WO2005010374A1

WO2005010374A1 - Self-priming centrifugal pump

Info

Publication number: WO2005010374A1
Application number: PCT/IB2004/002486
Authority: WO
Inventors: Giancarlo Sorgato
Original assignee: Varisco Spa
Priority date: 2003-07-30
Filing date: 2004-07-29
Publication date: 2005-02-03
Also published as: ITVI20030155A1

Abstract

A self-priming centrifugal pump comprises a pump housing (2) having at least one inlet (3) and one outlet (4) for a working fluid, an impeller (5) rotatably mounted in the housing (2) and mounted to a shaft (6) having a longitudinal axis (L), prime mover means acting on the shaft (6) to rotate the impeller, a volute (7) placed inside the pump housing. The volute (7) has an inner spiral chamber (8) with a predetermined axial extension, a suction port (9) in fluid communication with the inlet (3) and a discharge port (10) in fluid communication with the outlet (4) . The spiral chamber (8) is delimited by a substantially continuous outer peripheral wall (11) with no recirculation port. Furthermore, the axial extension of the spiral chamber (8) is greater than or equal to that of the impeller (5). The advantage is obtained of providing fluid recirculation in the volute (7) and a negative pressure in the inlet during the self-priming step, substantially with no additional volumetric loss.

Description

SELF-PRIMING CENTRIFUGAL PUMP

Field of the Invention

The present invention is generally applicable to the field of hydraulic plants systems and pump apparatuses and particularly relates to a self-priming fluid apparatus in accordance with the preamble of claim 1. Background art

A number of embodiments of self-priming pumps or fluid equipment are known, which are able to start or restart the pumping system or apparatus even when the suction line is filled with air. This feature is particularly advantageous when the pump operates in a suction lift configuration and has no non-return valve, or this latter does not operate properly. In this condition, the suction line is discharged of fluid and filled with air as soon as the pump is switched off.

If the fluid apparatus is of the centrifugal type, an auxiliary device may be used for generating vacuum at the inlet of the apparatus and drawing in fluid from the suction line until the system is filled. The auxiliary device may be, for instance, a positive-displacement pump or an ejector.

An apparent drawback of this arrangement consists in that an additional device is used, which may cause a considerable increase of fabrication costs. Also, the increased complexity increases the likelihood or risk of failure, thereby affecting reliability. A well-known and widely used arrangement for fabricating a self-priming centrifugal pump is disclosed in. US-A-3279386 and US-A-3898014. Particularly, these documents disclose two embodiments of a centrifugal pump comprising a pump housing adapted to house an impeller and its volute. The pump housing has a suction chamber upstream of the impeller and a separation chamber downstream of the volute. The separation chamber is in fluid communication with the volute through the outlet thereof and through a recirculation port, which is formed in the lower portion of the separation chamber.

Thus, when the suction line fills with air, the fluid in the separation chamber enters the volute through its recirculation port, mixes with air contained therein, and interacts with the rotating impeller. The latter forces the fluid back into the separation chamber, in which the fluid falls by gravity into the lower portion and passes again through the recirculation port. Fluid motion generates a negative pressure at the pump inlet and draws in fluid from the suction line.

An apparent drawback of this arrangement lies in that fluid recirculation motion continues even after pump priming. This severely affects the volumetric efficiency of the pump, and the continuous recirculation motion dissipates energy.

Furthermore, if the working fluid contains suspended solid particles or bodies, the recirculation port may become partly or fully clogged, whereby the self-priming feature is lost. An additional drawback of this arrangement lies in that the passage of the impeller blades near the recirculation port creates localized pressure changes, which may cause undesired vibrations and damage the pump. WO-A-03001065 discloses an arrangement similar to the above, which comprises a fluid recirculation port to generate an appropriate negative pressure during the priming phase. In order to prevent the fluid recirculation motion from occurring after pump priming, closing means are provided, that are able to selectively obstruct the recirculation port. Thus, the recirculation port is only opened when this is required to prime the pump.

A drawback of this arrangement is the high construction complexity, which involves relatively high fabrication costs. Also, once more there is a non negligible risk that the recirculation port may be clogged by suspended solid particles or bodies. Such clogging risk, as well as pump complexity, require relatively high maintenance costs.

Summary of the invention

A primary object of this invention is to obviate the above drawbacks, by providing a fluid operating apparatus with excellent self-priming properties.

A particular object is to provide an apparatus that can be used with fluids containing suspended solid particles or bodies, and affords a low clogging risk.

A further object of the invention is to provide an apparatus having a good overall performance and particularly an excellent volumetric efficiency.

An additional object of the invention is to provide a reliable apparatus, whose features remain unchanged with time. Another particular object is to provide a cost-effective apparatus, having relatively low maintenance costs.

Yet another object is to provide a sturdy apparatus, scarcely subjected to vibrations.

These objects, as well as other objects that will be apparent hereafter, are fulfilled, according to claim 1, by a self- priming centrifugal pump, which comprises a pump housing having at least one inlet and one outlet for a working fluid, an impeller rotatably mounted to a shaft, having a longitudinal axis, to rotate in the housing, driving means acting on the shaft to rotate the impeller, a volute placed inside the pump housing, the volute having an inner spiral chamber with a predetermined axial extension, a suction port in fluid communication with the inlet and a discharge port in fluid communication with the outlet, characterized in that the spiral chamber is delimited by a substantially continuous outer peripheral wall with no recirculation port, the axial extension of the spiral chamber being greater than or equal to that of the impeller, to provide fluid recirculation in the volute and a negative pressure in the inlet during the self-priming phase, substantially with no additional volumetric loss.

Thanks to particular configuration, a pump with excellent self-priming properties and a relatively high volumetric performance will be provided.

Brief Description of the Drawings

Further features and advantages of the invention will be more apparent from the detailed description of a few. preferred, non-exclusive embodiments of a self-priming centrifugal pump according to the invention, which are described as non- limiting examples with the help of the annexed drawings, in which: FIG. 1 is a sectional side view of a pump according to the invention; FIG. 2 is a cross-sectional view of a detail of the pump of FIG. 1; FIG. 3 is a first meridian section of the detail of FIG. 2; FIG. 4 is a second meridian section of the detail of FIG. 2; FIG. 5 is a third sectional view of the detail of FIG. 2.

Detailed description of a preferred embodiment

Particularly referring to the above figures, a self-priming centrifugal pump according to the invention is described, which is generally designated with numeral 1.

Pump 1 comprises a ho sing 2, which has at least one inlet 3 and one outlet 4 for a working fluid, a traditional impeller 5, for instance a centrifugal two-blade impeller, located in the housing 2 and mounted to a shaft 6 having a longitudinal axis L. Shaft 6 is supported by bearings 6' mounted in the pump housing 2 and is connected to motor means (for instance an electric motor or an internal-combustion engine, not shown) , to rotatably drive the impeller 5 and impart the desired pressure and flow rate to the working fluid.

A volute 7 is placed in the pump housing 2, and has an inner spiral chamber 8 with a predetermined axial extension, a suction port 9 in fluid communication with the inlet 3 and a discharge port 10 in fluid communication with the outlet 4.

According to the invention, the spiral chamber 8 is delimited by an outer peripheral wall 11, that has substantially continuous no recirculation port. Furthermore, the axial extension of the spiral chamber 8 is greater than or equal to that of the impeller 5, to provide fluid recirculation in the volute 7 and a negative pressure in the inlet 3 during the self-priming phase, substantially with no additional volumetric loss.

Particularly, the axial extension of at least one portion of the spiral chamber 8 may be at least twice that of the impeller 5.

Also, the spiral chamber 8 may be substantially radially adjacent an outer peripheral edge 12 of the impeller 5.

In order to increase fluid recirculation during the self- priming phase, the spiral chamber 8 may be substantially asymmetric with respect to a geometric median plane M of the impeller 5, orthogonal to the longitudinal axis L.

In the embodiment of the annexed figures, the spiral chamber 8 extends from an inlet section 13 to the discharge port 10, to deliver thereto the fluid flowing out of the impeller 5.

The outer peripheral wall 11, when seen in section along a meridian plane P passing through the longitudinal axis L, has a first lobe 14, axially projecting and proximal to the suction port 9 and a second lobe 15, axially projecting in the direction opposite to the first lobe 14.

Particularly, the axial extension of the second lobe 15 may be greater than or equal to that of the first lobe 14, thus rendering the spiral chamber 8 asymmetric.

In greater detail, the outer peripheral wall 11 may include a substantially flat bottom wall 16 on the meridian plane P. Further, each of the first and second lobes 14, 15 may have a wall 17 that is inclined with respect to the bottom wall 16 and substantially planar on the meridian plane P, PA A respective connecting wall 18 is further provided between the bottom wall 16 and the corresponging inclined walls 17.

The connecting wall 18 of the first lobe 14 may be curved on the meridian plane P, with a continuously increasing radius of curvature T all along the spiral chamber 8 from the inlet section 13 to the discharge port 10.

The spiral chamber 8 may have an initial portion 19, adjacent the inlet section 13 and an end portion 20, between the initial portion 19 and the discharge port 10.

The connecting wall 18 of the second lobe is identical to that of the first lobe 14 in the initial portion 19, and becomes different from it in the end portion 20. Indeed, along the initial portion 19, the connecting wall 18 of the second lobe 15 may be curved, with an increasing radius of curvature S, and along the end portion 20 it may include a curved portion 21 and a substantially planar portion 22.

Suitably, the angular extension α of the initial portion 19 may be greater than 270°. From this above description it clearly appears that the pump according to the invention fulfils all the intended purposes and particularly the above volute conformation provides excellent self-priming properties, as well as a relatively high volumetric efficiency.

The pump according to the invention is susceptible of a number of changes and variants all falling within the inventive concept disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the pump has been described with particular reference to the accompanying figures, the nume rals referred to in the disclosure and claims are only used for the sake of a better intelligence of the invention and shall not be intended to limit the claimed scope in any manner.

Claims

1. A self-priming centrifugal pump comprising: - a housing (2) having at least one inlet (3) and one outlet (4) for a working fluid; - an impeller (5) rotatably mounted in said housing (2) and rigidly mounted to a shaft (6) having a longitudinal axis (L); - motor means acting on said shaft (6) to import a rotation to said impeller; - a volute (7) placed inside said pump housing (2), said volute (7) having an inner spiral chamber (8) with a predetermined axial extension, a suction port (9) in fluid communication with said inlet (3) and a discharge port (10) in fluid communication with said outlet (4); characterized in that said spiral chamber (8) has a substantially continuous outer peripheral wall (11) with no recirculation port, the axial extension of said spiral chamber (8) being greater than or equal to that of said impeller (5) , to provide fluid recirculation in said volute (7) and a negative pressure in said inlet (3) during the self-priming phase, substantially with no additional volumetric loss.

2. Pump as claimed in claim 1, characterized in that the axial extension of at least one portion of said spiral chamber (8) is at least twice that of said impeller (5) .

3. Pump as claimed in claim 2, characterized in that said spiral chamber (8) is substantially radially adjacent to an outer peripheral edge (12) of said impeller (5) .

4. Pump as claimed in claim 2, characterized in that said spiral chamber (8) is substantially asymmetric with respect to a geometric median plane (M) of said impeller (5), said plane being orthogonal to said longitudinal axis (L) .

5. Pump as claimed in claim 4, characterized in that said spiral chamber extends from an inlet section (13) to said discharge port, to direct thereto the fluid coming out of said impeller (5) .

6. Pump as claimed in claim 5, characterized in that said outer peripheral wall (11) , sectioned along a meridian plane

(P) passing through the longitudinal axis (L) , has a first lobe (14), axially projecting and proximal to said suction port and a second lobe (15), axially projecting in the direction side to said first lobe (14) .

7. Pump as claimed in claim 6, characterized in that the axial extension of said second lobe (15) is greater than or equal to that of said first lobe (14) .

8. Pump as claimed in claim 7, characterized in that said outer peripheral wall (11) comprises a substantially planar bottom wall (16) on said meridian plane (P) .

9. Pump as claimed in claim 8, characterized in that said first (14) and said second (15) lobe has a wall (17) that is inclined with respect to said bottom wall (16) and substantially planar on said meridian plane (P) .

10. Pump as claimed in claim 9, characterized in that said first (14) and said second (15) lobe has a connecting wall (18) between said bottom wall (16) and the respective inclined wall (17) .

11. Pump as claimed in claim 10, characterized in that the connecting wall (18) of said first lobe is curved, with a predetermined radius of curvature on said meridian plane.

12. Pump as claimed in claim 11, characterized in that said radius of curvature (R) of the connecting wall (18) of said first lobe (14) continuously increases all along said spiral chamber (8) from said inlet section (13) to said discharge port (10) .

13. Pump as claimed in claim 2, characterized in that said spiral chamber (8) has an initial portion (19), adjacent said inlet section (13) and an end portion (20), between said initial portion (19) and said discharge port (10) .

14. Pump as claimed in claims 10 and 13, characterized in that the connecting wall (18) of said second lobe (15) is curved, with an increasing radius of curvature along said initial portion.

15. Pump as claimed in claim 14, characterized in that the connecting wall (18) of said second lobe (15) has a curved portion (21) and a substantially planar portion (22) along said end portion section (20) .

16. Pump as claimed in claim 15, characterized in that the angular extension (α) of said initial portion is greater than 270°.