Peripheral-longitudinal diffusser for a single-impeller centrifugal pump

The invention discloses a single-impeller pump with a diffuser (1, 40, 50, 60, 80, 100, 120, 130) arranged in front of the impeller (14, 46, 57, 107) on the suction side of the impeller (14,46,57,107) which evolves in the longitudinal direction toward the pressure chamber (21,67,112) with channels (10, 72, 90, 109, 128, 139) arranged around the periphery of the funnel or wall (13, 42, 52, 69, 88, 102, 125, 135) which is present within the pump casing (11, 66, 85, 114, 127, 136) and is comprised between the suction opening (27), or an eventual ejector (44, 104), and the casing cover (12, 56, 64, 84, 110, 123, 133). The channels (10, 72, 90, 109, 128, 139) act as diffusers and send longitudinally and without any rotation into the pressure chamber (21, 67, 112) the flow streaming out of the impeller (14, 46, 57, 107) which is conveyed into the longitudinal channels (10, 72, 90, 109, 128, 139) by baffles (17, 63, 83, 122, 132) and blades (16, 62, 82) arranged around the periphery of the impeller (14, 46, 57, 107).

BACKGROUND OF THE INVENTION 
The present invention concerns a diffuser for a single-impeller centrifugal 
pump, particularly suited to be advantageously applied on plastic 
self-priming swimming pool pumps or whirlpool pumps and to self-priming 
ejector pumps, usually known as "jet" pumps. 
It is a known fact that a self-priming pump is a pump for liquids which, 
when started, can suck by itself the air which is present in the suction 
piping, after the pump casing alone has filled up with liquid. A pump is 
primed when the waterways of the pump are filled with the liquid to be 
pumped. 
It is also a known fact that in the single-impeller centrifugal 
self-priming pumps there is a diffuser, i.e. a duct having a cross-section 
which increases in the direction of the flow, which has the task of 
transforming as much as possible the kinetic energy of the liquid 
streaming out of the impeller into pressure energy. 
The single-impeller centrifugal pumps of the above-mentioned types include 
a bladed diffuser having a round shape and radial outlets, which is 
arranged around the periphery of the impeller in the pump casing such a 
diffuser is positioned within an annular chamber closed around the 
periphery and axially open for the "jet" pumps, or within a chamber open 
both radially and axially in the swimming pool pumps. The known type of 
diffusers having blades with the mentioned radial outlets present, 
however, some inconveniences. 
A first inconvenience arises from the fact that the pumped liquid flows out 
of the diffuser with a tangential or a helicoidal direction and, during 
the priming phase, it drags along the air contained in the pump casing. 
The centrifugal effect separates the air from the liquid. The air has a 
tendency to collect around the axis of rotation in the pressure chamber or 
to flow back radially through the diffuser to the hub of the impeller and 
it arrives with difficulty at the delivery connection. For this reason the 
pumps built according to the known techniques require extensive 
longitudinal baffles or other devices, in order to slow down the rotation 
in the pressure chamber or they require manually operated adjustment 
devices such as throttle valves or methods of topping up with water 
through the delivery pipe, in order to obtain the priming with the maximum 
suction lifts. 
Another inconvenience consists in the fact that the presence of the radial 
diffuser causes an increase in the radial overall dimensions of the pump, 
since the blades are usually, although not always compulsorily, overlapped 
between the inlet and the outlet, in order to obtain a diffuser duct. This 
requires around the diffuser a relatively high circular rim, so that the 
outer diameter of the pump equals the diameter of the impeller plus the 
height of the diffuser, plus the height of a possible annular free 
chamber, plus the thickness of the pump casing. 
In the swimming pool pumps or whirlpool pumps with a traditional radial 
diffuser, the height of the axis of the pump casing exceeds the height of 
the motor axis. Because of the weight differences of the plastic materials 
of the pump and the metal materials of the motor, the center of gravity of 
the unit is under the motor, in spite of the larger volume of the pump 
casing. In order to hold the unit in a horizontal position, these pumps 
require an added support consisting of one or more parts fastened with 
screws which, when applied under the motor, must exceed the axis height of 
the pump or, when applied under the pump extends down to the center of 
gravity under the motor. This results in further inconveniences relating 
to the stability and the structural sturdiness, while entailing some 
complications for the manufacture and the assembly, and because of the 
increase in weight and costs. 
Moreover, in the mentioned swimming pool pumps or whirlpool pumps, the 
impeller and the diffuser must be placed within the pressure chamber of 
the pump casing and this entails one more inconvenience, i.e. it decreases 
the useful volume for the amount of water with which the pump casing can 
be filled up at the start for the self-priming process. 
Some "jet" pumps are known and they were disclosed by the patents 
DE/3718273, U.S. Pat. Nos. 2,941,474 and 2,934,021, wherein, in the 
attempt of solving the problem of the rotation and of the vorticity of the 
liquid and the air at the outlet of the diffuser, a separation wall or an 
added suitable component, such as a separating device or a perforated 
screen, is arranged behind the diffuser, in order to transversally divide 
the pressure chamber into a chamber with high vorticity and high 
rotational speed and a chamber with less turbulence and a decreased 
rotational speed. 
Moreover, both "jet" pumps and plastic swimming pool pumps or whirlpool 
pumps are known, wherein the rotation of the liquid and the air within the 
pump casing is slowed down by means of extensive longitudinal baffles. 
These devices present, however, the inconvenience that they do not 
eliminate the origin of the vorticity and of the rotation of the liquid 
and the air, but they only intercept them in order to decrease their 
intensity with negative effects on the efficiency and on the noise level. 
The obstacles used to slow down the rotation present yet the further 
inconvenience that they also increase the friction on the water in the 
pump casing, so that the temperature of the water reserve contained in the 
pump casing increases in a shorter period of time. 
This limits the self-priming capacity and reduces the period of time during 
which the pump can function without being damaged, if the water reserve is 
not renewed because of accidental causes, as when the pump keeps on 
running with a closed gate valve or with the suction pipe not immersed in 
the water because of the lowered water level of the pool. 
Another known "jet" pump is the one disclosed in the patent application 
EP0361328 by the same inventor which presents a diffuser of the axial type 
arranged in front of the impeller on its suction side, with some return 
channels converging to a central exit, without any rotation of water and 
air within the pressure chamber. Although this axial diffuser eliminates 
the inconveniences of the radial diffuser in the above-described 
applications and practically fulfils the same purposes of the present 
invention, it presents the inconvenience for the manufacturer that it 
requires two pieces (added between the pump casing and the casing cover) 
with a complicated blades system. It also requires the addition of a metal 
wear ring, in order to protect against abrasive substances the clearance 
of the non-contact seal ring on the impeller, when the impeller and/or the 
diffuser are made of plastic material. Said axial diffuser also presents 
the inconvenience that, if it is made only with the single central exit, 
it leaves in its interior and on the impeller side an air pocket when it 
is filled up for the first time and a water pocket when it is drained. 
SUMMARY OF THE INVENTION 
The purpose of the present invention is to eliminate the above-mentioned 
inconveniences. 
One purpose of the invention is to obtain a diffuser, the outlet flow of 
which enters into the pressure chamber of the pump without a rotational 
component, without separating water and air by centrifugal effect, so as 
to prevent the air from collecting around the axis and flowing back to the 
impeller hub and to make it easier for the air to exit from the delivery 
connection of the pump and to permit the self-priming process to become 
regular and automatic, the delivery connection remaining completely open 
even with the highest suction lift and without any need for additional 
devices other than the diffuser, which would have to be added, in order to 
reach this purpose. Another purpose of the invention is to obtain a lower 
noise single-impeller, self-priming centrifugal pump, by eliminating the 
rotation of the pumped liquid and of the water within the pump casing. 
Another purpose of the invention is to obtain a diffuser permitting the 
construction of a pump casing having a smaller outer diameter, as compared 
with the outer diameter of a pump offering equivalent performances, whose 
impeller has the same diameter but uses a radial diffuser. 
Yet another purpose of the invention is to obtain a diffuser having a 
single-impeller, self-priming centrifugal pump with a reduced axis height, 
in order to avoid the need for adding supports under the motor. 
Yet another purpose of the invention is to obtain a diffuser reducing the 
friction on the water in the pressure chamber, so that the temperature of 
the water does not rise rapidly. Yet another purpose of the invention is 
to obtain a diffuser allowing for a larger useful volume for the quantity 
of water with which the pump casing can be filled at the start for the 
self-priming process. Another purpose of the invention is to obtain a 
diffuser permitting a more compact construction, smaller overall 
dimensions and a lighter weight, as compared with a single-impeller 
centrifugal pump with a radial diffuser, with an impeller having the same 
diameter and with a pump casing made of the same material. Another purpose 
of the invention is to obtain a diffuser which can be completed by adding 
a single part to the structural parts which are at any rate necessary for 
the construction of the pump, such as the pump casing and the casing 
cover, said additional part acting also as a metal sealing ring on the 
impeller. Another purpose of the invention is to obtain a diffuser which 
will not leave air pockets negatively influencing the self-priming process 
at the first filling up and which will not leave stagnating water when the 
pump is drained, thereby permitting the complete emptying of the pump. All 
the above-listed purposes and others which will become apparent 
hereinafter are fulfilled by a diffuser for single-impeller centrifugal 
pumps, comprising: 
a pump casing provided with a suction opening with a delivery connection 
and a pressure chamber, into which an ejector is also eventually inserted; 
a casing cover closing the pump casing; 
a funnel or a wall within the pump casing comprised between the pressure 
chamber and the suction side of the impeller and also between the suction 
opening, or an eventual ejector, and the casing cover or a circular rim; 
an impeller inserted into the pump casing and comprised between the funnel 
or wall and the casing cover, 
characterized in that it consists of a plurality of channels connected with 
the pressure chamber of the pump, wherein said channels have a 
longitudinal direction which is substantially parallel to the axis of 
rotation of the impeller in order to prevent the rotation of the flow 
coming from the impeller, are arranged in front of the impeller on the 
suction side of the impeller, oriented toward the pressure chamber, around 
the funnel or wall periphery, wherein baffles arranged around the 
periphery of the impeller are connected with the longitudinal channels. 
According to a preferred embodiment the baffles are provided with blades 
arranged around the periphery of the impeller. 
According to a preferred embodiment, the diffuser of the invention is built 
so, that the task of the diffuser is divided among three components, each 
separate from the other, constituting the pump itself, and more precisely 
the pump casing, the casing cover or a circular rim and a funnel or wall, 
inserted into the pump casing between the suction opening or the ejector 
and the casing cover. The diffuser function can be obtained, as will be 
better explained hereinafter, also with the casing cover and the funnel or 
wall alone. 
Advantageously, the diffuser according to the invention eliminates the flow 
rotation in the pressure chamber, thereby making it easier for the air to 
stream out of the delivery connection during the self-priming process, and 
preventing the air from separating and collecting around the central area 
of the pressure chamber or to flow back radially through the diffuser to 
the hub of the impeller. 
Just as advantageously the diffuser according to the invention provides a 
single-impeller, self-priming centrifugal pump which is less noisy than 
the pumps built according to the known techniques and having equivalent 
characteristics and performances. 
Moreover, advantageously the diffuser according to the invention permits 
the building of a pump having a reduced axis height, which can, therefore, 
be manufactured while avoiding the need for a tall support under the motor 
to make up for the excessive height of the pump axis, or of a long support 
under the pump because of the position of the center of gravity under the 
motor, this being especially the case when the pump is made of plastic 
material like swimming pool pumps or whirlpool pumps. 
The pump also presents the advantage that it is more compact and weighs 
less than equivalent pumps with a radial diffuser, this feature being 
especially important for portable pumps and pumps which must be inserted 
into limited spaces, for instance against the sides of swimming pools or 
of whirlpool baths. 
Moreover, the diffuser of the pump according to the invention can be built 
with an arrangement of the channels which excludes the creation of air 
pockets during the first filling-up and of water pockets after draining. 
The possibility of emptying completely the pump prevents damages to the 
pump in case of freezing temperatures and, when it is used in swimming 
pools or whirlpools, it improves on the hygiene of the installation. 
Moreover, advantageously, since the diffuser according to the invention is 
arranged in the pump casing outside the pressure chamber, in spite of its 
reduced radial dimensions, it allows for a comparatively larger useful 
inner volume so that the pump can be filled with a larger amount of water 
for the self-priming process at the first start-up and also a larger 
amount of water remains within the pump after it has stopped running, 
which will be useful for the following start up. The funnel or wall, 
advantageously, can be made of metal also for the plastic pumps used in 
swimming pools and whirlpools, in which, for safety reasons concerning 
electricity, the water should never come into contact with the metal parts 
of the motor. In fact, the funnel or wall is perfectly insulated because 
it is located between parts made of plastic material and can preferably be 
made from a sheet of stainless-steel. Thus it acquires also the function 
of a metal sealing ring on the impeller, thereby preventing jamming or 
irregular wear due to abrasive elements, even with small clearances and 
the function of connecting the pressure chamber or the ejector with the 
opening of the impeller through the pressure chamber. 
By building the funnel or wall with a thin sheeet of steel, with a 
decreased volume of material, without any blades or baffles, a yet larger 
volume is obtained for the quantity of water with which the pump can be 
filled for the self-priming process at the first start up and for the 
quantity of water which remains in the pump after it has been stopped and 
which will turn useful at the following start up. 
This construction of the diffuser with smooth walls without blades or 
baffles reduces the friction on the water, thereby preventing its 
temperature from quickly rising. This improves the self-priming ability, 
the safety and reliability under accidental conditions (for instance if 
the pump runs with a closed valve or with a suction pipe not immersed in 
the water).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
As can be observed in FIG. 1, the diffuser according to the invention is 
indicated as a whole with 1 and it is connected to a single-impeller, 
self-priming centrifugal pump 2, suited for swimming pools or whirlpools. 
The description given hereinafter relates to the application of the 
diffuser according to the invention on the pump of the mentioned type. The 
description remains, however, valid, as will be seen more in detail 
hereinafter, also when applied to any other type of single-impeller 
centrifugal pump. Pump 2, as can be observed, consists of a pump casing 
11, closed by a casing cover 12, in the interior of which there are funnel 
13 and impeller 14, the latter being splined on the shaft 15 of the motor 
(not represented in the drawing). 
As can be observed in FIG. 1 and also in FIG. 2, the periphery of casing 
cover 12, on which the blades 16 are located and present a curve 6, 
extends around the periphery of impeller 14. As can be seen in FIG. 2, the 
blades do not overlap each other, on the contrary, they are separated by 
the free section marked with 25. The task of the blades is to scoop up the 
air as close as possible to the periphery of the impeller 14 and to convey 
it, together with the water, by preventing their separation due to the 
centrifugal force, in the direction marked by arrow 3 against the baffles 
17, which can be seen more in detail in FIG. 5. The task of the baffles 17 
is to divert the flow on to the front passages 18 of the longitudinal 
channels 10, represented in FIG. 1, in FIG. 3, in FIG. 4 and also in FIG. 
5, following the longitudinal direction indicated by arrow 4, which is 
preferably parallel with the rotation axis 5 of impeller 14. The baffles 
17 are also located around the periphery of casing cover 12 and, as can be 
seen in FIG. 2, they are circumferentially closed on the outer periphery 
through the annular wall 8 of the pump casing 11. Each longitudinal 
channel 10, with its front passage 18, is located on the pump casing 11 
and it is closed toward the interior of the tapered belt 19 of funnel 13. 
Each longitudinal channel 10, as can be observed in FIG. 1, opens into the 
pressure chamber 21, located within the pump casing 11. Each longitudinal 
channel 10 along the periphery of funnel 13 constitutes, therefore, the 
diffuser, which, because of its construction characteristics and of the 
type of flow which occurs within it, we can call a 
"peripheral-longitudinal diffuser". 
The application of casing cover 12 on the pump casing 11 occurs with the 
help of the locating rabbeted fit 20, as can be observed in FIGS. 1 and 2. 
The flow streaming out of the channels 10 of diffuser 1 follows the 
direction marked by arrow 4, as can be observed in FIG. 1 and it is led 
toward the interior of the pressure chamber 21, into which it flows with a 
longitudinal direction and without any rotation, without any separation of 
air and water, due to a centrifugal force, and without any back-flow of 
the air toward the hub of the impeller, so that during the self-priming 
process of the pump, the air can more easily stream out of the delivery 
connection 26. 
On the basis of this description it can be understood that the peripheral 
longitudinal diffuser 1 according to the invention reaches the proposed 
purpose of achieving a rotation-free flow into the pressure chamber 21. 
One consequence of this fact is a reduction of the noise level of the pump 
while it is running. The elimination of the rotation of the fluid, by 
means of the diffuser according to the invention, makes it possible to do 
away with longitudinal baffles or other devices positioned in the pressure 
chamber of the pump having the purpose of reducing the rotation, so that 
it is possible to have smooth walls with a minimum friction on the water, 
thereby insuring to the pump the regularity of the self-priming process 
with the delivery connection 26 completely open and solely with the 
filling up of the pump casing with liquid, before the start-up, even under 
the conditions of maximum suction lifts. 
On the basis of the description it is also easy to understand that the 
diffuser 1 according to the invention provides a single-impeller, 
centrifugal pump having more reduced overall radial dimensions as compared 
with equivalent pumps, thereby eliminating the need for the application of 
an added support on the center of gravity with unfavourable conditions of 
excessive difference of bulk and weight between the pump and the motor. In 
fact, it can be seen, by observing FIG. 1, that the radial distance 22 
between the periphery of the centrifugal impeller 14 and the interior of 
the pump casing 11 is reduced to the very minimum since, as can be seen in 
more detail in FIG. 2, the blades 16 of diffuser 1 do not radially overlap 
each other at any spot, but are separated from each other by the free 
section 25. It has also been observed that the diffuser according to the 
invention provides in the pressure chamber 21 a larger volume available 
for the water reserve which is needed at the start of the self-priming 
process. 
It has also been seen that the diffuser according to the invention is made 
by adding to the structural parts of the pump, i.e. to the pump casing 11 
and the casing cover 12, exclusively funnel 13, which is placed between 
the suction opening 27, with the interposition of seal 28 and the front 
part of casing cover 12. Thus, the funnel 13 also functions a metal 
sealing ring 29 on impeller 14, which will prevent possible jammings or 
irregular wear, even with small radial clearance, and also the function of 
connecting the suction opening 27 with the opening 30 of impeller 14, 
through the pressure chamber 21. According to the dimensions of funnel 13 
and to the technological methods used for its construction, the funnel can 
be made in a single piece by die-forming or it can be made of several 
parts, which will be welded or fitted together, whereby, in the latter 
case, it can also be built of different metals and/or the pieces can be 
detacheable from one another. 
In FIG. 1 and in FIG. 2 the inner diameter 23 of funnel 13 is larger than 
the inner diameter 24 of the blades 16 on casing cover 12, because funnel 
13 is also foreseen for an impeller 14 having a larger diameter than the 
one represented in the drawing. If impeller 14 has the maximum possible 
diameter, the blades 16 and/or the baffles 17 will have their diameter 
coinciding with the inner diameter 23 of funnel 13. The baffles 17 can be 
arranged directly along the periphery of impeller 14 without any need for 
the blades 16. 
It has been seen that the diffuser according to the invention eliminates 
the air pockets at the first filling-up and also the water pockets when 
the pump is drained. 
A different application of the diffuser according to the invention is shown 
in FIG. 6, wherein it can be observed that the diffuser 40 according to 
the invention is applied on a single-impeller, self-priming centrifugal 
pump 41 of the "jet" type. In this different application the constructive 
concept of the invention remains the same as the one previously described, 
with the single difference that funnel 42 is built in a different shape, 
which, in this case, does not present a suction duct through the pressure 
chamber. In fact, in this application the funnel provides the sealing wear 
ring 45 on the impeller 46, as has been seen before, and immediately after 
that, the terminal end 43 is applied on the ejector 44 of pump 41 through 
the interposition of washer 47. In this different application on "jet" 
pumps, diffuser 40 according to the invention also fulfils all the 
purposes and presents all the advantages that have been previously 
described, with the further advantage that, in this case, the flow of the 
propelling liquid going through ejector 44 is not forced into pre-rotation 
toward impeller 46. 
FIG. 7 shows a different application of the diffuser 50 according to the 
invention on a single-impeller centrifugal pump 51 with an open impeller 
57. In this variation of application, too, the construction concept of the 
diffuser according to the invention remains the same as previously 
described, with the single difference that the funnel 52 has a different 
shape, in that it presents wall 53, connecting ring 54 and the outer belt 
55 facing casing cover 56 and the open impeller 57. 
Several changes and variations are foreseen, which, based on the same 
inventive idea, permit different embodiments of the diffuser according to 
the invention. 
A different embodiment is shown in FIG. 8, where it is applied on a 
single-impeller centrifugal pump 61, where it can be observed that 
diffuser 60 consists, as has been previously seen, of blades 62 and 
baffles 63, which are visible in FIGS. 9 and 12, located around the 
periphery of casing cover 64, which are circumferentially closed around 
the outer periphery through the annular wall 65 of the pump casing 66. 
Each of the blades 62 and each of the baffles 63 joint with the front 
passage 68 of the longitudinal channel 72, which open into the pressure 
chamber 67. The front passages 68 and the longitudinal channels 72, as can 
be obeserved in the FIGS. 8, 10, 11 and 12, are no longer located around 
the periphery of the pump casing 66, but are rather located around the 
periphery of funnel 69 with the tapered belt 71 and they are closed toward 
the exterior by the cylindrical belt 65 of the pump casing 66. It will be 
noticed that the connection between funnel 69 and casing cover 64 is 
obtained through at least one locating dowel 70, while the front passages 
68 can be made in any possible shape. 
Another embodiment is represented in FIG. 13, applied on a single-impeller 
centrifugal pump 81, wherein it can be observed that diffuser 80 also 
consists, as previously described, of blades 82 and baffles 83, visible in 
the FIGS. 14 and 16, located on casing cover 84. The blades 82 and the 
baffles 83 are not circumferentially closed by the pump casing 85, but are 
rather incorporated into the annular wall 86 of casing cover 84. The 
annular wall 86, the baffles 83 and the terminal end of the blades 82 
extend longitudinally over the outer belt 87 of funnel 88, thus forming 
between funnel 88 and casing cover 84 the front passages 89 and the 
longitudinal channels 90. The divergence of diffuser 80 can be obtained 
either by giving a tapered shape to the outer belt 87 of funnel 88 and a 
cylindrical shape to the annular wall 86 of casing cover 84 or by giving a 
tapered shape also or only to the annular wall 86 of casing cover 84. In 
this differring embodiment there is no need for locating dowels for the 
angular connection between funnel 88 and casing cover 84 or between funnel 
88 and the pump casing 85 or between casing cover 84 and the pump casing 
85, and this makes the assembly and the taking apart even easier. 
Yet another embodiment is represented in FIG. 17, wherein it can be 
observed that the diffuser 100 according to the invention is applied on a 
single-impeller, self-priming centrifugal pump 101 of the "jet" type. In 
this embodiment, the constructive idea of the invention remains the same 
as described for the embodiment of FIG. 13, the only difference consisting 
in the different constructive shape of the funnel, which, in FIG. 17, 
consists of a wall 102, shaped so as to comprise the terminal end 103 
applied on the ejector 104 through the interposition of washer 105, the 
sealing wear ring 106 on impeller 107 and the outer belt 108, radially 
closing toward the interior the longitudinal channels 109 on casing cover 
110. 
Contrary to the embodiment represented in FIG. 13, the terminal end 111 of 
the outer belt 108 is not turned toward the casing cover, but it is rather 
turned toward the pressure chamber 112, as is the case of the embodiment 
of the funnel in the type of application represented in FIG. 7. 
In the embodiment of FIG. 17 the outer belt 108 of wall 102 is preferably 
made in a cylindrical shape and the divergence of the diffuser 100 is 
obtained with the tapered shape of the annular wall 113 of casing cover 
110. 
In this embodiment, too, no locating dowels are necessary for the angular 
connection between wall 102 and casing cover 110, nor between wall 102 and 
the pump casing 114 nor between casing cover 110 and the pump casing 114. 
The longitudinal positioning occurs by placing wall 102 between the front 
of the blades 115 on casing cover 110 and the catches 116 on ejector 104. 
Yet another construction embodiment is represented in FIG. 18, wherein it 
can be observed that diffuser 120 according to the invention is applied on 
a single-impeller, self-priming centrifugal pump 121 of the "jet" type. In 
this embodiment, the constructive idea of the invention remains the same 
as described for the embodiments of the FIGS. 13, 14, 15, 16 and 17, with 
the difference that the baffles 122, already described and illustrated for 
the previous embodiments, which are located on casing cover 123, extend 
longitudinally over the preferably tapered outer belt 124 of the funnel or 
wall 125 and also in the interior of the inner belt 126 of the pump casing 
127. 
In this embodiment the longitudinal channels 128 of the diffuser 120 are 
shaped by the junction between the pump casing 127, casing cover 123 and 
by the funnel or wall 125. 
In this embodiment, too, no locating dowels are required for the angular 
connection between the pump casing 127, casing cover 123 and the funnel or 
wall 125. 
Another embodiment is represented in FIG. 19. In this embodiment the 
concept for the construction of the diffuser 130 according to the 
invention, which is applied on a "jet"-type pump 131, remains the same as 
described for the embodiment of FIG. 18, with the difference that the 
baffles 132 are no longer located on the casing cover 133, but rather are 
located on a circular rim 134, positioned between casing cover 133, the 
funnel or wall 135 and the pump casing 136. 
In this embodiment the funnel or wall 135 preferably presents a shape which 
is similar to the one described in the embodiment of FIG. 17, but with the 
outer belt 137 preferably tapered. In this variation, the circular rim 134 
with the baffles 132 is kept its longitudinal position between the funnel 
or wall 135 and casing cover 133. The circular rim 134 can be prevented 
from rotating while the impeller is running, by coupling it in seat 138 in 
the pump casing 136 or by the pressure caused by the blocking between the 
funnel or wall 135 and casing cover 133. In this embodiment, too, no 
location dowels are necessary for the angular connection between the 
various parts forming the longitudinal channels 139 of diffuser 130. 
The various embodiments which have been described also fulfil all the 
purposes which have been proposed by this invention and also permit the 
achievement of all of its advantages. During the manufacturing process of 
the diffuser according to the invention, changes and modifications of a 
constructive or functional nature may be applied in order to improve its 
efficiency or its manufacture. Thus, for instance, it will be possible to 
vary the shape and the number of the blades, of the baffles and of the 
longitudinal channels, as can be varied their radial and axial dimensions. 
It is, however, understood that said possible changes, as well as all the 
combinations arising from the described and illustrated embodiments will 
not exceed the scope and spirit of the present invention.