 2 and the casing 4, such as to ensure its seal.

Claims

Locking device of the stator pack of a pump, comprising casing means (4) arranged to contain the pumping stages of a fluid to be pumped, flange means (2) suitable for closing said casing means (4), screw means (3, 8) cooperating with nut screw means (5, 14) for fixing together said flange means (2) and said casing means (4), characterised in that said screw means (3, 8) has a contour that is, at least at a non-active thread side (16), substantially non-complementary to a further contour of said nut screw means (5, 14).
Device according to claim 1, wherein said screw means (3, 8) has an axial height (C) less than said nut screw means (5, 14).
Device according to claim 1, or 2, wherein said screw means (3, 8) has a longitudinal axis (Z) and comprises an active side (15) that is more tilted in relation to said axis (Z), at least at its crest means (27), than said non-active side (16).
Device according to any preceding claim, wherein said nut screw means (5, 14) comprises a further active side (18) more tilted in relation to one of its longitudinal axes, at least at its own further crest means (28), than a further non-active side (19) of said nut screw means (5, 14).
Device according to claim 4 as appended to claim 3, wherein said active side (15) and said further active side (18) are arranged substantially perpendicularly in relation to said axis (Z).
Device according to claim 4 as appended to claim 3, or according to claim 5, wherein between said non-active side (16) and said further non-active side (19) an axial mechanical clearance (G1) is defined.
Device according to claim 6, wherein said mechanical clearance (G1) is such that said screw means (3, 8) may be shifted from an operative configuration (X) in which said active side (15) is in contact with said further active side (18) to a non-operative configuration (Y) of said device (1) in which said active side (15) is distant from said further active side (18).
Device according to any preceding claim, wherein between said screw means (3, 8) and said nut screw means (5, 14) radial mechanical clearance (G) is defined.
Device according to claim 6, or 7, or 8, wherein said axial mechanical clearance (G1) and/or said radial mechanical clearance (G) has a width (A) such as to enable the passage between said screw means (3) and said nut screw means (5) of particles of solid encrusting matter dispersed in said fluid.
Device according to any preceding claim, wherein a thread means (8) of said screw means (3,8) has a depth (h) greater than the depth (H) of said further thread means (14).
Device according to any preceding claim, wherein said screw means (3) is obtained in said flange means (2).
Device according to any preceding claim, wherein said nut screw means (5, 14) is obtained in said casing means (4).
Device according to any preceding claim, wherein at least said nut screw means (5, 14) has a substantially constant thickness.
Device according to any preceding claim, and further comprising seal means (24) arranged to insulate said screw means (3, 8) and said nut screw means (5, 14) from said fluid.
Device according to claim 14, wherein said seal means (24) is interposed between said flange means (2) and said casing means (4).
Device according to claim 14, or 15, wherein said seal means (24) comprises first gasket means (9) arranged upstream of said screw means (3, 8) and of said nut screw means (5, 14).
Device according to claim 16, wherein said first, gasket means (9) is received in cavity means (12) obtained in said flange means (2).
Device according to claim 16, or 17, wherein said first gasket means (9) comprises appendage means (25) arranged to partially envelop an edge zone (26) of said casing means (4).
Device according to any one of claims 15 to 18, wherein said seal means (24) comprises second gasket means (10) arranged downstream of said screw means (3, 8) and of said nut screw means (5, 14).
Device according to claim 19, wherein said second gasket means (10) is received in housing means (13) obtained in said flange means (2).