WO1998023864A1

WO1998023864A1 - Diffuser and conveyor device for a single-impeller centrigugal self-priming pump

Info

Publication number: WO1998023864A1
Application number: PCT/EP1997/006591
Authority: WO
Inventors: Carlo Serafin
Original assignee: Calpeda S.P.A.
Priority date: 1996-11-27
Filing date: 1997-11-26
Publication date: 1998-06-04
Also published as: DE69705296D1; AU5655398A; ITVI960192A1; ES2160375T3; CN1214107A; EP0879360A1; BR9707307A; CN1082630C; IT1287367B1; ATE202407T1; EP0879360B1

Abstract

The invention relates to a diffuser and conveyor device (2, 102, 202, 302) for a single-impeller centrifugal self-priming pump, with conveyor channels (15, 115, 215, 315) radially located outside the diffuser (13, 113, 213, 313) and inside the pump casing (3, 103, 203, 303) with a width comprised between the casing cover (7, 107, 207, 307) and a frontal wall (16, 116, 216, 316) next to the circular wall (17, 117, 217, 317) of the diffuser but not frontally overlapped to the latter. The diffuser and conveyor device (2, 102, 202, 302) deflects the flow from the tangential peripheral direction towards a centripetal direction reducing the rotation and the speed of said flow, it can be constructed in a single piece and it provides for frontal ports (25, 125, 225, 325) for the inspection of the internal parts of the pump.

Description

DIFFUSER AND CONVEYOR DEVICE FOR A SINGLE-IMPELLER CENTRIFUGAL SELF-PRIMING PUMP.

The present invention concerns a diffuser and conveyor device particularly suitable for being applied to single-impeller centrifugal self-priming pumps with incorporated ejector, commonly said shallow-well jet pumps and to self- priming pumps without ejector of the kind suitable for swimming pools and whirlpools.

It is known that a self-priming pump has to be installed on the surface at a normal suction lift from the water using the atmospheric pressure suited to rise the liquid with a plunged suction pipe full of air at the starting time, having filled with the liquid, the pump casing only. The self-priming phase after the starting time is a separation process from the liquid contained in the pump casing and an evacuation process from the delivery side, of the air contained in the suction pipe pushed into the pump by the underneath raising up liquid. The water is held in the pump casing while the air is dispersed at the delivery side. Said phase ends when the liquid coming from the suction pipe arrives in the pump and begins to exits from the outlet. The process continues during normal operating conditions if air pockets or gas arrive occasionally from the suction source to the pump or pumping water containing a remarkable quantity of air or gas.

It is known that the separation of air or gas from water or liquid in a hydraulic circuit, as in a self-priming pump, can be made by two different methods, utilizing for both the different specific weight of the air and the water and the different behaviour of the lighter air in the heavier water in state of rest or in the rotational motion of the liquid:

- utilizing the gravity in a rest chamber, with reduced turbulence and speed, where the air separates by bubbling till the floating on the liquid;

- utilizing the centrifugal force of the rotating liquid, as a centrifugal or cyclone separation device, collecting the air in the most centripetal part. It is known that some shallow-well jet pumps contains a diffuser and conveyor device which has the double function of transforming the kinetic energy of the flow coming out from the impeller as much as possible in pressure energy and of conveying the flow, through an exit having a ring shape or a plurality of outlet openings located around the ejector or suction duct of the impeller, so that said flow can enter in the central part of the pressure chamber with residual rotation and speed as much as possible reduced, in order to facilitate the separation of the air from the water during the self-priming phase, even with the greatest suction lift, utilizing the gravity in the state of rest obtained in the pressure chamber. Said known devices, as the one described in the patent EP 0361328 by the same inventor and as the ones described even in EP 0401670, US 5100289, EP 0406787 and US 5040946, present some inconveniences. An inconvenience is that the flow conveying towards the pump axis in the central part of the pressure chamber through a channel between two walls needs at least two assembled pieces to create the structure of the device.

In case of a shallow-well jet pump, another inconvenience is that the peripheral circular continuity of the diffuser and conveyor device prevents from the visual and manual access during the assembly when the ejector is built with incorporated suction chamber to be keyed on the up located inlet and makes difficult the alignment and the insertion of the parts in not coaxial places.

The lack of frontal ports prevents from the inspection of the internal parts and makes difficult the disassembly of the diffuser, without detaching the suction pipe from the pump casing or vice versa, especially if there is some calcareous deposit or similar, due to lack of internal hooking during the extraction.

Further, said diffuser and conveyor devices, provided for the jet pumps in which the liquid circulates always in the same direction in a continuous circuit through the ejector, are not suited to be used with self-priming pumps without ejector, as those suitable for swimming pools, where the water during the self- priming must return with a continuous back flow from the pressure chamber to the impeller to pick up, from the suction, new air to be dispersed at the delivery. The exit in the central part of the pressure chamber would cause a too long way for a fast back flow and would make unusable the liquid portion with less air contained in the lower part of the separation chamber, under the central outlet opening.

It is even known the embodiment of a self-priming pump described in the patents EP 0460597 and US 5226790 by the same inventor made with a diffuser having a peripheral longitudinal flow. The last embodiment, even if it avoids the inconveniences above mentioned obtaining the same functional purpose, presents the inconvenience of not offering an equal low noise functioning when the peripheral flow runs in a pump casing made of a thin sheet-steel and an additional inconvenience of requiring even two pieces in order to form the diffuser and conveyor device, with the addition of a bladed rim inserted between the pump casing and the casing cover, when even the casing cover is made of pressed rolled steel.

All the above mentioned devices belonging to known embodiments of self- priming pumps attempt to reduce the vortical motion of the flow in the pressure chamber of the pump using for the separation of the air from the water only the gravity, reducing the negative effect of centrifugal force. Devices are known belonging to shallow-well jet pumps which use, for the separation of the air from the water during the self-priming phase, even the centrifugal force. Among them, it can be mentioned the known embodiments of the patents GB 1201721 , US 2941474, US 2934021 and EP 0323384. Also these known embodiments of shallow-well jet pumps present the same inconveniences: they need multiple pieces to form the device for the separation of air from liquid, since frontally overlapping walls and undercuts do not allow the forming of a unique piece, unless obtained by molding with core; further they prevent for the visual and manual access by the assembly when the ejector is to be keyed on the inlet and they obstruct the inspection of the parts inside the pump.

Further, even these devices of shallow-well jet pumps which uses the centrifugal force are not suitable for self-priming pumps without ejector. The present invention proposes to overcome all the mentioned inconveniences.

It is one of the purposes of the present invention to provide a diffuser and conveyor device which can facilitate the separation of the air from the water during the self-priming phase, reducing as much as possible the duration of the phase with the heighst suction lifts, using the force of gravity and, if necessary, even the centrifugal force, avoiding the above mentioned inconveniences.

It is another purpose of the device of the invention obtain the elimination or a great reduction of the peripheral tangential component at the exit of the diffuser, deflecting the flow in a tendentially radial centripetal direction so that it can enter in the pressure chamber with reduced residual rotation and speed. It is another purpose of the invention to reduce the noise due to the motion of the flow inside the pump casing, to the impact and to the sliding on its walls, by a suitable driving of its direction and the decreasing of its turbulence and of its speed at the exit of the diffuser-conveyor.

It is another purpose to obtain the functions of the diffuser and conveyor device with single piece, inserted among the other necessary parts of the pump, formed by die forming without undercuts and without junction of several separable pieces and even without the junction of several pieces only in the production process and after inseparable, excluding even the necessity of a molding by fusion with core.

It is a further purpose to obtain a diffuser and conveyor device where it is possible to provide for frontal ports useful for the visual inspection of the internal parts of the pump and to facilitate the assembly and the disassembly, without increasing the pump dimensions.

It is not the last purpose to obtain a diffuser and conveyor device with a suitable configuration also for a self-priming pump without ejector, the one for swimming pools. Said purposes are reached with the realization of a diffuser and conveyor device belonging to a single-impeller centrifugal self-priming pump, that according with the main claim comprises:

- a pump casing;

- a stationary suction duct connected to an impeller and surrounded by the pressure chamber; - a casing cover; said diffuser-conveyor device, keyed between said casing cover and said pump casing and connected to said suction duct by a circular wall located between the impeller and the pressure chamber, presenting a diffuser located around the periphery of the impeller and consisting of one or more diffuser channels, said diffuser developing in radial centrifugal direction beyond said circular wall, being characterized in that each of said diffuser channels continues as conveyor channel radially located outside said diffuser and inside said pump casing with a width comprised between said casing cover and a frontal wall located next said circular wall leaving between said two walls an outlet opening in radial centripetal direction communicating with said pressure chamber, said frontal wall being radially extended without frontal overlapping with said circular wall, said conveyor channel developing angularly by an arc till a final wall suited for deflecting the flow from the tangential peripheral direction towards a tendentially radial centripetal direction through said outlet opening.

The above mentioned purposes and others that will be more clear from the drawings and from the following description, are obtained with the embodiments of the invention given as an example for the interpretation of the descriptions and of the claims, but not as a restriction, represented in the enclosed drawings, wherein:

- fig. 1 shows a longitudinal section of the device of the invention applied to a jet pump;

- fig. 2 shows a front view of the device of the invention taken from A of fig. 1 ; -fig. 3 shows a section of a conveyor channel of the device of the invention taken from B of fig. 1 ;

- fig. 4 shows the development of a conveyor channel of the device of the invention taken from C-C in fig. 2;

- fig. 5 shows a longitudinal section of the device of the invention in a different embodiment; - fig. 6 shows a front view of the device of the invention taken from A of fig. 5;

- fig. 7 shows a section of a conveyor channel of the device of the invention taken from B of fig. 5;

- fig. 8 shows the development of a conveyor channel of the device of the invention taken from C-C of fig. 6; - fig. 9 shows the longitudinal section of the device of the invention in another different embodiment;

- fig. 10 shows the section of a conveyor channel of the device of the invention taken from B of fig. 9;

- fig. 11 shows the longitudinal section of another different embodiment of the device of the invention applied on a self-priming pump for swimming pools.

As it can be observed from fig. 1 to 10 the diffuser and conveyor device, pointed as a whole with 2, 102, 202, belongs to a single-impeller centrifugal self-priming pump, pointed as a whole with 1 , having an included ejector, containing: a pump casing 3, 103, 203 provided with an inlet 4 and outlet 5, where the pressure chamber 6, 106 is included; an ejector unit 10 keyed on the inlet 4, comprising even the suction chamber

11 , surrounded by the pressure chamber 6, 106; a casing cover 7, 107, 207; an impeller 8, 108, 208 keyed on the driving shaft 9, 109, 209 and located between the casing cover 7, 107, 207 and the diffuser-conveyor device 2, 102, 202; a stationary suction duct 12, 112, 212 can be placed between the ejector 10 and the impeller 8, 108, 208.

Said diffuser-conveyor device 2, 102, 202, keyed between the casing cover 7, 107, 207 and the pump casing 3, 103, 203 and connected to the suction duct

12, 112, 212 by a circular wall 17, 117, 217 placed between the impeller 8, 108, 208 and the pressure chamber 6, 106, presents a diffuser 13, 113, 213 which develops in a centrifugal radial direction farther said circular wall 17, 117, 217 and placed around the periphery of the impeller 8, 108, 208, said diffuser defined by the junction with the casing cover 7,107, 207 and formed by one or more diffuser channels 14, 114.

In a different embodiment, as it can be observed in fig. 11 , the diffuser and conveyor device, pointed as a whole with 302, belongs to a single-impeller centrifugal self-priming pump, pointed as a whole with 301 , suitable for swimming pools.

Also this pump comprises: a pump casing 303 provided with an inlet 304, outlet 305 and containing the pressure chamber 306; a stationary suction duct 312 rounded by the pressure chamber 306 connected to the impeller 308; a casing cover 307; an impeller 308 keyed on the driving shaft 309 and placed between the casing cover 307 and the diffuser-conveyor device 302; said diffuser-conveyor device 302, keyed between the casing cover 307 and the pump casing 303, connected to the suction duct 312 by a circular wall 317 placed between the impeller 308 and the pressure chamber 306, presents a diffuser 313 which develops in centrifugal radial direction farther said circular wall 317 and placed around the periphery of the impeller 308.

The mentioned embodiments are belonging to the known technique. The new common characteristic of all the different embodiments and applications just mentioned consists in that each of the diffuser channels 14, 114 continues as conveyor channel 15, 115, 215, 315 radially placed outside 20, 120, 220, 320 of the beginning part of the diffuser 13, 113, 213, 313 and inside the pump casing 3, 103, 203, 303, with a width comprised between the casing cover 7, 107, 207, 307 and a frontal wall 16, 116, 216, 316 located next said circular wall 17, 117, 217, 317 outwardly of which the diffuser 13, 113, 213, 313 develops radially leaving between the two walls 16, 116, 216, 316, and 17, 117, 217, 317 an outlet opening 18, 118, 218, 318 in a radial centripetal direction communicating with the pressure chamber 6, 106, 306, said frontal wall 16, 116, 216, 316 of the conveyor channel 15, 115, 215, 315 radially extended without frontal overlapping with said circular wall 17, 117, 217, 317, said conveyor channel 15, 115, 215, 315 develops angularly as an arc till a final curved wall 22, 122, 222 tangent to the peripheral wall 23, 119, 219, 223, 323 and to the radial direction 24, 124, said final curved wall 22, 122, 222 suitable for deflecting the flow from the peripheral tangential direction to a tendentially radial centripetal direction through the outlet opening 18, 118, 218, 318. According to a preferred embodiment, the final wall 22, 122, 222 of the conveyor channel 15, 115, 215, 315 is located angularly in order to leave between it and the next diffuser channel or the initial part of the diffuser channel, if it is only one, a free frontal port 25, 125, 225, 325 between the outside 20, 120, 220, 320 of the diffuser 13, 113, 213, 313 and the inside of the pump casing 3, 103, 203, 303.

The conveyor channel 15, 315 can be comprised between the casing cover 7, 307 and a frontal wall 16, 316 belonging to the diffuser-conveyor device 2, 302 and connected to the circular wall 17, 317 and to the outside 20, 320 of the diffuser 13, 313 by the initial wall 21 and the final wall 22, in between of which develops angularly the conveyor channel 15, 315 being the whole achievable by die forming in a single piece without undercuts and without joints providing for the frontal wall 16, 116 an inner diameter 27, 327 equal or greater than the external initial outline 20, 320 of the diffuser 13, 313. The embodiment with an unique monolithic piece without undercuts and without joints is obtained realizing the conveyor channel with a frontal wall 16, 316 not_. frontally overlapping said circular wall 17, 317.

The conveyor channel 115 can be also comprised between the casing cover 107 and a frontal wall 116 belonging to the pump casing 103, keeping the realization of the diffuser-conveyor device 102 in a single piece and maintaining the presence of frontal ports 125, providing for the frontal wall 116 a minimum diameter 127 equal or greater than the external initial outline 120 of the diffuser 113.

With a worse embodiment than the purposes of the invention, disregarding the advantage of a diffuser-conveyor device in a single piece, the frontal wall 216 and if necessary also the peripheral wall 223, could be, obviously, obtained with a detachable piece and also made of a material different from the other part of the diffuser-conveyor device. In this last case the frontal wall 216 could be also performed partially and frontally overlapped to the circular wall 217 of the diffuser 213 considering that the overlapping of walls belonging to separate pieces doesn't form an undercut for the forming of the different parts. Also with the frontal wall 216 formed of a separate piece, a free frontal port 225 can be equally obtained, if such a port is considered useful or necessary, with an internal diameter of the outlet opening 227 equal or greater than the external initial outline 220 of the diffuser 213. The conveyor channel 15, 315 can be radially closed towards the outside by a peripheral arc shaped wall 23, 323 belonging to the diffuser-conveyor device 2, 302, or can be partially or totally closed towards the outside by the cylindrical walls 119, 219, 319 of the pump casing 103, 203, 303 and/or of the casing cover 207 or by the peripheral wall 223 of the diffuser-conveyor device 202 combining in different way the connection of the said three pieces: 202, 302; 103, 203, 303; 207.

Even if figs. 2 and 6 show respectively, an embodiment with three and four diffuser-conveyor channels, the channels number can be whatever, from one to the maximum number which allows a free frontal port 25, 125, 225, 325 among the channels, if such a port is desirable and considering that the diffuser should have a number of blades different from that of the impeller and that one blade number should not be a multiple of the other or should not contain a common divisor, in order to avoid vibrations caused by interference, for the purpose of reducing the noise. The diffuser and conveyor device of the invention does not need an increase, of the radial dimensions of the pump because it uses radial available spaces between the pump casing 3, 103, 203, 303 and the outside 20, 120, 220, 320 of the diffuser 13, 113, 213, 313, between the end of a diffuser channel 14, 114 and the following or the initial part of the diffuser, if the diffuser channel is unique. The slowing down of the flow rotation at the entrance in the pressure chamber 6, 106, 306 is obtained reducing the peripheral tangential component of the flow after the diffuser channel 14, 114, deflecting it towards a tendentially radial centripetal direction through the frontal wall 16, 116, 216, 316 and the final wall 22, 122, 222.

The slowing down of the speed of the flow at the entrance in the pressure chamber 6, 106, 306, is obtained with the outlet port 18, 118, 218, 318 of the conveyor channel 15, 115, 215, 315, formed by the axial position of the frontal wall 16, 116, 216, 316 next to the circular wall 17, 117, 217, 317 of the diffuser 13, 113, 213, 313 and by the angular position of the final wall 22, 122, 222 compared with the initial one 21 , 121 , 221.

The reduction of the rotation and of the speed of the flow at the entrance in the pressure chamber (at steady state) or separation chamber (during the self- priming phase) allows to obtain the rest state so that the air can be separated from the water by the gravity, moving the air upwards.

If the remaining turbulence of the flow with the mentioned embodiment is not reduced at optimum condition due to peculiar choices or dimensional links and if it results still excessive for a fast separation of the air from the liquid, the diffuser-conveyor device of the invention let a further possibility to facilitate the expected separation with two subsequent phases.

A first separation of the air can be obtained just at the exit of the conveyor channel 15, 115 utilizing the centrifugal force of the liquid with its tangential component on the periphery inside the conveyor channel 15, 115. Dividing the outlet opening 18, 118 of the conveyor channel 15, 115 in at least two angular sectors by at least one intermediate blade 26, 126 tendentially radial and positioning said intermediate blade 26, 126 towards the axis of the pump on a maximum diameter 26 preferably located under the half of the radial extension of the conveyor channel 15 or on a minimum diameter 126 which corresponds to the external outline 120 of the diffuser 113, the external part and the downstream part of the intermediate blade 26, 126 because of the centrifugal force will be mainly covered by the liquid while the air, lighter, will be obliged by the centrifugal force of the liquid to cover the more centripetal way upstream the intermediate blade 26, 126. In this way, the terminal wall 22, 122 will deflect in a radial centripetal direction the most part of the liquid and the intermediate blade 26, 126 will deflect in a radial centripetal direction the most part of the air.

It is obtained in this way a first separation of the air from the water in subsequent angular sectors, the liquid exits in the outlet opening sector 18b, 118b in between the intermediate blade 26, 126 and the final wall 22, 122 with a reduced contents of air, while the air tends to exit towards the sector of the outlet opening 18a, 118a upstream the intermediate blade 26, 126. The intermediate blade 26, 126 is useful also for reducing the residual tangential component of the flow on the diameter of the outlet opening 27, 127 in the frontal wall 16, 116 at the entrance in the pressure chamber 6, 106 (at steady state) or rest chamber or separation chamber (during the self-priming phase).

The reduction of the residual turbulence by the intermediate blade 26, 126 improves the condition of rest of the liquid in the separation chamber 6, 106 where, by gravity, the air is definitively separated moving upwards, tending to float.

The remaining turbulence can be further reduced placing in the arc of the conveyor channel 215 a sequence of deflecting blades 226 arranged starting from increased diameters according to the direction of the flow, from the initial wall 221 to the final one 222, with the minimum diameter corresponding to the external profile 220 of the diffuser 213 until the diameter of the peripheral wall 223.

The intermediate deflecting blades 26, 126, 226 can have different breadths also in the width of the conveyor channel 15, 115, 215, 315, they can extend only on the port of the outlet opening 118 between the frontal wall 116 and the circular wall 117 or on all the width of the conveyor channel 15 between the frontal wall 16 and the casing cover 7, or it is possible place several intermediate deflecting blades having different width or of increasing width according the direction of the flow, with rounded initial edge and reversed towards the coming of the flow, similar to the shape of the final wall 122 as in fig. 8. The number, the disposition, the width and the shape of the intermediate deflecting blades can be whichever and several optimum embodiments can be provided for reducing the turbulence and the noise of the flow, for facilitate the separation of the air from the water. The initial wall 21 , 121 , 221 and the final one 22, 122, 222 of each conveyor channel 15, 115, 215, 315, and the possible intermediate blades 26, 126, 226, can proceed radially towards the more central part of the circular wall 17, 117, 217, 317 of the diffuser 13, 113, 213, 313 assuming in this way even the function of ribs reinforcement of said circular wall 17, 117, as highlighted with dotted lines in figs. 2 and 6. Advantageously, the diffuser-conveyor device of the invention facilitates the separation of the air from the water during the self-priming phase obtaining a flow with reduced residual rotation and speed and it permits also the possibility of facilitating said separation with two subsequent phases, using first the centrifugal force in the conveyor channel and then the gravity force in the rest chamber.

The elimination of the tangential component on the periphery by the described device reduces the noise caused by the motion flow inside the pump casing, by the impact and by the flowing on its peripheral walls, last barrier for the damping of the noise that can be heard in the surroundings. Advantageously further, the diffuser and conveyor device of the invention can be obtained with reduced production costs because it can be made in just one piece inserted between the other parts anyhow necessaries to the pump, obtained by die forming without undercuts and without junctions of several pieces and without the necessity of a fusion moulding with core and because provided of frontal ports useful for the assembly and the disassembly, with the advantage for both the producer and the user, for any maintenance of the pump.

The construction with just one monolithic piece without undercuts and without junctions is obtained realizing the conveyor channel with a frontal wall not frontally overlapped to the circular wall of the diffuser, placing and limiting the radial extension of the conveyor channel in a space, between the inside of the pump casing and the outside of the diffuser, of sufficient width to deflect the flow in centripetal radial direction, eliminating or reducing as necessary the peripheral tangential component. The conveyor channel of the invention does not need an increasing of the_. radial dimensions of the pump because it utilizes radial spaces available outside the diffuser at the end of a diffuser channel, between the pump casing and the beginning of the subsequent diffuser channel or the beginning part of the diffuser, if the diffuser channel is only one. In case of a jet pump, when the ejector unit has to be inserted on the upward inlet, the assembling of the ejector unit in the pump casing with the diffuser- conveyor device, is facilitated by the possibility of introducing a pusher tool (as a screwdriver, a punch or similar) in the frontal port angularly provided, between a conveyor channel and a diffuser channel, locating said frontal port in front of the inlet, to push in that point the ejector on the inner seat.

The frontal ports allow the visual inspection of the internal parts of the pump and the holding of the diffuser-conveyor device from the internal, making easy its extraction even in the presence of calcareous deposits or similar. Advantageously further, the device of the invention can be applied even in self-priming pumps without ejector as the one suitable for swimming pools, because it provides for a short path for a fast back flow of the liquid to the impeller during the self-priming, using even the liquid contained in the lower part of the separation chamber. In case of application in a jet pump, the described embodiment is suitable preferably for a pump with a pump casing and a casing cover made of rolled steel and with the ejector unit keyed on the inlet of the pump. Nevertheless, the described device can be applied in shallow-well jet pumps made of other material and with the ejector in any way disposed in the inner part of the pump as in single-impeller self-priming pumps without ejector. The diffuser and conveyor device of the invention can undergo modifications to improve the efficiency or to facilitate the realization. So, for example, the dimensions, the width and the shape of the channels 14, 114, 15, 115, 215, 315, of the openings 18, 118, 218, 318, 27, 127, 227, 327, of the intermediate blades 26, 126, 226 and of the final wall 22, 122, 222, can be changed and also the dimensional and space ratio among the various parts can be different. It can be chosen materials, shapes, dimensions, and configurations different from those illustrated and described, it can be possible to renounce to some mentioned advantages or it will be possible to point out other ones related or connected to the device of the invention. It is to be understood that all the mentioned modifications and all the possible variations combining among them the illustrated and described embodiments are to be considered protected by the following claims.

Claims

1 ) Diffuser and conveyor device (2, 102, 202, 302) belonging to a single-impeller centrifugal self-priming pump (1 , 301 ) comprising: a pump casing (3, 103, 203, 303); a stationary suction duct (12, 112, 212, 312) connected to an impeller (8, 108, 208, 308) and surrounded by the pressure chamber (6, 106, 306); a casing cover (7, 107, 207, 307); said diffuser-conveyor device (2, 102, 202, 302), keyed between said casing cover (7, 107, 207, 307) and said pump casing (3, 103, 203, 303) and connected to said suction duct (12, 112, 212, 312) by a circular wall (17, 117, 217, 317) located between the impeller (8, 108, 208, 308) and the pressure chamber (6, 106, 306), presenting a diffuser (13, 113, 213, 313) located around the periphery of the impeller (8, 108, 208, 308) consisting of one or more diffuser channels (14, 114), said diffuser developing in a radial centrifugal direction beyond said circular wall (17, 117, 217, 317), characterized in that each of said diffuser channels (14, 114) continues as conveyor channel (15, 115, 215, 315) radially located outside (20, 120, 220, 320) said diffuser (13, 113, 213, 313) and inside said pump casing (3, 103, 203, 303) with a width comprised between said casing cover (7, 107, 207, 307) and a frontal wall (16, 116, 216, 316) located next to said circular wall (17, 117, 217, 317) leaving between said two walls (16, 116, 216 and 17, 117, 217) an outlet opening (18, 118, 218, 318) in a radial centripetal direction communicating with said pressure chamber (6, 106, 306), said frontal wall (16, 116, 216, 316) being radially extended without frontal overlapping with said circular wall (17, 117, 217, 317), said conveyor channel (15, 115, 215, 315) developing angularly by an arc till a final wall (22, 122, 222) suited for deflecting the flow from the tangential peripheral direction towards a tendentially radial centripetal direction through said outlet opening (18, 118, 218, 318). 2) Diffuser and conveyor device according to claim 1 ) characterized in that the final wall (22, 122, 222) of said conveyor channel ( 15, 115, 215, 315) is located angularly in order to live a free frontal port (25, 125, 225, 325) between the outside (20, 120, 220, 320) of said diffuser (13, 1 13, 213, 313) and the inside of said pump casing (3, 103, 203, 303). 3) Diffuser and conveyor device according to claim 1 ) characterized in that said conveyor channel (15, 315) is comprised between said casing cover (7, 307) and a frontal wall (16, 316) belonging to the diffuser-conveyor device (2, 302), said frontal wall (16, 316) being realized in a single piece with the diffuser-conveyor device(2, 302). 4) Diffuser and conveyor device according to claim 1) characterized in that said conveyor channel (115) is comprised between said casing cover (107) and a frontal wall (116) belonging to the pump casing (103).

5) Diffuser and conveyor device according to claim 1 ) characterized in that said frontal wall (216) of said conveyor channel (215) is obtained through a piece detachable from the other part of said diffuser-conveyor device( 202).

6) Diffuser and conveyor device according to claim 1 ) characterized in that said conveyor channel (15, 315) is radially closed towards the outside by a peripheral wall (23, 323) belonging to said diffuser-conveyor device (2, 302).

7) Diffuser and conveyor device according to claim 1 ) characterized in that said conveyor channel (115, 215, 315) is at least partially closed towards the outside by a wall (119, 219, 319) belonging to said pump casing (103, 203, 303) and/or to said casing cover (107, 207, 307) or by the peripheral wall (223) which is detachable or belonging to said diffuser-conveyor device(202).

8) Diffuser and conveyor device according to claim 1 ) characterized in that said outlet opening (18, 118) of said conveyor channel (15, 115) is divided into at least two angular sectors by at least one intermediate deflecting blade (26, 126) having a tendentially radial development towards the axis of the pump.

9) Diffuser and conveyor device according to claim 1 ) characterized in that inside said conveyor channel (215) is located a sequence of deflecting blades (226) arranged starting from increased diameters, according to the flow direction.