Self priming centrifugal pump

Abstract: A self-priming centrifugal pump includes a cylindrical metal plate case (2) forming a pressure chamber (13, 13', 13'') and provided with a suction inlet (5) and a pressure outlet (6). The pressure chamber (2) has a bladed impeller (12) with a peripherally arranged diffuser (17), an axial ejector device (19) including a venturi tube (20), and a torus-shaped interspace adapted to convey the emitted flow from the radial diffuser (17) towards the pressure chamber (13'). A single curved blade (26) is arranged in the lower portion of the interspace (16) and extends from the peripheral region of the radial diffuser (17) up to a central annular outlet passage (22) of the interspace (16) which extends all around said ejector device (19) in such a manner to counteract the rotational component of the fluid speed direction and to promote separation of air.

Description: The present invention relates to a self priming centrifugal pump comprising a metal plate case with a substantially cylindrical shape defining internally thereof a pressure chamber with an inlet port and an outlet port, within this pressure chamber a rotatable impeller and a radial diffuser being arranged at an axial end thereof, an axial ejector device being located at the opposite axial end thereof, and an intermediate torus-shaped interspace being arranged in an intermediate position to direct the outlet flow issued by the radial diffuser backwards to the pressure chamber. In the known pumps as above, the flow emitted by the diffuser and accelerated by the impeller has an outlet speed with a high rotational component. Thus, most of the air trapped in the pumped fluid is directed to the pressure chamber and passes through the ejector several times before being discharged through the outlet port, thereby lengthening the priming times of the pump. US -A- 2.941.474 discloses a centrifugal pump having a torus-shaped interspace which forms a vortex chamber with an annular central opening extending around the periphery of the ejector. The trapped air present in the fluid is subjected to a swirling action and is finally discharged through the outlet port in the pressure chamber without being previously separated. This arrangement is inadequate and does not afford significant reduction of the priming times. The pumping apparatus described in the GB-A- 1.201.721 and in the EP-A- 401 670 comprises an interspace which is provided with a plurality of substantially radial blades adapted to counteract the rotational component of the fluid flow thereby promoting separation of air. Similarly the reconvey interspace applied to the pump described in the IT-A- 1.225.597 is provided with a number of substantially radial blades which form recirculator channels, however this pump makes use of an axial diffuser which is arranged to face the impeller on the low pressure side thereof, and therefore the flow entering the recirculator channels has a speed direction with a relatively high rotational component. Moreover, the structure of these latter pumps is excessively complicated and brings about remarkable fluidodynamic losses. The self priming centrifugal pumps known from the DE-A- 3718273 and the EP-A- 0323384 have an interspace with a single blade that offers the advantage of a lower complexity and reduced frictional losses. However, such interspace has a wall with one or more outlets for the fluid with relatively limited sizes which are located only in the upper half of the interspace wall. Thus, the trapped air tends to swirl and to be retained into the interspace thus elongating the priming times and reducing the efficiency of the pump. One aim of the present invention is to eliminate the above mentioned drawbacks by providing a self priming centrifugal pump incorporating an ejector which is capable of operating with high efficiency and is very simple in structure. This aim, these objects and others, which will become apparent to those skilled in the art, are achieved by a centrifugal pump according to claim 1. Advantageously, the interspace is substantially funnel-shaped and is formed by a pair of substantially frusto-conical and parallel walls extending inwardly with a conicity oriented towards the end of the case in the vicinity of the venturi tube. Due to the presence of the single blade having a curved and smoothened shape, the rotational speed component of the fluid is effectively counteracted thus reducing the fluidodynamic losses. Moreover, because of the conical shape of the interspace and of the size of the annular passage, the air-liquid solution is not retained within the interspace and is promptly discharged through the outlet port. Experimental tests have shown that the pump according to the invention achieves the stated objects insofar as it sets forth reduced priming times as well as a high fluidic efficiency. Additionally the pump has a relatively simple and inexpensive construction. Further characteristics and advantages of the invention will become apparent from a reading of the detailed description of a preferred but not exclusive embodiment of a self priming centrifugal pump according to the invention, illustrated only by way of a non-limiting example in the accompanying drawings, wherein: FIG. 1 is a partially sectioned side view of the pump according to the invention; FIG. 2 is a cross-section view taken along the vertical plane II-II of FIG. 1; Fig. 3 is a front view of the detail having the reference numeral 15 in FIG. 1. With reference to the figures, the pump, generally indicated by numeral 1, comprises a case 2 made of a metal plate with a lateral wall 3 of substantially cylindrical shape and with a slightly outwardly bulged bottom wall 4. These walls are provided with inlet port 5 and outlet port 6 respectively which mount corresponding nozzles for connection with suction and pressure tubes. The end portion of the case remote from the bottom wall 4 shows a connecting flange 7 for connection with a support 8 of an electric motor 9. A fluid-tight partition wall 10 is interposed between the flange 7 and the support 8 and is centrally provided with bearings and wear rings mounted on the shaft 11 of the motor 9, and a bladed impeller 12 rigidly fixed to the end portion thereof. A pressure chamber 13 is formed in the inner space of the case 2 between the lateral wall 3, the bottom wall 4 and the partition wall 10 to collect the pressurized fluid. A pair of walls 14, 15 of substantially frusto-conical shape are axially spaced to partition the pressure chamber 13 into sub-chambers 13' and 13'', so as to form therein a funnel shaped interspace 16. The walls 14, 15 have an angle of conicity α ranging between 5° and 20° according to the wished axial acceleration of the fluid. The conicity angle α is preferably set at 10°. The impeller 12 is rotatably supported within the sub-chamber 13'' and is encircled by a radial diffuser 17 having front apertures 18 adapted to impart to the fluid a minimum axial speed directed towards the sub-chamber 13'. Moreover, a conventional ejector device 19 is arranged in the sub-chamber 13'' in substantially central position, such device comprising a venturi tube 20 adapted to supply a diffusion duct 21 which is, in turn, connected at one end thereof 21' with a suction port 5 and, at the opposite end 21'', with the suction eye 12' of the impeller 12. Preferably, the frusto-conical wall 15 is unitary with the radial diffuser 17 and has a central portion 15' for supporting the end 21'' of the diffusion duct 21. The frusto-conical wall 14 shows a central annular passage 22 provided with an outer collar 23 which forms a discharge aperture for the interspace 16, which aperture extends peripherally to the diffuser over 360°. Advantageously, the frusto-conical wall 14 may be unitary with the outer wall of the diffusion duct 21 and is joined to this latter by means of a pair of webs 24, 25 extending in a vertical axial plane. Alternatively, a second pair of webs 24', 25' may be provided in a substantially perpendicular plane to the first pair 24, 25. These webs have the ancillary function of aligning the outlet flow issued by the impeller through the central annular passage 22, to thereby promote regular feeding of the Venturi tube separation of air bubbles. According to the invention, a single blade 26 is located in the interspace 16. Blade 26 is slightly curved to counteract the rotational speed component of the fluid leading the diffuser 17 and to entirely direct it towards the annular passage 22. More particularly, the blade 26 is disposed in the lower portion of the interspace 16 and extends from the outer periphery of the diffuser 17 up to the central area 15' of the partition wall 15 in correspondence of the outlet 22, to thereby upward direct the fluid containing the bubbles of air. Thus, the fluid issued by the impeller is collected and pressurized by the diffuser 17, is further directed to the interspace 16 reducing its rotational speed component and finally is discharged in the sub-chamber 13 wherein it is completely deprived of rotational speed component and is smoothened by the longitudinal webs 24, 25. Because of this smoothing action, the trapped air in the fluid flows upward towards the outlet port so that the venturi tube is supplied in few seconds by air-free fluid. The pump according to the invention is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept. All the details may furthermore be replaced with other technically equivalent elements, within the limits of the claims. In practice, the materials employed, as well as the dimensions, may be any according to the requirements. Having thus described one particular embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements as are made obvious by this disclosure are intended to be part of this disclosure though not expressly stated herein, and are intended to be within scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A self-priming centrifugal pump comprising a metal plate case (2) of substantially cylindrical shape forming a pressure chamber (13, 13', 13") and provided with a suction inlet (5) and a pressure outlet (6), said pressure chamber (2) housing a bladed impeller (12) with a peripherally arranged diffuser (17), an axial ejector device (19) including a venturi tube (20), a torus-shaped interspace adapted to convey the emitted flow from the radial diffuser (17) towards the pressure chamber (13'), said interspace having a central annular outlet passage (22) extending between a maximum and a minimun diameter all around said ejector device (19), a single blade (26) arranged in the lower portion of said interspace (16), said blade having a curved profile with an upwardly directed concavity extending from the peripheral region of the radial diffuser (17) up to a location of said central annular outlet passage (22) comprised between its maximum and minimum diameter in such a manner to counteract the rotational component of the fluid speed and to direct the flow upwardly towards the pressure outlet (16) to promote separation of air. Pump according to claim 1, characterized in that said interspace (16) is substantially funnel-shaped. Pump according to claim 2, characterized in that said interspace (16) is formed by a pair of substantially frusto-conical walls (14, 15) which are axially spaced and extend from the periphery to the center of said chamber (13) with an angle of conicity (α) oriented towards the bottom wall (4) of the case adjacent to the venturi tube. Pump according to claim 3, characterized in that said angle of conicity (α) of the transverse walls of said interspace (16) is comprised between 5° and 20° and is preferably equal to 10°. Pump according to claim 1, characterized in that the ejector device (19) is joined to the frusto-conical wall (14) of said interspace at the low-pressure side thereof by means of at least one pair of diametral webs (24, 25, 24', 25') so adapted to align the outlet flow issued by the bladed impeller towards the venturi tube of the ejector device. Pump according to claim 1, characterized in that the radial diffuser (17) is unitary with the frusto-conical wall (15) of said interspace (16) closer to the impeller (12). Pump according to claim 6, characterized in that said frusto-conical wall (15) unitary with the diffuser (17) presents a plurality of front apertures (18) in correspondence of the leading edge of the blades thereof so as to impart to the fluid an axial component of predetermined value.

Inventors: TADIELLO ARNANDO, TADIELLO, ARNANDO
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1993
Main classification: F04D9
IPC codes: F04D9, F04D29